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Project Specific Discussions => Preamplifiers => Topic started by: jsteiger on May 11, 2009, 08:42:34 PM

Title: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on May 11, 2009, 08:42:34 PM
***ATTENTION!! The stepped VP25 & VP26 kits are now shipping with Grayhill switches that have factory set stops. This means there will be no stop-pins or stickers shipped or required. A quick glance at the switch should give this away as there are no holes to put the stop-pins in!!***

As the title states, this is the official support thread for the VP2X, 500 series mic pre build that can be found at our capi-gear.com (http://www.capi-gear.com) website. Per a private email request, I felt I should start this thread.

So, if you have any questions feel free to let them fly.

I will also post a few assembly pointers as I have no true "assembly guide". It is a super simple build. About as vintage API as you can get.

--------------------------------------------------------------------------------------------------------
September 21st, 2015 Update:
All support docs for this project can be found on the recently added Support Docs (http://capi-gear.com/catalog/support_docs.php) page at www.capi-gear.com
--------------------------------------------------------------------------------------------------------


Here are some general tips that I like to send out when guys are having trouble. It's a good place to start.

First, what DOA is it? A pre-built or a DIY? If it's a kit, swap the opamps and see if the problem follows. Also, have you seen the DOA install page DOA install (http://classicapi.com/catalog/DOA_Install.php) I highly recommend never testing a new preamp build with a new opamp build. There are too many variables and you may never know what the issue is. If it's a pre-built opamp from me, chances are, it is not bad. Gary and Scott both run them in for many hours before sending them to me.

Have you completed the pre-start tests at the end of the old VP2x Assembly Guide? If you are building a VP312, the C to O DCR value will be about 8.5 ohms. Make sure all voltage readings are correct.

Double check all component values and make sure caps are facing the right way. Resistors cannot be measured once both ends are soldered to the PCB. You will get many odd readings. Either use the color codes to verify or one end must be desoldered to get an accurate DCR reading.

Double check the lead colors/pads for the output transformer. Take your time and be sure. Countless times I have heard back from folks who checked and checked and then a few days later realized that some of the leads were placed incorrectly.

Next, reflow the solder on the 3 pushbutton switches.

If it's the Grayhill stepped gain option, do you have 25k when measuring between the to outside pins of the switch? If not, check with a magnifying glass as there probably is a short between some solder pads. These can be checked end to end by probing between adjacent pins. You should get the resistance of each of the R's on the pdf as you work from one end to the other.

Scan the board and check all solder pads with a magnifying glass of some kind. The biggest issue, besides what I mentioned above are cold solder joints. Sometimes they can look fine but not be good.

--------------------------------------------------------------------------------------------------------
Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Skylar on May 12, 2009, 03:09:05 PM
True, this is a simple build, and a very awesome project.

It's a snap to put together, the PCB is probably the easiest I've ever done.
Lot's of space [makes me not want to do another tiny DOA!]

Can't wait to hear how they sound!



...just waiting for input transformers...

(http://i73.photobucket.com/albums/i222/skylargray/API/th_SG_VP-25-CH1.jpg) (http://s73.photobucket.com/albums/i222/skylargray/API/SG_VP-25-CH1.jpg)

Thanks for sharing this Jeff!



I'm going to put 4 of these in a 3U chassis with a +/-16V/48V power supply.
Here's the frontpanel layout I'm going for:

(http://i73.photobucket.com/albums/i222/skylargray/API/th_VP25_3U_FP-7.gif) (http://s73.photobucket.com/albums/i222/skylargray/API/VP25_3U_FP-7.gif)


Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: geoff004 on May 19, 2009, 07:30:33 AM
Got both pres almost finished up last night
Here's what I'm wondering:
I opted to go without the output attenuator.  What do I wire to what for output?

Also, with the phantom power - does the switch get wired to points 1 and 2 (next to where it's labeled SW1)?
Thanks
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 19, 2009, 07:56:51 AM
Got both pres almost finished up last night
Here's what I'm wondering:
I opted to go without the output attenuator.  What do I wire to what for output?
Hi Geoff,
For the VP25 build with no attenuator, the Blue wire from the output x-fo goes to Pin #2 where the silk says "Opt-Blu" and the Orange wire goes to Pin #4 that is labeled "Opt-Ora". Directly left of the gold fingers.

Quote
Also, with the phantom power - does the switch get wired to points 1 and 2 (next to where it's labeled SW1)?
Thanks
I have them shown on schemo with a number inside a circle. You are correct though, to 1 and 2.
Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on May 19, 2009, 11:00:31 AM
Looks very nice.
To Jeff: why you have pushbuttons and a toggle switch? why dont you use another pushbutton? looks very nice tough..
thanks.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 19, 2009, 11:17:00 AM
Looks very nice.
Thanks 3nity.  ;)
Quote
To Jeff: why you have pushbuttons and a toggle switch? why dont you use another pushbutton? looks very nice tough..
thanks.
A few reasons really. I wanted to separate the 48V from the other switches to help avoid an accidental ribbon problem. I also wanted a little different look than most of the 4 button 500 pres.

Lastly, which is a 2 part answer, I was happy with the boards layout this way. Gave me more freedom to not have another PB footprint crammed in there. I have another pre in the pipeline that has a very similar layout to this with a lot more components. I am able to use most of this layout and then just "add on", if that makes sense. It will make more sense when I get the other one out there.

Thanks, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: DIYnoob! on May 20, 2009, 05:14:24 AM
any idea how these sound? just like the 312 or better?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on May 20, 2009, 10:48:58 AM
@ Skylar.
You plan to hold the L bracket against the front panel by screwing the 2 pots?
looks nice! are those 990 modded to run on +/- 16V?

Thanks..
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Skylar on May 20, 2009, 01:11:02 PM
3nity,

I think I will do a combination of small L-brackets on the big aluminum L-bracket to hold it to the bottom of the chassis as well as using anchoring the pots to the front panel.
I'm going to experiment and see what works best.

Correct, the 990s are mnats modded to run at +/-16V.

I'm going to try out some different DOAs in these pres...again, see what works best.



Jeff,
Got the input transformers on Monday!
Now, I'm just waiting for some PSU parts from Owel, and I can fire 'em up!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on May 20, 2009, 01:23:24 PM
if you use 990 DOAs in a custom rack with a custom PSU I just would run them at +/- 24V
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Skylar on May 20, 2009, 01:33:45 PM
Well, other DOAs I might try in there may require +/-16V, so I decided to stick with that.

But it's an adjustable power supply, so maybe I will un-mod the 990s back to +/-24V.

I guess that should increase headroom, correct?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 20, 2009, 11:43:51 PM
any idea how these sound? just like the 312 or better?
They sound a little different than a vintage 312 card. They are similar for sure...from the same loins, if you will. To my ears, these pres are slightly tighter and a bit more focused in the mids and low mids. The 312 is a "c" hair brighter/more open in the top. Keep in mind though, the 312's we compared with, had the old Jensen 110K input transformers which are 1:8. I did not closely look at the rest of the card. It was an old BAE racked card.

On that note, these boards could quite easily be populated exactly like a 312 if one would want. Jumper over the coupling caps and series resistor. Next, leave out 2 decoupling caps and a post DOA load resistor. Oh, and use the 2503 version.

You plan to hold the L bracket against the front panel by screwing the 2 pots?...
This is how my face-plate mounts as well. Held by the pot nuts.

Hey Skylar, couple of questions.

I noticed you went flying leads on the 25K pot instead of PC mount. I'm guessing for versatility in your rack?? I think I mentioned an 1/8" temporary spacer between pot body and board. (See the [silent:arts] post a few down for a much better solution). I wanted the pots centered in the panel.

Speaking of your rack, how is that coming? Did you order it or are you manufacturing it? Solidworks is darned cool!

Cheers, Jeff

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Skylar on May 21, 2009, 01:47:16 AM
Jeff,

Yes, I didn't board mount the pots because I'm doing a custom front panel.
I just wanted to be absolutely certain that the shafts will line up with the holes on my front panel.
Leaving them free from the board gives me some wiggle-room.


I'm using a par-metal rack with a custom front panel.
I was hoping to have the front panel done by ddt, but I haven't heard from him in a while.
So, I may just have the holes cut by FPE and then have the 2-color silkscreen done locally.
Not totally sure how I want to have the front panel done yet...a lot of options.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: DIYnoob! on May 21, 2009, 04:30:13 AM
sorry about getting of the subject...but has anyone heard how the VP25 or VP26 sound in comparison to API kike pre's?
I'm very interested in purchasing, and you guys seem like you're enjoying the pre's..

Thanks!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on May 29, 2009, 01:43:51 PM
went off earlier from work today to discuss my parcel out of the customers, took only 1 hour  :o  ;D

what a great project - went home, opened a beer, opened the parcel, fired the soldering iron up - and the pre was finished before this first beer was empty  :o :o :o
drinking now the second one to Jeff.

this is a really very fast and easy project.
now, when the knobs I want are in stock I will order a second one.

(http://www.silentarts.de/DIY/GDIY51X/VP2X_side.jpg)

will do some measuring tomorrow if anybody is interested,
and I think I will do a little mod to have a phantom power LED (easy)

Jeff, thanks for bringing this to us  :) :-*

btw, if you don't have an 1/8" cardboard handy to solder the gain potentiometer (you won't in europe):
I did completely mounted everything with the unsoldered potentiometer.
the PCB brackets can be soldered from top  ;)
disassemble and solder the bottom.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 30, 2009, 04:13:40 PM
went off earlier from work today to discuss my parcel out of the customers, took only 1 hour  :o  ;D

what a great project - went home, opened a beer, opened the parcel, fired the soldering iron up - and the pre was finished before this first beer was empty  :o :o :o
drinking now the second one to Jeff.
Nice Volker! Was the beer warm by the time you finished? Wait, I forgot, it was maybe warm when you started!  :)

Quote
this is a really very fast and easy project.
Yes, but there seems to be a lot of mud-slinging going on these days in regards to "paint by numbers". My kit falls into that category completely. Is that a problem? I don't think so. I would have killed for a kit like this 15-20 years ago!

Quote
...will do some measuring tomorrow if anybody is interested
I have to warn you, it won't look pretty. Phase shift and distortion for sure, but in a very pleasing way. The first time we AP'ed a mic input on my board, we thought channel 1 was f-ed up. Then we went to 2, then 3 and all were f-ed up looking in the same way! A big part of it is Ed's 2622. The best measurements that you can take on these pres, is taken with the ears.  8)

Quote
...Jeff, thanks for bringing this to us  :) :-*
No problem Volker. Been very much a pleasure. And :-* back at you with a little :P on the side.

Quote
btw, if you don't have an 1/8" cardboard handy to solder the gain potentiometer (you won't in europe):
I did completely mounted everything with the unsoldered potentiometer.
the PCB brackets can be soldered from top  ;)
disassemble and solder the bottom.
Now I feel like an idiot! That is a much easier, cleaner and more accurate way for sure! German ingenuity at it's finest!! The joys of plated thru-holes. BTW, did you like the massive solder pads?

Now, please report back when you've had the chance to A-B with you vintage BAE racked 312's. Curious on the input x-fo on yours. Is it AP2622 or JE 110K? The 110K will be a little "brighter" I believe.

Thanks and regards, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on May 30, 2009, 05:36:54 PM
Nice Volker! Was the beer warm by the time you finished? Wait, I forgot, it was maybe warm when you started!  :)
cold. up to the last sip.

... there seems to be a lot of mud-slinging going on these days in regards to "paint by numbers". My kit falls into that category completely. Is that a problem?
well I didn't bought a kit. but nearly. ;D
there are not too much parts in here, but since most parts are somehow special it makes sense buying it in kit form.
the capacitors have some special values, and some have a specific design / footprint. offering them for a perfect fit is great. the potentiometers aren't of the shelf too, and I hate metal work.

the "paint by numbers" - in my understanding - is more like people demanding this BOMs, Kits, what ever. I don't want to feel guilty if I don't offer this when selling just PCBs for a project.

for the measuring:
since there seams to be no interest here don't worry ;D
[and yes, the measuring doesn't say anything about sound - but is a part of my paying-job, and I'm curious]
anyhow, I will do comparable measuring against my BAE, which is with a Jensen input.
will mail you the results.

thanks again for the work you put in this.
you might have seen I try to sell another (very good sounding) API "clone" in the Black Market. they just don't fit the format I want to use in the future anymore ...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: canidoit on May 30, 2009, 06:00:11 PM
I like how this is for the 500 series. I have a lunch box and I would like to know if you will be making an EQ kit in the future with the same way you are selling your pre-amp kits. It would be great if someone was doing the 550a or 550b thing.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 30, 2009, 06:09:45 PM
I like how this is for the 500 series. I have a lunch box and I would like to know if you will be making an EQ kit in the future with the same way you are selling your pre-amp kits. It would be great if someone was doing the 550a or 550b thing.
550a's and 550b's are no simple task. I have many other projects if front of me that I would like/need to do first.

However, thanks to the fine work of Peterc, you can find a kick-butt version of the API 553 in this thread (http://www.groupdiy.com/index.php?topic=33790.0). Now is the time to get in on this. I am.  8)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 30, 2009, 06:25:22 PM
...for the measuring:
since there seams to be no interest here don't worry ;D
[and yes, the measuring doesn't say anything about sound - but is a part of my paying-job, and I'm curious]
anyhow, I will do comparable measuring against my BAE, which is with a Jensen input.
will mail you the results...
Volker,

By all means, test away my friend. Direct comparisons will be interesting. And please, post the results here.

As a reminder (I know you are well aware), there should be a noticeable difference between the 2 preamps, especially in THD+N and of course Phase.

When will the "ear" tests take place? You may need more beer for that.  ;)  :D

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on May 30, 2009, 06:44:26 PM
for sure I will do the measuring ;)

...When will the "ear" tests take place? You may need more beer for that.  ;)  :D

doesn't depend on beer ;D
my guess for a real ear test is end of october at some test concerts.
next project (http://www.rammstein.com/Tour.html) ;)
(they have been the cause for me to DIY - always in the need of something never existed before).
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 01, 2009, 09:13:01 PM
...next project (http://www.rammstein.com/Tour.html) ;)
(they have been the cause for me to DIY - always in the need of something never existed before).
Now that's some pretty cool stuff. I need to brush up on my Deutsch though I think. Did you notice, one of their web-shops looks like a heavily modified osc store?

Anyhow, keep an eye out for a little package. 8) I dropped a few love nuggets or goodies as Peter says for your AP extravaganza. I sent you one of Scott's SL-2520 red dots, a gar2520 and a Huntington 2520 from my personal stock. So, test away my friend. This will be interesting!  :)

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on June 02, 2009, 12:27:56 PM
... Did you notice, one of their web-shops looks like a heavily modified osc store?
haven't ever visited the shop until you mentioned it. yes. cool ;)
some more guys I can ask for support  ;D ;D ;D

Anyhow, keep an eye out for a little package. 8) I dropped a few love nuggets or goodies as Peter says for your AP extravaganza. I sent you one of Scott's SL-2520 red dots, a gar2520 and a Huntington 2520 from my personal stock. So, test away my friend. This will be interesting!  :)
8) 8) 8) 8) 8) 8)
with my stock of different DOAs we will have more than 10 to test.
this will get very interesting. all test will be done according to the German broadcast norm called "Pflichtenheft".
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 16, 2009, 12:37:20 PM
Some t-pad advice...

Hey yall,

After a couple of help email-conversations behind the scenes, I have created a little PDF document that should make the t-pad wiring for my pre's a snap. I will also include this doc in the provided zip file for the future.

Anyhow, here's the pdf:
(http://www.classicapi.com/catalog/images/gallery/VP26/PCB/t-pad-wiring.gif) (http://www.classicapi.com/catalog/images/gallery/VP26/PCB/t-pad-wiring.pdf)

Have fun!

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on June 16, 2009, 12:57:39 PM
 8) 8) 8)
cool, this exactly how I did it  ;D ;D ;D
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 18, 2009, 09:03:50 AM
*Attention* to all who have purchased the first run of these boards...

Thanks to Volker, [silent:arts], an error has been discovered in regards to the polarity being inverted at the input. It is a silly mistake that is at least easily rectified. I guess I will blame it on Murphy and his damned law as I have no other logical explanation!  :(

This is in reference to "Classic VP25 Rev A" and "Classic VP26 Rev A.1" only.

The schemo's are correct(mostly). C1 and C2 are reversed but that is of no real consequence at all. Basically, the mic input signal at pins #8 and #10 should be reversed.

The end result of this polarity reversal, can be done a few ways.

Option #1 is how the next revision of boards will be. It is theoretically the most correct way. Here is how I am handling the fix on my boards. Cut 2 traces and add 2 small jumpers.
(http://www.classicapi.com/catalog/images/gallery/VP26/1st_version_Fix/option-1-phase-fix.gif) (http://www.classicapi.com/catalog/images/gallery/VP26/1st_version_Fix/option-1-phase-fix.pdf)

Option #2 is much simpler as will give the same end result. All you have to do is reverse the 2 primary leads on the output transformer. The colors are different depending upon which version you have.
(http://www.classicapi.com/catalog/images/gallery/VP26/1st_version_Fix/option-2-phase-fix.gif) (http://www.classicapi.com/catalog/images/gallery/VP26/1st_version_Fix/option-2-phase-fix.pdf)

And that will handle it. Sorry about the error. I guess it's not the first time these things happen and it probably won't be the last. Still doesn't make me feel good but they sure as hell do sound good!  :)

Thanks and best regards, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on June 18, 2009, 06:01:55 PM
Jeff,

thanks for offering the fix. no problem here with it.

have some time next week, where I will do the output fix first.
than do some measuring.
after that I will reverse it, and do the input fix.
than do some measuring.
I doubt there will be a difference ;D

and since there is a polarity switch and the sound engineers decide by ear no problem.
I'm just a measuring guy  ;D ;D ;D
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 19, 2009, 10:26:44 AM
...I doubt there will be a difference ;D ...I'm just a measuring guy  ;D ;D ;D
I also doubt there will be a difference. Will be interesting to see for fun.

In glancing down this page of this thread...I started to wonder if we should just have this conversation in private. Kind of like that anyhow...tap, tap, tap, check one two...is this damned thing on ? ?  ::)

Did you have the time to record any of your DOA tests? I am curious to see how they compare under scrutiny. I saw the pile of them on your bench in the "show me your workbench" thread. Cool! ;D

Cheers!
Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on June 19, 2009, 10:57:25 AM
Jeff - one thing to learn, my friend:
10 sold PCBs, one build  ;D
sometimes it looks like 100:1  :o :o :o

the DOA tests are done, and all DIY units are spot on !!!
just need some time to put the results in some form.

but to tease:
the gar2520 is very close to your vintage huntington.
only misbehavior: 1 dB less noise.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 19, 2009, 11:17:56 AM
...the DOA tests are done, and all DIY units are spot on !!!
just need some time to put the results in some form.

but to tease:
the gar2520 is very close to your vintage huntington.
only misbehavior: 1 dB less noise.
Ahh Volker! !  :D  That is some good info and a nice tease!

To the ears, which cannot be trusted, they are also very close.

I will have to speak with Gary to see if he can increase the noise a tad  ;D :D ;D

Take your time compiling the results. We will wait patently with baited breathe.  ;)

best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 20, 2009, 08:21:59 PM
Hey guys,

Volker sent me a few links to some of the AP tests he has been running. He said to feel free and post them so I am.

Most are of the VP26 pre with various DOA's.

The first one is a vintage BAE racked 312.

**All of the AP graphs and test results have been temporarily deleted by [silent:arts]. Scott Liebers had noticed a difference in results to the tests he has ran. This prompted Volker to reevaluate his test procedure and criteria. I'm sure he will have this info back up soon. See his post a few down from here.**

Quite interesting I think. Plus, this gives us all a little taste of what Volker will be putting into the 51x website!

Very cool Volker! ! !  ;D ;D Thanks much for providing this info!  ;)

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Skylar on June 20, 2009, 10:10:11 PM
Volker...wow!

You've obviously put a considerable amount of work into this.

Thank you, and...thank you!
What an excellent source of information on DOAs!
(http://i73.photobucket.com/albums/i222/skylargray/GreatGuinness_small.png)




I've got my VP25 channels up and running with Pier's APP2050s.
They sound great, but I'm waiting for the front panel to be engraved before I can put the whole thing together and rock.
I have a couple of DIY 990s that I tried swapping in there, but I think I feel the same way as Jeff...not my thing.
The APP2050s sounded great however.

I'll post some pics as soon as the front panel is here and the whole unit is put together.



Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: gar381 on June 21, 2009, 01:34:58 AM


but to tease:
the gar2520 is very close to your vintage huntington.
only misbehavior: 1 dB less noise.

 :o :o :o  WOW !!!
Thanks for the nice review Volker !!!

(I'll have to work on increasing the noise ;D)

GARY
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on June 22, 2009, 04:14:32 AM
sorry guys, I deleted all measuring since some manufactures complained about it  :o

no, this is not the reason  :)

actually Scott Liebers SL-2520 curves he made are different to mine, and rechecking with other measuring equipment / set up tells me he is right. :-[

since I don't know if I have mixed up the curves, the AP at work is broken, the measuring routines of my colleague are faulty, I took all the files down. we don't want to mess with may be faulty measuring.
another thing I just realized while playing with Scotts SL-2520: there is a huge different if the DOA is just powered on or measured 20 minutes later.

anyway, I will check the AP, will write my own test routines and will re-check every DOA at home with an A2.
this will take some time, but we want real & proven results.

in the meantime I might buy some more DOAs for testing ...
thanks Scott for doubting the results, you have been right.
on the A2 I see even a peak at 20 KHz (after ten minutes on)

I feel very sorry for this (but you should always trust your ears anyway)
end of next week we should be ready again ...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Tubemooley on June 23, 2009, 04:40:03 AM
Volker..... Don't worry. Take your time. I would much rather wait for reliable test results. The fact that you pulled down the results because you're questioning your test procedure and your test equipment shows that you are honest and scientific. And two guys on two different continents (you and Scott L.) are working independently but collaborating on one inquiry. This is fabulous. Take all the time you need. And by the way...... I believe the "heat up" time phenomenon is real. I have no direct evidence of this. But the junctions have to heat up and stabilize for the best performance. Even at 25C room temperature, those junctions are going to be up over 50C I believe after running for 30 minutes. Possibly higher. Einstein had to wait three or four years for his theory of General Relativity to be independently confirmed experimentally. DW.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: ultra-alex on July 05, 2009, 10:47:16 AM
finished two 26´ today. this is indeed a very relaxing build. perfect for a weekend afternoon. thanks for the tipp with the beer, volker! now i just wait for my frontpanels, some nice knobs and of course the 11 slot rack...  ;D
thanks jeff!
cheers, alex
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on July 28, 2009, 11:12:28 AM
hey guys,

just about to mount my profile 4804 (aka 2503) output transformers on my VP25 boards - it seems that the mounting holes are plated and therefore appear to be connected to the ground plane... (sorry, i don't have a multimeter with me right now to check for sure).

so do i need to insulate the transformer core using washers or anything? the schematic doesn't show any connection to the output transformer core...

cheers,
Haima
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on July 28, 2009, 11:27:09 AM
yes, the output transformer core is grounded ;)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on July 28, 2009, 11:47:04 PM
nop dont insulate them!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 01, 2009, 11:47:41 AM
As I packaged up a kit with a raw face-plate yesterday, I got to wondering how you guys who have the raw plates have finished them.

I would quite enjoy some pics if you have any.

BTW, Pan60 over at GS has an assembled VP26 with 4 different DOA's from members here at the Forum. He got it last week. We are just starting a little interview process that will include Ed, Gary, Scott, Pier and myself. Pan60 is of course completing a full product review in the way only he can! Should be quite fun and interesting not to mention some good "kudos" to our great forum here.  ;)

Best, Jeff  :)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: ultra-alex on August 02, 2009, 05:34:43 AM
As I packaged up a kit with a raw face-plate yesterday, I got to wondering how you guys who have the raw plates have finished them.

I would quite enjoy some pics if you have any.

...

jeff,
my faceplate design is still not "perfected", but here is the "pre-release"...  ;D ;D ;D
cheers, alex

(http://www.ultraton.net/33609diy/26-1.jpg)

(http://www.ultraton.net/33609diy/26-2.jpg)

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 02, 2009, 06:42:47 PM
jeff,
my faceplate design is still not "perfected", but here is the "pre-release"...  ;D ;D ;D
cheers, alex
8) Hey Alex...I love it! 8)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 02, 2009, 06:54:20 PM
Hey everyone,

I just finished building a pair of pre's for a friend. He wanted a more authentic 312 card instead of the "console" version that is the VP2x. After completing the assembly, I thought I would take a few pics and add the info to my site. It is very easy to do, actually easier than one of my regular VP2x builds. Basically, you just leave off a few components, add 2 jumpers and change the feedback cap value.

That's it! Instant 312...just add milk. I will start including a VP25.312 schemo in the zip with the support docs.

So, here's the skinny:


(http://www.classicapi.com/catalog/images/gallery/VP25/VP25.312-side-close.jpg)

(http://www.classicapi.com/catalog/images/gallery/VP25/VP25.312-back.jpg)

FWIW, 3nity is working on a straight up 312 clone that will include a DI with a switch to select Mic/DI. 500 series also.

Cheers all!
Jeff  :)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Brolik on August 16, 2009, 07:00:10 PM
hey guys, this must be winner of the stupid question of the year award, but how do I put the pushbutton switch caps on? I've fiddled with them for awhile now, there's no installation information on the datasheets. I feel like they must just push on, but I've tried and don't wanna push any harder unless I'm sure it's right.  Other than that assembled my VP25 in the better part of a day, nice and easy! Thanks Jeff!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 16, 2009, 07:55:01 PM
hey guys, this must be winner of the stupid question of the year award, but how do I put the pushbutton switch caps on? I've fiddled with them for awhile now, there's no installation information on the datasheets. I feel like they must just push on, but I've tried and don't wanna push any harder unless I'm sure it's right.  Other than that assembled my VP25 in the better part of a day, nice and easy! Thanks Jeff!
I have noticed the same thing with the switch caps. The old ones are almost too loose. They will just push on. I use a jewelers screw driver and slightly pry open the cap where the 2 slots are at. I engage the the pushbutton then push them on. Sometimes the rubber handle of a pair of pliers makes for better leverage. I small drop of dish soap will help a little too. I little pressure and they will snap right on.

Please don't ask how to get one off!  ???  :o

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Denyle Guitars on August 17, 2009, 11:39:08 AM
Another stupid question: Is there any reason why I shouldn't hang a led on one of the rails for the +48v switch?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on August 17, 2009, 11:54:59 AM
Another stupid question: Is there any reason why I shouldn't hang a led on one of the rails for the +48v switch?
no
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Denyle Guitars on August 20, 2009, 07:20:02 PM
Here's a shot of my semi-temporary front panels.

(http://www.denyleguitars.com/images/vp_26)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Holger on September 02, 2009, 09:09:13 AM
Got my kit today, took 2 hours to finish.
I did the red-orange flip mod.
Thanks for this cool and easy-to-build project.
(http://audiofor.tv/diy/ProjectFotoFolder/51x/26-5.jpg)
 (http://audiofor.tv/diy/ProjectFotoFolder/51x/26-6.jpg)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Moby on September 02, 2009, 09:49:52 AM
jsteiger and others, sorry for off-topic question but can you explain difference in the classic api's 4 versions of output transformers? Does all of them have same inductance and freq. response? What about sonic differences?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: edanderson on September 02, 2009, 12:47:57 PM
all three 2623 types are the same electrically, just different mounting options.  the core is a 1/2 inch size, EI shape, steel lamination.  this is bit smaller than most common "modern" output transformers, but was very common in older consoles.

the 2503 is a 5/8 inch size, EI shape, steel lamination.  this is the same size as the common transformers from jensen, cinemag, etc, and the same type of transformer that you'd find on a vintage 312 or a new 512 module. 

though the 2503 is physically larger, it has fewer turns than the 2623, so the inductance is actually lower.  frequency response is similar, as they are both flat well beyond the audio band.

ed

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 13, 2009, 01:17:04 PM
Hey guys,

I have some info below that pertains more to the actual "sound" of the VP2x preamps. I have noticed a few threads over at GS pertaining to them.

Mark Linett has has posted some very kind words that make me all warm and fuzzy inside!  ;D 8) :)
First thread in "High End" is here. (http://www.gearslutz.com/board/high-end/422143-anyone-using-vp-25-26-classic-api.html)
Second thread in "So much Gear" is here. (http://www.gearslutz.com/board/so-much-gear-so-little-time/422061-thoughts-500-series-vp25-26-a.html)

This is very cool to see, especially coming from an engineer with Mark's ears and credentials (http://music.msn.com/music/artist-credits/mark-linett.2/?startingItem=1&ipp=25). Clapton, Red Hot Chili Peppers, Santana, Brian Wilson, The Beach Boys, and on and on...More Mark info is here (http://www.studioexpresso.com/profiles/markLinett.htm).

Cheers all, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on October 09, 2009, 01:55:48 PM
Jeff- just want to thank and congratulate you on a fantastic preamp kit! i've been using my pair of VP25s for a few weeks and i can tell i'm going to want more as soon as i can afford them. they were so easy to put together - awesome.

i used them today for DI'ed bass (via a diy passive cinemag transformer DI box) and they won out over all my other preamps (including oep G9, cinemag baby animals etc) for the sound i wanted - the tone is very nice, clear and punchy but not harsh at all.

on drums they sound awesome too. also, the output attenuator works wonders on drums, you can really drive it and the distortion character is crisp and upfront.

if anyone is looking for a 500 series preamp kit - this one get's my vote.
thumbs up!

Haima
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 10, 2009, 09:31:27 AM
Thanks for the very kind words Haima!  :)

Your passive DI definitely gives you the benefit of the EA2622.  ;)

Continue enjoying!
Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Skylar on October 21, 2009, 08:25:47 PM
SERIOUSLY

These pres ROCK!


I just finished a vocal session using a Blue Cactus > VP25 > Lucid 8824 > DAW.

Magnificent vocal sound.

These amps really made the Cactus mic come to life...I wasn't really liking the mic until I used it with the VP25.
(previously I had used the Cactus with my G9, Seventh Circle N72, Octopre, and my own BA283-based pre)

Holy Geez.


By the way, I'm using Pier's APP2050 DOAs.


As you can see, Jeff, I need to buy two more channels from you at some point!



Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: dmp on November 10, 2009, 04:48:35 AM
Hi, I'm building two of these VP25 preamps and I was wondering if a stepped switch like a 12P Grayhill would fit to use for gain? Has anyone tried this?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on November 10, 2009, 08:32:45 AM
dmp - i'd say you MIGHT be able to fit one of those small blue elma switches. like the ones used in the helios channel strip on this page:

http://recforums.prosoundweb.com/index.php/m/291238/0/

dunno if grayhill make something similar. they probably do...

you'll probably have to get your calipers/ruler out, look at the switch datasheets and see if it'll fit. if it looks promising - buy one and see.

good luck!

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: dmp on November 11, 2009, 12:01:49 PM
Thanks Haima, I measured the board and there's about .350" from the center of the mounting hole to the board. That's smaller than all the rotary switches I've found so far, but I haven't found a datasheet yet for a elma or grayhill switch. I'll see if I find something...

Holger, what is the red-orange flip mod? looking at the datasheet and schematic it looks like it flips one lead of the primary to secondary. I don't understand that...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on November 11, 2009, 12:46:03 PM
Thanks Haima, I measured the board and there's about .350" from the center of the mounting hole to the board. That's smaller than all the rotary switches I've found so far, but I haven't found a datasheet yet for a elma or grayhill switch. I'll see if I find something...

Holger, what is the red-orange flip mod? looking at the datasheet and schematic it looks like it flips one lead of the primary to secondary. I don't understand that...
I am not sure about the rotary switches and layout. I only had the Bourns pots in mind when working things out.

The orange/red mod is for polarity reverse. Depending upon which Rev PCB's you have, there needs to be a polarity correction made. I have that noted in the READ ME file of the docs zip. BTW, all the polarity pushbutton is doing is flipping these 2 leads of the output transformer's primaries.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: dmp on November 14, 2009, 08:39:05 PM
Thanks, the polarity flip makes sense. I was confused because of a different color coding of the primary leads.
 
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on November 14, 2009, 09:42:45 PM
dmp - re: rotary switch, if you can find one that is small enough in diameter it might be able to fit without it touching the pcb... but it would have to be seriously small, you'd probably need to drill out the mounting hole in the panel and bracket too.

if i was you i'd just build one or two with the standard pots from jeff - at least to begin with... and go from there.

good luck!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: dmp on November 14, 2009, 09:53:43 PM
Thanks haima,
I ordered the standard pot to do just what you suggest...
I'll try the rotary swith on a later project...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: dmp on November 18, 2009, 02:27:00 PM
I have my preamps assembled and just waiting on the psu to try them out...
I was wondering about the output attenuator in this application?
If the preamp sounds better with a 600 ohm load on the output, shouldn't one put a 600 ohm resistor on the secondary, if omitting the attenuator? My recording interface has a much larger input impedance ~10k.
Any links to the theory on how a 600 ohm load affects the 2520 output versus a higher (~10k) would be appreciated. Frequency filtering from the inductance of the transformer? Give me something to do while waiting on my psu board...
Thanks!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on November 18, 2009, 05:19:48 PM
dmp - the output attenuator presents a 600 ohm load to the secondary of the output transformer - performing the same task as a 600 ohm termination resistor... so you are all good.

the advantage of the output attenuator is that you can run your preamp a little hotter to get more colouration - and then attenuate the output to suit your recording format :). this is similar to the technique of turning the preamp up and the fader down that many people do on consoles.

i'm not an expert on the sonic effect of 600 ohm loads on API preamps - i do know some output transformers require proper termination to be flat in the top end (old neve's etc). i don't think this is the case with API as these output transformers are very flat out to 100s of khz. however, 600 ohms is a heavier load than 10k - which DOES loads down the opamp and makes it work a little bit harder, which will effect the sound - more harmonics, etc.

try it with and without a 600R load and see what you like...

i'm guessing the effects of this load change would probably be fairly subtle, the 2520 is quite a burly opamp - it can handle some tough conditions - but like everything it does have a sound. it's not 100% clean, but it's not a fuzz box either by any means. remember that many great sounding albums have been made entirely using these console preamps. "mixing and matching" preamps is a relatively new thing. william wittman (cyndi lauper) is one engineer i can think of who prefers not to buy into this recent trend - instead he prefers to use one preamp design for all sources - coincidentally he often uses API consoles...

i guess what i'm saying is that these preamps sound good enough to use for pretty much everything :)

have fun!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: gar381 on November 18, 2009, 05:40:58 PM
If you are omitting the attenuator
and drop a 604R or 620R (what ever you got)
accoss the trafo output
your Pre won't mind it a bit and your 10k input
of your next device won't mind it either.  :) :)
Listen to it both ways and pick what you like.

GARY
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Sleeper on November 20, 2009, 03:01:06 PM
Just about to start mine up.
I'm going to rack mount them but I have a question

I already have a -2, -5, -10, -20db bridged-H   600 ohm stepped pad
I'm thinking about this on the output...  
It's all 1/4 watt though
I looked up the clarostat 70 series and it looks like the output attenuator is 1/2 watt .
I'll admit to being a tad lazy here--(I've found the info and calculated something similar before but I was hoping to avoid doing math today)
I'll get back to searching in a few hours, but maybe one of you guys already knows if 1/4 watt will be OK.
Couldn't hurt to ask.
Thanks
Kelly
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: dmp on November 21, 2009, 12:16:42 PM
Well, Power = V^2/R (from ohm's law, V=IR and P=VI)
so for a 1/4 watt, a 600 ohm load can handle Voltage = ~sqrt(.25*600) = ~12V
This would be a pretty high RMS output from a preamp wouldn't it? 24 dBv I think?
I'm sure others know a lot more, but I think it would be fine.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Sleeper on November 21, 2009, 01:52:31 PM
Hi DMP and thanks for looking at that.
I've been running some of the calculators on the net, but my confusion stems from the API specs which (with a plus minus 20v psu) claim 30 dbM output.  24.4949 vRMS  according to this calculator.
http://www.sengpielaudio.com/calculator-volt.htm (http://www.sengpielaudio.com/calculator-volt.htm)
That's a full 1 watt of power (unless I'm plugging these figures in the wrong way)
Not that I'll be running sine waves at full level and padding down the output...

Wouldn't the power dissapation resistor requirements for a balanced signal (post-transformer and all) be halved with a bridged-H because I'm attenuating on both legs?  gotta check this.
But OTOH it's close to the edge and I'm going to try what I have on hand anyways...
I'm pretty sure in real practice this will not be an issue at all.
We'll see.
Thanks again
Kelly


Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on November 22, 2009, 09:40:45 AM
The VP26 has a headroom of about +25.8dBu when driving a 600 ohm load. +27.4 without being terminated.

+26dBm is about .4 watts. +24dBm being about .25 watts.

Those levels are more like absolute peaks, not an average signal levels.

With an average level of say +18dBu, which is very high IMHO, you have about .063 watts. Well below the capacities of the Clarostat t-pad or even 1/4 watt resistors. I would say a real world average level may be more like +6dBu or so. That would give you a wattage of .004.

BTW, the Clarostat series 70 pots capacity drops from 1/2 watt to 1/4 watt when going to a 3 deck configuration. I'm not exactly sure why.

In a real world application, there should be no issues at all. If one plans on running sine waves at +25dBu for long term...there will be some issues!  :) I know this will never happen.

Someone correct me if my math is wrong.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Sleeper on November 22, 2009, 02:00:54 PM
Hi Jeff,
Thanks. and that's also awesome because my attenuator should work
Your math is in line with what I got.
I'm just so lousy at the maths- I'm always concerned that I'm not plugging things into the formula correctly.
I'm pretty sure the balanced H should be great for this application, and I have room so away we go.
Thanks again
K

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on November 22, 2009, 02:09:52 PM
...I'm pretty sure the balanced H should be great for this application, and I have room so away we go...
Yes, I agree. Let us know how things work out.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: TheGuitarist on November 22, 2009, 07:40:41 PM
Could anyone describe the differences between the vp25 and 26 please?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: funkymonksf on December 09, 2009, 04:36:50 PM
Does anyone have a FPD file for the face plate that I can use to design my own faceplate with. I want to send it to frontpanelexpress.com and make mine look oh so sexy. Anyone? I would highly appreciate it.

[email protected]
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 09, 2009, 05:26:24 PM
TheGuitarist - the only difference is the output transformer.

the VP25 uses the 2503 output transformer (as used in the 312 and most of the api made 500 series)

the VP26 uses  2623-1 output transformer. these are what was used in the api consoles i believe. this transformer is $10 cheaper... slightly smaller, but it is wound differently so that doesn't necessarily mean it's lower headroom.

i have made VP25s and i'm very happy with them - i chose that model as i already had 2503s in stock. i'm interested to compare the two - i have no doubt they are both awesome. i imagine the difference would be subtle, they are both pretty high headroom transformers.

jeff has more info on his site:

http://classicapi.com/catalog/product_info.php?products_id=33 (http://classicapi.com/catalog/product_info.php?products_id=33)

http://classicapi.com/catalog/product_info.php?products_id=79 (http://classicapi.com/catalog/product_info.php?products_id=79)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Sleeper on December 09, 2009, 06:35:47 PM
Does anyone have a FPD file for the face plate that I can use to design my own faceplate with. I want to send it to frontpanelexpress.com and make mine look oh so sexy. Anyone? I would highly appreciate it.
OK this post reminds me, I said I was going to start next week and that was a few weeks ago, but I've got a nice break coming up so I'm really getting started.

I DO have to design a front panel and since I'm out of town at the moment, it would be a good time to knock this design together. I'm making mine as a side by side pair in 1 rack space.  I was planning on taking my measurements off the boards, but I didn't bring them with me on this trip. (much as I'm excited to get started)

If there's an FPD or illustrator file maybe someone can post it or PM me.
or Jeff- if you know the spacing between the front panel items,  that's all I really need to know.
It would be a great help.
Thanks
Sleeper
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: funkymonksf on December 09, 2009, 11:38:30 PM
That exactly what I need to is the spacing information between the holes. If anyone has these, can you please send them to me at [email protected]

-Thanks
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on December 12, 2009, 09:57:57 PM
Just got a pair of these beautiful kits today with the GAR2520 DOA kits. Can't wait to build these and slide them into my Lunchbox for a test drive. Thanks to Jeff and Gary for making these kits and to all others who participated in the development.

On another note, what became of Silent:arts' re-measurements of the various DOAs? Did I miss it?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 14, 2009, 04:13:20 PM
Hi,
I finish building my VP26 and unfortunately it seems I'm the first one to have any problems.

Every time I connect this Pre there's smoke coming out of the GAR2520 Opamp.

I rechecked Caps polarity, diodes resistors and solder joints and everything seems fine.

I swapped the burnt OPamp for another GAR2520 that I had and it also burned imediatly after I applied power to the rack, I couldn't figure out from what component was the smoke coming from maybe the BD139, Im not sure, but it was definitely coming from the opamp.

Any ideas of what might be the problem?

thanks a lot

here are some images:

(http://www.twin-x.com/groupdiy/albums/userpics/vp26_2%7E0.JPG)

(http://www.twin-x.com/groupdiy/albums/userpics/VP_26_1%7E0.JPG)
 
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 14, 2009, 04:42:51 PM
maybe some hi res shots of the solder side? maybe you've bridged something...

my experience smoke usually happens when you've got the power supply reversed somewhere or the power supply voltage is too high for a component, or you're drawing WAY too much current somewhere. a short could cause things like that...

did you make the opamps yourself? is there a chance both of them have a reversed component or bridged track?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 14, 2009, 04:45:03 PM
what rack are you using, out of interest?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 14, 2009, 05:09:33 PM
did you make the opamps yourself? is there a chance both of them have a reversed component or bridged track?

A friend of mine did one of the OPamp's last week, and I did the other one sometime ago.
I re-checked the components in the OPamps, couldn't see any reversed component, the tracks and solder joints were also really clean on both OPAMPS.

what rack are you using, out of interest?

I'm using the API 500V. Rack is fine, other preamps are connected there and working fine, in the same slot I used.

thanks a lot for your help and interest

Here are some hi res shots of the solder side:

(http://www.twin-x.com/groupdiy/albums/userpics/solder_side_1.JPG)

(http://www.twin-x.com/groupdiy/albums/userpics/solder_side_2.JPG)


Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 14, 2009, 05:16:34 PM
Yes, Haima makes good and valid points. Like he says, is it possible that both of the gar's had the same issue?

Can you check your voltage rails with power to module and no DOA? I have got into the habit of testing my projects with a bench supply before I drop an opamp in. I like to test right at the DOA sockets.

I think I can make out from the pics that you have only soldered from the bottom of the board? Like Haima says, check the bottom for a bridge or short of some kind. I also like to solder each component I can from the top and the bottom to insure there are no cold or faulty joints.

I had a similar situation once on a summing amp card. The DOA started to get real hot and smell funny. Completely smoked one of the power rail diodes. Removed it, cleaned up the board a bit, dropped in another and made damn sure it was solder very good from top and bottom. No issues and still running good right now. I can only assume I had a shoddy solder joint at the diode.

Let us know.

Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 14, 2009, 05:39:18 PM
Hi Jeff,
thanks a lot for your input and Haima.

You are right I only soldered from the bottom of the board, I will solder from the top also.

Like I said, the opamps were built at different times, by different people, components all seem to be pointing in the right direction and the solder joints are really clean, so I don't think the problem is coming from the Opamp themselves but I took some pictures anyway.

(http://twin-x.com/groupdiy/albums/userpics/2520front.JPG)

(http://twin-x.com/groupdiy/albums/userpics/2520top.JPG)

(http://twin-x.com/groupdiy/albums/userpics/2520bottom.JPG)

I can't clearly see which component or components burned, but R11 and 12 have a different color, darker for sure.



 


Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on December 14, 2009, 05:43:21 PM
what went wrong with the black cable of the output transformer?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 14, 2009, 11:15:46 PM
as jeff said - if you have a bench power supply capable of +/- 15v, power up the card using that. connecting the power to the the protection diodes where it would come in via the "finger" of the board, and a good 0v point, and measure the voltages present at DOA sockets - without the DOA installed.

if you don't have a bench supply, clear enough room to the right of the module in the rack to get your multimeter probes in to measure the voltages at the DOA socket - again, without the DOA in there.

let us know what voltages you have where.

looking at the bottom of your board, there's a few solder points that look a bit "bulge-y" - like there's perhaps too much solder there, and perhaps not enough heat... i'm looking at the secondary of the output transformer for example. not that a shorted secondary would cause the opamp to burn up - but i'm just saying, might be worth cleaning up the points a little, perhaps removing some excess solder, making sure you've got good "flow" into the joint.

** EDIT: i noticed the output transformer PRIMARY solder points look like they might be shorted due to excess solder... these are the two points near the output transformer nut. measure the resistance between them - are they shorted? **

good luck! we'll get there...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 15, 2009, 01:44:09 AM
some more measurements that are worth doing - with the card out of the frame, no opamp installed:

A) what's the resistance of from the opamp output pin socket to ground/0v? (related to the possibility of output transformer primary being shorted, mentioned in my previous post)

(the following stuff shouldn't be a problem given the rack seems happy with the module installed (no fuses blown etc)... but what the heck, these things are good to check:)

B) resistance from +ve to -ve on the opamp sockets?

C) resistance from +ve on the opamp socket to ground?

D) resistance from -ve on the opamp socket to ground?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 15, 2009, 12:42:17 PM
what went wrong with the black cable of the output transformer?

I cut it too short by mistake, so I had to extend it a bit by soldering a bit more lenght, and then used heat shrink tube over it.

as jeff said - if you have a bench power supply capable of +/- 15v, power up the card using that.

Thanks Haima,
I will do that. A friend of mine has an external Edac connector to test these modules, so I will perform the measurements and report here.
Thanks a lot for your input.

I will also do a checkup on all the solder joints.

Green and brown wires of the output transformer are not shorted, although I'm readind 13,5 ohms between Red and orange wires. Could that be right?

thanks a lot once more
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: mus1k_freak on December 23, 2009, 06:05:43 PM
I have a question about phantom power on a build i did with a vp26. I used a JLM input transformer instead of the one from jeff and a purple kdj4 op amp (i think i used a jlm99v for testing). I left out the output attenuator and added a blue led for phantom power switching, i think the led may be my problem. i i wired from the load side of the switch to a 10k resistor to the led and the other side of the led to ground (pin 1 i believe on the card) would this make my phantom power not work? The led comes on when i flip the switch and slowly fades out when i turn it off like it should. maybe the way i wired my input transformer has something to do with it? since theres only 1 primary and 1 secondary on the jlm i left pins 2 and 3 open, and just wired the primary to 1 and 4. Without phantom power everything seems to work fine, with a sm57 it sounds similar to a 512c but with a little more low end, excited to get the phantom power working and try it with the purple op amp!

also with leaving out the output attenuator, do i need to solder anything in its place?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on December 24, 2009, 10:51:54 AM
I just built a pair of these beauties. I ordered ready made DOAs to make it easy on myself. I put them in my API lunchbox and checked the voltage at the DOA sockets without the DOAs installed. All looks good there. #1 fired up and sounds like API Heaven. Holy Vintage, Batman!!! Pre#2 has a problem that I am unable to track down. These is audio passing thru the unit but it is very low level and sounds like it is single-ended. I am guessing that I might be shorting one side of the input before the transformer. I tried to swap the DOAs but that did not change anything. I suspected a problem with the Pad switch so I removed that, it checked out ok, then I re-soldered it. I am getting a bizarre resistance reading from the -16 input to pin 3 of the switch. 148k, like it is shorted across to the other pole. But the first 2 pins show 0 resistance to the inputs so it should work in the open position regardless. The pad switch may not be the main problem is what I am thinking.

I spent much time examining parts placement and soldering, checking for shorts and comparing things to the working pre, all to no avail. All resisters and caps appear correct, and polarities look good. I hope someone can point me to a few test procedures to narrow the problem. I do not have a test jig to power the pre on the bench while plugged into the Lunchbox. I do have a 16 volt supply that I can power it on the bench without audio I/O.

I saw Haima's post #85 and was going to try these but he does not say what they should read. Any signs pointing in the right direction would be appreciated.

Happy Holidays to all.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 24, 2009, 02:46:37 PM
I have a question about phantom power on a build i did with a vp26. I used a JLM input transformer instead of the one from jeff and a purple kdj4 op amp (i think i used a jlm99v for testing). I left out the output attenuator and added a blue led for phantom power switching, i think the led may be my problem. i i wired from the load side of the switch to a 10k resistor to the led and the other side of the led to ground (pin 1 i believe on the card) would this make my phantom power not work? The led comes on when i flip the switch and slowly fades out when i turn it off like it should. maybe the way i wired my input transformer has something to do with it? since theres only 1 primary and 1 secondary on the jlm i left pins 2 and 3 open, and just wired the primary to 1 and 4...
Did you try completely removing the LED and see about the phantom? If all is fine like that, which it should be, try connecting the LED to the PSU common-pin #13 instead of pin #1. Not sure what if anything pin #1 is connected to on your rack. Sounds like the input iron wiring is fine to me.

Quote
also with leaving out the output attenuator, do i need to solder anything in its place?
No, it has been taken care of on the PCB. You will just need to connect the output transformer's secondary to the holes labeled "Opt-(whatever color)" right near the gold fingers for pins #2 and #4. The color's are output transformer dependent.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: mus1k_freak on December 24, 2009, 09:05:39 PM
ah right i do remember moving those two wires on the output transformer, that makes sense, thanks jeff! i haven't had a chance to try it without the led yet, but hopefully ill have some free time in the next day or two and try pulling it out and see what happens, thanks! and merry christmas!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: djmukilteo on December 24, 2009, 09:55:07 PM
I need to build one of these
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 24, 2009, 11:09:18 PM
Hey Surfkat,

Double check your wiring on the t-pad and output transformer. I had a guy who described similar problems before. Turns out he made a small error when wiring the attenuator.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 25, 2009, 03:23:09 AM
OK, here's some clarification on the basic troubleshooting tips above. i'm hoping this is all correct - i can't verify exactly as - my units are "permanently borrowed" right now...  >:( :)


with the card out of the frame, no opamp installed:
---------------------------------------------------------

Quote
A) what's the resistance of from the opamp output pin socket to ground/0v?
should be "SOME RESISTANCE" (i.e. not a short)

Quote
B) resistance from +ve to -ve on the opamp sockets?
should be VERY HIGH

Quote
C) resistance from +ve on the opamp socket to ground?
should be VERY HIGH

Quote
D) resistance from -ve on the opamp socket to ground?
should be VERY HIGH


now with the card in a rack or connected to a bench power supply, no opamp:
---------------------------------------------------------------------------------------

E) check +ve and -ve power supplies are at the correct pins - both voltages are present and not reversed etc


if all these checks are positive, install the opamp and test for audio :)


--
mus1k_freak: if you were using a JLM99v to test, was it the  +/-16v version? i'm not sure how happy the standard one is at +/-16v - it's more designed for +/- 24v to 34v as far as i know...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: mus1k_freak on December 25, 2009, 07:56:02 AM

mus1k_freak: if you were using a JLM99v to test, was it the  +/-16v version? i'm not sure how happy the standard one is at +/-16v - it's more designed for +/- 24v to 34v as far as i know...


yup its the 16 volt one, it actually sounds pretty good! i also tested it in another vp26 i have thats built to spec and i like it alot, not as much as the gar2520 though! but i think it sounds better in the vp26 then it does in the eisen i pulled it out of, maybe next ill try the gar2520 in the eisen and see what happens! purple kdj4 on its way for the new vp26 with the jlm input transformer ;D
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 25, 2009, 07:39:15 PM
Hi,
after carefully re-checking every component in the Gar2520 opamps I realized that the BD140 and BD139 are swapped with each other.
So this might be the cause for the burning Opamps and not the mic pre board.

What do you think?

thanks

(http://twin-x.com/groupdiy/albums/userpics/2520front.JPG)

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 25, 2009, 09:14:28 PM
Hi,
after carefully re-checking every component in the Gar2520 opamps I realized that the BD140 and BD139 are swapped with each other.
So this might be the cause for the burning Opamps and not the mic pre board.

What do you think?...
Well, the BD139 is NPN and the BD140 is a PNP so I would agree that this is a/the smoking problem.

A friend built one and you built the other right? Odd that both of you guys made the same error but I guess "sh*t happens" as they say.

It is as clear as day in your first pic. I was so worrying about think of the preamp board that I didn't look real close at your DOA pics.

The preamp is a pretty simple build. Much easier than the gar2520.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 25, 2009, 09:26:00 PM
that sounds like the problem (or at least A problem!) ;D

i'd replace those BD140 and BD139 & probably those higher wattage output resistors... hopefully you'll be good to go! not having the schem, it's hard to say - but hopefully that's the only parts that would be damaged.

be careful removing components from a double sided board like these - best to snip the transistors off and then pull out each leg individually - otherwise you run the risk of overheating the board and lifting traces.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 25, 2009, 09:32:36 PM
...be careful removing components from a double sided board like these - best to snip the transistors off and then pull out each leg individually - otherwise you run the risk of overheating the board and lifting traces.
A very nice tip indeed! Thanks haima!  ;)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 25, 2009, 09:43:47 PM
Thanks a lot for the tips,
I will replace the transistors.

The resistors don't seem Burned out, the look fine, should I replace them also?


Do I need to buy a specific brand , or that is not really important?


Yes Jeff, it's a shame that we both did the same mistake when building the OPamps, it's my fault because I did the first one, and he used the one I built as a reference for the second one. And what a bad reference it was!!!

thanks, once more

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 25, 2009, 09:54:31 PM
someone with a better understanding of opamp design theory would have a clearer idea of what would be damaged by reversed ClassAB NPN PNP pairs.

my thinking was - they are cheap parts, just replace them and get on with life - but i have a large stock of these kind of parts, if you have to order new resistors it'd be worth checking them first.

when you have the transistors removed you could measure the resistance of the resistors - if they check out ok you're probably fine... no need to replace them.

personally i wouldn't worry about the brand of either the resistors or the transistors - just use what you can get easily.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 27, 2009, 08:48:15 PM
Hi,
first of all I want to thank Haima, Jeff and Silent Arts for the helping me in my build.

I replaced the transistors in the OPamps, re-checked all the solder joints and components in the boards, and I also soldered the components from the top of the Pre board and not only from the bottom.

The Opamps are not burning any more, they seem fine, although there's no sound coming out of the preamp.
I can't figure out where the problem resides.

I did some measurements,

measure the voltages present at DOA sockets - without the DOA installed

at socket V+   there's   15,57 volts
Socket V-  there's    -15,59V


I measure the resistances also, my DMM doesn't measure resistance above 2Megs , so above that there's no read.

A) what's the resistance of from the opamp output pin socket to ground/0v?

Above 2Megs, no read

B) resistance from +ve to -ve on the opamp sockets?

Above 2Megs, no read

C) resistance from +ve on the opamp socket to ground?

Above 2Megs, no read


D) resistance from -ve on the opamp socket to ground?

Above 2Megs, no read


Sometimes when I measure the resistance in this cases, the multimeter starts to read 1500 and then gradually increases the value , until it reaches 2M and them stops reading, like if it went to +infinity


I checked the resistance after the T Pad attenuator, and it seems to be performing fine, the resistance value decreses when you turn it up, reaching zero when it's turned full clockwise


there's any other tests I could perform to help the troubleshooting?

thanks a lot once again
my best regards

Tiago

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on December 27, 2009, 09:09:13 PM
try another DOA in working condition first..
If it burns then the fault its on the VP board..
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 27, 2009, 09:09:46 PM
Might be a silly thing to say but is the "Mute" switch functioning at all?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on December 27, 2009, 09:17:10 PM
could be that other components burnt when the darlingtons were switched.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 27, 2009, 09:21:28 PM
try another DOA in working condition first..
If it burns then the fault its on the VP board..

Hi 3nity, I've tried 3 Opamps today, the 2 I already had, and another one that was working in a 312 pre.
None Burned , but there was still no sound coming out from the pre


Might be a silly thing to say but is the "Mute" switch functioning at all?

Not silly at all, I thought exactly about the same thing.
I measure continuity from the orange and red wire of the output transformer to the switch, and when in normal position  there's was continuity from those wires going to the mute switch and then to the Phase switch.
When the mute switch was pressed there was no continuity going to the phase switch at all.

Maybe there's some better way of checking this....

thanks a lot guys

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 27, 2009, 09:25:10 PM
could be that other components burnt when the darlingtons were switched.

Maybe, but all the resistors in the VP26 board seem fine, they retain the blue colour as new.
The capacitors also look fine, at least i couldn't notice any change, but I don't know how do you see if a capacitor has burned.
The resistors I know that they burn and you can easily see it, the capacitors I dont know if they blow or can be damage inside without you even noticing it.

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 28, 2009, 12:02:38 AM
whoops - do you have a way to trace signal - like a signal injection probe and a little amp? if not you should make one... you can make a probe out of a old cable and a DC blocking capacitor. have a search online.

that way you can start at the input or output and see where the signal stops (if it does) - you shouldn't need to even have the preamp powered up to do most of this.

A) signal should make it from the inputs on the card edge to the opamp input

B) signal should make it from the opamp output pin to the output on the card edge.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 28, 2009, 12:28:33 AM
whoops - do you have a way to trace signal - like a signal injection probe and a little amp? if not you should make one... you can make a probe out of a old cable and a DC blocking capacitor. have a search online.

that way you can start at the input or output and see where the signal stops (if it does) - you shouldn't need to even have the preamp powered up to do most of this.

A) signal should make it from the inputs on the card edge to the opamp input

B) signal should make it from the opamp output pin to the output on the card edge.


yes Haima I have a probe that I used in the past to trace signal in some guitar pedals I built.
What signal should I inject? what should I use?

I don't need to power the preamp to trace it?

thanks
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 28, 2009, 11:05:25 PM
hey whoops, you need two things:

1) a signal source (signal generator, ipod etc) with a cable that ends in alligator clips or some other type of clips

2) a signal probe to listen to the signal source


with the opamp removed and the preamp NOT powered, sitting on your bench, check the input up to the opamp non-inverting input:

A) connect signal source, to "In Hi" & "In Lo" (pin 10 & 8 on the edge connector, or the side of the 750R resistors that doesn't connect to the 160R resistor)

B) connect the 0v/ground of the probe to a 0v point on the  preamp.

C) probe the non-inverting input pin on the opamp - you should hear the signal source.

D) if you don't trace the signal from the input, following the schematic - see where it stops.


i'll write similar instructions for the output section if you need it...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 28, 2009, 11:49:01 PM
Hi Haima ,
thanks a lot for taking you time to explaining.

I did signal probe tracing today, the sound was interrupted in the connection from the phase switch to the Mute Switch. The traces are on the top of the board, but you cannot reach the pins in the switches from the top, to solder them also.
I redid this soldering points as much as I could, problem seems to be solved (I have continuity now from phase switch to mute switch) the signal doesn't seem to be interrupted any more.

I will check tomorrow in the studio in the rack and with a microphone.

Thanks a lot for all your help, I'll let you know how the conclusions tommorow.

 
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 29, 2009, 12:07:44 AM
 :) let's hope that's it!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on December 29, 2009, 06:03:38 PM
HAIMA - thanks for writing those explicit troubleshooting directions. I would appreciate it if you could write instructions for troubleshooting the output as well as I am still struggling to get one of my VP26 pres to work properly. I took sometime off for Christmas and went back to it today. Jeff suggested that I might have a problem with the attenuator or the output trans wiring. I double checked all of that today but found no problems. I made a signal probe today and was going to check the circuit tomorrow and came here looking for help with that. Thanks
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 29, 2009, 06:33:00 PM
no probs... here's one way to trace the output stage:

opamp removed, no power supply attached, preamp sitting on the bench.

A) connect your signal source - attach the "signal" lead to the opamp "O" (output) pin socket. attach the "0v/sheild/ground" lead to a 0v point on the preamp.

B) connect your probe "0v/sheild/ground" to the same 0v point on the preamp.

C) probe the opamp "O" (output) pin socket to confirm you have your signal source. you should hear it!

D) probe the output transformer primary "red" connection - you should hear signal. if not try actuating the phase and mute switches. still nothing? do step E. otherwise skip to step F

E) trace along the schematic to follow the signal out of the opamp output pin, from left to right (C10, phase switch, mute switch) till the signal stops - your problem might be around there.

F) now test the output all the way to the end - with your signal generator still connected as before, connect your probe "0v/sheild/ground" to the "black" lead on the output transformer or card edge pin 4.

G) probe the "blue" lead of the output transformer - got signal? if so,

H) probe the card edge pin 2 - turn the output attenuator - got signal? if not look at the attenuator wiring, everything on the output transformer secondary.

GOOD LUCK!

BTW - it's always good practice to be careful with your alligator/jumper clips - not that you can hurt anything with the preamp un-powered like we are with this test - but if you DO have the unit powered up for other tests it can be easy to cause damage if you let the clips short across power supply rails etc...

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 29, 2009, 06:39:00 PM
Hi Haima,
tested the Pre today in the studio.

Everything seems to be working fine, so the late problem was really realted to the connections between phase and Mute Switch, the traces are on top of the boards but it's impossible to solder the switch pins , because they are close together.

Anyway, I'm really happy.

thanks for you help and Jeff also.

Now I need to fix one of the Gar Opamps that burned, I replaced the resistors ans BD transistors and it still doesn't work, but I keep that to the respective thread.

Thanks


Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 29, 2009, 06:43:03 PM
whoops - glad to hear  :)

i'm sure you'll get the opamp going - even if you have to replace ALL the components. in fact, sometimes with a little circuit like this it's the easiest way - life's too short  ;D
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 29, 2009, 07:41:43 PM
Very good to hear whoops.

Interesting situation that was your problem. All of the holes are "plated thru holes" so technically, the top and bottom solder pads are connected by the plating that runs thru the hole on the PCB. I think it is good, solid build practice to solder any part or component you can from the top and the bottom. Not 100% necessary but still good. Naturally, some of the components cannot physically be soldered top and bottom. Like on the PB switches and the 2622 for instance. The tails are thin and rectangular so a nice flow of molten solder down into the hole is definitely doable and preferred. I use a very small and conical tip so I can "get down into" the holes as much as possible. I'll tell you one thing, desoldering a 2622 that had real good flow down into the holes can be a real PIA.  ???

Anyhow, sorry you had to go thru all of this with the pre.

BTW Haima, your trouble shooting tips are very detailed and well written.  ;) I have been working on a detailed, step by step assembly guide for the VP2x pres the last few weeks. I can't even begin to count the hours I have into it. I have maybe 30 more pics to crop and insert into the text and then I am done. I have been thinking about adding some basic test procedures that could/should be done. The posts here the last few weeks are perfect info for some testing. I am directing the guide more towards the DIY virgin but hopefully there is a little something there for others too. A lot of first timers have been buying the kits as of late.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 29, 2009, 08:14:21 PM
the step by step guide sounds good jeff!

basic signal tracing skills and concepts are essential if you want to fix just about anything audio/electronics related - even just if it's just troubleshooting everyday studio problems...

and DIY is a great way to learn these skills - anyone who has to FIX a problem on their preamp will learn a lot more than someone who manages to get it right first time  :)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 29, 2009, 11:45:10 PM
Thanks a lot for the words Jeff, and for the the continue support you provided.
Although I think it's not a difficult build the Step by step guide will be quite useful for everyone,
even for more experienced people as it will make the build faster.
It's great that you are doing that.

and you are right all the tips on testing and signal tracing from Haima in the last weeks were great.

my best regards
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on December 30, 2009, 08:01:39 PM
I have followed haima's trobleshooting tips and tracked my problem down. The output section is fine. The input has a greatly reduced level on the + input rail as compared to the - input at the opamp pins. I traced the + input and the signal is good until pin 5 of the input transformer. I inspected and re-soldered this pin but the problem remains. Is it possible I have a bad transformer? I don't know what else it could be. Any ideas?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 31, 2009, 12:01:59 AM
Hey surfkat,

Can you post a pic of the top and bottom of your board?

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on December 31, 2009, 10:15:28 AM
Here's a pic of the top.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on December 31, 2009, 10:22:16 AM
Here is the bottom, a bit out of focus.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on December 31, 2009, 10:24:21 AM
One more of the top. I did not get a good shot of the 4 output transformer wires but I am look and test ok.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on December 31, 2009, 10:37:20 AM
hey surfcat - the placement of C11 is wrong... not that that makes a huge difference. should be one hole over, where the line is.

haven't had a chance to look further than that...

happy new year!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on December 31, 2009, 11:25:32 AM
i wonder if soldering the t-pad directly to pcb will help to avoid mistakes...
I'm sure it can be done on a dual layer pcb..
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 31, 2009, 11:27:39 AM
Hey surfkat,

I noticed the same as haima with C11. C3 is also in the wrong position.

I have posted some pics regrding those caps and also C1 and C2 since they will accommodate a 2.5mm or 5mm lead spacing. The signal track must be connected too or those caps will do nothing. these are some pics from the upcoming VP2x Assembly Guide that I am nearly done with.

Anyhow, here's C3 details.
(http://i276.photobucket.com/albums/kk12/jsteiger1965/C3closesmaller.jpg)

Here is C11 details.
(http://i276.photobucket.com/albums/kk12/jsteiger1965/C11close.jpg)

And here are C1 and C2 details.
(http://i276.photobucket.com/albums/kk12/jsteiger1965/C1andC2closesmaller.jpg)

Like haima said, I'm sure these things are not you problem but they do need to be corrected.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 31, 2009, 11:30:04 AM
i wonder if soldering the t-pad directly to pcb will help to avoid mistakes...
I'm sure it can be done on a dual layer pcb..
Yes, this is true. Actually my friend Hairball Mike has a solution for this that I will probably offer too. Still, flying leads shouldn't be too much of an issue for a DIY'er!  ;D
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 31, 2009, 11:33:35 AM
surfkat, your t-pad looks to be wired correctly although I think the black lead to the t-pad solder lug could made a little more stout.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on December 31, 2009, 11:41:07 AM
i wonder if soldering the t-pad directly to pcb will help to avoid mistakes...
I'm sure it can be done on a dual layer pcb..
Yes, this is true. Actually my friend Hairball Mike has a solution for this that I will probably offer too. Still, flying leads shouldn't be too much of an issue for a DIY'er!  ;D
don't make it too easy ;D ;D ;D
more complicated builds wouldn't have a chance anymore :o :o :o
no, we won't offer the PoorMan with pre build or PCB mounted attenuators!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on December 31, 2009, 11:45:34 AM
I dont mind but but some people cant even solder caps in its right place...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on December 31, 2009, 11:49:15 AM
I dont mind but but some people cant even solder caps in its right place...
those people will learn and grow with it :)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on December 31, 2009, 11:59:17 AM
well its a sugestion...and its up to the deisgner to take considerations...
Whats the poorman anyways?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 31, 2009, 12:10:22 PM
...Whats the poorman anyways?
What? 3nity, the Poor Man 660 is a legendary DIY tube comp build. Where have you been my friend?  :o
http://www.groupdiy.com/index.php?topic=28274.0 (http://www.groupdiy.com/index.php?topic=28274.0)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on December 31, 2009, 12:10:43 PM
well its a sugestion...and its up to the deisgner to take considerations...
for sure, sorry for my comments about it.

Quote from: 3nity
Whats the poorman anyways?
nothing.

happy new year
Volker
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: 3nity on December 31, 2009, 12:14:49 PM
lol........of course i know what that is...
Just breaking balls. ;)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on December 31, 2009, 12:53:52 PM
I dont mind but but some people cant even solder caps in its right place...
those people will learn and grow with it :)

Definitely DIY is just a learning process, and this is a simple project and besides the Opamp where you need to have a good (small tip) soldering iron and soldering skills, this project is perfect for people to learn.

The T-Pad wiring with Jeff's document is a breeze. no tricks in there

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 31, 2009, 01:32:58 PM
OK surfkat, here a few things for you to check.

I did some quick tests using an MR1 signal generator and a Fluke 177. No power connected to the PCB and no DOA in the sockets.

Apply a balanced sine wave signal to the + and - inputs of the PCB, pins 8 and 10. I set the level to -12dbu. I then get a reading of 161.7mv/ac when probing between pins 8 and 10 of the PCB. It's a touch low due to the MR1 driving the load of the preamp. The reading when probing between the "+" DOA socket and the "C" DOA socket is 1.1v/ac. There should be no significant reading between the "-" DOA socket as it is only for feedback gain control of the DOA. The signal is unbalanced(by the 2622) when entering the DOA and only enters the non-inverting side. A very similar reading will be obtained from probing between pins 5 and 8 of the 2622.

If you don't get a similar result, you will probably and end up desoldering the 2622 for a quick test. The 2622 has a voltage gain of about 16.9dbu(1:7). When applying a -12dbu signal to the paralleled primaries of a 2622 (connect "+" to pins 1 and 2, connect "-" to pins 3 and 4), probing between pins 5 and 8 will give you an approximate reading of 1.353v/ac. 1.377 is +5dbu so, nearly 17db of resulting gain.

Hope this all helps in some way.
Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on January 02, 2010, 08:33:32 PM
Hey guys,

I have just finished the step by step, detailed assembly guide for the VP2x projects. I have a link in the first post of this thread and will soon have it on all the relevant pages over at my website. It is more geared toward a newbie DIY person but hopefully a little something for others too. Open the link and save to your computer.

VP2x Assembly Guide.pdf (http://www.classicapi.com/catalog/images/gallery/VP26/VP2x-Assembly-Guide.pdf)

Let me know what you think.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on January 02, 2010, 08:57:56 PM
Congratulations Jeff,
I read the document and I think it's great.

even someone that never touched a soldering iron will be able to do your project.

more experience people can also use it for reference while building also,
making the process not only faster but slicker!

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on January 02, 2010, 09:35:20 PM
looks great jeff!

i'll have a read when i get a chance & let you know if i spot any typos  ;)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: gar381 on January 03, 2010, 12:36:52 AM
1st Class Jeff.

Very Nice :) :) 

Just about any beginning DIY guitar cord solder guy with this manual
should be able to build a VP2x with GREAT success.  Lots of good
tips for us old timers too!!  No one should be afraid to try
this assembly as the manual is bullet proof. Looking forward to building mine.

GARY
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on January 03, 2010, 08:33:18 AM
 :o :o :o :o
what a great guide. don't want to know how many time you put in this.
I'm sure even my wife, no - even my daughter could finish one without my help.
unsure of the pets since they don't speak english.

great work Jeff !!!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on January 04, 2010, 09:50:43 PM
The guide looks great. I wish I had waited a few weeks until it was available before I built my first two. But the good news is I got my second pre working today. Thanks to Jeff and haima for their help with troubleshooting techniques. Your instructions were great and introduced me to some new circuit troubleshooting concepts. That is one of the great things about his site, the way you guys offer your support. Now I want to build a pair with different transformers and DOAs for another flavor in the Lunchbox.

Thanks to Jeff for a great design and to Gary for an awesome DOA. What else you guys got up your sleeves?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on January 04, 2010, 10:05:57 PM
The guide looks great. I wish I had waited a few weeks until it was available before I built my first two. But the good news is I got my second pre working today. Thanks to Jeff and haima for their help with troubleshooting techniques. Your instructions were great and introduced me to some new circuit troubleshooting concepts. That is one of the great things about his site, the way you guys offer your support. Now I want to build a pair with different transformers and DOAs for another flavor in the Lunchbox.
Hey very good news surfkat! I am curious to hear what the problem was, if you don't mind. It may help someone else in the future.

Quote
What else you guys got up your sleeves?
Well...to take a play from Peter Purpose's playbook, "a bunch of hair and some flabby skin!".

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on January 05, 2010, 10:05:56 AM
It appears that one leg of my Pad switch was a cold solder joint. I had originally suspected this and I finally confirmed this with Jeff's method of troubleshooting. Not sure why I did not find it sooner but it was all part of my DIY lesson and now I am a tiny bit smarter. I plan to record some guitar tracks today with these pres and see how they sound. Thanks Jeff!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on January 05, 2010, 10:19:49 AM
It appears that one leg of my Pad switch was a cold solder joint. I had originally suspected this and I finally confirmed this with Jeff's method of troubleshooting. Not sure why I did not find it sooner but it was all part of my DIY lesson and now I am a tiny bit smarter. I plan to record some guitar tracks today with these pres and see how they sound. Thanks Jeff!
Cool deal surfkat. Let us know what you think after some tracking time.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Whoops on January 05, 2010, 05:58:39 PM
It appears that one leg of my Pad switch was a cold solder joint. I had originally suspected this and I finally confirmed this with Jeff's method of troubleshooting. Not sure why I did not find it sooner but it was all part of my DIY lesson and now I am a tiny bit smarter. I plan to record some guitar tracks today with these pres and see how they sound. Thanks Jeff!

[EDITED after I realized my problem was with in the Phase Switch and not the PAD switch]

The Phase switch is in the middle of the 2 other pads, so after um place them , you cannot solder it from the top of the board.

Jeff, maybe you should add in your guide and advise so that people, place the Phase switch on the board before the other 2 switches.
Solder it's pins  from top and bottom of the board, and only place the other switches after hand.

what do you think?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on January 05, 2010, 06:03:58 PM
it isn't really necessary to solder from top,
it is just comfortable.

I soldered from the bottom (only).
except the gain Pot at the beginning ;)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on January 05, 2010, 10:48:43 PM
i agree - i generally always solder only from the bottom, unless there's a particular reason to do the top of a component...

not that it hurts to solder both sides, but i wouldn't sweat it.

i usually heat the pad only first for a half a second before touching the iron to the component leg - tends to make the solder flow INTO the via, rather than staying at the top.

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on January 06, 2010, 11:30:45 PM
Quote from: haima
i usually heat the pad only first for a half a second before touching the iron to the component leg - tends to make the solder flow INTO the via, rather than staying at the top.

This is a great tip. Thanks.

I am wondering if anyone has built this pre with other transformers that fit this layout and if so which models. I am thinking of doing that and I am open to suggestions. While I love this vintage API sound with Ed's trannies I might like to find something different for a contrast. Anyone tried Cinemag or Jensen on these?

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bdubya on January 07, 2010, 03:06:52 AM
I haven't tried Cinemag or Jensen, but I made one with a Carnhill 9045 input, and I like it alot.  You have to get creative with mounting it, mind you, as well as changing other components in the circuit, which makes it a bit more involved than the straight-up VP25, but the end result is potent, IMHO.  I had a Purple KDJ4 in for the op-amp at first, but I have PPA's 2055 in there at the moment and I like it alot.  Not that the Purple was bad in any way at all; it kicks ass.  The upper midrange and highs were different with the 2055, though, in a way that I like.  The output was the 2503.  Its more or less the same circuit as an Eisen "neveish" that I built a while back with the tables on their site, but with EA-2503 instead of the Profile 4804 that I had in the neveish, and, ultimately, the 2055 instead of the KDJ4.  Oh and I left out the attenuator, mostly cuz I'm cheap, and I was concerned about there being enough space for the 9045 with it in there,  and I knew the output would be more tame than the VP25.  BUT I think I'll put one in eventually because it WILL fit and its a nice feature.  Thanks, Jeff  :D



ben

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: surfkat on January 07, 2010, 07:09:05 PM
bdubya - I would be curious to see how you mounted those transformers. Maybe you can post a pic or two.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bdubya on January 08, 2010, 01:01:10 PM
bdubya - I would be curious to see how you mounted those transformers. Maybe you can post a pic or two.


Hey surfkat.  Will do as soon as my wife hands over the camera.  She's the visual, I'm the audio.  I located it more or less where the 2622 would go, but moved resistors to the underside of the PCB as needed to free up more topside space.  I then used permanent double-sided tape tabs, 4 of them, placed on the pcb surface, but not over any traces, as I'm uncertain if the tape will interact with the pcb over time (the package says its good for plastics, but better safe) to hold the transformer snugly in place.  I thought about using little L-brackets with the existing mounting screws of the 9045, but didn't really want to drill up the PCB that much.  The tape, while a bit domestic, worked nicely for me.  I really will post some pics in the next couple hours/days. 




ben
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: pjdiy on February 17, 2010, 03:17:51 AM
Jeff I am wiring up the VP26  in and out xlrs.
Is it input (high to pin 2) and (low to pin3), audio grd. to pin1?

Thanks PJ
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Denyle Guitars on February 17, 2010, 07:55:01 AM
Jeff I am wiring up the VP26  in and out xlrs.
Is it input (high to pin 2) and (low to pin3), audio grd. to pin1?

Thanks PJ

http://51xaudio.com/alliance/pinout.html
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on February 17, 2010, 08:01:02 AM
Jeff I am wiring up the VP26  in and out xlrs.
Is it input (high to pin 2) and (low to pin3), audio grd. to pin1?

Thanks PJ

http://51xaudio.com/alliance/pinout.html
Hey PJ, Denyle beat me to it!!!

Connect your shield to pin 5. Use the pin-out info on that 51x link for the rest of the connections.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: regularjohn on February 26, 2010, 08:49:25 PM
If I'm adding a vu meter to a vp25 I would add it off the extra winding of the 2503, right?  (I can't remember what the lead colors are offhand).  Of course with the meter's proper external resistor.

I tried doing that, but I think something is funny because the meter shows more level when the tpad attenuator is all the way down then when it is all the way up with the same input signal.  
Is this normal?
Any insight would be mucho appreciated!
Thanks!

Edit:  Nevermind...made an absurdly stupid mistake!!!!  Insert pic of guy banging his head on a wall!!!!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: smallbutfine on April 23, 2010, 02:49:23 AM
Hi guys, I just recently came to read more often around here and stumbled upon the VP2x when sneaking how the 51x alliance is doing in the meantime...
I have to say I am pretty impressed by the build manual you did, Jeff!
This is a great job done right.
I remember when I first tried to do a fabio board with all those options and bar/non documentation really, assuming everybody who starts building a 312 copy is able to figure all out in DIY style or discussing it in looong build threads. (No offense against fabios boards, they were really cool.)
Your VP's are a different beast really and I hope many will do them, pushing the idea of 51x diy lunchboxes forward.
I think they are a great opportunity for beginners to start sincere diy, because everything is well-thought and build guide is exceptionally well made.

Phew...had to be said.

Now I have a general question about output transformers in 500/51x style that I stumbled upon reading the build guide.
I remember the API style out trannies are not really lightwights, so to speak. Due to 500/51x card concept, the out trannies are mounted on-board. Since launchboxes might be moved from time to time (to live events or other studios), how is mechanical stability taken into account? I have seen (rackmount-style) units where trannies broke the pcb due to fast 'tour-style' movements of the case. Did anyone experience something similar with lunchbox modules? Or, is there a possibility e.g. in the 51x cases to mount heavy transformers off-board in the case? (I know, this may be a tradeoff against fast swapping of modules.....)

Kind regards,
Martin
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Curran on June 24, 2010, 03:04:57 PM
no 200kOhm reading on the V= lug of the op amp section. readsing are 200-500Kohms for every other lug test. The lug tests for V+ are not coming up
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 24, 2010, 04:01:22 PM
No problem. It's just beyond your DMM. Sounds like you are OK.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Curran on June 24, 2010, 08:46:55 PM
yeah I dropped in the one of the four gar2550's and it fired right up and sounds awesome. I got three built and all the gar2550 kits done in about 8 hours. right now they are all waiting to get used on the next session!!!! the layout PDF is awesome and the build is super easy!!! the opamps are tiny and a ***** but the layout PDF is wonderful for getting that tiny little thing populated and ready for your opamp needs!!! one more kit to build and then I am gonna enjoy the fruits of my labor with some heavy duty recording!!!

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 24, 2010, 09:22:50 PM
yeah I dropped in the one of the four gar2550's and it fired right up and sounds awesome. I got three built and all the gar2550 kits done in about 8 hours. right now they are all waiting to get used on the next session!!!! the layout PDF is awesome and the build is super easy!!!
Nice!  ;)

Quote
the opamps are tiny and a *****...
Yes, they are tiny... and a ***** is a good description too. Very rewarding though indeed.

I am curious to hear what you think after a good session, especially when compared to the OSA.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Curran on June 24, 2010, 09:32:06 PM
I will definitely let you know, I will also put them up against the Five Fish MK-II's I have with the cinemag input transformers.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: babyhead on July 23, 2010, 03:06:13 PM
I have just finished QCing 4 of these and I want to finish the last 2. I have some original Melcor 1731 that are stickered +/- 15. The problem is that my 500 rack puts out +/- 18. Am I risking my opamps by putting them in circuit? Should I replace the protection diodes with drop down resistors?

So far these amps sound GREAT!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: letterbeacon on July 23, 2010, 04:14:59 PM
I'm thinking about putting two AP26 pre amps horizontal in a 1U rack.  What do I need to supply the modules with power wise?  Is it +/-15v and +48v for the phantom power?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: babyhead on July 23, 2010, 06:13:03 PM
I'm thinking about putting two AP26 pre amps horizontal in a 1U rack.  What do I need to supply the modules with power wise?  Is it +/-15v and +48v for the phantom power?


It depends on your opamps, but otherwise, yes.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on July 23, 2010, 11:57:13 PM
The problem is that my 500 rack puts out +/- 18.

+/- 18v? what 500 rack is it? i thought the 500 standard was +/- 16v.

the VP2X boards have series diodes on the power rails which should drop 0.6ish of a volt per rail, depending on your current draw. so if you rack is in fact bipolar 16v you could be close to 15v at the actual opamp pins anyway...

check the voltage at the opamp pin sockets while another, higher voltage opamp is installed - you might need to use an external card edge connector and bench power supply to get access to the pins though...

if you are really worried you could run the original Melcor 1731s off a bench power supply for a while and slowly edge up the voltages from 15v up to your final "measured at the pin sockets in the rack" voltage. look and listen for problems - too much heat, excessive current draw, strange noises, (EXPLoSIoNS and fire...haha :P) etc

if you need to drop the voltage down a bit you could try replacing the series power supply diodes (near the finger edge) with 2 or more diodes connected in series (all facing the same direction!) that can drop the voltage a little more if you need to. you might have trouble if you want to go all the way from 18 to 15 using that method though... lots of diodes needed!

if you really need to drop some more serious volts you could kludge a little zener diode "regulator" onto the board or some veroboard - check out schems for the JLM baby animal for an example... you'll need to adjust the resistors and zener values to suit though.


Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: letterbeacon on July 24, 2010, 08:48:33 AM
I'm thinking about putting two AP26 pre amps horizontal in a 1U rack.  What do I need to supply the modules with power wise?  Is it +/-15v and +48v for the phantom power?


It depends on your opamps, but otherwise, yes.

Great, thanks.  I've built +/-15v power supplies for my modular synth before, but are there any designs out there that can output +48v?  Has anyone else put these pre amps in a 1U rack before?  I had a search on the forums here but I can't see anything...

Cheers!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on July 24, 2010, 08:50:56 AM
http://www.jlmaudio.com/JLM%20Power%20Supply.htm
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on July 24, 2010, 08:59:28 AM
Has anyone else put these pre amps in a 1U rack before?

jeff also makes the VP312 boards that can be trimmed to squeeze 4 channels in a 1RU box.

also - being a synth guy, you might be interested in his upcoming VP312DI which is the same thing but with some great DI options built in. i think they will be available from his shop within the next few weeks.

volker, JLM ACDC? i second the emotion :P - i've used lots of those. handy and compact!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on July 24, 2010, 11:04:24 AM
Don't forget about Owel's nice PSU kit from FiveFish (http://fivefishstudios.com/index.php/PSU-2448mk2-Kit.html). You can buy the full kit with toroid for only $75! That is a pretty good deal I think.  :o

I have also built a JLM Powerstation and you cannot go wrong there either.  ;)

jeff also makes the VP312 boards that can be trimmed to squeeze 4 channels in a 1RU box.
  ;)  :)  8)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Tweekhead on July 28, 2010, 11:37:06 AM
Can anyone tell me what components I would need to substitute if I was to build a VP25, or VP26 and use a Carnhill 9045 for the input?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on July 29, 2010, 02:56:32 AM
you'd need to adjust any input transformer "zobel" or loading resistors (C3 and R2 in this case AFAIK). these components that sit on the secondary of the input transformer and adjust the loading for best squarewave response.

as far as what to replace these components with, look at what's done with neve preamps and copy that for a start. i believe you might want to try a 180p cap and maybe a 5k resistor - in PARALLEL (not series like the VP2X) across the transformer secondary (pin 7 to 10?). check the "EZ1290 assembly.pdf" file for more info...

and you'd need to secure the transformer using cable ties - you may need to drill some holes in the PCB for this - be very careful not to hit any traces on the top or bottom of the board!

let us know how it goes, or if you need more help!



Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Peterson Goodwyn on July 29, 2010, 07:26:39 AM
jeff also makes the VP312 boards that can be trimmed to squeeze 4 channels in a 1RU box.

This sounds great!  How much current would a setup like this need?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on July 29, 2010, 07:36:15 AM
depends entirely on the opamps... some opamps use more than others - i can't find any specs around right now, but there should be some around on the forum.

i did a quick google search for the API 512 specs - "Power Consumption:     ±12/18 Volts/DC, @40 ma." so that gives you a rough guide...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on July 29, 2010, 07:37:15 AM
Well, a VP preamp driving a 600ohm load draws around 51mA. So that X 4 plus some headroom and you are in business. If you want the PSU in the case, the case will have to be deep enough. Otherwise, outboard will eliminate and potential toroidal induced noise issues.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on July 29, 2010, 07:38:29 AM
I should note, that 51mA was a single channel with a gar2520. Scott's SL2520 is nearly identical as far as current draw.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on July 29, 2010, 07:41:02 AM
oops- i should have shut my mouth - the real info, straight from the horses mouth! thanks jeff  ;D
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on July 29, 2010, 08:39:57 AM
oops- i should have shut my mouth - the real info, straight from the horses mouth! thanks jeff  ;D
No, no, no...the help is appreciated indeed!  ;)

Interesting spec you found though. I bet that is idle or no load on the DOA. Ours are about 23mA idle. Maybe the extra juice is for the LM39xx and the IC meter buffer?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Peterson Goodwyn on July 29, 2010, 09:09:54 AM
Wow, 51ma, pretty light.  Makes me think I should just get a 16VA-or-so torroid and build 8 preamps.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: dbeeson on August 13, 2010, 03:37:51 PM
Well, it looks like I'm the third reported case to have swapped the BD140/BD139. Smoked one of them anyway.  I was wondering if I could just swap them for the NTE equivalents, as I can get them locally. Will this work all the same? 
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: haima on August 13, 2010, 10:47:41 PM
the BD140/139 are general purpose medium power transistors, nothing too fancy. i don't know what the specs of the NTE parts are, but i'd be surprised if they didn't work - providing the pinout is correct!

but those BD parts are very common - you shouldn't have tooo much trouble finding them if you want to go that way.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: gar381 on August 14, 2010, 09:30:28 PM
bdeeson

The NTE parts should work but are probably 5 to 10 times the price
of the real thing but I have never tried them.  Both mouser and digikey have the real ones.
Did you reverse them in a gar2520 or a gar1731 DOA kit??
PM me if you did.

GARY
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: fucho! on February 04, 2011, 06:49:01 PM
Hello,
I'm an enthused DIY newbie with a troubleshooting issue. I just built the first of two VP26's (from kit & caboodle packages).

With phantom power on, condenser mics seem to work, but for dynamics w/o it, the signal is just barely audible. In fact, the signal for the condenser may be fairly low too- nothing to compare it too without having built the other unit yet, but I was surprised during initial tests not to hear major clipping with the gain maxed and no attenuation.

I think I may have blown something, as I got a good signal from a Dynamic BEFORE ever having tried a condenser, but never again! Also, DMM tests (as per the assembly guide) with no power and no op amp seem to be fine. I don't have a way to power from the bench, so can't test with power but no op amp.

I've double checked the assembly. Some resistors are reading funny in the PCB (is this normal, or a terrible sign?) e.g. R4 reads a mere 12.9ohms,  R13 reads all over the place, R7 & R8 3.4K ohms (half of their rated value), R9 144ohms, and  R10 & R11 417ohms.

Everything else looks good as far as I can tell.

Can anyone point me to a particular suspect area based on this behavior?
Any help is appreciated!
Thanks!
-Ian
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: fucho! on February 05, 2011, 12:36:00 PM
Here are some pics...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: fucho! on February 05, 2011, 12:37:32 PM
...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: fucho! on February 05, 2011, 12:38:57 PM
...
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Infernal_Death on February 05, 2011, 01:10:12 PM
I've double checked the assembly. Some resistors are reading funny in the PCB (is this normal, or a terrible sign?) e.g. R4 reads a mere 12.9ohms,  R13 reads all over the place, R7 & R8 3.4K ohms (half of their rated value), R9 144ohms, and  R10 & R11 417ohms.

Cannot help you on your main issue as i don't have a VP2X. But stuffed resistors on a pcb can always give funny readings, that's normal. If you really want to measure the resistance, you have to at least take off one leg and measure then. If not you might measure a different resistance than the one "over your resistor".
That's why you always should check resistors before soldering in.

Flo
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: fucho! on February 05, 2011, 06:35:24 PM
Thanks, Flo!
OK- I thought that would be the case. Actually I did measure before putting them in and they all read fine- so I guess there's no problem there...
I wonder if the output transformer is the culprit, but don't know how to test it. Any advice?
Thanks again,
Ian
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on February 05, 2011, 10:52:32 PM
Hi Ian,

Sorry I just saw this now. My notifications from this thread got messed up with all of the maintenance that Ethan was doing a little while back.

For sure as Flo said you cannot measure the R's while both ends are soldered in place.

The first thing I will ask is was the pad engaged when you were doing this testing? Make sure it is out if so. If the pad is acting more like a "mute" than a 20dB pad, double check the black bodied R's. I had a small back ordered batch from a vendor that came in as 750K instead of 750R. Like a dummy, I did not check these right away so a few kits got shipped out with these incorrect 750K's instead of 750R's. I did send an email blast out to all of my store customers but only heard back from one person.  :(  Maybe the email ended up in everyone's spam folder. I have heard from a few guys since then. So, let me know if that is the case and I will get you the proper parts right away.

That goes for anyone else who may stumble across this too.  ;)

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: fucho! on February 06, 2011, 07:13:31 PM
Thanks for getting back, Jeff!
I'm pretty sure the Mute wasn't engaged; I was trying every combination- but will test again as soon as I get a sec!

Does the fact that the dynamic worked before trying a condenser provide any clues?

It may also be possible that some solder connections aren't solid- I initially had trouble with Op amp socket test between 0 & C- then went back and retouched a sockets and a number of other points (kind of at random, as they all look good to me) and this fixed the problem. I could just retouch everything, but don't want to put stress on the PCB/ components if not necessary.

Thanks again,
Ian
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on February 06, 2011, 07:21:40 PM
You know Ian, I just went back and looked and I see some pins for the C&K pushbuttons that do not look soldered. This can for sure be the cause. I would double check all of those and touch them up/reflow. Especially the ones that are tied to the ground plane.

(http://www.groupdiy.com/index.php?action=dlattach;topic=33501.0;attach=6344;image)

Let me know how you do!
Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: a zombie on March 01, 2011, 03:23:06 AM
Jeff, Any idea when the VP26 pcb's will be back in stock?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on March 01, 2011, 08:51:57 AM
Jeff, Any idea when the VP26 pcb's will be back in stock?
I just received an email from them. Very frustrating. When I ordered (1 week after their Spring Holiday) the confirmation date was last Friday the 26th. Yesterday they told me the boards would not be done until the 8th & I would receive the 10th  ??? This morning's email says that they will be out of production the 5th. I should have them here on the 9th. Crazy.

Sorry to rant but between this and the 2503's no kits have been in stock for over 2 weeks. I hate responding to all the emails with bad news.

So, the long and short is by mid next week.  ;)

Thanks!
Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: a zombie on March 01, 2011, 04:25:35 PM
Jeff, Any idea when the VP26 pcb's will be back in stock?
I just received an email from them. Very frustrating. When I ordered (1 week after their Spring Holiday) the confirmation date was last Friday the 26th. Yesterday they told me the boards would not be done until the 8th & I would receive the 10th  ??? This morning's email says that they will be out of production the 5th. I should have them here on the 9th. Crazy.

Sorry to rant but between this and the 2503's no kits have been in stock for over 2 weeks. I hate responding to all the emails with bad news.

So, the long and short is by mid next week.  ;)

Thanks!
Jeff

Wow! that sounds like a royal pain in the A**!

cheers,
James
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Brolik on April 14, 2011, 11:30:23 AM
Heyhey,

I've got this VP25 Rev A that working all smooth and shiny except for this annoying white noise/crackle when I engage phantom power. The +48v rail seems to be working fine as condensor mics do pass audio as they should, aside of course from the static. The problem exists whether a mic is attached or not. I've check the component placement and can't see anything out of order. I've switched out the 2520 for a working one, even though I'm sure this is unrelated.

Any ideas off the top of your heads? I'm going to go in and reflow all the solder joints tonight hopefully, but I thought it was worth a shot to see what you think. Thanks!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on April 14, 2011, 02:37:55 PM
Hey Brolik,

Is R6 10K or 200ohm? If it's 10K, try changing it to 200ohm. Otherwise you could try the other side of the toggle switch. Might help.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: fucho! on April 20, 2011, 04:04:05 PM
Hey Jeff,
I just wanted to say that, after being hugely sidetracked, I finally got a chance to go back over the problem unit I posted about above. After a few rounds of retouching, it's working perfectly!! Now on to some actual tracking with it... Can't wait to hear it in action. Thanks so much for the help!
Ian
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on April 20, 2011, 05:02:52 PM
Hey Jeff,
I just wanted to say that, after being hugely sidetracked, I finally got a chance to go back over the problem unit I posted about above. After a few rounds of retouching, it's working perfectly!! Now on to some actual tracking with it... Can't wait to hear it in action. Thanks so much for the help!
Ian
Excellent Ian. Thanks for the update.  :)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: fucho! on April 21, 2011, 08:21:56 PM
??? Oh No!!! The unit went south again for no apparent reason. It's outputting a whopping 30db quieter than the second. This is true for both condensers and dynamics, with pad & phase engaged/disengaged. I went back and retouched again but to no avail. I've retouched the whole board several times now, and really don't want to put any more stress on it. The resistance tests between V+, V-, C, & 0 all read fine. I switched out the op amps and this had no effect. Everything read correctly before I populated the board. I double checked the 750R resistors in the R10 & R11 slots and they are indeed 750Rs. Any other ideas??
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Brolik on April 29, 2011, 11:03:59 AM
Thanks for the suggestions Jeff. I replaced the 10k R6 with a 220 ohm (didn't have a 200, close enough?) flipped the phantom switch wiring to the other side and retouched all the solder joints on the PCB. Still the same static when I flip the phantom power on. Still works, but still noisy.

Any other suggestions? Is there a chance that getting an actual 200 ohm for R6 will make a difference?

I think I'm going to replace the phantom switch and wiring next.

By the way my VP312DI is healthy as a horse and sounds great!

Thanks.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on April 29, 2011, 11:12:53 AM
Thanks for the suggestions Jeff. I replaced the 10k R6 with a 220 ohm (didn't have a 200, close enough?) flipped the phantom switch wiring to the other side and retouched all the solder joints on the PCB. Still the same static when I flip the phantom power on. Still works, but still noisy.

Any other suggestions? Is there a chance that getting an actual 200 ohm for R6 will make a difference?

I think I'm going to replace the phantom switch and wiring next.

By the way my VP312DI is healthy as a horse and sounds great!

Thanks.
220R should be close enough. I don't think this will make any difference here really. It is possibly the switch. If you have ruled out all other outside possibilities (rack slot and all related cabling) You can try the switch. Not that it couldn't happen but it would be the first bad one out of a few thousand. The phantom circuit is really almost nothing so not a whole lot to go wrong.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Brolik on April 29, 2011, 11:51:30 AM
Thanks Jeff. That's what mystifies me, there's almost nothing there so what the hell could go wrong? I've tried it in several slots (all that work) and with cabling that is in use with working gear, so thats covered. I'm going to try the switch, but that doesn't seem that likely to me either as the phantom power itself works, just noisily. Here's some pics of the build in question.
http://www.flickr.com/photos/[email protected]/sets/ (http://www.flickr.com/photos/[email protected]/sets/)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Brolik on May 01, 2011, 02:47:57 PM
Just an update on my progress. I've replaced the phantom switch and wiring, retouched all pcb solder joints and replaced R6 with 220 ohm. Still got that damn crackle when the 48v is engaged. Also, it makes a pretty substantial pop when the switch is hit, louder than on the working vp312. I'm gonna work my way back and try switching out C9 next. Let me know if you have any suggestions.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 01, 2011, 02:58:24 PM
Might be a silly question but have you 100% ruled out rack-slot and all cabling? Don't know if you are testing this on your bench or not. I have heard more of these problems get solved with cable issues over others. Pardon me if I already mentioned this. Just a thought.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: Brolik on May 02, 2011, 09:32:32 AM
Not silly at all, stupider things have happened. Just to be sure, I popped it into the slot that the working VP312 was in with the same results. Wish it was just a bum wire, that would be easy to fix.  >:(  Guess I'll just keep pokin...  ::)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: zmgwg on June 15, 2011, 07:39:39 AM
has anyone build one without the T-pad attenuator? how should I do/wire it?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on June 15, 2011, 08:33:30 AM
Yes, I have had a lot of guys do this. Just jumper from Pad A to Pad C on the main PCB (near where the t-pad would go). Make sure you stay away from Pad B. That's it!

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: sea_man on July 05, 2011, 03:50:33 PM
Hi !

I bought a VP26 complete kit.. but i have a question about the transformer wiring.

i have the board rev A.2 and the transformer EA2623-1 ( whit different color order ( from right to left in this order: red, yellow, blue, gren, brown, black ) , i need make any modification whit the wires colors or can i connect whit the colors in the PCB directly ? ( ie.. black to black blue to blue .....)

Thanks !
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on July 05, 2011, 07:37:48 PM
( ie.. black to black blue to blue .....)
Yes, the order is different but the colors are still the same so black to black, blue to blue and so on. You will need to cut the leads to different lengths than what the Assembly Guide shows though so be careful there!!

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: sea_man on July 05, 2011, 08:12:25 PM
Thanks !

Now my two VP26 are ready !  8)

Some pics:

http://www.flickr.com/photos/mar1o_bross/sets/72157627001844167/
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: etheory on August 06, 2011, 10:42:05 AM
I haven't yet turned it on for testing, but here is a link to the build of another beautiful-looking VP26:
http://www.evolutionarytheory.com/2011/08/classicapi-vp26-build/ (http://www.evolutionarytheory.com/2011/08/classicapi-vp26-build/)
Thanks Jeff!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: etheory on August 17, 2011, 12:09:11 PM
For those here who are interested, here is the first part of racking a VP26 up ( along with an MP73 ).  I will post the other 2 parts once they are done:

http://www.evolutionarytheory.com/2011/08/boxing-an-mp73-and-a-vp26-part-1/ (http://www.evolutionarytheory.com/2011/08/boxing-an-mp73-and-a-vp26-part-1/)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 01, 2011, 03:35:27 AM
This is going to be my first real DIY build and I can't wait(aside from some random led kits I did to practice soldering.) Prepare for newbie stupidity coming your way or maybe surprising myself and us all and it just working first time. I'll go slow and be tedious and keep you posted if I've got questions. I'd love to show other newcomers to this hobby that its possible to build this kit if you are diligent and willing to read all the wonderful help on this forum ...... hmmm, we'll certainly find out soon enough!


in the meantime........ here's the panel I had made for it. Kinda went overboard but its a gift for my brother (he's got the lunchbox). (http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/ebe9d9e4.jpg)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 06, 2011, 12:34:05 AM
Hey folks,

I'm new to the thread and a very new DIYer. Thanks to Jeff for pointing out this thread (that was right beneath my nose in the documents he provided)

I've assembled a VP25 w/ a stepped gainswitch and a Gar1731 DOA (kit)
(The DOA and stepped gain definitely tested my novice soldering skills for sure)

Heres where i'm at:

Audio passes through but its super thin and nasty at higher volumes.
Gainswitch - works
Mute - works
Phase - DOES NOT WORK - cuts signal totally
Pad - works

Output - worked seemingly backwards at first, but after some retouches all over the place it was working normal - then effed the leads up by accident so i redid them - now its seems backwards again.

When testing the DOA sockets on the board I got a weak reading between C and O - then i retouched things a bit and i got a better reading.. but its doesn't seem to be consistent.

I've retouched any joints that looked shady - but surely i'm missing something.

Any and all input would be super appreciated - super newbie here - i'm all ears.

Thanks
Max







Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 06, 2011, 08:20:54 AM
Max

I would suggest resoldering the pins for the 3 C&K pushbutton switches. Those are the biggest stumbling block for guys. The pins that connect to the ground plane are a little harder to get a good joint on. A few pics could help to, especially around the t-pad area.

Also, what DOA are you using? If it's a kit, then that can be another can of worms. Either way, make sure you check out my DOA install page for some tips. http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 06, 2011, 01:39:38 PM
Max

I would suggest resoldering the pins for the 3 C&K pushbutton switches. Those are the biggest stumbling block for guys. The pins that connect to the ground plane are a little harder to get a good joint on. A few pics could help to, especially around the t-pad area.

Also, what DOA are you using? If it's a kit, then that can be another can of worms. Either way, make sure you check out my DOA install page for some tips. http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)

Cheers, Jeff

Hey there! Thanks for the advice. Here are some pics down below - you can see its pretty amateur hour. After reading through the whole thread - I retouched as many shoddy joints as i could before posting my questions - I might have gone too far.

When you say to resolder the pins - should i just remove all three switches, clean it all up as much as i can and start totally fresh - following the instructions in the guide?

As far as the DOA - yes i got the Gar1731 full kit bundle. I should have started with an assembled one - I'm not proficient enough yet for that build. Very likely a mistake lies within there.. though i thought the nature of DOAs was to either work or not work..? (not sure where that came from..)
Pretty sure I got the seating figured out though as I did review your 'DOA Install Guide' - Thanks!

Should I try to locate or just buy a new tested and functioning DOA? Then i'd know what works, and flush out any other mistakes from there - and then i'd also have a reference to compare my build to..

Super thanks for the help!




Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 06, 2011, 01:43:22 PM
another pic - am i missing something bout posting multiple pics?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 06, 2011, 01:44:30 PM
and one more..
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 06, 2011, 06:05:38 PM
Your t-pad looks to be wired correctly. I would double check the lead colors on the output transformer to make sure they are right.

You don't need to remove the pushbutton switches. Just reheat the solder/pin area until the solder becomes molten again. You can add just a dab of fresh solder if need be. Try to only heat a minimum of time.

There is an in between with the opamps. The problems can be coming from there. It is definitely best to have a known good working amp to check your preamp build with. Once you know you are set there, then you can try an opamp build. Right now, you may have too many variables to really diagnose what is going wrong. Maybe a friend who is close can loan you one?

I also like to limit the attempts to fix things to one thing at a time. If you do more than that, you will never know what the exact problem was.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: etheory on September 08, 2011, 07:05:32 AM
I FINALLY got round to powering up my first VP26 build ( which is also my first EVER DIY preamplifier build.... ).

It went without a hitch.  Powered up perfectly and sounds absolutely and utterly amazing.

Here are some photos:

http://www.evolutionarytheory.com/2011/09/classicapi-vp26-built-and-tested/ (http://www.evolutionarytheory.com/2011/09/classicapi-vp26-built-and-tested/)

Thanks Jeff!  It was such a pleasurable build for someone reintroducing themselves to DIY after a break of many many years.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: oudplayer on September 09, 2011, 06:30:33 AM
I just got around to building mine as well - the sound is great, I'm getting a bit more noise when driving a dynamic mic than I'd expect but I haven't started trying to diagnose where that's coming from yet. The only real problems I had were with the millmax sockets (the opamp isn't held super firmly by the sockets, has a tendency to jump out), but most significantly in fitting the newer t-pad output attenuator.

Next to the shaft of the pot there is a small metal clip to help secure the pot to the faceplate and prevent the entire pot assembly from being able to freely rotate. But with the tpad board installed (in what I think is the correct orientation), the tpad circuit board gets in the way of that support clip. I hacked a solution since I had a recording to do tonight - bending the support clip under and just having the pot being free floating. I thought I might have gotten the mini circuit board orientation wrong, but the pot does do what I'd expect, so I'm a bit stumped. I might be able to get pictures up tomorrow, but any ideas based on my description?

Thanks for a great preamp, looking forward to making several more!
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 10, 2011, 03:41:52 AM
first off, big thanks to Jeff for making such a superbly fantastic product. This thing has been a dream to work on(regardless of if I did it 100% correctly). Also, thanks to the amazing members of this forum for helping us all out...

this posting is slightly premature as a full report but I've finished my build finally tonight!! and had a few questions/concerns off the bat. I will be able to really test it in my studio tomorrow, tonight I just threw it in a lunchbox and tested it on my laptop mobile rig.

1- when testing my resistance values were odd(at least I think they were).
for example: the -V and v+ read 8.32 M but the value was constantly climbing.  -V and C 1.6M and climbing, +V & C 11 M not climbing, C and O 6.83 M and climbing, +V and O 17.6 M and climbing, and -V and O .77 m and climbing.
this concerned me because I'm new to this and it didn't seem to be correct. I've done continuity tests and also measured resisters before but perhaps I'm doing something wrong with my DMM?

2-When i did finally throw it in the lunchbox and do a super quick test I was very pleasantly surprised that it worked, there was no immediate harsh noise or problems and it seemed to function correctly EXCEPT for that it seems like the PHASE switch somehow got reversed. If i leave the switch out it sounds like I have a high pass filter on at like 10k, it gets super thin and sounds super tinny. If i reverse the phase by engaging it then it sounds wonderful, just like I'm assuming it should sound.  I will follow up tomorrow with a more complete and controlled test in my studio where I know which gear sounds exactly like what but i guess I'm just wondering what I could have done wrong...

Lastly, what is the typical breakup point of this pre Jef? I know my neves like the back of my hand but I want to make sure I didn't screw it up and that it works the way it should, I found that it sounded pretty damn amazing even with a shure sm58 tonight and didn't get too nasty until well past 12 o clock.

Here are some pictures in the meantime if you spot something and say "you idiot!! you reversed the thingamajabber" or whatever.
Thanks SO much


(http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/th_88e434ff.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/88e434ff.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/th_322f864d.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/322f864d.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/th_11561745.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/11561745.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/th_37fd5d35.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/37fd5d35.jpg)

I've picked up the gar so I can build that and see how the sound changes with the different opamps, that'll be next project.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 10, 2011, 04:42:46 PM
I just got around to building mine as well - the sound is great, I'm getting a bit more noise when driving a dynamic mic than I'd expect but I haven't started trying to diagnose where that's coming from yet. The only real problems I had were with the millmax sockets (the opamp isn't held super firmly by the sockets, has a tendency to jump out), but most significantly in fitting the newer t-pad output attenuator.
Sounds like your opamp is not fully seated in the sockets. Take a look here for some tips on that. http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)

A few pics of the t-pad area would help. If you have the smaller 388 t-pad, I just bend the tab over or cut it off. The small adapter PCB is designed to be about .05" away from the back of the L-bracket so something may need to be changed here.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 14, 2011, 08:17:01 PM

1- when testing my resistance values were odd(at least I think they were).
for example: the -V and v+ read 8.32 M but the value was constantly climbing.  -V and C 1.6M and climbing, +V & C 11 M not climbing, C and O 6.83 M and climbing, +V and O 17.6 M and climbing, and -V and O .77 m and climbing.
this concerned me because I'm new to this and it didn't seem to be correct. I've done continuity tests and also measured resisters before but perhaps I'm doing something wrong with my DMM?

2-When i did finally throw it in the lunchbox and do a super quick test I was very pleasantly surprised that it worked, there was no immediate harsh noise or problems and it seemed to function correctly EXCEPT for that it seems like the PHASE switch somehow got reversed. If i leave the switch out it sounds like I have a high pass filter on at like 10k, it gets super thin and sounds super tinny. If i reverse the phase by engaging it then it sounds wonderful, just like I'm assuming it should sound.  I will follow up tomorrow with a more complete and controlled test in my studio where I know which gear sounds exactly like what but i guess I'm just wondering what I could have done wrong...


That was my initial test done very quickly on my laptop and a Apogee One interface. Today I had a chance to really dig into it in my full studio that I know in and out and unfortunately it seems I certainly have a way to go on my soldering and building..... The signal is very quiet and super thin when compared to my other preamps. It sounds like there is a hipass on it at all times, although the mute, and pad switches seem to work, the polarity seems to add some low end back when depressed. The output fader is capable of cutting the output but it doesn't seem to mute it completely when rolled all the way back(perhaps this is as designed). The gain on the preamp also seems to function except that I have to have the gain very far up to even get a useable signal at which point it is very distorted yet still super thin sounding.

I posted pics above ( http://www.groupdiy.com/index.php?topic=33501.msg572952#msg572952 ), will take off the L bracket and post more detailed pics, let me know any thoughts you may have. Thank you so much
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 14, 2011, 08:30:16 PM
It looks as though most of the lead colors for the 2503 go to incorrect holes. From what I can see, Brown is the only one that is right?
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 14, 2011, 09:05:37 PM
Yea, I meant to solder them in the way they're in now. I must have gotten confused because in the pictures in the manual the colors were different so I substituted based on the order of them coming out of the transformer. This must have been a stupid mistake on my behalf. What would be the proper way? I'm assuming now just to put yellow in yellow, orange in orange. etc....


(http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/th_431b2afe.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/431b2afe.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/th_d81a4ead.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/d81a4ead.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/th_ac104592.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/misc%20forum%20linkage/ac104592.jpg)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 14, 2011, 09:28:49 PM
Yes, yellow to yellow, red to red and so on. Sometimes the order that the leads come out is reversed but the colors always mean the same thing.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 14, 2011, 09:31:50 PM
Wow I'm an idiot. I thought I was being so clever since the order was different. I hope I didn't cut em too short! I guess we'll find out in an hour or so. :-) will report back asap. Thanks for the help Jeff

p.s crazy question but when disassembling, do I remove the push button knobs? I don't want to break anything by trying to pull em off.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 14, 2011, 09:44:17 PM
The switch caps are fine to leave on. You may have to splice some of those leads to make them long enough. Just shrink wrap your splices to insure no shorts. Not the most optimum way but worst things have happened. Use the same color leads from the trash if the garbage man hasn't came yet.  ;)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 14, 2011, 09:53:09 PM
( places order for another EA 2503........ :-[ )
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 19, 2011, 02:43:13 AM
Ok, this weekends update.
Luckily I was able to salvage the transformer I'd botched before and get all the wires through the correct corresponding color holes(see new pics). I did the best desoldering/cleaning and re soldering that I could and after finishing securing it back in place I was ready to test using my DMM. unfortunately to my disappointment my readings were once again strange again. At first I was stoked because I did see 200k Ohms resistance which began climbing but then changed to 6.3M. My readings were as follows:
-V & +V: 6.3M and increasing
-V &  C: 6.12M and increasing
+V & C 20k and then changed to 1.1M and rising
C & O .85 M and increasing
+V & O .57M and increasing
-V & O 1.01M and increasing


luckily or unluckily I stripped one of my screws removing the L bracket so until the new L bracket arrives I've got nothing but time to troubleshoot! I'm going to attach pics of where it is at present and maybe someone will be able to point out some other places I could start. Also, are there other tests I could perform using my DMM to find the problem area?

Thanks so much for the help!
Jeff & all you guys rock

(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/th_7c0479df.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/7c0479df.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/th_8bbbeff4.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/8bbbeff4.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/th_6156f951.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/6156f951.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/th_60827165.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/60827165.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/th_b0aa87c3.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/b0aa87c3.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/th_b4671528.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/b4671528.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/th_d0bd07fe.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/d0bd07fe.jpg)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 19, 2011, 08:46:00 AM
A lot of times, the strange really high readings are DMM related. If they were all closer to zero I would be worried. Did you try it yet? I would try firing it up. Your soldering work looks solid so it should work.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 19, 2011, 12:44:19 PM
awesome,
I'll throw it together soon as I get the screws and we'll see!! I'll keep my fingers crossed.

In the meantime would it be a good or bad idea to use a small piece of double sided tape on the tPad (as done with the input transformer)? I used clamps the first time but since i had to disassemble/ rework it I noticed it could be a helpful thing.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: etheory on September 21, 2011, 12:15:16 PM
I just finished 1u racking a VP26 and a Sound Skulptor MP73 and I've blogged about it.  You can check it out here:

http://www.evolutionarytheory.com/2011/09/classicapi-vp26-and-sound-skulptor-mp73-preamps-are-finished/ (http://www.evolutionarytheory.com/2011/09/classicapi-vp26-and-sound-skulptor-mp73-preamps-are-finished/)

They both sound AMAZING, it's incredible being able to mix and blend between both sounds.

(http://www.evolutionarytheory.com/wp-content/uploads/2011/09/MG_4660.jpg)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: bigevil on September 23, 2011, 03:14:24 AM
so, after re soldering my transformer leads and re-assembling the VP25 tonight I finally got it plugged it in and gave it a quick test. all I can say is WOW. I swapped it directly in my normal chain instead of the 1073 and hands down everyone in the room preferred it on my vocal. WHAT a fantastic DIY and incredibly piece of gear. Thanks so much Jeff!
i'm actually nervous I did something wrong cause it sounds so damn good...... couldn't be ACTUALLY working could it????


I'm gonna really dig in tomorrow and give it a full workout on acoustics, bass, more vocals(different mics) and some other fun..... will report back!

In the meantime here she is in her final resting place! (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/th_60e2efe5.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25/60e2efe5.jpg)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 23, 2011, 05:48:38 PM
Your t-pad looks to be wired correctly. I would double check the lead colors on the output transformer to make sure they are right.

You don't need to remove the pushbutton switches. Just reheat the solder/pin area until the solder becomes molten again. You can add just a dab of fresh solder if need be. Try to only heat a minimum of time.

There is an in between with the opamps. The problems can be coming from there. It is definitely best to have a known good working amp to check your preamp build with. Once you know you are set there, then you can try an opamp build. Right now, you may have too many variables to really diagnose what is going wrong. Maybe a friend who is close can loan you one?

I also like to limit the attempts to fix things to one thing at a time. If you do more than that, you will never know what the exact problem was.

Cheers, Jeff

Hey all -

I finally got a pair of functional SL Red Dots to assist in my vp25 build. I also went through and touched up the push button pin/solder joints. Upon testing it out in the lunchbox - I still have all of the same problems..
Here they are again:

-Signal is thin - sound like a very extreme HPF
-Phase switch cuts signal
-Output attenuator is working backwards ( though we confirmed the wiring is correct.. )

I also checked the output transformer wiring (thought i had it right) but after reading some recent posts, I realized that i had wrongly wired the GREY and VIOLET leads coming off the output transformer. I had them going into the 2 holes closest to the transformer ... not the holes that were a label "GREY" and "VIOLET" - Thought I was clever - turned out not!

So, I fixed that mistake and then plugged it back into my lunchbox - and I still have the exact same problems.

Did I damage the output transformer?

I had questionable reads between the 'C' and 'O' sockets when I first built the unit.. now that i've got the Red Dot DOA in it .. i see that the DOA isn't utilizing the 'C' socket..


Thanks for the help so far Jeff - though i've gotten shut down over and over on this maiden voyage - I'm still when sit down and work on.

Thoughts?

Thanks
Max

PS - I've tried multiple mikes, cables, inputs and slots on the lunchbox. Also verified the mics or cable on othe rworking pres.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 23, 2011, 06:02:53 PM
Max,

I would like you to measure all 4 of the 2503's windings. You will be checking the DC resistance. Unfortunately, you will have to desolder all of the leads from the PCB to do this.

Once desoldered, measure:
1. red to brown
2. orange to yellow
3. green to blue
4. violet to gray

Each of these should give you around 8.5 ohms.

Let me know what you find.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 23, 2011, 06:31:52 PM
Max,

I would like you to measure all 4 of the 2503's windings. You will be checking the DC resistance. Unfortunately, you will have to desolder all of the leads from the PCB to do this.

Once desoldered, measure:
1. red to brown
2. orange to yellow
3. green to blue
4. violet to gray

Each of these should give you around 8.5 ohms.

Let me know what you find.

Best, Jeff

Hey there!

I desoldered and measured the DC resistance between all 4 of the windings.

Here are are the reads: (approximately)

Red to Brown - 8.8 ohms
Orange to Yellow - 8.8 to 9.8 ohms
Green to Blue - 9 ohms
Violet to Grey - 8.8 ohms

I'm guessing that since the reads are closed to 8.5 Ohms that the transformer is OK?

SERIOUS THANKS!
-Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 23, 2011, 06:38:46 PM
Yes the 2503 is all fine. You can resolder those leads again.

Next, let's remove the t-pad from the circuit. Desolder the 3 leads where they connect to the main PCB. Leave the rest of the t-pad alone and set it to the side. Take another small jumper wire and solder from pad A to pad C on the main PCB (where the t-pad leads were). Make sure you do not touch pad B at all.

Power it up and check again.

Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 23, 2011, 07:36:45 PM
Yes the 2503 is all fine. You can resolder those leads again.

Next, let's remove the t-pad from the circuit. Desolder the 3 leads where they connect to the main PCB. Leave the rest of the t-pad alone and set it to the side. Take another small jumper wire and solder from pad A to pad C on the main PCB (where the t-pad leads were). Make sure you do not touch pad B at all.

Power it up and check again.

Jeff

Ok. So I re-soldered the 2503 in there .. and plugged it back in to just double check that i was back at the same place.. then I pulled the T Pad out and put a jumper between A and C  - plugged it back in and i got nothing -

I did not clean the solder from the B hole - was that a mistake?

Thanks
Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 24, 2011, 09:30:26 AM
Max, no problem on cleaning the B hole as long as it's not shorting to A or C.

I would recommend starting form the beginning of this thread and skimming thru posts. It appears that you problem is more near the input of the circuit, not the output. We have covered this in earlier posts. Basically, you will have to do some diagnostic work while injecting a mic level signal and following the signal thru the circuit until it dies out.

The previous issues you described with the
Polarity switch make me still think it could be around the Mute and Polarity switches.

Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 24, 2011, 12:14:13 PM
Alright - will do! I remember reading over some posts bout injecting and tracing. I'll go back through and do the homework.

Thanks for all the help!
Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on September 24, 2011, 01:29:53 PM
Hey  Jeff - got one more question - Should i reconnect the T Pad when i start tracing the signal or leave it out for now?

Thanks
Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on September 24, 2011, 02:30:39 PM
Either way Max. If you leave it out and solve the problem, then putting it back in will be the only change so you will know what to look for if things don't work then.
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 05, 2011, 11:02:39 PM
Either way Max. If you leave it out and solve the problem, then putting it back in will be the only change so you will know what to look for if things don't work then.

Alright - I'm back. Thanks for taking the time to answers these questions - I know I'm be presenting you all with some pretty 'amateur hour' problems. I've learned the hard way on just about every step of this project - glad for it though.

I built an injector and probe and started tracing signal through out.
I followed the tracing directions found on page 6 of this thread - ( starting somewhere around post 106 or 107 )

I was able to trace decent signal on the Input side of things following the directions - and i was able to trace decent signal on the Output side up until the output of the EA2503 transformer (blue, green, yellow, orange, grey and violet) - signal is significantly reduced in volume and sounds as if everything below 1K is rolled off.

I've discovered a few things of interest along the way that i don't quite understand.

1) - I can trace signal from the Input all the way to the Output with the OpAmp removed. Did I make some crazy mistake or is this normal? (same occurrence on the output side of the 2503 - low vol and sounds like a hpf)

2) - Once I honed in on the 2503 as the possible source of my issue - i removed it to test it, again - and while it was removed I randomly did some exploratory probing..  When i probed the top mounting hole of for the 2503 on the PCB ( the mounting hole opposite of the Grey, Violet, Yellow and Green points ) I get full signal coming through.
I'm not the best following a schematic.. but that really had be stumped.
the output trans tested fine again.

Through all of this, even more touching up of any remotely suspicious joints - and double checking all my resistors and caps - I still have the exact same issues. 

Seems to me either the 2503 or i made some gnarly mistake that kinda botched it all ??? ???

Thanks so much again.
Max








Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 06, 2011, 08:41:20 AM
Max

Can you post some top and bottom pics please?

Was your last run thru with or without the t-pad? I helped a guy thru email last week that was describing a very similar problem. After he put his t-pad back in, he discovered it must have been something faulty with his original t-pad wiring as it was fine then.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 09, 2011, 01:14:54 PM
Max

Can you post some top and bottom pics please?

Was your last run thru with or without the t-pad? I helped a guy thru email last week that was describing a very similar problem. After he put his t-pad back in, he discovered it must have been something faulty with his original t-pad wiring as it was fine then.

Best, Jeff

Howdy -

I tested the unit both with the T Pad removed ( A and C jumpered ) and with the T Pad reinstalled.
Just like before I started tracing and retouching, the removed T-Pad testing yielded no signal on the second time around.
When i reinstalled the T-Pad  I was back to the same weak, HPF sounding signal.

Here are some photos of the top and bottom. Its all pretty ugly. At this point - i've mangled just about everything. This should serve as a solid lesson to any other DIY newbies. The part of your super detailed assembly guide that says "CHECK TWICE, SOLDER ONCE" is golden advice. Somewhere in there i think it also stresses taking your time. Like a fool I did not follow either rules that well.

You can see that I have a stepped gain switch in there. The tight space of that board was a stretch for my iron skills at that point.. any chance that a mistake at that stage could yield these results?

Thanks again - I'll track it down at some point - and hopefully not botch the whole build in the process. ;)

-Max

Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 09, 2011, 01:15:51 PM
one more
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 09, 2011, 01:54:31 PM
I don't see anything jumping right out at me although it seems strange that you had different (both not good) results with the t-pad in or out.

Does the gain switch seem to work at every position, even though the signal seems HPF sounding? We can easily eliminate it just for good measure. You can remove the 2 jumper wire connections that go to the main PCB. In their place, solder a short jumper wire from 1 to 3 on the main PCB for the gain pot area. WARNING!!! This is the equivalent to the gain switch being set to wide open, full gain, so be prepared for that. Let me know how that sounds.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 09, 2011, 06:46:48 PM
I just tried removing the Stepped Gain and got the same result.

When it was installed, all the steps of it seemed to work just fine..

When I traced the signal through out the circuit - i noted a very similar HPF change in the sound on all of the output leads of the transformer... orange, blue, grey, violet, yellow and green -

Does that raise any flags? I've tested the 2503 multiple times.. but the similarity seems strange. I could also be a misunderstanding its significance.

The fact that the Phase switch cuts signal when engaged is still floating somewhere in this strange soup as well. I've touch those tips up way to many time - i can see that i've got flow from top to bottom on the board.. and tripled checked the resistor value, and cap value associated with it.

Just rambling now. Thanks for the help and ideas as usual.
-Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 09, 2011, 09:44:09 PM
Can you add a couple of small jumper wires from SW3 to SW4 as shown in the pic below? You can just solder them onto the solder lugs that are above the white epoxy sealant on those switches. If your 2503 leads are long enough, you can move Brown and Red to the respective solder lugs on SW3. Red towards the bottom of the switch, brown towards the plunger.

Report back with your findings.  ;)

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 10, 2011, 06:28:47 PM
Well, I jumpered the two switches as you showed - and the problem remains. HPF sound and loss of signal when the Phase is engaged.

The leads Brown and Red leads on my transformer might be long enough.. but I've soldered and desoldered those points so many times already that I'm a little leery of pushing my luck. I'm gonna give it a better assessment and if doable, I'll give it a shot and report back those findings.

Dig it.
Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 10, 2011, 06:37:58 PM
Max,

I am starting to think it may be the 2503 even though all the winding's DCR measure out OK. You did say that you traced the signal to just before the 2503 and it was fine right? You could probe right on the solder lug of SW4 where the red lead goes to verify.

I asked ED via email last nite if he could think of a reason the 2503 would produce this result if all the winding's DCR was correct and he said nothing comes to mind but stranger things have happened.

Let me know and we'll go from there.

Cheers, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 10, 2011, 07:00:59 PM
Heyo-

Strangers things have definitely happened.. and they've definitely happened to me.

Yes, the signal is good up to the 2503 - and i just double checked again - at the switch 4 lugs and right at the solder point of the leads to the board.

Can I attempt a similar sort of signal trace directly on the 2503? Should I change anything about my probe set up?

THANKS!
Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 10, 2011, 07:14:12 PM
Max

With the Polarity switch out, the signal will be coupled to the red lead of the 2503. You could check there by probing from the bottom of the PCB.

With Polarity switch engaged, signal will be coupled to the brown lead of the 2503. See if the signal is good at the brown lead with the switch in. It should be.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 10, 2011, 08:00:46 PM
I get signal on the Red and Brown leads regardless off the position of the Phase switch.. In fact I can probe all 6 lugs of all 3 Switches and get good signal regardless of the switch position.  ???

My probe set up is an iPod wired to alligator clips attached to In Lo and In Hi (J8 and J10)
The probe is hooked up to a small set of speaker with a 10uf 100v Non-Polarized Capacitor inline.

-Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 10, 2011, 08:09:38 PM
Max

What about setting your DMM to ACV and probing for a mV reading. You can hook the black probe to the upper lead of R13, closest to the top edge of the board or the Bourns gain pot.

I am about to test a VP26 built for a customer so I will see if I get anything like what you are describing.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 11, 2011, 03:01:13 AM
Hey Jeff -

I gave this probing a shot. I wasn't super sure about how to do this -

My DMM ACV settings only has 300V and 200V.
I set it at 200V and connected the Black lead to the top side of R13.
I then probed with the Red lead at J8 and J10 and I got a reading of approximately 3.4 from both inputs.
(both readings started a little higher and seemed to drop - the more that i double and triple checked)

I was a little unsure about the reading because you noted looking for a mV reading.. So I set the DMM to DCV  (which has a mV range) and conducted the same test -  I got a approximately 1.78 from both inputs.

Results were the same regardless of Switch 3 being engaged or not.

Not sure if this is what you were looking for.

-Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 11, 2011, 08:55:27 AM
Close Max but you need to stay on ACV. That is the only way you will be able to measure if audio is present. With a source injecting signal, the black probe where it was, probe with the red to all 6 of the solder lugs on SW4. Let me know what you get for each one.

BTW, a mic level input will be very low. It will increase if you check at the + side of C6 due to the gain of the 2622. It will increase more after the DOA if you check either side of C10 (depending on how high you gave the gain pot set). That is the same reading you should get on some of the lugs of SW4.

I myself have never used the iPod/speaker probing method. Only a DMM, scope or an AP.

Best, Jeff
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: vDo on October 11, 2011, 02:03:10 PM
Thanks for the directions.. I had a feeling i might be missing it.

I injected signal at J8 and J10 - connected my DMM Black lead to the top lead of R13 and then probed with the DMM Red lead at all 6 of the lugs of Switch 4 - I got no reading on all 6. Not an error reading but nothing.. Maybe a limitation of my DMM? An upgrade wouldn't hurt.

I think i'll change up my signal injection process a bit and perform the readings you noted around C10.

Thanks
Max
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on October 11, 2011, 04:01:54 PM
The module is under power right? You should get signal at 2 of the pins on the Mute switch. You can easily follow the signal from C10 thru the Polarity switch and then over to the Mute switch. Also, a mic level signal needs to be injected. I set me AP to -43dB and 150ohms.

It may be an auto-ranging setting on the DMM. I hear of a lot of that with customers. I had someone recently tell me they got a bad 150k resistor as it read open. Once I mentioned checking the DMM settings, they got it sorted.  ;)
Title: Re: classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Build Support Thread
Post by: mulletchuck on October 19, 2011, 10:40:26 PM
Finished mine!   I had one or two solder bridges on the gar2520 that i had to correct.     And then, i had to leave phantom power on and let the pre run for a good 20 minutes before the pops/clicks went away as the DOA 'broke in'.

I tested it on my housemate, using a dynamic (RE20) and a condenser (414B-ULS).  Here's what it sounded like:

http://www.zshare.net/download/9495354277071b4e/ <<< Condenser

http://www.zshare.net/download/949535652b7ced61/ <<< Dynamic


The text message sound during the condenser is Jeff Steiger sending me a text saying "Awesome Job!!"  lolololololol
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: johnnyscotch on December 19, 2011, 03:59:15 AM
I'm having an issue with my VP26 modules.

I put them in my 51x rack (which works with all my other 500 modules) and when I turn on my power supply, I lose my +-16v rails, and phantom rail. The phantom fuse blows everytime. The 16v fuses don't blow, but they don't put out power either. When I take the VP26 out, I get my 16v power back, and upon changing the 48v fuse, it works as well.

I took out the GAR2520 from a module and put it in the rack where I get phantom working OK, the LED lights up and I don't lose my 48v rail, but the 16v rails still go out.

Any suggestions on what I might check out???

Any key voltage checks? I have rack extenders to use. Since it's both modules, I'm assuming I may have assembled them incorrectly? I followed the guide to a T, and this isn't my first build.

thx
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 19, 2011, 08:40:34 AM
Did you add the drain wire to the 48V phantom switch for when it's off? My guess is something with that is wrong. Do you have a pic of that area? Try removing that wire and things should be fine.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: earl on December 19, 2011, 09:14:41 AM
sounds like dead short to gnd make sure the thing is going in the slot right
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 19, 2011, 09:30:43 AM
...I followed the guide to a T...
The old guide? You saw all the new BOM changes for the Rev B version of the VP26 right? Just making sure.

sounds like dead short to gnd make sure the thing is going in the slot right
Could very well be a possible issue. Maybe add a spacer to block the lower 3 pins of the 18 pin connector.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: etheory on December 20, 2011, 05:48:55 AM
Just a quick interjection to share my first ever song recorded with a ClassicAPI VP26 ( it's equal parts VP26 and Sound Skulptor MP73 ).  The vocals were recorded through an SM7b in a home studio then through a VP26/MP73 split that I built (http://www.evolutionarytheory.com/2011/09/classicapi-vp26-and-sound-skulptor-mp73-preamps-are-finished/ (http://www.evolutionarytheory.com/2011/09/classicapi-vp26-and-sound-skulptor-mp73-preamps-are-finished/)), and then blended post record to taste.  It was about 50% of each in the end:

http://soundcloud.com/evolutionarytheory/we-jump-lee-safar-featuring (http://soundcloud.com/evolutionarytheory/we-jump-lee-safar-featuring)

Shameless iTunes plug:
http://itunes.apple.com/us/album/we-jump-single/id475952828 (http://itunes.apple.com/us/album/we-jump-single/id475952828)

It's very early stages of doing all this stuff at home, so you'll all no doubt be able to get better results, BUT, it's a quantum leap from what I had before, so thanks Jeff for making it possible along with Gary for one kick-ass DOA.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on December 21, 2011, 01:28:03 AM
Is there a new potentiometer ? Just got up to section 9.1 and noticed mine looks very different. Are there new instructions for this? Thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 21, 2011, 08:19:21 AM
Is there a new potentiometer ? Just got up to section 9.1 and noticed mine looks very different. Are there new instructions for this? Thanks!
IIRC, your main PCB is green. The t-pad will have a small adapter PCB with it. The proper orientation can be seen here. http://classicapi.com/catalog/product_info.php?cPath=48&products_id=255 (http://classicapi.com/catalog/product_info.php?cPath=48&products_id=255) The pot's PC pins must be soldered to the adapter PCB. You would bot believe how many people have asked me if it needs to be soldered. Then only 3 jumper wires are required to the main PCB. Notes for that are on the link above.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: johnnyscotch on December 26, 2011, 04:19:07 AM
sounds like dead short to gnd make sure the thing is going in the slot right

Finally had more time to troubleshoot. This was indeed the problem. Everything is working fine.
It's weird though, it seems to be VERY particular about going in the 18pin slots. More than I would have thought. It has to be pretty much dead-ass dick in there to work properly.

Usually the simplest explanation is the correct one. I was making it more difficult than it needed to be. This was a very easy build and even the GAR2520 was relatively easy, I was really more worried about that than anything.

Thanks for your help guys.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: TimS on December 26, 2011, 05:37:45 PM
A bit off topic, but any word on the state of the EQs you were working on, Jeff?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mjenki14 on December 29, 2011, 12:18:18 AM
Hi, newbie post here.  I recently ordered two vp26 w/ red dots and an A Designs 500hr power supply.  I've previously built two guitar amps from kits (Super Reverb & JTM45) so I have some experience soldering, but am no electronics expert.  The vp26s are the new Rev B.   I double and triple checked resistor/cap values before stuffing the board with the new BOM.  I soldered slowly and thoroughly, or so I thought.

I completed the build after a couple of hours, checked the resistance values between pins of the op amp sockets, but when I tried to test it, no sound at all.  I went back and re-soldered all the pins on the switches because I read those could be trouble areas, as well as the t pad.  Still nothing.  Went back and checked for any visible shorts from but couldn't find any.  Changed cables, mics, etc.  I have no other 500 series to test the rack unit with.

Finally I hooked the vp26 into the line input on another pre amp, a vintech x73, with an sm7b.  If I cranked the line input gain, I could hear my voice with both the preamp and output attenuator all the way open.  The signal was really quiet and distorted, but it raised and lowered with the gain knob and attenuator.  It also muted and decreased in volume with the pad switch.

Tonight, I took it apart and re soldered, reseated the op amp, etc.  Still no luck.  So here I am.  Any troubleshooting advice is greatly appreciated.  I read through this thread, but its been hard for me to translate some of the issues to the new rev b board.  Here are some pictures.  I know the soldering is a little sloppy because I've gone back a couple of times trying to touch things up.

Any help is greatly appreciated.  Thanks so much.

Michael

(https://lh6.googleusercontent.com/-uZlCW6YQZAM/Tvv2bF0qdwI/AAAAAAAAEec/NMsQdUIRHKQ/s1280/IMG_1150.JPG)

(https://lh4.googleusercontent.com/-f2pAH_J8U5M/Tvv2CimWZ5I/AAAAAAAAEdo/VFr1hy44fcI/s1280/IMG_1145.JPG)

(https://lh5.googleusercontent.com/-ptQto4rPb5Q/Tvv2NVign-I/AAAAAAAAEeA/6Zi5G0bzLAY/s1280/IMG_1148.JPG)



Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 29, 2011, 09:30:30 AM
It is odd that both pre's are acting the same way. After looking briefly over the pics, nothing is jumping out at me. We haven't seen the bottom of the boards but will assume all pins have been solidly soldered.

Since your rack is new and has not been used with other modules, I would look at that next. I have never had that version in front of me but customers have mentioned being able to remove the top from the case to gain easy access to the edge connectors and innards of the rack. You could remove the red dot, insert the module and power the rack. It will be easy to check the voltage at both the -V and +V pins of the opamp sockets. The last one I heard about was between 13 and 14V at the edge connectors. That would not cause this exact symptom but is still not right. It could be something similar.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mjenki14 on December 29, 2011, 03:45:46 PM
Thanks Jeff for the quick reply.  It is not an issue with both units, because I've only built the first one.  I am waiting to get this one working so I don't make the same mistake twice on the next build.

I checked the voltages and got 31.4 V between the V+ and V-.  Between both the V+ and C, and V- and C, the reading was 15.7 V.  I went through the troubleshooting measurements again, and one was off.  Between the C and O, my reading were constantly changing and lower than 200K Ohms.

Attached are some pictures of the bottom of the board.  I checked continuity between all the closest solder points to see if they were shorting and none  were.

Again, I really appreciate the help.

Michael

(https://lh4.googleusercontent.com/-3ThQddQMHWo/TvzNPoqBeCI/AAAAAAAAEfA/IlaJfnc3GlA/s1280/IMG_1153.JPG)

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 29, 2011, 04:30:54 PM
Nothing really jumping out on the bottom either except what looks to be solder on the gold finger #8. I don't think that would be an issue though.

The reading between C and O is most likely DMM related. Either battery, range or auto-range related. As long as it's not a dead short, you should be fine.

While the rack is open, with no module installed, power off, you might as well verify the rear XLR connections to the card edge connector. I would beep them out or measure resistance. For the input, XLR pin 2 should go to card edge pin #10 and XLR pin 3 should go to card edge pin #8. For the output, XLR pin 2 should go to card edge pin #2 and XLR pin 3 should go to card edge pin #4.

Next up would be injecting some signal at the input and tracing with a scope probe or DMM set to ACV. You will need to follow the signal along the schematic probing at each side of each component to see where it stops. As a tip, a balanced H-pad is a great thing for this. Using this calculator (http://www.nu9n.com/tpad-calculator.html), you will want an input Z of 10,000 ohms, output Z of 150 ohms with a pad loss of around 36dB. You can then use a sig generator from a sound card or whatever to inject around a -43dB signal, with the gain knob around 2:00, should give you an output of around +4dB. Make sure you match the like R's to as close as your DMM with measure. .1% precision R's are great for this but hard to find without spending an arm and leg.

Be careful when probing around not to wedge a probe tip between a component lead and the top of the PCB. This could possibly cause a short to the ground plane which is on top of the PCB.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mjenki14 on December 29, 2011, 05:37:59 PM
Checked the continuity between xlr inputs and they are fine.  I've never done any signal generation testing, and my schematic skills are missing, so I'll be reading up on that stuff and hopefully will be able to check the rest soon.  Thanks again!

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mulletchuck on December 30, 2011, 06:12:22 AM
Bro, what is up with one of the gold fingers on the card?   it looks like it doesn't have any gold at all on it.   Also, are you sure you used a *working* op amp when you fired it up?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 30, 2011, 08:36:48 AM
Bro, what is up with one of the gold fingers on the card?   it looks like it doesn't have any gold at all on it.   Also, are you sure you used a *working* op amp when you fired it up?
Chuck, I think some solder was dropped on that gold finger. The opamp is one of Scott's red dots so that should be OK.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: 3nity on December 30, 2011, 10:46:59 AM
looks like a lots of cold solder joints...
At least from my pov.

Talking about 500 rack options im thinking to get a Chameleon Labs CPS-500.
it holds 1 x 500 unit and price is 169$

Thanks.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mjenki14 on December 30, 2011, 11:19:08 AM
mulletchuck, i accidentally got some solder on the finger, got off as much of as i could.  I checked its continuity when hooked up to the power supply and seemed to be fine.

I tried both op amps I have in the board with no difference.

3nity, I have re soldered multiply times, but will again.  I will try removing all I can to try and start from scratch on the solders. 

Still working on getting a signal probe and understanding schematics better.  I can follow the schematic to the layout, but I'm having trouble understanding the T and H pad calculations.

Again, thanks for all the help.  I'm sure i've made some mistake I keep overlooking.

Michael
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 30, 2011, 12:42:02 PM
...Still working on getting a signal probe and understanding schematics better.  I can follow the schematic to the layout, but I'm having trouble understanding the T and H pad calculations...
You can use a DMM for this just measuring ACV.

I think I will add a resister kit to the store that is prefect for a line in on one of my preamps (or any other preamp). That will take all the guess work out of things for guys with the H-pad config. It will just be 5 resistors but the like pairs are .1% precision 15ppm.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on December 31, 2011, 06:56:09 PM
and I was so proud of myself for getting through this build with no major hiccups (took my time and did it right [i thought]).... unfortunately after returning from holiday I threw it into a lunchbox to test it and it actually causes the whole lunchbox to not function right (the power seems to drop and all of my other modules no longer light up fully, the API power indicator on the lunchbox glows weakly but not at full). When I remove the VP25 everything goes back to normal. Also, it seemed like I smelled that electronic component burning smell but for the life of me I can't locate any damaged components.

Any help is greatly appreciated, not sure what I must have missed here....

attached are pics(as great as I could) that cover the most recent build. if anything sticks out, by all means, please!

(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_7c12f65e.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/7c12f65e.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_7e57ca01.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/7e57ca01.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_27bc9156.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/27bc9156.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_34e93dae.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/34e93dae.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_7897bbd8.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/7897bbd8.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_e9bdb9a8.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/e9bdb9a8.jpg)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 31, 2011, 08:14:01 PM
bigevil, is the opamp a known good one that has been tested in another preamp? I would try removing the DOA and then inserting the module to see if you still get the same issues with the rack. My first guess is something opamp related. If the rack seems fine then insert a known good working opamp from another build in this preamp to test out.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on January 01, 2012, 04:41:18 PM
Jeff.
good idea. Swapped it out with a known good one and it doesn't have the power issues anymore and infact seems to work great. The audio is lower compared to the other pre's in the rack but when I get the chance I'll A/B it with my other VP25 and see if its consistent with it.  I'll head over to the GAR2520 to troubleshoot that.

Thanks much, keep you posted!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: chunger on January 13, 2012, 03:00:38 AM
World's best newbie preamp kit just got easier!  I've started a build to hopefully help jsteiger put together a revised assembly manual as complete as the original.

Let's see what's in the box?

(http://studio939.zenfolio.com/img/s11/v30/p1033901657-4.jpg)

And here we go.  Pretty new Rev. B PCB:

(http://studio939.zenfolio.com/img/s3/v39/p114807957-4.jpg)

And contents (note: front faceplate missing from photo)

(http://studio939.zenfolio.com/img/s3/v39/p399783143-4.jpg)

I decided to follow the general format of the VP26 assembly manual and start with the resistors. . .

(http://studio939.zenfolio.com/img/s3/v39/p456693564-4.jpg)

well, actually, I decided to just go ahead and sort the components according to the new REV. B BOM.

(http://studio939.zenfolio.com/img/s3/v39/p789317813-4.jpg)

Careful with the little capacitors.  The markings are small.

(http://studio939.zenfolio.com/img/s11/v35/p1056685423-6.jpg)

Resitors placed.

(http://studio939.zenfolio.com/img/s3/v38/p716868999-4.jpg)

(http://studio939.zenfolio.com/img/s3/v39/p619147592-4.jpg)

The recommended assembly method now is to bend the leads and solder from the back side. . . the ground plane on the new PCB has shifted to the other side.

(http://studio939.zenfolio.com/img/s3/v38/p587002091-4.jpg)

(http://studio939.zenfolio.com/img/s11/v33/p1024256822-4.jpg)

(http://studio939.zenfolio.com/img/s11/v29/p661316586-4.jpg)

Next, I hit the 2 diodes in the same manner making sure to place them in the correct polarity.

(http://studio939.zenfolio.com/img/s3/v39/p711715008-4.jpg)

Next, I do the small ceramic capacitors

(http://studio939.zenfolio.com/img/s3/v41/p994012967-4.jpg)

(http://studio939.zenfolio.com/img/s11/v33/p837874063-4.jpg)

The WIMA film capacitor. . .

(http://studio939.zenfolio.com/img/s3/v41/p747225929-4.jpg)

And then the axial capacitors.  Polarity is important on these.  Please double check and make sure they are facing the right way.  Solid line indicates "-" side of the capacitor.

(http://studio939.zenfolio.com/img/s11/v30/p870963419-4.jpg)

(http://studio939.zenfolio.com/img/s11/v33/p727144135-4.jpg)

Then the radial capacitors. . . again, these have polarity.  Make sure you insert the longer of the legs into the "+" marked hole.

(http://studio939.zenfolio.com/img/s11/v37/p757846658-4.jpg)

Next, sort the hardware. . .

(http://studio939.zenfolio.com/img/s11/v29/p863372269-4.jpg)

Locate the Milmax sockets and place them from the back side of the PCB.

(http://studio939.zenfolio.com/img/s3/v38/p815796730-4.jpg)

And solder. ..

(http://studio939.zenfolio.com/img/s3/v40/p872683256-4.jpg)

(http://studio939.zenfolio.com/img/s3/v38/p668306431-4.jpg)


Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: chunger on January 13, 2012, 03:18:57 AM
Next, install the screws and standoffs on the back side of the L-bracket competely.

(http://studio939.zenfolio.com/img/s11/v29/p810932769-4.jpg)

And the front side of the L-bracket, we install the screws half way so we can slide the PCB and attached switches/pots over the standoff.

(http://studio939.zenfolio.com/img/s11/v35/p1041521774-4.jpg)

Next, we attach the gain pot, but remember NOT to solder yet!  (Note: I am building the standard configuration here with a Bourns pot. . . there is an option for a stepped grayhill switch on the PCB).

(http://studio939.zenfolio.com/img/s1/v20/p1057648412-4.jpg)

And, place the T-pad. . . again, DO NOT solder yet.  You may need to bend some of the legs to straighten them.

(http://studio939.zenfolio.com/img/s11/v36/p921300903-4.jpg)

Next, assemble the main PCB to the L-bracket with the pot and T-pad loosely placed.

(http://studio939.zenfolio.com/img/s11/v37/p1041812822-4.jpg)

Align the pots to center on the L-bracket holes to the best of your ability.

(http://studio939.zenfolio.com/img/s8/v11/p730056604-5.jpg)

Install the nuts to lock the pots into final position. . .

(http://studio939.zenfolio.com/img/s3/v38/p570394923-5.jpg)

And solder everything you can reach from the front side.

(http://studio939.zenfolio.com/img/s11/v32/p684673467-4.jpg)

(http://studio939.zenfolio.com/img/s3/v41/p807697509-4.jpg)

Next, disassemble the PCB and solder the remaining lugs from the back side.

(http://studio939.zenfolio.com/img/s11/v32/p547269394-4.jpg)

(http://studio939.zenfolio.com/img/s11/v33/p985427055-4.jpg)

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: chunger on January 13, 2012, 03:27:52 AM
Next, place the 3 push-button switches pressing firmly to the PCB surface

(http://studio939.zenfolio.com/img/s3/v40/p928315991-4.jpg)

I solder only 1 center lug on each switch.

(http://studio939.zenfolio.com/img/s3/v39/p645932414-4.jpg)

Then, I re-assemble the PCB to the L-bracket and the front panel to check for optimal alignment of the 3 push-button switches.  I slightly tweak the angle to optimize if necessary.  Keep in mind there is still a little bit of adjustment possible on the front panel positioning, so I try to get this as close as possible, but still have some room to maneuver if necessary.

(http://studio939.zenfolio.com/img/s11/v36/p767916362-5.jpg)

And, solder in the rest of the lugs.  I jump around a lot to keep from overheating the switches during this operation.

(http://studio939.zenfolio.com/img/s3/v41/p945605273-4.jpg)

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Ben on January 18, 2012, 05:50:38 PM
Hi guys!

just completed a VP26 build. Instructions were very clear and easy to follow.
the good news is the pre amp is passing sound, the bad news is that it doesn't sound like it should.

these are some problems I've encountered:

-The preamp passes sound, but I have to completely crank it to get some kind of level and the sound is rather thin
-output knob does nothing
-Mute and pad both work, phase changes my sound (and I'm only recording with 1 mic so this shouldn't happen right?)
-phantom power works

any idea's what might be wrong?

thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 18, 2012, 06:31:29 PM
Ben

Unsolder all the leads for the output transformer and measure the DCR between the following:

Red to orange
Brown to black
Green to blue

The resistance measurements should all be between 16 ohms and 31 ohms, or so.

Report back with your findings.

Cheers, Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: canidoit on January 18, 2012, 10:13:44 PM
Chunger, you should start a new thread on your build. Your build threads are really inspiring and also educational and I think it would be more useful as a thread on its own like your 51x rack thread.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mjenki14 on January 18, 2012, 10:21:52 PM
For any interested, it turns out my output transformer was bad.  When replaced with a different one, everything seems to work.  Hopefully all will go well with the next unit.  I appreciate all the help!

Michael
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: chunger on January 30, 2012, 11:06:13 PM
OK. . . time to finish out the VP26 build. . . since the ground plane was moved to the front side, it's a little bit more critical in the rev. B to use some sort of insulating tape on the input transformer. 

(http://studio939.zenfolio.com/img/s3/v40/p134942802-4.jpg)

Here, I purchased some double sided tape.

(http://studio939.zenfolio.com/img/s3/v45/p120031238-4.jpg)

Note the position of pin 1 which is marked with a dot on the transformer's label sticker and clearly labeled on the PCB.

(http://studio939.zenfolio.com/img/s3/v42/p152534492-4.jpg)

(http://studio939.zenfolio.com/img/s11/v35/p120579195-4.jpg)

I cut a piece of double sided mounting tape

(http://studio939.zenfolio.com/img/s3/v44/p386806512-4.jpg)

And apply to the bottom of the transformer

(http://studio939.zenfolio.com/img/s3/v45/p461163479-4.jpg)

(http://studio939.zenfolio.com/img/s3/v44/p501754642-4.jpg)

Next, place the transformer making sure to align pin 1.

(http://studio939.zenfolio.com/img/s3/v44/p52805882-4.jpg)

And solder from the back side.

(http://studio939.zenfolio.com/img/s3/v44/p437380562-4.jpg)





Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: chunger on January 31, 2012, 01:08:07 AM
output transformer next. . . find screws and washers and put in this configuration.

(http://studio939.zenfolio.com/img/s11/v37/p38364866-4.jpg)

Next, insert into output transformer.

(http://studio939.zenfolio.com/img/s3/v39/p409796960-4.jpg)

Put 2 more washers on under the transformer.

(http://studio939.zenfolio.com/img/s3/v38/p456056995-4.jpg)

Position carefully on the PCB and place 2 lock washers.

(http://studio939.zenfolio.com/img/s3/v44/p478837123-4.jpg)

Then, the nuts go on. . . I found it easier to tighten from the screw side while holding the nuts in place.

(http://studio939.zenfolio.com/img/s3/v41/p70483398-5.jpg)

Carefully trim the output transformer wires to the correct length. . . it's easier to leave them longer than necessary and trim several times to get to the correct length than to trim them all at once and too short. . . if that happens, hilarity would ensue.

(http://studio939.zenfolio.com/img/s3/v40/p38770160-4.jpg)

Once length is determined, strip back about 1/8" and tin the tips before inserting into the color-marked hole and soldering from the back side.

(http://studio939.zenfolio.com/img/s3/v45/p473744898-4.jpg)

I used a couple short pieces of shrink tubing to clean things up a bit.

(http://studio939.zenfolio.com/img/s11/v35/p258498720-4.jpg)

Repeat for all the other output transformer leads.  Lengths will vary.

(http://studio939.zenfolio.com/img/s3/v44/p470427099-4.jpg)

(http://studio939.zenfolio.com/img/s11/v35/p186827484-4.jpg)

(http://studio939.zenfolio.com/img/s3/v39/p230437492-4.jpg)

Next, grab the excess red and orange leads from the output transformer.

(http://studio939.zenfolio.com/img/s3/v41/p379110683-4.jpg)

Strip back about 1/8" on the ends and tin them.

(http://studio939.zenfolio.com/img/s11/v35/p509797718-4.jpg)

. . . and solder these leads into the holes labeled "1" and "2".

(http://studio939.zenfolio.com/img/s3/v43/p186182188-4.jpg)

now, re-mount the PCB to the L-bracket hopefully for the final time.

(http://studio939.zenfolio.com/img/s3/v43/p342586546-4.jpg)

Use lock nuts this time to secure the PCB on the standoffs.

(http://studio939.zenfolio.com/img/s3/v43/p96333053-4.jpg)

. . .and snug them down.

(http://studio939.zenfolio.com/img/s3/v44/p326559196-4.jpg)

voila!

(http://studio939.zenfolio.com/img/s11/v35/p212538020-5.jpg)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: chunger on January 31, 2012, 01:29:09 AM
to protect the finish on the front panel, I used console tape on the sockets to tighten the nuts onto the knobs.

(http://studio939.zenfolio.com/img/s11/v35/p157807929-4.jpg)

(http://studio939.zenfolio.com/img/s3/v38/p380526766-4.jpg)

reference the top edge of the L-bracket and front panel to make things straight when tightening the nuts.

(http://studio939.zenfolio.com/img/s3/v39/p18755396-4.jpg)

Next, locate the phantom power switch.

(http://studio939.zenfolio.com/img/s3/v41/p530238524-4.jpg)

Thread one of the included nuts onto the switch. . .

(http://studio939.zenfolio.com/img/s3/v40/p319264227-4.jpg)

Then, add the lock washer.

(http://studio939.zenfolio.com/img/s3/v41/p204130416-4.jpg)

Position the switch onto the front panel.

(http://studio939.zenfolio.com/img/s3/v39/p186875214-4.jpg)

And secure the remaining nut from the front side being careful not to mar the front panel

(http://studio939.zenfolio.com/img/s3/v42/p145905017-4.jpg)

Next, cut the red and yellow leads to length and solder to the phantom power switch.

(http://studio939.zenfolio.com/img/s11/v36/p300266081-4.jpg)

The preamp is now complete as far as the electronics go.

(http://studio939.zenfolio.com/img/s3/v39/p491015579-4.jpg)

Next attach the knobs with the allen key set screws.

(http://studio939.zenfolio.com/img/s3/v42/p80596001-4.jpg)

Locate the push-button caps

(http://studio939.zenfolio.com/img/s3/v45/p102017933-4.jpg)

And press them on. . . a little force might be required here.  I use the rubber, padded end of my wire strippers.

(http://studio939.zenfolio.com/img/s11/v36/p458295653-4.jpg)

Next, apply the colored decals to finish up the cosmetics.

(http://studio939.zenfolio.com/img/s3/v43/p523972189-4.jpg)

(http://studio939.zenfolio.com/img/s3/v39/p400030327-4.jpg)

And the VP26 rev. B kit is complete.

(http://studio939.zenfolio.com/img/s11/v35/p148452406-5.jpg)

(http://studio939.zenfolio.com/img/s3/v45/p321164162-4.jpg)

Follow the test procedures outlined in the original build manual, and install the opamp of your choice.  Here I'm using one of Gary's fine GAR2520's.  A great fit for this pre and righteously priced.

(http://studio939.zenfolio.com/img/s3/v40/p207846944-4.jpg)

(http://studio939.zenfolio.com/img/s3/v38/p376918197-4.jpg)

And, fully assembled.

(http://studio939.zenfolio.com/img/s3/v42/p516969720-4.jpg)

(http://studio939.zenfolio.com/img/s11/v35/p322644613-5.jpg)

Humans win!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 31, 2012, 02:05:32 AM
Absolutely beautiful work as usual 'Chung! Your attention to detail is impeccable!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: minor_glitch on January 31, 2012, 03:14:05 PM
Quick question for Jeff.  I have the original green board version of the VP26 and I was planning to get a second so I could have a relatively matched stereo pair.  Is the rev b too different to make a stereo pair with the original version?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 31, 2012, 08:35:22 PM
Quick question for Jeff.  I have the original green board version of the VP26 and I was planning to get a second so I could have a relatively matched stereo pair.  Is the rev b too different to make a stereo pair with the original version?
Good question. No worries, the audio signal path is identical. You will indeed end up with a stereo pair. That holds true for all the updated Rev's of my mic preamp boards.

Cheers, Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: minor_glitch on January 31, 2012, 10:44:05 PM
Excellent, thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: nuts on February 06, 2012, 05:19:17 PM
Hi Jeff, i bought 2 VP26 kits with Grayhill stepped gain pots.

How am i supposed to mount the Grayhill pot (with dedicated PCB)  on this VP26 rev A.2 PCB ?

I found it can only be mounted upside down: Grayhill's pcb facing the ceiling if the VP 26 PCB is the floor. And  solder 2 wires in pin 1 and 3 from grayhill PCB to pin 1 and 3 of R14 position.

Am I right ?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 06, 2012, 05:26:41 PM
Hi Jeff, i bought 2 VP26 kits with Grayhill stepped gain pots.

How am i supposed to mount the Grayhill pot (with dedicated PCB)  on this VP26 rev A.2 PCB ?

I found it can only be mounted upside down: Grayhill's pcb facing the ceiling if the VP 26 PCB is the floor. And  solder 2 wires in pin 1 and 3 from grayhill PCB to pin 1 and 3 of R14 position.

Am I right ?
Indeed you are exactly right nuts. I have pics on my site that show it just as you describe.

(http://www.classicapi.com/catalog/images/gallery/switches/rotary/VP-Gainswitch/VP-GS-In-4.jpg)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: nuts on February 06, 2012, 05:40:03 PM
Sorry i didn't seen it, thanks for your answer.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF on February 14, 2012, 11:05:36 PM
Hi Jeff,
I built a couple of VP26 modules a few weeks ago and one is perfect while the other often gives me a bit of fuzzy distortion along with the signal.  the signal is loud and pretty clear compared to the working module but there is the distortion along with the audio.  i have opened the module twice now and resoldered all points, especially on the stepped attenuator, but still have the problem.  Everything else functions as it should.  It sounds great when the distortion is gone, but then it will appear, so it can't be used in session.  Any thoughts?  i can pop it out and take some pics if that would be helpful.
Thanks very much for such a wonderful sounding pre.  i've sold all of my 512s since yours sound so much better. 
David

btw- i LOVE the verification questions need to post.  you need to know your American history and astronomy!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 15, 2012, 02:25:20 PM
David

What opamps are they and who built them?

Are they seated correctly? Take a look here. http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)

If they are pre-builts from me, they were either built by Scott or Gary. They both test and burn them in so probably won't be the opamp if it's a pre-built. If the opamps were kits, that will most likely be the issue. Swap the opamps to see if the problem follows the opamp or stays with the pre.

Cheers, Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: andreconde on February 15, 2012, 04:52:16 PM
I'm sorry if this is not the right place but... is there anyone selling these kits in Europe or do I need to order directly from the USA?

Cheers,
André
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF on February 15, 2012, 10:45:57 PM
Hi Jeff, thanks for the reply.  the red dot was pre-built and i did follow the document on installing.  i've already switched the op amps between the 2 pres and  the problem stays with the pre.  i did re-solder the pins for the op amp but no improvement.
I've had this sound before with other gear and generally it is a poor connection- sometimes even just a dirty patch cable at the console- but i have touched up all of the solder joints twice now, even sucking the solder from all of the points on the stepped pot and re-doing them.  Still can't find the issue.  wondering if it could be something internally on one of the 2 pots.  is it possible to bypass them to test.  i remember reading that on an earlier thread, but i think it was for the non-stepped pot bridging points A and C (stay away from B!)
thanks again for your help.  I've got some downtime this weekend and aim to solve it once and for all.
thanks again for the help,
David
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 16, 2012, 10:32:15 AM
... i remember reading that on an earlier thread, but i think it was for the non-stepped pot bridging points A and C (stay away from B!)
That is correct for bypassing the t-pad. What version of PCB do you have? If the t-pad is mounted directly to the main board, it will most likely be fine. If it has the adapter board, I would try the bypass. This distortion will probably not be a component especially the t-pad or switch.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF on February 16, 2012, 02:49:37 PM
i have  the latest black board which has the pot mounting directly to the board.  i thought perhaps i might have bridged two resistors with solder or if one of the resistors had a poor connection it would degrade the signal, no matter what setting the pot is at.  does the signal pass through the resistors in series, accumulating resistance as you increase the pot?
i don't think i have the letters A or C on my board.  aren't there numbers instead.  will pop it open this weekend and get to the bottom of it.
thanks again,
David

at least now i know who Patrick Henry is.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 16, 2012, 03:28:27 PM
You will not have the A, B, C pads on your board with the latest Rev. I don't think it will be around the t-pad. That is the main reason I wanted the footprint of the Bourns version right on the PCB. It really eliminates any errors associated with the t-pad.

The stepped preamp gain R's are a string in series. Bridging 2 will only change the gain where 2 adjacent steps will be the same. It should not cause audible distortion. Never say never.

Now, a poor solder joint directly in the signal path could produce results like what you are saying. A lot of times though a joint will either be good or bad but for sure there is also a point in between.

I assume you have also eliminated the rack slot and all associated cabling?

Cheers, Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: J Adams on March 01, 2012, 02:04:00 AM
Question for Jeff:
So far I have built 2 vp25s and 2 vp312s.  On one of my vp25s, the pad button seems to do some weird things like not 'un-pad' after I push it.  I then have to push it a few times and it eventually work.  Any ideas before I start poking around?  These are my first builds ever, so I am not up to par on troubleshooting yet.  Thanks man!

p.s. really like these new black pcbs and being able to mount the gain pots onto the board (stepped and output)!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 01, 2012, 09:18:19 AM
I would try a simple reflow of solder on the pad switch. It is extremely rare that the switch will be bad. I usually work each switch a dozen or so times when I do a build just for good measure.

Cheers, Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 06, 2012, 09:09:57 AM
i've fixed up lots of gear... usually just doing basic things like replacing caps that are obviously blown out... or resistors that aren't reading correctly... or reversing polarity on channels, changing things from 3 to 2 pin hot...  i guess i'm still a beginner though.

thought i did a really good job building the preamp.  all my connections seem solid (don't think i made any cold connections).  soldering all the resistors in for the stepped gain was pretty insane though... never worked on anything that close together before !  i don't see any solder bridges there or anything though...

i have the preamp all put together... but i'm not getting any sound at all out of it, even when the gain is cranked.  the rack seems to be okay.  tried it on different slots (all with no sound)... after figuring out how to use my ddm for voltage (thanks jeff !)  getting 15.98 v dc when the red is on +V and the black is on C... and getting exactly -16 dc volts when the red is on -V and the black is on C.

any suggestions?  would love to hear this preamp going :)  i have one of scott's red dots installed.  do you think the output transformer could be bad like in the other case?  how do i test it?  thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 06, 2012, 09:33:53 AM
just did the test that michael did... tried running the preamp into another a preamp... i'm in worse shape than he was though... as i still don't get anything...

when the second preamp is cranked (not the capi one)... i hear a low electrical feedback noise... the pad, mute, etc. on the capi preamp does not affect this sound.  however !  the output attenuator does.  if i back the output attenuator all the way down, the second preamp sounds pretty quiet.  however, the louder i bring up the output attenuator, the more of a wahhhhhh, low buzz i hear... the low buzz does not increase or decrease with the preamp gain higher or lower... only the output attenuator. 

interestingly... the power supply for this osa rack makes the same frequency buzz when turned on.  when the power suppy for the rack is turned on or off, still getting the same amount of hum... but i think maybe it is interesting that the power supply is humming the same tone as i'm hearing through the preamp? 

maybe this is insignificant, but as this hum is the only sound i'm getting from the pre, reamped, i guess it is significant to me :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 06, 2012, 12:01:09 PM
Here are some general tips that I like to send out when guys are having trouble. It's a good place to start.

First, what DOA is it? A pre-built or a DIY? If it's a kit, swap the opamps and see if the problem follows. Also, have you seen the DOA install page DOA install (http://classicapi.com/catalog/DOA_Install.php) I highly recommend never testing a new preamp build with a new opamp build. There are too many variables and you may never know what the issue is. If it's a pre-built opamp from me, chances are, it is not bad. Gary and Scott both run them in for many hours before sending them to me.

Have you completed the pre-start tests at the end of the old VP2x Assembly Guide? If you are building a VP312, the C to O DCR value will be about 8.5 ohms. Make sure all voltage readings are correct.

Double check all component values and make sure caps are facing the right way. Resistors cannot be measured once both ends are soldered to the PCB. You will get many odd readings. Either use the color codes to verify or one end must be desoldered to get an accurate DCR reading.

Double check the lead colors/pads for the output transformer. Take your time and be sure. Countless times I have heard back from folks who checked and checked and then a few days later realized that some of the leads were placed incorrectly.

Next, reflow the solder on the 3 C&K pushbutton switches.

If it's the Grayhill stepped gain option, do you have 25k when measuring between the to outside pins of the switch? If not, check with a magnifying glass as there probably is a short between some solder pads. These can be checked end to end by probing between adjacent pins. You should get the resistance of each of the R's on the pdf as you work from one end to the other.

Scan the board and check all solder pads with a magnifying glass of some kind. The biggest issue, besides what I mentioned above are cold solder joints. Sometimes they can look fine but not be good.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on March 07, 2012, 02:59:39 PM
So,
I built a 2nd and was troubleshooting some errors I was having (I posted previously about the Opamp problem I solved [it was my fault, I switched two transformers]). I've put in a new Opamp that I've been able to confirm has no problems by trying it in my known working VP25 and luckily last night got lucky and figured out that the problem I'm having (very low intermittent audio) seems to be centered around the output knob. If i mess with it, push on it etc.... sometimes the audio will return to perfect levels etc..... usually it just stays at the low crackle output so I figured I need to start there, remove it and resolder?

Just wondering if there are any thoughts before I dive in.... maybe I did something wrong in that part.

Pictures below.

Thanks as always for the help!

(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_70214dcd.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/70214dcd.jpg)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_dd56d291.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/dd56d291.jpg)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 07, 2012, 03:19:01 PM
It's most likely a cold solder joint somewhere. I would start by touching up the 9 interior pads of the t-pad adapter PCB as well as the pads for the 3 short leads. If that doesn't do it, try wiggling around the 3 short leads to see if there is a direct effect on the problem. It could also be the leads for the output transformer.

FYI, I was troubleshooting a build once and had a similar issue when the gain knob was touched. It was the GH on the main PCB stepped version. Naturally, you start looking at the switch and the R's around it. Turned out to be a half iffy solder joint on the 470uF coupling cap, halfway across the PCB.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on March 07, 2012, 03:20:18 PM
ha, amazing.
ok off to the bench for some detective work.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF! on March 12, 2012, 02:00:19 PM
hi Jeff,
i posted a couple of weeks ago about getting a distorted signal on one of my vp26 pres.  i have resoldered every point twice and checked with a magnifying glass for messy solder points, but nothing worked.  this morning i turned the output pot fully off and yelled loudly into the mic (frustrated?)  now it sounds great.  what could cause this?  a very loud signal clearing up the distortion.  i've got a session with vibes today and will try it out.  until today this pre has been just sitting idle because i fear it's going to fail mid-session.
- also i have poked around many times while speaking into the mic, and wiggling everything on the board and nothing changes, so it doesn't seem like a solder connection.  pressing the 3 buttons many times doesn't change anything either.
thanks very much for the help,
David
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 12, 2012, 02:33:09 PM
Hi David

Hard to say exactly what that could be. It still sounds like a solder joint thing to me. I saw above about the red dot so you should be fine there. Have you ruled out the rack slot and potential issues with external cabling? I myself have not run across this issue with a build. I'm sure other guys have but it is hard to say if the problem is identical to yours or not.

If the issue comes back, you could always try bypassing the t-pad to rule that out. In all the thousands of t-pads we have sold, I have only sent out one replacement and that was one of the few 388 blue ones we had as hold me overs. Never a Bourns or the 5/8" mod pot style. I doubt that it is the pot be never say never.

Best, Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF! on March 12, 2012, 03:15:51 PM
thanks for the reply Jeff,
yes i've switched rack slots and the problem followed the unit.  switched op amps and the problem stayed with the unit.  i will use it tonight and if it still distorts i'll try bypassing the pot as you say.
btw- love the pre and will be ordering more and perhaps some of your new 28s too.
thanks,
David
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 20, 2012, 03:33:54 AM
hey!  re-checked the color codes on every resistor.  i tested every single resistor before putting them into the preamp.  i tested them with the dmm and then separated them on paper.  the only mistake i could have made… is that i followed the numbers he had (and the ones jeff listed) and matched them to the resistor numbers… i.e. R1, R2, etc.  did those change at all from the original BOM? 

i'm sure that isn't the problem… but just a trouble shooting thought. 

thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 20, 2012, 03:37:01 AM
also -- is there a way someone could post a photo of the empty LED part on the board going to the output attenuator?  i just soldered that jumper cable between them (which chunger didn't do in his build).  do you think that this could be the problem?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 20, 2012, 09:06:40 AM
....the only mistake i could have made… is that i followed the numbers he had (and the ones jeff listed) and matched them to the resistor numbers… i.e. R1, R2, etc.  did those change at all from the original BOM?...
I just verified the new Rev B PCB that 'Chung built and the R's are indeed correct. I will have to look at his pic of the R's on the sheet but I will assume if they made it to the correct position on the board, they are correct in his pic.

Below is a copy of the email text I have been sending out with the new Rev B boards.
Since we are now shipping the Rev B version of these boards, the support docs have change. It is crucially imperative that the first step you make is to read the "1_VP25-26 Rev B Addendum.pdf" file that is in the attached zip file. Read it completely start to finish before doing anything else. This way, things will go very smooth!

Did you check out the Addendum PDF before you started? Below is tip #1 from the Addendum.
1. Use only the proper Rev B BOM when stuffing your boards. Following the BOM shown in the
Assembly Guide or an older Rev A BOM will cause many issues.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 20, 2012, 09:10:18 AM
also -- is there a way someone could post a photo of the empty LED part on the board going to the output attenuator?  i just soldered that jumper cable between them (which chunger didn't do in his build).  do you think that this could be the problem?
This will most likely cause other issues. The drain wire jumper will go from the typically unused lug on the phantom toggle to the LED hole that the little arrow points to. Post a pic of yours and I will verify if it's correct.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 03:33:56 AM
"I just verified the new Rev B PCB that 'Chung built and the R's are indeed correct. I will have to look at his pic of the R's on the sheet but I will assume if they made it to the correct position on the board, they are correct in his pic."

>> Cool, thanks man!  I mostly followed his markings on the paper and cross-referenced many of them with the rev b bom as well.  Will double check to see if the components on my board match up.

"Below is a copy of the email text I have been sending out with the new Rev B boards.
'Since we are now shipping the Rev B version of these boards, the support docs have change. It is crucially imperative that the first step you make is to read the "1_VP25-26 Rev B Addendum.pdf" file that is in the attached zip file. Read it completely start to finish before doing anything else. This way, things will go very smooth!'"

>> The first thing i did was read the addendum (lots of times) :) 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 03:32:45 PM
photo 1
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 03:33:24 PM
photo 2
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 03:33:53 PM
photo 3
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 03:34:33 PM
photo 4
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 03:35:19 PM
photo 5
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 03:36:28 PM
the only thing that i notice that is different from chunger's… is that i have the panasonic cap in the opposite way.  there is no polarity on that cap though, right?  also, took a photo of how i soldered the green cable to the other lug of the 48 volt switch, etc.

thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 22, 2012, 04:06:21 PM
Well, the drain wire for the 48V switch is correct. Your other components appear to be correct as well.

The WIMA cap is not polarized so no worry there.

I think the easiest thing to check next is the output transformer. This is posted somewhere above but to simplify, you need to desolder all the leads for the 2623-1 and make sure they are in mid air and not touching each other. Using your DMM set to measure resistance, measure the DCR from red to orange, green to blue and then brown to black. Those will all be around 30 ohms or under but not less than 15 ohms.

Next, make sure that no windings are shorted. Start at one end of the colors as they come out from the bobbin. Check for resistance between that lead and all the others. Then go to the next color, rinse and repeat. Here you are looking for a direct short or resistance of say 1 ohm or less.

I just went thru a similar situation via email with a guy. His problem was a cold solder joint on one of the components that the signal directly passes thru (the 1K R, 470uF Cap). It doesn't hurt to add a tiny bit of solder while reheating the pads. I see none coming up onto the top which is not a problem but there is typically a few pads that have the solder flow thru when all is heated good and solder is applied well.

FWIW, on future builds, the circle in the silk for the vertical resistors indicates where the body should go. When done like this, there is enough room as the bodies alternate position when the R's are directly in a row.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 05:34:48 PM
thanks for the quick response, jeff.  will desolder and unscrew the output transformer and test for resistance on the color cables as you've described. 

if it reads correctly, will re-solder all the connections on the board and then will return with results.  thanks sir.

ps -- i tried placing the vertical resistors in their markings where the gain stage is... i think they might have just moved a tiny bit when soldering &c.  moved them a tiny bit to ensure that none of their leads were touching :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mulletchuck on March 22, 2012, 07:32:41 PM
none of your thru-hole stuff has solder running all the way from one side of the board to the other.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 22, 2012, 09:56:04 PM
cool -- i'll try and get more solder in there :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 22, 2012, 10:13:22 PM
none of your thru-hole stuff has solder running all the way from one side of the board to the other.
Well, as long as you have a good solid joint on the bottom, it is not really necessary to solder from the top. I use to recommend that before I changed the ground plane location. Some inexperienced guys had trouble soldering the pads that connected to the ground plane. It is much easier on the new Rev B boards. It will not hurt anything though.

I would still check the trafo first.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 23, 2012, 11:00:59 PM
Unsoldering the cables on the transformer as we speak. When only putting a bit of heat on one of the wires, I noticed something on the board flaking off -- when inspecting closer, noticed it was one of the circular gold traces flaking off!  I remember a similar thing happening/flaking off when soldering in another component. Without the gold trace in the hole on the bottom that easily flaked off, would it still be making a connection? Should I solder from the top too just in case?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 23, 2012, 11:07:06 PM
Can you post a close pic of this? It is pretty rare to loose a pad on these boards. The majority of the traces are on the bottom of the PCB so you would be best to gently scrape a little solder mask off the trace immediately adjacent to the hole and solder there. If the complete pad is gone from the bottom and the trace is on the bottom, chances are, the pad on the top will not be connected to the trace.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 23, 2012, 11:13:34 PM
Red-orange about 16.8. Green to Blue about 33. Brown to black about 31.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 23, 2012, 11:18:21 PM
Cool - will grab my camera in a second. Looks like a tiny piece is still there. I remember losing the whole bottom ring on another part of the board though, which flaked off easily.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 23, 2012, 11:33:23 PM
attached is the broken gold ring.  you can see there is a tiny bit still there on the right… i guess as long as i don't lose that i'm cool… but i remember losing a whole ring on some other connection.  soldering from the top wouldn't help me if i lost the bottom, huh?  and please explain more about how to check those windings for a direct short.

thanks so much for your immediate help!  i just posted and i already have a response :)  even though this has been a long process, your quick responses are amazing and will leave me recommending your kits to friends (as soon as i can get the first one working) :) :) :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 24, 2012, 12:54:09 AM
On testing for a direct short on the output transformer... Do you mean test each color against each other coming out from the bobbin? For example... I read 16 ohms between red and orange, but read zero ohms between red and blue or red and black etc. is this what you mean?  Is my output transformer bad (and maybe I've lost some of my traces on the board)?

Thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 24, 2012, 12:19:01 PM
On testing for a direct short on the output transformer... Do you mean test each color against each other coming out from the bobbin? For example... I read 16 ohms between red and orange, but read zero ohms between red and blue or red and black etc. is this what you mean?  Is my output transformer bad (and maybe I've lost some of my traces on the board)?

Thanks!
Yes, this is what I mean. If anything is less than 1 ohm, there is a problem with the transformer.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 24, 2012, 01:58:24 PM
ah man -- yeah, it reads zero. 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on March 25, 2012, 05:44:19 AM
Man -- I just tried the other output transformer... Same thing -- it is shorted out.  Feel better that it might just be bad parts... Unless I did lose all of that one gold pad.  Should it be the same test with the 312 transformers?

How do we move from here?  Should I send you in the bad transformers?  Would you send me some working guys back along with the screws that were missin in the input knobs?  Thanks Jeff! 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 25, 2012, 09:47:58 AM
Hmm, the odds of 2 bad transformer together are huge, especially with the exact same symptoms. It's hard to imagine but not impossible I suppose. I know Ed will want those back to investigate. We have had very few bad out of the many that we have sold. Either way, I am not happy about it and I know Ed won't be either.

Send me an email and I will get you replacements out pronto. Also remind me of how many set-screws and for which knob. I have them all here so no problem.

The 2503's are similar to test. All 4 windings will be around 8.5 ohms. Measure red to brown, blue to green, orange to yellow and violet to gray.

Also, be sure of your DMM auto ranging settings. I have had many guys have many problems over the past all related to cheap DMM's that are set the the wrong range and so on. This could surely give a false reading here if not careful.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 01, 2012, 02:30:03 AM
on transformer readings -- i made a stupid mistake.  i read about 15.8 between red/orange and 32 resistance on all other pairs... between the other ones, i wasn't reading 0.0... i was reading 0.L, which i interpreted as zero... when really this means that there is no resistance!  oops  :-[

anyways -- i re-soldered every single connection on the bottom… i have some sound but it is hiss / white noise.  as i increase the stepped gain, the hiss gets worse, so the stepped gain seems to be working.  the output attenuator knob brings the hiss down when backed off.  the mute button kills the hiss completely… so that all seems to be working.

i tried different opamps -- tried two of scott's.  tried taking it apart and re-soldering for a 3rd time... still with the same results.  already tried the voltage test with the opamp removed to test the rack...

thanks!!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 01, 2012, 10:20:23 AM
The hiss you hear is most likely from the opamp so the input pad will not change it. That is not surprising but normal.

At the point you are at, I would recommend injecting signal and tracing thru the circuit to see where it stops. There are pointers for doing this near the beginning of this thread.

Are you 100% sure this has nothing to do with the rack cabling? I have heard of this happening a lot.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 01, 2012, 07:14:42 PM
cool -- so with the hiss, you wouldn't still recommend swapping the transformer? 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jmpizzoferrato on April 01, 2012, 10:42:11 PM
I'm having a strange problem with my vp26. Using an API 2520 as a test opamp, my unit causes the other units in my lunchbox NOT to work, yet my vp26 seems to be working.

Ive tried it with two different lunchboxes. Where should I begin testing?

Thank you.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 02, 2012, 12:34:26 AM
i just tried michael, mjenki14's test... same thing... when i go out of the vp26 and into another preamp and put the gain up, i can hear signal!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jmpizzoferrato on April 02, 2012, 01:38:29 AM
Scratch mine. I traced the problem - seems that it was a cold solder joint to a capacitor. I was able to trace it and fix it right up. Sorry for the false alarm. Excited for the next pair! Hoping those input transformers get back in stock soon! Thanks.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 02, 2012, 09:06:18 AM
dang, scratch that it was the output transformer (unless i have 2 bad ones, which i probably don't). 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 02, 2012, 09:55:11 AM
so i should try and build a listening signal probe? 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 02, 2012, 10:03:10 AM
so i should try and build a listening signal probe?  is that the best way to move forward?   ???
Yes or something similar. A scope or DMM set to ACV can also be used. Think of the circuit as a highway. Using the schematic, inject signal and probe along the "highway" to see where your injected signal stops.

You can use two 4.99k R's and a 160R as a U-pad to inject line level signal into the mic input.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 02, 2012, 08:09:12 PM
i see that r5 connects to r12 on the schematic and can follow the traces on the back of the board.  when i set my dmm to ac volts, it reads 0.000 V between then.  is that what you mean by acv?

thanks.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 02, 2012, 08:15:38 PM
The unit must be under power and you need to be sending a signal to the input that can be measured.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 02, 2012, 08:21:57 PM
okay -- but how can i get to the back of the board when the unit is powered on?

also, when you say sending it signal... you mean In Hi on the schematic?  J1-10, which if i'm reading the board right is the 6th gold marking from the top?  so i'd solder those resistors and a cap together and just place them on the 6th gold finger?

also, if it is the rack... would it make sense i'm still getting signal through after going in and out of the rack and then getting gain from another preamp?  signal is passing through the unit then i'm guess... it just isn't getting amplified properly.

thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 02, 2012, 08:30:49 PM
When trouble shooting like this, the module needs to be flat on a bench or table, laying flat in front of you. It cannot safely, effectively or scientifically be carried out while installed in a rack.

Not sure what "cap" you are referring to.

An audio mic level signal needs to be applied to the typical input for the module. This needs to be something like a 1k sine wave from a signal generator of some sort.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 02, 2012, 08:43:56 PM
"When trouble shooting like this, the module needs to be flat on a bench or table, laying flat in front of you. It cannot safely, effectively or scientifically be carried out while installed in a rack."

>> how do i get power to the module if it isn't in the rack?  you said it needs to be under power?  could i find some other type of power generator? 

Not sure what "cap" you are referring to.

>> oops, i meant resistors.

An audio mic level signal needs to be applied to the typical input for the module. This needs to be something like a 1k sine wave from a signal generator of some sort.

>> that old EL instruments circuit design system / signal generator i got doesn't power on...  after i learn how to fix the preamp, i'll try to fix the instrument that could have been useful in helping to fix the preamp (or itself).  i guess i need to buy some kind of signal generator in the meantime then, yeah?  would you recommend buying a scope?  would it make sense to invest in these things if i plan to continue building equipment from these pages?  Also, is a signal listening probe something you could build or is it something you'd have to pick up?

in this description (which sounds safer to me, to have the unit not powered) --

1) a signal source (signal generator, ipod etc) with a cable that ends in alligator clips or some other type of clips
2) a signal probe to listen to the signal source
with the opamp removed and the preamp NOT powered, sitting on your bench, check the input up to the opamp non-inverting input:
A) connect signal source, to "In Hi" & "In Lo" (pin 10 & 8 on the edge connector, or the side of the 750R resistors that doesn't connect to the 160R resistor)
B) connect the 0v/ground of the probe to a 0v point on the preamp.
C) probe the non-inverting input pin on the opamp - you should hear the signal source.
D) if you don't trace the signal from the input, following the schematic - see where it stops.

my questions on this -- is HI the 6th gold finger down from the top of the unit?  what point is a 0v point on the preamp?  also, which is the non-inverting input pin?

sorry for the young questions.  thank you to the electronic gurus (especially jeff) -- thanks for teaching.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 03, 2012, 10:31:48 PM
i set my dmm to continuity.  i followed every point in the schematic.  every point beeped. 

anything that even looked like a slightly cold, non-shining solder i re-heated.

have been working on this project every day for a month now.  at a loss.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 03, 2012, 11:07:43 PM
Continuity is not the exact sort of test to do be doing here. You will need to apply a balanced, mic level audio signal to the input. A line level sine wave can be used if you create a U-pad with the resistors I described earlier. From there, you will need to follow that signal thru each and every component to see where the signal stops. Use the schematic as your guide. Most likely, whatever is just before the point where the signal stops is the problem.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 04, 2012, 04:23:35 AM
alright -- did more homework.

first off, for anyone wanting to build a signal / listening probe, i followed this guide -- http://www.seymourduncan.com/tonefiend/diy/three-ridiculously-useful-easy-cheap-diy-tools/

successfully built that guy/gal, but instead of soldering cables to the ends, i soldered alligator clips.  connected the jack, rca, into a speaker.  then took crappy headphones, clipped them, and soldered alligator clips to the ends where the earbuds used to be... connected that to an ipod.  thanks haima!

input test -- connected signal generator to pin 8 & 10.  signal probe to ground and then started searching around.

my findings --
on the input side... first off, i was worried my diy test equipment was made wrong at first as i wasn't hearing any signal from pin 8 & 10... then went forward and connected the alligator clip to the side of r11 and r9 (the 750r resistors) that didn't connect to r10 (the 160r resistor)... then i was able to get signal throughout the pre.  when putting the alligator clips back on outside gold finger pins 8 & 10... i was able to get signal, but the hi (pin 10) was very finicky. only if the signal generator (alligator clip) was placed just right on it, would it produce signal through the preamp, which was my first note.

on the input side i got signal almost everywhere... probed through the different points on the schematic, moving along the electronic highway.  however, on the input stage... there was a ton of noise and the signal i got was very quiet almost everywhere with a lot of hum as if something weren't grounded right (even though i connected the ground of my signal probe to a ground point (one of the gold outside rings of the preamp)).  some parts of the signal were much louder than other parts though.  for example, pin number 5 of the input transformer connected to c1 (220pf) were among the loudest and clearest!  i can't wait to get a pin 5 input transformer sound out of this preamp.  and further, for example, that side of the c1 cap was louder than the other side of it connecting to r2 & r2 was much quieter.  the side that connected to r3, was much louder and clearer... and r3 was much louder and clearer.  r3 and pin 5 of input transformer were the clearest of this test.  however, i got signal pretty much everywhere (with these different volume levels)

on the input side -- i heard signal on every op-amp lug.

there are only 2 places i had strange signals.

1) all 4 connectors, which solder in the output attenuator have no signal... unlike the connectors soldering in the input stepped gain, which all have signal...  (however the actual connectors underneath the output attenuator all passed signal... just the 4 outside ones didn't)

2) cr1 and cr2 -- the sides connected to pin 12 and 14... i mostly hear buzzing on both of them (and only a tiny bit of signal).  on the other sides (connecting to c6 & c5), i hear some better signal though.

for the output test -- connected the signal generator to O on the op-amp.  the other side of the signal generator to ground (gold circle on side).  connected the ground of the probe to the same gold circle... and used the other side to probe around.

on the output side of things -- wow!  testing the output... the signal is MUCH louder... it has NO ground buzz... super clear all the way through the circuit.  get really loud, clear signal throughout the whole preamp.

again though, the 4 solder points that hold the output attenuator in... have no signal on the output test.  (and again, the actual connectors underneath the output attenuator all passed signal... just the 4 outside ones didn't)

also, cr1 and cr2 connected to pin 12 and 14 send signal, but extremely, extremely quietly compared to all the other components.

looking forward to your thoughts!  have signal everywhere (of varying volumes), except for those outer 4 on the output attenuator and much reduced signal from cr1 and cr2 connected to pin 12 & 14.

THANKS!

ps -- if these results happen to be normal -- how do i test the rack? :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 04, 2012, 09:25:15 AM
Matt

Sounds like you made a little headway. You are on the right track now.

A few things to point out. The only place you will want to connect your signal generator are the main inputs of the card, gold finger 8 and 10. There is no need to ever connect it anywhere else, IMHO.

Out of the 4 larger mounting holes, only the top right (near the output transformer) connects to the ground plane. The rest make no connection by design.

I see no reason to ever connect your listening device to the power rails like JP1-12, 14 or anywhere on CR1 or CR2. You should only be concerned with the audio signal path.

Pin 5 of the 2622 is it's output which boosts the signal at the input by 17dB.

From there, check at the opamp input or the left side of R4. The signal should be nearly the same as pin 5 of the 2622.

Next, check the + side of C10. This is the output of the opamp. The gain pot (or switch) should effect the level of the signal probed here.

From there, I would check the cards output at card edge 2 and 4. If you have good, strong signal here, I would start looking at the rack & cabling. There you can use your DMM set to beep continuity.

The 4 outer pins of the t-pad are only the bracket. They are there for mounting only and carry no signal.

Cheers, Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 04, 2012, 10:49:33 AM
thanks jeff!

troubleshooting has been an awesome lesson so far -- thank you so much again for your time.  sorry for listening on the power rails... i followed to about the op amp along the schematic highway and then just started poking around to hit every component.  ha.  thanks so much, i will check those readings... but first...

just checked the rack.  on every channel, at the xlr on the back, pin 1 beeps out at 1 (input / output)... but i'm not getting a continuity beep on any channel 2 with 2 or 3 with 3 at the xlr...  is this correct?  i can get 2 and 3 (on both input and output) to beep when touching different points on the card slot though... so maybe this is normal.

thanks again jeff!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 04, 2012, 10:10:01 PM
with the new grounding... my results are very different.  actually, i have no signal at r4 at all.

there is also no signal at other components i.e. r6 (pin 5 of the input transformer still sounds great, but now more than half of the components carry no signal)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 04, 2012, 10:42:29 PM
the problem starts (at the beginning of tracing things in).  the side of r8 that connects to r7... continuity between them is good, but i have no signal either on r8 or r7 (the two sides that connect)... strangely, the other side of r7 has signal.  but i guess it could be picking up signal through the pad? 

well it seems like there's one place to resolder at least, yeah?  the solder point is good and shiny though.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 05, 2012, 12:19:40 AM
Not all the components are series components. They do not all have audio passing thru them. Forget about R6, R7 and R8 right now. Those are the phantom power resistors. I never said to probe for signal there. I did say to probe the left end of R4 though. Did you do that?

If pin 5 on the 2622 sounds great, that is good. You need to follow the schematic from there. Where does the signal go from pin 5 of the 2622? Hint, it is going in the direction of the + or non-inverting side of the opamp. That is why I told you to probe at the left end of R4. I never said anything about R6, R7 or R8. There are only two series components between the 2622 and the + input of the opamp. Probe all ends of those and report back. Also, tell me what their labeled names are so I know you are following me.

I also never heard about you verifying the rack. That is a must do right away. I am sure you don't want to chase your tail thru a preamp to possibly find out the problem is not preamp related.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 05, 2012, 02:28:09 AM
Hey Jeff -- thanks man !  sorry, please see my responses above the last one I made -- confusing as I responded a few times above as I got results (r6, etc was an after-thought post).  I had checked r4 and said there is no signal on either end of it (reply #366).  Also wrote a bit about the rack in the post above that one (please see that post (reply #365) to see my results trying to verify the rack).

R3 has good signal.  C2, c3, and r4 have no signal.  I resoldered all of their points again.  All still shiny (not cold solders), but no change in their passing signal.  Thanks again man!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 05, 2012, 08:51:38 AM
Only the signal path side of R4 will have signal. They other end is to gnd so no signal will be there.

If R3 has signal at both ends that is good.

The next thing in the signal path is C2. You say no signal is there but which end? At both? If you have no signal at the - end of C2, you will have to look closely because there is only a small trace between R3 and C2. Really no good reason unless that end of R3 is a cold joint.

One step at a time since you never specified if one or both ends of C3 had no signal.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 05, 2012, 08:59:09 AM
As for the rack thing, you need to be specific.

Quote
...beep when touching different points on the card slot...
does not really help.

The input XLR pin 2 should go to card edge 10.
Input XLR pin 3 goes to card edge 8.
Output XLR pin 2 goes to card edge 2.
Output XLR pin 3 goes to card edge 4.

That is info that you can get from my schematic or any 500 series pin-out legend.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 05, 2012, 05:39:08 PM
There is no signal on either side of c2, c3, or r4.  Neither side pass signal.  When desoldering and resoldering, I noticed that I might have lost that gold pad on the bottom of c2.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 05, 2012, 06:26:36 PM
Well, somewhere in there lies your problem. Your signal at both ends of C2 should be the same as it is after R3. If not, you will have to solve it one way or the other.

The thru holes are plated on both sides of the board. Loosing the side where the trace that runs to R3 is could be the issue. Without looking, that is most likely on the bottom. At the worst, just solder a short jumper wire in between R3 and C2 then run your signal tests again.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 09, 2012, 08:12:05 AM
just wanted to give an update --

it did end up being that trace -- soldered in a jumper cable and now it sounds so good.

since this, i built 3 more preamps -- vp26 and 2 vp312... all i have to say is... they SOUND Amazing! ! !

thanks so much to jeff...  you are not only a genius designer, but an amazing person for giving us so much for your time.

next project -- building some gar2520 op amps

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on April 15, 2012, 08:09:41 PM
It's most likely a cold solder joint somewhere. I would start by touching up the 9 interior pads of the t-pad adapter PCB as well as the pads for the 3 short leads. If that doesn't do it, try wiggling around the 3 short leads to see if there is a direct effect on the problem. It could also be the leads for the output transformer.

FYI, I was troubleshooting a build once and had a similar issue when the gain knob was touched. It was the GH on the main PCB stepped version. Naturally, you start looking at the switch and the R's around it. Turned out to be a half iffy solder joint on the 470uF coupling cap, halfway across the PCB.

So i retouched all the solder joints that appeared even remotely unstable or less than solid but unfortunately I'm still having the problem. Audio passes through completely but its very very quiet. I think i may need to order a new t pad and tpad adapter but in the meantime I didn't know if these pictures would help point out any obvious I may have missed (still very much so a newcomer when it comes to this!)

(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_d04d496f.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/d04d496f.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_59e68776.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/59e68776.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_172d0de1.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/172d0de1.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_cb0b1ebf.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/cb0b1ebf.jpg)


thanks so so much all!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 17, 2012, 07:48:31 PM
You can bypass the t-pad to rule it out. Just remove the t-pad by desoldering the 3 leads at the main PCB. Then solder a small jumper wire from pad A to pad C while not touching B.

If the symptoms are the same as before, I would skim backwards thru this thread. I had the last guy inject a sine wave signal into the pre and trace along the audio path to see where it stops.

You can also measure the DCR of the output transformer and test to make sure nothing is internally shorted. That is all explained and very recent in this thread as well.

Good luck and keep us posted.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Seditionary on April 19, 2012, 04:33:21 AM
would definitely recommend the signal generator that jeff is talking about !  you can diy build one -- posted a how to link above.  really worth it to have a signal generator + listening probe (and you can build them for 5 bucks if you already have an ipod or phone or cd player or anything with an audio out, etc)... i used to test old gear with a dmm testing for continuity... but a signal generator and signal probe gets you to the problem much faster... (plus you get to hear some bits of tunes passing through your circuit along the way)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on April 23, 2012, 09:19:56 PM
You can bypass the t-pad to rule it out. Just remove the t-pad by desoldering the 3 leads at the main PCB. Then solder a small jumper wire from pad A to pad C while not touching B.

If the symptoms are the same as before, I would skim backwards thru this thread. I had the last guy inject a sine wave signal into the pre and trace along the audio path to see where it stops.

You can also measure the DCR of the output transformer and test to make sure nothing is internally shorted. That is all explained and very recent in this thread as well.

Good luck and keep us posted.

Thanks again for the continued help!!

Removed tpad and soldered jumper from A to C (no b!) but no improvement unfortunately....
Removed  output transformer and measured resistance on the 2503 and all were 8.6 Ohms...

next step seems to be the signal tracing with an audio probe/signal generator along the schematic path and seeing where it stops....

I will keep you posted.
Thanks
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: olafrec on May 09, 2012, 10:24:12 PM
Hello everyone,

Newb here who just completed my first VP26 pre. First, let me say WOW! This preamp sounds incredible. I tested using a Neumann TLM 49 which is a great mic but relatively flat sonically. I was instantly amazed at the new character and richness I was hearing!

But, my build is not without faults. The output attenuator does not attenuate. I get maybe 1dB of attenuation about half way towards -infinity and no more after that (it might even get slightly louder again at infinity?). Also, the phase switch in the pushed-in position gives a big boost in the signal; of course reversing phase can alter frequency repsonse and possibly the volume a tad but this is probably around a 6dB boost or so... seems something is wrong.

Other than that, the unit works (and sounds) great. I was hoping someone could point me in the right direction to begin trouble shooting. I've searched this forum to no avail. I'll try reflowing the solder on the switches and following the CAPI DOA install instructions as this seems to have helped others' initial build issues. But beyond that, I don't know where to start.

Here's some pertinent information:

- revB board (I used the correct new documentation, i.e., BOM, etc..)
- gar2520 op amp; built myself; I should mention I have good to great solder skills having built numerous guitar pedals and other electronics over the past decade.
- wired jumper from unused phantom switch to LED lead with arrow pointing to it.
- checked all resistor values with my DMM, all good there.
- when checking resistance at mil max sockets per assembly guide, I would initially get really low values upon contact that would take a few seconds to rise to beyond my DMM's metering ability (and well above the 200k spec) but it was weird that is would start low and rise. Not all configurations would do this.

Many thanks for any help!

Cheers,

Jason
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 10, 2012, 12:29:16 AM
The switch and t-pad issues possibly sound like bad solder joints to me. I never recommend a new preamp build with a new opamp build. Too many things can be wrong. You need to first make 100% sure that opamp is good. Do you have another module you can test it in?

Might be a silly question but have you dbl checked the lead colors on the output transformer? That would explain both issues you are having.

There should be no level change at all when engaging the polarity flip switch.

Some pics may help.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: olafrec on May 10, 2012, 02:59:30 AM
Thanks for the fast reply Jeff!

I reflowed the t pad and three switches, no change.

This is, unfortunately, my only opamp currently (hope to have more soon  :D)

Interesting, but my only other high-end pre (vintech 573) exhibits the same level bump (and high end shift) if I invert its phase. Inverting the phase on my rme interface exhibits the normal minor change you'd expect. There's perhaps other issues with my set up so I'll just concentrate on the output attenuation issue for now as that's obviously not working.

I can buy another 2520 to test with that as I'll certainly use it in a future build. Do you have any other suggestions? Are there tests for the output trans?

Below is a pic of the transformer leads (I guess I can only post one pic at a time?)

Thanks,

Jason
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 10, 2012, 11:07:30 AM
There should be no measurable level change when flipping a polarity switch. It may be a perceived change with the ears but not by measurement. I would look at other things in your setup especially if it is happening with another preamp.

If you scroll backwards thru this thread, you will find how to measure the DCR of the output transformer and check for shorts. I would do that and if there is no change, I will most likely send you another t-pad. If memory serves, I have never had a bad t-pad from Bourns but sh!t does happen. The t-pad should be checked with a DMM as well.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: olafrec on May 10, 2012, 11:19:07 AM
Thanks Jeff,

I'll check the transformer and t pad and report back. I assume I need to desolder the t pad and monitor resistance while actuating the knob, correct?

Thanks!

Jason
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 10, 2012, 11:24:27 AM
Yes on the t-pad.

I would check the 2623-1 first.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: olafrec on May 13, 2012, 03:02:06 AM
So, both the 2623-1 and t pad seem to be fine.

For the 2623-1 I get the following resistance values:

red to orange = 14.6
green to blue = 22.6
brown to black = 22.4

I did not get any reading when checking each lead against all other colors (except for the above, of course).

Unfortunately, I butchered the t pad trying to desolder it but I don't think it was defective: I get the stated resistance values or near zero resistance depending on knob position and terminal combination.

Since these components are currently decoupled are there any tests I can perform on the pcb that would help narrow anything down?  Should I start to suspect the opamp at this point?

Thanks,

Jason
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 13, 2012, 11:57:59 AM
It could possibly be the opamp I suppose. The t-pad is just across the 2623-1's secondaries. Do you have access to a known good working 2520 style opamp?

This is definitely why I don't like testing a new preamp build and a new opamp build at the same time. Can be a lot of tail chasing.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: olafrec on May 19, 2012, 03:04:38 AM
Problem solved  :)

So, I've learned that logic and careful thought are your friend. Long story short: my vp26 build never had a problem at all. I soldered in the new t pad and the output attenuate still did not work, which I mostly expected as my tests suggested that the original one was fine. But, there I was, staring at the schematic wondering what could possibly be wrong. It just didn't make sense. There had to be a bridged connection somewhere. The fact that I decided to look past the issue of the polarity switch causing an extreme level bump started to creep into my conscious. I grabbed an xlr and ran the preamp output directly into my interface, thus bypassing my patch bay which I normally (pun) employ in my set up. (Yes, I should have done this test much earlier in my troubleshooting). Low and behold, the polarity switch now works as expected: no more level bump. And.... the output attenuation works too! So, there seems to be a bridge or short somewhere downstream in my set up. This probably also explains the horrible hum I get when using the DI of one of my other pre amps.

While it's frustrating that I've been troubleshooting a perfectly good pre amp, this process has exposed a rather gnarly but veiled issue and my rig will be better as a result. This is why DIY rocks!

Thanks so much for your help Jeff. I didn't expect the already great value of this product to come with tech support  :) You rock!

Cheers,

Jason
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 19, 2012, 02:55:20 PM
No problem Jason. At least you know what is what. Everyday is a learning experience!  :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on May 26, 2012, 02:21:49 AM
You can bypass the t-pad to rule it out. Just remove the t-pad by desoldering the 3 leads at the main PCB. Then solder a small jumper wire from pad A to pad C while not touching B.

If the symptoms are the same as before, I would skim backwards thru this thread. I had the last guy inject a sine wave signal into the pre and trace along the audio path to see where it stops.

You can also measure the DCR of the output transformer and test to make sure nothing is internally shorted. That is all explained and very recent in this thread as well.

Good luck and keep us posted.

Thanks again for the continued help!!

Removed tpad and soldered jumper from A to C (no b!) but no improvement unfortunately....
Removed  output transformer and measured resistance on the 2503 and all were 8.6 Ohms...

next step seems to be the signal tracing with an audio probe/signal generator along the schematic path and seeing where it stops....

I will keep you posted.
Thanks



Well.... after many hours of signal tracing and other misc troubleshooting I've decided my best bet is to grab another PCB and components. I can make use of all of the rest of my stuff so the cost is minimal and I'll be able to start fresh and see what happens. That being said, do you think this is a problem (see pics)

(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_5bc3abb1.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/5bc3abb1.jpg)
(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_9391f2b4.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/9391f2b4.jpg)
while desoldering/removing my parts the EA2622 seems to have lost a leg. Its still there, just really short, I think it will actually go into the PCB and be fine, just a harder solder job. My concern however is that the short lead almost came out, i pushed it back in with needlenose pliers, is there any way to test that it still works before soldering it?




I beat up the old pcb nicely (for giving me such trouble!)(http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_c821b30a.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/c821b30a.jpg)

but the new one went together very well and will test this evening (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/th_df6b91cb.jpg) (http://i221.photobucket.com/albums/dd299/BigEvilCorp/VP25%20x%202/df6b91cb.jpg)

Thanks much!

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Pliplo on June 27, 2012, 02:08:13 AM
hey guys, is it common for the VP26 to make some noise when you engage phantom switch? im pretty sure my vp312di doesnt make any noise when i turn phantom on, even at high gain... could that be a mistake i made?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 27, 2012, 09:38:49 AM
You will usually here a pop when engaging the switch but no noise. That part of the circuit is identical to the VP312DI so they will work exactly the same. I would re-flow the solder on the 200R, 6k8's and the 120uF cap. My guess is you may have a shady solder joint on the cap.

I always use the mute switch before flipping the phantom toggle on or off.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Pliplo on June 27, 2012, 10:40:43 AM
You will usually here a pop when engaging the switch but no noise. That part of the circuit is identical to the VP312DI so they will work exactly the same. I would re-flow the solder on the 200R, 6k8's and the 120uF cap. My guess is you may have a shady solder joint on the cap.

I always use the mute switch before flipping the phantom toggle on or off.

yes yes a pop! well, more like 3, a big one and 2 small ones heheh... ill roll a joint and check my joints... (im sure no one made that one EVER BEFORE)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: andre tchmil on July 08, 2012, 10:19:24 AM
I build two REV2 boards, both with stepped gain.
On one of them , the output attenuator doesn't work, CCW or CW , output is at full.
I measured both boards and att. pot side by side. All values are pretty much the same.
I'm stuck.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 08, 2012, 10:30:20 AM
I would look at reflowing the solder to the 9 inner pins of the t-pad. I would also check the lead colors to solder pads for the output transformer.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: andre tchmil on July 09, 2012, 05:58:43 AM
Aaaaaaaarhhhgg ! Solved.

one of the legs on the T pad wasn't properly inserted.

thanks for your time.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF! on July 10, 2012, 02:38:45 PM
Hi Jeff,
I bought a pair of VP26 a while ago.  one has worked perfectly from the start and the other never worked right- always a faint output.  i have both on the bench so i can A/B.  While following the tracing path outlined by HAIMA on thread #113, I have found that:
I get signal fine to the input of the opamp.
I get signal from the output pin of the opamp on the board to the RED transformer wire, but then when checking at the BLUE wire i get the faint signal.  i have once again resoldered the tranny wires and they are indeed correct (!).  The attenuator does work, but it's only getting the faint signal to work with.  Does this mean the problem is inside the transformer? 
Funny, it only took a couple of hours to build these, but troubleshooting this module has added another 8 hours.  Frustrating to say the least.
thanks very much for any help,
David
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF! on July 10, 2012, 05:03:27 PM
just to update testing my output tranny.  all leads desoldered from PCB.
red to orange= 33 ohms
brown to black= 17 ohms
green to blue= 1k ohms

this green to blue reading is way off, correct?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 10, 2012, 10:27:21 PM
just to update testing my output tranny.  all leads desoldered from PCB.
red to orange= 33 ohms
brown to black= 17 ohms
green to blue= 1k ohms

this green to blue reading is way off, correct?
Indeed, this should also be around 17 ohms. Does your 2623-1 have a white sticker on the side or no markings at all? Send me an email thru the store and I will get you squared away.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF! on July 10, 2012, 11:58:52 PM
will do.  thanks Jeff.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OOF! on July 15, 2012, 02:35:07 PM
Jeff thanks for sending the new tranny so quickly.  the pre sounds great!
David
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 15, 2012, 02:49:51 PM
Jeff thanks for sending the new tranny so quickly.  the pre sounds great!
David
No problem David. It's what I do.  :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jordandau on July 31, 2012, 03:18:47 AM
Just finished getting it all together, VERY nice tutorial you email.

Oddly enough, I have a problem with mine. I have to turn both knobs up 100% full to get any signal. The mute works, the pad works, but when I use the phase flip I can hear a sound difference. I checked the value's on the resistors while setting up, do you see anything off that bat that could indicate a problem?




(http://i70.photobucket.com/albums/i94/jordandaugmail/apiwire.jpg)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 31, 2012, 10:40:27 PM
Yes I see your problem. You have a 200R and a 20k flipped with each other.  R5 should be 20k and yours is 200R and vise-verse for R6. R5 is the feedback R which is why you have no gain.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jordandau on August 01, 2012, 10:34:58 PM
Thank you! Works great!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Asiandude on September 06, 2012, 12:54:48 AM
Classic api VP25 not working properly after assembled : turn on no sound, so I turn the input and output gain to max out and got a very nasal sound. If you do have this problem just make sure you re-touched every solders joint and problem solve on most likely is the case and rarely dude to malfuntion of the tranformers fault. Hope that will help a liltle.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: poiesznbeats on September 06, 2012, 05:47:18 PM
I just finished building my first VP312 VPR Rev A.... I was doing the tests recommended in the VP26 build manual and I'm concerned because I have failed two:
12.1.d
When I check impedance between "C" and "O" sockets for the op amp I get a value of 8.8...

12.2.a
When I have it plugged in my lunchbox (still no DOA installed), I get a value of -16V DC between "+V" and "C", the same value I get for "-V" and "C"

I don't want to install the opamp and fire it up because I'm worried about frying something.  Any ideas?  Or am I ok?

Thank you!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 06, 2012, 06:23:54 PM
12.1.d
When I check impedance between "C" and "O" sockets for the op amp I get a value of 8.8...
That measurement result is specific to the VP25-VP26 and has a different result for a VP312. You should get around 8.5 to 9 ohms as you are essentially measuring the DCR of the 2503's primary so it is a pass, not fail.  ;D

Quote
12.2.a
When I have it plugged in my lunchbox (still no DOA installed), I get a value of -16V DC between "+V" and "C", the same value I get for "-V" and "C"
Try this one again while making sure the black lead for your DMM is on the "C" socket. Only move the red lead to measure the DCV.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: poiesznbeats on September 06, 2012, 09:16:43 PM
Success! Thanks Jeff!  I am all up and running!

Now the only thing left is what to do about THIS????? (edited for more clarity because I can't figure out how to post my photo)

My alignment on the push button switches was slightly off and I can't get the buttons on... or if i do they stick in the "in" position.  I'm guessing I sat my pots too far down on the PCB as the switches are hitting the right side of the housing and faceplate.  I have a feeling I'd need to desolder my pots to fix this.  Surely I'm not the only one to make this alignment mistake.  Or am I...  Is there any easy fix?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 06, 2012, 09:46:23 PM
Yeah, hard to say with no pics. When typing a reply to post, go just below the text box and click the "Attachments and other options" to post a pic.

If you did not follow the dry fit procedure before soldering in your pots, that could be the issue. Unfortunately, desoldering them will be the only fix.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: poiesznbeats on September 06, 2012, 10:42:51 PM
Ahh.. here it is.  I thought I did the fitting appropriately, but when it came time to add the switches I saw I was off.  I'm going to try to get my second one built properly before I mess with this one again.  I've never desoldered anything so I'm a bit apprehensive that I might damage something in the process, all for a cosmetic fix.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 06, 2012, 11:05:45 PM
I would assume that the PCB is farther away from the front of the L-bracket than the length of the 1/4" standoffs?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: poiesznbeats on September 06, 2012, 11:23:17 PM
Yes. By the same amount as you can see in the switches.  I did the whole fitting check when I soldered the pots to the PCB, but I don't think I was precise enough with the spacing of the 1/4" standoff, like you said.  I ended up soldering the pots all the way down in their holes in the board, instead of up a little bit as I see in some photos now.

What am I risking by trying to undo this?  I do have at least a functional preamp with no button caps... I would hate to ruin parts trying to get it right.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 06, 2012, 11:40:23 PM
Well, with a decent desoldering tool like the Hakko 808 you will ruin nothing as long as you jump around and don't heat up the pots and PCB pads too much.

'Chung shows pretty well (I do to in the original VP2x Assembly Guide) how the pots should be dry fit into their holes and then the PCB assembled to the L-bracket with standoffs & faceplate fitted before soldering the pots in.

I myself would change it but it's your call.

BTW, you are not the first person to do this and I'm sure you won't be the last.  ;)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: poiesznbeats on September 07, 2012, 12:49:01 PM
Ok, thanks Jeff, I will be building my second (hopefully correctly) and then try to fix the first. 

One last question:
My tests with a dynamic mic are all great, but when I connect a condenser, I need to activate the pad AND have the gain all the way down, along with some output attenuation in order to get a sound that is not clipping.  This is just with my voice, by the way.  Is this normal?  Have I screwed up some part of my phantom power?  Again the dynamic mic works flawlessly with a full range of settings.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 07, 2012, 12:52:50 PM
That doesn't sound exactly normal but depends on the mic maybe? The phantom would not cause this. I would build the 2nd pre and compare the end results. Can it be a converter setting or something? That has happened to many times to count.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Dvaughn on September 13, 2012, 11:55:48 PM
Just wanted to drop some good vibes on this thread.

I'm an electronics noob for sure but I can take my time, be neat, and follow directions to a T.  Finished assembling 2 gar2520's and 2 VP26's and they all powered on and sound AWESOME!  Had to wait anxiously for my api lunchbox to arrive to see if anything I put together actually worked.  I was considering building the 51X rack with PSU but I figured that between the pre, rack, and op-amps I was bound to screw something up and then go through hell troubleshooting.  The two pre's act and sound the same as far as my ears and eyes tell me, I need to do some research and figure out how to do some further testing but overall i'm ecstatic.  THANK YOU JEFF!! these pre's beat the hell out of my digi's and presonus stuff (8ch) and for 200 a pop, you make the home studio guy on a budget really happy! 

Next project = mix buzz and 1176 clones : )...   and more VP26's!!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drumslinger on September 25, 2012, 10:11:50 AM
Hey guys was just gettting around to building my VP modules (with Rev B boards) 25, 26 and 312 but have run into a snag with one of the VP26 builds, no output sound.  I traced the signal and everything seems to be ok.  Unsoldered the transformer wires from the 2623 and tested the resistance (red/orange 14.6ohms, brown/black 22.3ohms and green/blue 22.3ohms).  Checked the remaining 3 2623s (total of 5 VP26) and they ohm out the same.  Retouched solder on all components (same issue, no output sound).  Compared the working VP26 to the non working one and all the components are what they seem with color code and capacitor value.  All 9 DOAs have been tested and work fine, even after swapping them out on the non working VP26.  I'll report back more after i have swapped out a component I suspect.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drumslinger on September 28, 2012, 11:35:47 PM
**Update**

     Faulty resistor found and replaced.  2nd VP26 up and running!  Helpful stuff in this thread helped me pin point my problem.  Many thanks guys!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: TheLavaBed on September 29, 2012, 03:34:57 PM
Can anyone help with what might be an obvious question?  I just got around to building my VP26's, and I can't find Jeff's assembly instructions anywhere on the Classic API sight.  I checked, and I don't have an email from Jeff with instructions (then again, I didn't email him and ask for one).  I followed Chunger's instructions, and am 85% there, but I don't see any instructions on which resistors go in the spots for my stepped Grayhill potentiometer.  Everything is assembled except those resistors (labeled RG1-RG11).  Any help?

Thanks!!

Mike
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 29, 2012, 03:56:23 PM
Mike

Send me an email and I will send them right away. I send all docs out the morning or 2 after I ship. They often end up in spam folders.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Cosmonaut on October 21, 2012, 06:34:04 AM
Hi , I have just finished a pair of VP25...and was the easiest build I have ever done! I'm wondering if I could use my altran transformers from the mitsos 312 groupbuy, without modifying anything (zobel network?) using the VP25 boards from Jeff.

 I have done some measurings comparing ed transformers and altran...and in the output transformer I have 8.3 ohms in my DMM in all the secondaries and 6.3 ohms in the altran secondaries.

Some help?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on December 10, 2012, 12:06:18 AM
I have two questions !

just finished a new VP26 which works and sounds incredible! I f*cking love these things.

question 1). any reason why my led wouldn't be working? I tested it beforehand, using a led tester thing I have and it was great. I installed the R1 resistor and then installed the phantom switch as outlined by chung's pics and also the ammended instructions for rev b. The phantom power(and switch) works great (infact my tests today were all with a mic requiring phantom power). but the led simply doesn't turn on. I'm wondering if i missed something here...  (led polarization was most certainly correct when I installed).

LED was most certainly NOT installed correct. (to the other newcomers... take your time!)


lastly, I'm curious why the measured values on the O, C, V+, V- etc etc are always strange on my end. They're all over the place, (I've posted about it before with specific numbers but was never able to find out if its a problem or not). I mean, the things work, they sound great, so I guess its not a problem, I just don't like the feeling like i missed something or screwed up at the final step.  I use the fluke 177 as recommended in the assembly guide and have no other issues with it. It's not all that important, just wished i could confirm I've done a good job in some way other than just throwing it in the rack and getting sound and having all the knobs/buttons work.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: buildafriend on December 26, 2012, 12:34:11 PM
CCW Stepped gain option = 25k reverse log? (original API 312 gain uses reverse log, thats why I ask)
the numbers look "loggy" to me.

Stepped gain R's

82ohm -----------------------RG1 or RG11?
120ohm
169ohm
249ohm
357ohm
511ohm
787ohm
1.24Kohm
1.97Kohm
4.99Kohm
14.7Kohm----------------------RG1 or RG11?

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 26, 2012, 12:44:02 PM
Yes, the VP Gainswitch will work perfect in an API style preamp circuit with a 20k feedback R. I also use a series 200R in typical fashion. I have the skiz attached although I usually email it out with a preamp or kit purchase. Maybe you just purchased the R's only? I remember an order like that recently.

The lowest 2 steps are 4dB and the rest are 3dB to the top. I would call it more linear than "loggy".  ;)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: buildafriend on December 26, 2012, 01:06:51 PM
thanks jeff, you rule.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jtrolka on February 09, 2013, 08:58:25 PM
Hey everyone, I hope someone can come in with any ideas here regarding my VP26 with the stepped gain option.  I built two simultaneously, one works mostly flawlessly, in as much as it sounds amazing but the led for the 48v doesn't light up.

The other one is radio silence.  Ironically enough, the led does light up when I switch it on, but that's about it.  I get signal spikes when I engage the mute and phase invert buttons, but nothing with the pad.  I went over the solder joints, and touched up a few that looked suspicious.  I have to say that I had a bunch of problems getting the wires from the output transformer soldered onto the PCB board, and worry that I may have damaged it.  I touched those up too.

Any thoughts or suggestions would be greatly appreciated!

Best,

Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 09, 2013, 09:17:52 PM
First, the non working LED is most likely in backwards.

The first thing to rule out is the opamp. What opamps are they and who built them? If they were kits, swap them in the preamps and see if the non working status follows the opamp or stays with the pre.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jtrolka on February 10, 2013, 11:22:54 AM
Thanks for the fast response Jeff!

'Chung and I built one of the op amps, one of the GAR 1731 variety and then I built the other on my own which is identical.  I swapped them out and there was no difference in the working unit.  I'll get around to flipping the led once the other unit is up and running, I don't want to have two down.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jtrolka on February 10, 2013, 03:03:18 PM
Good call on the led, decided to take it apart after all and it lights up and all tests out fine...
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bigevil on February 10, 2013, 04:29:32 PM
in my experiences, 98% of the problems I've run into are usually resolved when jeff kindly points out a simple yet stupid mistake I've made.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jtrolka on February 10, 2013, 05:14:10 PM
Exactly, and I think I can claim that here too.  After having switched the op amps to make sure the one in the "non-working" unit was operable, I went from component to component comparing them to make sure everything was in its right place, and more importantly, that their polarities were correct.  Despite the led in the working unit being reversed, everything in the "non-working" unit appeared to be installed with the correct polarity.  I flipped it over at that point, and did more investigations of the solder work. I touched up a few things which I honestly doubt were bad, but did so anyway.

Here's the thing, when I went to test it, I noticed that I hadn't put the op amp back in from when I had switched them.  I'm a total, total newb when it comes to this stuff, the only other things I have soldered were back in eighth grade shop and none of them worked.  My point here is that I tend to be a little timid with the PCB board and components.  In putting the op amp back in, it clicked a little more firmly than I had originally set it into the millimax sockets.  Between not putting it in fully, and the slight angles on the pins, I don't think it had originally been making contact.

Having done this, when I fired it up it worked fully and perfectly and sounds identical to the first one.  The stereo set is up and running and I couldn't be more pleased!  Thanks Jeff, for the help on the led and getting me moving in the right direction!

Jeff
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 10, 2013, 05:18:38 PM
Did you see this page on opamp installation? Maybe this will help make the cure permanent. http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jtrolka on February 10, 2013, 08:24:26 PM
Thank you, Jeff, I had not seen that!  I stand in direct violation of rule number one, read all the directions first!  Thanks again!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Colorblind on February 14, 2013, 08:00:02 PM
Hey gang,

I'm building my first VP26, and so far so good (I think). I'm unsure how to install the LED. Does the shorter lead go where the arrow points, or vice versa?  Maybe that's been answered, but I couldn't find it in this thread.

Thanks,

C
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 14, 2013, 08:40:51 PM
Yes the shorter lead goes to the pad that the arrow is pointing to.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Colorblind on February 15, 2013, 08:18:58 AM
Thanks Jeff!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: tfunster on February 17, 2013, 04:18:02 PM
Help Please!
I have started on my VP 26 build (and I'm a bit of a noob).  I have the stepped gain option and put in the RG resistors and measured the resistance of the switch pad to the left of RG11 and the switch wiper pad, and my resistance continues climbs up and sometimes goes down.  I inspected my soldering carefully and it looks OK.  Included are some pics. 

Could there be something else that's causing the strange readings, or should I just retouch all the solder joints.  Thanks!

(http://i27.photobucket.com/albums/c196/tfunster/photobucket-45926-1361134365183_zpsf15e9874.jpg)

(http://i27.photobucket.com/albums/c196/tfunster/photobucket-38498-1361134349311_zpsa8697b9d.jpg)

(http://i27.photobucket.com/albums/c196/tfunster/photobucket-1403-1361134314596_zps6ac6254f.jpg)


Below are the two points I measure - is this correct?
(http://i27.photobucket.com/albums/c196/tfunster/23373ac5-1b23-432a-9b5e-5266d56db894_zps8d2edb2d.jpg)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Harpo on February 17, 2013, 05:17:15 PM
... and measured the resistance of the switch pad to the left of RG11 and the switch wiper pad, and my res...
Below are the two points I measure - is this correct?
No. Without the switch installed there is no connection to the wiper pad. Measure total resistance of this series string between the switches outer pins.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: tfunster on February 17, 2013, 05:34:32 PM
... and measured the resistance of the switch pad to the left of RG11 and the switch wiper pad, and my res...
Below are the two points I measure - is this correct?
No. Without the switch installed there is no connection to the wiper pad. Measure total resistance of this series string between the switches outer pins.

Thanks Harpo - when I measure it like you say, I do get 25k.  However I was going by this bit of instruction in the guide that Jeff sent me: "Before moving on, using your DMM, probe between
the switch wiper pad and the switch pad just left of RG11. You should have around 25k +."

So, the guide is incorrect?  Or did I just read it wrong? 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 17, 2013, 06:42:11 PM
Yeah, it must be a typo/wrong info in the instructions. Just do exactly like Harpo said.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: tfunster on February 17, 2013, 07:10:40 PM
Yeah, it must be a typo/wrong info in the instructions. Just do exactly like Harpo said.

Thanks Jeff.  Also, for the LED, does the longer lead go into the terminal where the arrow is pointing?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 17, 2013, 09:42:36 PM
Thanks Jeff.  Also, for the LED, does the longer lead go into the terminal where the arrow is pointing?
No, the shorter lead goes to the pad that the arrow is pointing to.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Drumbreak on March 05, 2013, 02:57:42 PM
Hey all-
I have two A.2 versions of the VP26.  I was adding the stepped gain knob and ran into a problem with the first one- I'm not the best at desoldering and managed to lift the top solder pad on #3.  The bottom pad was still there.  Regardless, there seems to be a bad connection somewhere as it now always passes a weak signal- if its cranked full on or at the bottom step.  I checked all my points on the stepped resister board and there's no bridged points.  I haven't had a chance to spend much time looking it over, but was hoping there was an obvious fix.  I could have bridged pad #2 on the main board with one of the other pads without knowing it...  It's a bummer because they sound great!  I was just in a hurry to upgrade them a little for a session.

Thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 05, 2013, 03:29:33 PM
Can you post a close pic of the problem area?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Drumbreak on March 05, 2013, 08:51:38 PM
Hi Jeff,
I will if I get some time in the next few mornings, or it will be this weekend.  Stay tuned!
Thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Drumbreak on March 28, 2013, 08:00:46 PM
So... I finally had time to double check my work after getting stuck in the studio for the last three weeks.  I missed trimming a lead on one of the new wires and it was shorting out on another pad.  Simple fix, but I should have checked all my connections first!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Curran on April 27, 2013, 07:13:45 PM
getting ready to buy up some more API Classics from Jeff. I have four of the VP25's with the GAR2520'sand love them. I producer metal bands and want to add four to six more pre's. What is the sound differance I can get from the VP25's to the VP26's to the 312's with the Di's. Just want to try some new flavor from Jeff but I want to go the correct way. My 500 rack is not a 51X  :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Winetree on April 28, 2013, 07:41:18 PM
There's a lot of posts on here and on Gearslutz about the differences in sound between the pres.
Just a quick description. The VP25's and 312's have the larger output transformer.
VP26 -  Smaller output Transformer, more of a closed sound. Like original console.
VP25 -   Closed but a little more open.
VP312-  Open sounding
You might look into the dual stage stage VP28's. VP26 Mic pre with Transformer, opamp output.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mulletchuck on April 29, 2013, 02:24:44 PM
There's a lot of posts on here and on Gearslutz about the differences in sound between the pres.
Just a quick description. The VP25's and 312's have the larger output transformer.
VP26 -  Smaller output Transformer, more of a closed sound. Like original console.
VP25 -   Closed but a little more open.
VP312-  Open sounding
You might look into the dual stage stage VP28's. VP26 Mic pre with Transformer, opamp output.

isn't "open-sounding" just whether or not the high end is rolled off or not?   I have a 26, a pair of 312DI's, and four 528s.   they're awesome!!   daisy-chaining the 528s makes an amazing tube mic pre on loud sources!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Winetree on April 29, 2013, 05:58:05 PM
No. With 2-VP25, 3-VP26, 2-VP312, 2-VP312DI, 4-VP28 and 2-VC528's,  I don't notice any difference in high end between them.
To me Closed seems smaller, tighter, maybe a little compressed sounding,  has  to do with the smaller output transformer. Where Open is seems bigger, punchier, more headroom, Bigger output transformer.
Where did the tube come from? Do you mean "Tube like" sound?

 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Curran on May 01, 2013, 02:50:34 PM
thankyou gentlemen! this was the info I needed!!! he search kind of never works goodlyish for me, So sometimes I have to just post the idiot question and pray for mercy from the interweb overlords!! thanks for the help!!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: McAulayK on May 01, 2013, 10:51:29 PM
Dear GroupDIY,

I built a VP26 Rev. B with Stepped Gain a few months ago. However, I think I messed up the stepped pot. It goes 1 click past the last marking on the faceplate. The step past the last marking seems to be all the way up though. I can't figure out how to get the number of steps to match the faceplate.

Sorry if that's confusing, I'm quite new when it comes to the DIY community. Please let me know if you need any other information. Thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 02, 2013, 12:33:12 AM
This is correct. There are 12 gain positions. Depending on how you fix the knob, either the highest setting or lowest setting is "hidden".
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: McAulayK on May 02, 2013, 01:05:57 AM
This is correct. There are 12 gain positions. Depending on how you fix the knob, either the highest setting or lowest setting is "hidden".

Thank you very much for the quick response. I assume there is no easy way to change the "hidden" setting from full blast to nothing?

Thanks again.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 02, 2013, 09:43:36 AM
No you can't go to "nothing" with this style of pre, the way the original circuit is.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: McAulayK on May 03, 2013, 05:26:40 PM
Thanks for your help! I realized putting it back together that all I had to do to make the hidden setting zero gain was to adjust the knob  :-[. Oops..
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on May 03, 2013, 05:31:44 PM
Thanks for your help! I realized putting it back together that all I had to do to make the hidden setting zero gain was to adjust the knob  :-[. Oops..
Hahaha....that's what I thought first!
But then..........it was too.......eeeehhhhhhmmmmmm..........easy?

Have fun,

best,

Udo ;)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 03, 2013, 05:52:21 PM
Thanks for your help! I realized putting it back together that all I had to do to make the hidden setting zero gain was to adjust the knob  :-[. Oops..
Well, there is technically no "zero" gain but the lowest gain possible.  ;)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: McAulayK on May 03, 2013, 06:09:50 PM
Learn something new everyday!   ;D
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Bassphil on May 21, 2013, 11:51:05 PM
Hi, I have a quick polarity question.

I'm assembling the new rev of the VP26 and there is a 470uM Vishay capacitor that goes into C10. Which side is + and -? There are arrows running from one side to another, right to left if you're reading the writing. I'm assuming that they're pointing in the direction of + right? This cap doesn't have a strip on the negative side like it should...

Thanks!

-Phil

UPDATE: Never mind- arrows point to negative....  ::)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: poiesznbeats on May 22, 2013, 12:02:32 AM
How "matched" should any given batch of VP312s be when at the same gain settings?  I have one pre out of six that gives about 1/3 less output at minimum gain with the same input as the others.  Its still very usable, but when I'm doing a stereo thing I've needed to avoid that channel because I'm giving it more gain to get the same signal.

I'm double checking the build as best I can, but thought this might be a worthwhile question in general. 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 22, 2013, 09:54:50 AM
A stepped gain pre will match to withing about a .25dB, typically better. A variable pre can be a little farther off but should not be drastic like you are mentioned.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Bassphil on May 23, 2013, 02:21:14 AM
Okay, I've read every post on this great forum and haven't found a definitive answer that will let me sleep better tonight.

I just finished my first build of the VP26. Like a few people here in the thread, I also noticed the weird issue of the moving numbers on my Fluke multimeter when I got to the final step of checking the ohms of the op-amp sockets.

I have a nice Fluke 179, but I might very well be using it incorrectly! When I set it to ohms and touch the different sockets of the op-amp, the numbers are moving up. Is that normal? My Fluke is set to auto range.

I also noticed that the readings change depending on which lead of the Fluke touches which op-amp socket. For instance, if I touch the red lead to the o and the black lead to C, I get a reading of 1.6M that continues climbing from there. If I switch that around, I get a reading of -1.35M.

I want to make sure that, as of this point, everything seems to be normal. Here are my readings:

-V & +V = starts at 200K and climbs
-V & C = starts at 1.06M and climbs
+V & C = starts at 168K and climbs
C & O = starts at 1.6M and climbs if the red lead from the Fluke is on the O (like I mentioned)
+V & O = 480K and climbs
-V & O = 1.2M and climbs

I'm definitely not an electrical engineer, but I'm good at following orders. I was pretty thorough in checking the solder joints, and I organized all of the resistors with my multimeter, so those are definitely working and should be sorted correctly. I can't imagine I'd have any problems, though if there's one thing I've learned from reading this thread is that people with more knowledge than me can misplace a resistor...  ;)

Anyway, before I take it to the next step, I just wanted to get a confirmation that the moving numbers thing when I was performing the first check was normal, and that the numbers I posted look to be okay.

Thanks!

-Phil
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 23, 2013, 09:40:45 AM
Phil, this is totally normal due to capacitor charging during the measurements. Looks like you are all good.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: JuniusRecordingCo on June 06, 2013, 11:54:13 AM
Finished up two new VP26 with variable gain - and the first of my six to have the phantom LED. Question about those LED's behavior: both unit's LED lights immediately upon flipping the 48V on, but one of my units ramps down, slowly dimming after flipping it off, and the other unit turns off immediately. I inspected the boards and couldn't find an obvious visual difference. What is the correct behavior? Where might I look more closely to find what might be the cause of the difference?

Thanks - and enjoy your stay in Nashville, Jeff.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: qmp audio on June 06, 2013, 02:27:42 PM
Finished up two new VP26 with variable gain - and the first of my six to have the phantom LED. Question about those LED's behavior: both unit's LED lights immediately upon flipping the 48V on, but one of my units ramps down, slowly dimming after flipping it off, and the other unit turns off immediately. I inspected the boards and couldn't find an obvious visual difference. What is the correct behavior? Where might I look more closely to find what might be the cause of the difference?

Thanks - and enjoy your stay in Nashville, Jeff.

I can't speak exactly for the new VP26 as i haven't built one ( I think I read that Jeff changed where the LED is power is coming from ),   but the vp312di's i have the LEDs do fade out when disengaging 48v.   This is due to the LED draining current from the cap.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: abechap024 on June 06, 2013, 02:31:31 PM
To me thats almost more useful, so you can see when phantom is actually off.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: JuniusRecordingCo on July 03, 2013, 11:39:32 AM
Wanted to check in again on my "fading vs. fast out LED" question. I've since used both preamps in sessions, with 48v, and nothing seems awry. But still, the different behavior unsettles me.

Also, I have two RevA boards. I'm thinking of drilling the faceplates for a 48v indicator LEd, because it's a nice feature, and I like consistency. Looking at the RevA and RevB schematics, it looks like the LED can be introduced to a RevA board pretty easily. Just a 10k resistor prior to the LED, terminated in parallel to the chassis and to ground via a 10R .5W resistor.

Looking at it again, perhaps the short to ground from the switch's off position is making the difference between the two LED's behavior. I'll have to check the actual board to see.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Terryb on August 04, 2013, 11:10:58 PM
Jeff, I was following these instructions on my own build and encountered loss of signal at the + of c10.

*******

Next, check the + side of C10. This is the output of the opamp. The gain pot (or switch) should effect the level of the signal probed here.
*****

Signal was fine on pin5 of 2622.

I tried to reflow the c10 joint a couple of times, but still no signal
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on August 05, 2013, 12:17:38 AM
Jeff, I was following these instructions on my own build and encountered loss of signal at the + of c10.

*******

Next, check the + side of C10. This is the output of the opamp. The gain pot (or switch) should effect the level of the signal probed here.
*****

Signal was fine on pin5 of 2622.

I tried to reflow the c10 joint a couple of times, but still no signal
That to me would make look at the opamp.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Terryb on August 05, 2013, 12:21:56 AM
I did not have an opamp inserted when testing with the audioprobe.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on August 05, 2013, 10:22:25 AM
Aha, that is why the audio stopped at the opamp. You will need to install an opamp to continue testing.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Terryb on August 05, 2013, 03:06:11 PM
Does it need to be powered in order to check the stuff post-opamp?

And if so, where can I find such a unit?

Thanks for all your help.  I feel like I'm really close to figuring this out.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on August 05, 2013, 03:07:47 PM
Yes indeed. You will need a 500 series rack of some sort or a bench type PSU.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Terryb on August 05, 2013, 03:44:35 PM
Semi-success!

I plugged the vp26 into my 500 rack and then ran that into a pa.  I'm definitely passing audio and the gain pot, mute, and -15db pad are all working fine.

However, when I turn the attenuating pot I don't notice any difference.
Should I?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on August 05, 2013, 05:51:22 PM
Yes, fully CW will be no attenuation. Turning fully CCW will basically pass little to no signal. Guys have forgotten to solder all the pins before.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Terryb on August 05, 2013, 10:32:41 PM
Ok, I also noticed my phase switch is not working.  When I press it, all audio cuts out.

So, i reflowed solder to switch-2 pads and rv1 pads.

Still don't work.   Is there a component that is upstrean of both that would not affect switch 4?
I will also continue combing this entire thread to see if anyone has had the exact same issue
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Terryb on August 06, 2013, 12:16:45 AM
Jeff, disregard that last post, I figured out the problem.

Basically, like most other issues, it was an oversight on my end.  I hadn't soldered the 3 posts on SW4 furthest from the other switches.

Thanks so much for your time and patience.  I will absolutley continue buying your kits and hopefully get good enough at building them so I won't have to bug you with my dumbass mistakes.

Thanks again!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drew571 on August 19, 2013, 10:15:41 AM
I've put together several of the VP26's now and on one of them I'm having a problem.  It passes audio fine, all the knobs/switches work fine, but there is a very low level "clicking" or "popping" that is happening at a constant rate.  Like a 16th note.  Here's a link to the file.  It's subtle, but there.

https://soundcloud.com/drew571/vp26-clicking

I switched out the opamps to eliminate that issue.  The one I built was a gar2520, and I also tried a Red Dot.  Issue happens with both of them. 

Any other suggestions for what could be wrong? 

Thanks,
Drew

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on August 19, 2013, 10:24:53 AM
I would eliminate the rack slot and associated cabling next.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drew571 on August 19, 2013, 01:35:30 PM
Hey Jeff,
They're eliminated.  Also switched to all the other slots in my 500 series rack and they all do the same thing.  I built another VP26 to see if swapping the VP26 would do it and the other one doesn't make the same noise.  I've now tried the problematic VP26 with 2 different Red Dots and one GAR2520 and I get the same issue with all of them.  It's currently very faint but definitely still there.  Any other ideas?

Thanks,
Drew
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on August 19, 2013, 01:45:24 PM
Hello Drew,

may I ask if you had anything connected to the input of your faulty VP26 when doing this test?
Also what was the gain setting at that moment,was it fully cw?
Might be a faulty cap discharging periodically,but I'm unsure,so therefore the questions.
Just curious.

Best regards,

Udo.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drew571 on August 19, 2013, 02:14:44 PM
I had a SM57 attached, and then also a SM7B, just to eliminate the mic....  :) 

Gain setting just turns the loudness of the clicking up or down, so I believe I could assume that since it's not the op amp, not the 500 series rack, and because the output attenuator quiets it down that it's gotta be on the VP26 itself? 

Could a poor solder joint cause something like this? 

Maybe I'm looking at this wrong, maybe this is a really cool effect and would be great with a back beat played to it.  But I'd like to know how to turn it off all the same. :)

Drew
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on August 19, 2013, 02:43:08 PM
....Could a poor solder joint cause something like this?....
Yes and most likely the problem since you have ruled out the other things. I would re-flow the entire board just to be sure.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drew571 on August 19, 2013, 03:37:06 PM
Ok, I'll report back when I'm done.  Thanks.  Someone should design snap-in resistors/caps.  Just sayin.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drew571 on August 19, 2013, 10:53:31 PM
Ok, I went back and heated up all the soldering points, then double checked for any soldering bridges.  Looks clean.  hooked it back up and the problem persists.  I changed the D plug on the back of my Tonelux V4 500 series lunchbox.  I ran a power cable to a different room in the house to plug in the 500 series rack.  changed out all the XLR cables once again.  Still there. 

Any other suggestions? 

Also, I just put together another VP26 this evening and it has the same problem. 

Maybe it's the internals of the Tonelux?  Should be under warranty yet.  Anyone near West Palm Beach, FL area that I could plug my modules into their 500 series rack so I can eliminate that?  I have now had 3 of these units that have all had the same problem.  Either I seriously suck at DIY or something else is going on. 

Drew
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on August 20, 2013, 02:38:32 AM
Hello Drew,

so summing this all up it says all three VP26 modules in that Tonelux rack seem to have the same issue,right?

My next questions are:

1.:Does this pumping sound appear immediately after switching on or does it get worse when heated up,say for 20-30 minutes?

2.:Do the modules behave all the same in the same slot or does it get worse from outmost left to outmost right module slot?

3.:Does the pumping sound get worse the more modules you plug in?

From what I feel by now is there is either a series build error on your modules (unlikely) or there is an issue with the power rails/psu inside the Tonelux box.

4.:Do you have a scope to check the voltage rails?

5.:And a last question for today (hahaha....),does the box have any jumpers or switches to change ground connections?

Let us know please,

Udo.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drew571 on August 20, 2013, 10:37:00 PM
1. It does happen immediately.  Although, not every time.  I plugged them in tonight and it was still there, then I took the power and ran it to a UPS and it went away.  Then to confirm that it was just the fact that I hadn't been plugged into a UPS, I switched to the regular wall power.  It came back.  My joy was near.  I switched back over to the UPS in full hopes that i had solved it, and it was back on the UPS as well.  Suck.

2.  The clicking is DEFINITELY increasingly louder as the slots get closer to the power supply.  For example, the furthest slot out I can barely hear, have to have it cranked.  And the closest slot is very noticeable right away.

3.  No, loudness seems to stay the same, although I only have two modules to try this out with.

4.  I do not have a scope.

5.  I don't believe so. 

Does the above indicate that it is in fact the Tonelux?

That would actually be good news because it's under warranty I believe. 

drew

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on August 20, 2013, 11:23:44 PM
O.k. Drew,

thanks for answering these questions.

Especially answer #2 leads us to induced noise coming from the built-in psu.

So my guess is that the Tonelux Box is the issue,not the preamps,would say 95% sure.

Either the shielding of the psu isn't good enough or something is going wrong inside there.
Don't know if this psu is linear or a smps.
Anyway,to confirm (finally) might be best to check back in a different 500 series or 51x rack with an external psu.
Hopefully you can find someone in your area,I'm sure there are people there who can help you.

Best,

Udo.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: dandeurloo on August 31, 2013, 09:50:42 AM
Hey guys I made a really dumb mistake with a VP 312 DI.  I put the relay pcb in backwards for the DI section.  When I powered up nothing worked obviously.  That is when I discovered my mistake.  I've gotten the pcb out and turned around now and the DI works but the mic pre doesn't.  Did I fry the transistor on the board or something else while I had the pcb turned around?



Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: sorozcojr on September 25, 2013, 12:43:00 AM
Hello Guys!

So I recently purchased 2(x) vp26s w/ SLRedDot OpAMps and (2x) vp312s w/ the gar2520 opamps. So far I have two vp26s built. One of them works and sounds great! However the other one has some issues. First the Led light does not light up when phantom power is engaged (I think I might have to switch the leads. Hopefully when bending back the LED legs I don't break them off :/ ). I ran a sm57 and I get signal. I ran a condenser mic and if the phantom power is off and I crank the pre amp I get signal. Now, when I engage the phantom power it boosts the signal significantly. It's not the microphone or the lunch box because I tested it already with the other working vp26. I double checked all the resistors and made sure everything was where it's suppose to be, even re-soldered everything to insure proper connection. Any help would be greatly appreciated. Thanks
 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 25, 2013, 11:18:37 AM
I think I responded to your email with some things to try. First flip the leads for the nonworking LED. Next see how that condenser mic works. You can measure DCV at the switch to make sure it's fully off. Depending on how long you waited, maybe there was still enough DC stored in the 120uF cap and that's why the condenser was working very low. The backwards LED will keep that cap from discharging quickly.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: JBHamby on September 27, 2013, 10:42:44 AM
Hello everyone! 
This is my first post.  Thank you to everyone that has contributed to this tread.  I believe that I have read over a large portion of it and still not found what I was looking for.  I just recently built three vp26 and have run into the same problem with all three.  The preamps work great and all of the functions work correctly on all three except the phantom power which does not work on any of them.  There is something that I missed or got wrong on all three builds and I really am unsure of where to start in order to correct this.  But as I was saying as long as I am using a dynamic mic the preamps function and sound great but they do not work at all with a condenser.  Any help or suggestions would be awesome!  Thank you!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: qmp audio on September 27, 2013, 11:29:21 AM
Hello everyone! 
This is my first post.  Thank you to everyone that has contributed to this tread.  I believe that I have read over a large portion of it and still not found what I was looking for.  I just recently built three vp26 and have run into the same problem with all three.  The preamps work great and all of the functions work correctly on all three except the phantom power which does not work on any of them.  There is something that I missed or got wrong on all three builds and I really am unsure of where to start in order to correct this.  But as I was saying as long as I am using a dynamic mic the preamps function and sound great but they do not work at all with a condenser.  Any help or suggestions would be awesome!  Thank you!!

I would say,  first measure your power supply/rack to make sure it is sending out 48v.   Could be a fuse in the power supply.   If you can confirm you have 48v, does the condenser work on a known working preamp?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 27, 2013, 11:35:03 AM
Yes, the fact that none of the 3 builds have phantom working points to the PSU or maybe the return path from your mic cable(s).
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: JBHamby on September 27, 2013, 03:33:34 PM
Yeah I have several other preamps with phantom power and they work with them.  I also agree that it sounds like a power supply issue since it is affecting all 3 preamps.  My rack is a older API 6b lunchbox (non-dsub).  Does anyone have any advise about how to begin with it?  I have never really messed with it before, it was a recent purchase from ebay :-\
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: qmp audio on September 27, 2013, 03:41:07 PM
Yeah I have several other preamps with phantom power and they work with them.  I also agree that it sounds like a power supply issue since it is affecting all 3 preamps.  My rack is a older API 6b lunchbox (non-dsub).  Does anyone have any advise about how to begin with it?  I have never really messed with it before, it was a recent purchase from ebay :-\
have you checked for +48 using your DMM. 
w/ your DMM,  put the + lead in pin 15,  - lead in pin 13 in the lunchbox card slots.  is your meter reading +48v?
if not perhaps there is a blown fuse in the lunchbox.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on September 27, 2013, 04:05:56 PM
Nearly double posted with gunpoint recording.
I'd do this too.
I guess the +48 led is on?
If so then do as gunpoint suggests,measure pin 15 to pin 13.
If you have no reading try to measure pin 15 to pin 5.
There are two gnd points,maybe the ground reference is missing on pin 1 on the female xlr then.
If both measurements don't give you readings but the led is on then it could be that the lunchbox has been modified.I have read that pin 15 must be disabled when the lunchbox is used with a certain type of api eq.The mod is normaly done on the eq module by cutting a trace,but who knows,maybe the former owner wanted to go safe.Just a thought of course.

Tell us what your readings are,

best,

Udo.

P.S.:There's a cool chart in Jeff's floorbox assembly guide on page 8 for reference,look:
http://www.classicapi.com/catalog/images/FB-build/Floor-Box-Assembly-Aid-Rev_1.pdf
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: sorozcojr on September 27, 2013, 11:58:27 PM
So I finally got a chance to work on the pre amp today and I switched the LED light's leads and the preamp lights up and works like it should. You're the man Jeff!

Quick Question: Is a burn in period required when assembly is finished? If so, what are the benefits and whats the proper way to go about it? THanks
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: JBHamby on September 28, 2013, 12:20:26 AM
Hey guys measured for +48 on pin 15 and 13 and then 15 and 5.  Both positions show 48.5v.  So it looks like its getting power. Im just not sure what would be causing this.  After the phantom power is switched on there is a loud pop when I engage the pad in or out (this is with a dynamic mic, it still does not power a condenser).  Does anyone have any suggestion of what I should look for now?  Thanks everyone!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on September 28, 2013, 01:04:54 AM
Hello,

yes,this is correct.
Next step is to measure the female xlr,so the input on the back of the lunchbox.
Again measure with your dmm set to dc voltage and measure both xlr pin 1 against pin 2 as well as pin 1 to pin 3.You should get two identical readings here.
The loud pop with phantom on while using the pad indicates that there seems to be the dc in the circuit already.
I hope your mic cable is o.k.,you can check the phantom on its' female end too,same way as described before.
Or is the signal running through a patchbay or so?

Good luck,

let us know,

Udo.

Edit:You must have a module plugged in on the slot you measure at of course.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on September 30, 2013, 12:48:18 PM
  I'm suspicious about a part I received in my VP26 Rev. B BOM. R14 is listed as a 10 ohm resistor on the RevB BOM sheet. After stuffing the rest of the board I am left with a single resistor which has only a single black color band on it. My DMM reads this resistor as having less than 1 ohm of resistance, and the BOM calls for 10 ohms in the R14 position. Do I need to find an additional 10 ohm resistor to sit in it's place?

Thanks for the help,

-P
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on September 30, 2013, 12:54:33 PM
Hi,

that's not a normal resistor but a bridge or jumper,same as a piece of wire.
So you get that close to zero reading.

Best,

Udo. ;)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: JBHamby on September 30, 2013, 12:54:59 PM
I just wanted to give a quick update.  After messing with the vp26's  a little more this weekend I did find the problem.  It was the mic cable, for what ever reason it would not pass 48+, but I still am having one problem.  I have tested the preamps with several different mics, but for what ever reason it will not power my CAD m179 microphones which is what I use for toms.  Im really not sure what to even think about this (but at the end of the day I could use it as a great reason to pickup some more mics!!!   ;D)

Thanks everyone!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on September 30, 2013, 01:05:09 PM
Glad you got it sorted!

Udo.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: JBHamby on September 30, 2013, 05:15:12 PM
Yeah I wish I could just figure out why its powering my other condenser mic's and not the CAD m179 though! I would almost suggest that I have an issue with the mic but it doesn't seem likely that all 3 mics would go bad/break at the same time. 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: kante1603 on September 30, 2013, 10:51:25 PM
Hello,

you should post this over in the mic build thread.
I'm sure it is mic related.
Just to keep this thread clean.

Best,

Udo.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on October 01, 2013, 10:39:39 AM
In a quick google search it looks like the m179's are known for phantom power issues. The 48V circuit on my pre's is about as simple as it gets. If other mics are working with phantom, it could be a rack or PSU issue with a small phantom supply. Did you try one mic at a time or all 3 at once?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 05, 2013, 05:48:12 PM
  I just finished a Rev B. VP26. My signal level from the mic pre is low and requires the stepped gain grayhill switch to be completely turned up to get any kind of signal. I believe all of my resistor values are correct.

  Some things that I've thought may be the problem are, the resistor at R1. The DIY build does not have a resistor in that position. Also, I neglected to put a piece of double sided tape underneath the input transformer. Could there be a problem there? Also, is it worth checking the output transformer resistor values? Also, the resistor at R14, listed as a 10 ohm resistor on the bill of materials, did not come in the bag of resistors. Instead, I had an extra shorting resister. I put in a 10 ohm resistor at R14, is there a chance that the shorting resistor is supposed to live there instead?

  Thank you for the help.

  -P
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on October 05, 2013, 05:57:21 PM
Some things that I've thought may be the problem are, the resistor at R1. The DIY build does not have a resistor in that position.
This is on the BOM and schematic. It's just a R for the phantom LED.

Quote
Also, I neglected to put a piece of double sided tape underneath the input transformer. Could there be a problem there?
No.

Quote
Also, is it worth checking the output transformer resistor values?
Maybe, but not yet.

Quote
Also, the resistor at R14, listed as a 10 ohm resistor on the bill of materials, did not come in the bag of resistors. Instead, I had an extra shorting resister. I put in a 10 ohm resistor at R14, is there a chance that the shorting resistor is supposed to live there instead?
This was a packing error on a handful of resistor packs that went out. 10R is the right value. Sorry about that.

The first and foremost question is always "who built the DOA"? If the DOA and preamp were both fresh builds, it is very hard to figure out where the problem can be unless you have another way to test the DOA or another DOA to test the preamp with.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 05, 2013, 05:59:35 PM
This is a pre assembled GAR 2520. I have a JH 990C that I can swap out. Should I try that?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on October 05, 2013, 06:05:29 PM
If the gar was prebuilt it will not be that. Gary burns them in and tests them before he sends them to me. Is it seated properly? http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)

If it's not that, you must make sure it is nothing outside of the pre. Rack, cabling, converters and so on. Next it will be time to inject signal and see where it stops. There are many posts in this thread about how to do that.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 05, 2013, 06:14:27 PM
Thanks Jeff, I checked out that link and am now confident in the seating of the op amp. Also, the attenuation pot attenuates at the 0 marking and does not attenuate at the infinity marking. Is this the opposite of what it should be?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on October 05, 2013, 06:16:26 PM
Yes, that is very weird. Dbl check your output transformer wiring.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 05, 2013, 06:25:19 PM
Here's a picture of my output transformer. The brown and green leads were cut a little short but they are in properly.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 16, 2013, 03:25:00 PM
I'm not getting adequate signal from my VP26. I have noticed two significant issues. The phase switch kills all signal, and the attenuate signal works in reverse where the pot set to 0 on the face plate results in a fully attenuated signal, and 0 passes signal. I have passed all tests listed at the end of the install guide, and am passing signal with both dynamic and condenser microphones, but the signal is distorted and requires the stepped gain as well as the input attenuate pot, (in reverse,) to be set to full. The output transformer is wired to the PCB properly, and I have also swapped out the pre built GAR op amp with a JH990C that I know is in good working order. Here is my PCB. Please let me know if you can help. I probably did something really juvenile here.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 16, 2013, 03:25:47 PM
.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 16, 2013, 03:26:11 PM
.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 16, 2013, 03:26:43 PM
.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 16, 2013, 03:27:02 PM
.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: qmp audio on October 16, 2013, 04:07:05 PM
Do you have a solder bridge between the two resistors above T1?
can't tell but looks like thats possible from the photo in post 518 http://groupdiy.com/index.php?topic=33501.msg688331#msg688331 (http://groupdiy.com/index.php?topic=33501.msg688331#msg688331)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 17, 2013, 02:52:41 AM
I know what your saying. It was just a piece of flux left over. No bridged connection there.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Harpo on October 17, 2013, 07:58:55 AM
Sounds like you might have connected the transformer balanced preamps output  (signal is across XLR-pins2/3, XLR-pin1 is only shield) to a following stage with unbalanced input, only sensing XLR-pin2/XLR-pin1 ?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 17, 2013, 09:22:57 PM
How do I check the path of the T2 windings?  Is it possible that the colors from the output transformer are not correct? Jeff's first suggestion was to check the wiring of the output transformer, but I know, and have posted pictures of this wiring termination and know this is right. I've found another posting on here with a output transformer that needed to be swapped out, is it possible that mine may need to be swapped out as well?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on October 17, 2013, 10:08:18 PM
I don't recall having a bad 2623-1 since we switched to this new winder a while ago but you can check. You will need to desolder all 6 transformer leads and make sure they are not touching anything. Then measure DCR between red->orange, green->blue then black->brown. You can also make sure one lead is not internally shorted to any other lead this way. Report the results here.

BTW, like Harpo said, make sure this is not a converter, rack slot or cabling issue of any sort. Read Chuck's last post on the VP28 thread to see what I mean.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 18, 2013, 12:15:32 AM
Jeff, This is what I'm getting. Can you also send a link to the post that you mentioned?

Black & Brown: 22.7 Ohms
Red & Orange: 14.4 Ohms
Green & Blue: 23.4 Ohms

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on October 18, 2013, 09:12:46 AM
Those results are as expected so I would guess that the 2623-1 is fine. I would investigate what devise you have following the pre.

Here was Chuck's post http://groupdiy.com/index.php?topic=48610.msg688337#msg688337
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Triscuit on October 19, 2013, 03:40:26 PM
Hello everyone! I need some help troubleshooting. Just completed the VP26 kit Rev B.1 and the gar2520 opamp kit last evening. I put it into my Lindell rack to test this morning and ... you guessed it ... nothing.

Here's what I've done:
1. Checked the resistance in the millmax pins per the directive - all checked out fine.
2. Scanned and reflowed solder on components where it looked a bit weak; I admit, there are some more spots that I could probably go over, but nothing looked offensive per se (I won't take it personally if you tell me otherwise).
3. Checked that I placed the resistors in correctly; I am 99.99% certain I did. I sorted them pre-install and measured each with a DMM.
4. Cleaned the board with some flux cleaner and a toothbrush to make sure I didn't leave any grossness on there.

Here's what I see may be a problem:
1. I only soldered from the bottom of the board; I notice at a lot of the pads on the top that the solder hasn't come through. Will this cause a problem?
2. I didn't have double face tape to attach the 2622 - I rolled some duct tape and used that to insulate between the board and the transformer. This doesn't SEEM to be problematic, but am I wrong?
3. I haven't checked resistance at the output transformer yet - sort of waiting on that because .. (see 4).
4. I may have done a terrible job at completing the opamp. I have attached photos. Maybe I need to go back and reflow some solder on the top of the board? I do not have a preassembled opamp to test, and sort of wanted to avoid this because I really wanted to nail that kit.  :P

Here's what's happening in the rack:
1. When I power on the rack with the VP26 in, I do get a pleasant "pop" - nothing LOUD or OFFENSIVE .. just a little "poof" that lets me know something's happening.
2. The 48v LED comes on appropriately with the flick of the switch, and then fades nicely as it drains when I turn it off.

That's pretty much it. Tried an SM57 and a frankenstein condenser. No output sound.

I won't take anything personally - please take a moment if you can to see the photos. Tell me what your thoughts are. I obviously want to get this VP26 up and running, but I also want to learn here because I want to do more!

Thank you all in advance! I am new to the forums here, so this is my first post. Sorry to bring a problem to the table.  :-\ (Will post additional pics consecutively)

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Triscuit on October 19, 2013, 03:41:55 PM
Bottom of board:
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Triscuit on October 19, 2013, 03:43:23 PM
gar2520 bottom of board (I can take this to the official thread if necessary):

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on October 19, 2013, 04:32:24 PM
I would reflow the bottom of the opamp. It is hard to tell in the pic but a few pads look like they may be cold or not have enough solder. You should be careful when doing this. It is not a problem to only solder from the bottom. The holes are plated thru and connect the top layer to the bottom layer.

It is very hard to test a fresh pre build with a fresh opamp build. The issue could be in one or the other or both.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Triscuit on October 19, 2013, 04:42:43 PM
Thank you, Jeff!

It's apparent now when I have a full-res photo on my laptop - there are some rough spots there! Also, I know it's hard to test with a fresh build on both; that's what's sort of frustrating me.

Donny

UPDATE: problem was with the opamp; we're up and running! Long live VP26!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on October 20, 2013, 05:00:24 PM
Is there a compatibility issue that I'm missing in trying to get my VP26 to run on my system? I'm attempting to run this pre on a new API 6b lunchbox over XLR connections. I know that VP26 units can be used on the 51X systems. As of right now I'm using my lunchbox with a UA Apollo running TRS to XLR connectivity, where the mic pre is fitted into a slot that I have used before with a different pre running properly.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on October 20, 2013, 05:02:27 PM
The VP26 is 100% VPR or 51x compatible.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mellsonic on November 06, 2013, 07:54:00 PM
Hello everybody,

I need to consult those of you who possibly have any idea of what could be the solution to the technical problem I'm having.


What I have:
-4xvp26 Capi Preamp
-4xOp Amp SL-2520 Red Dot
-1xLindell Audio Power 506

The problem with one of the pre amps is:

Half of the waveform is missing/much lower than the other one. When I reverse the phase it switches from the bottom up, as you can see in the screenshot.

-basically audio can pass through
-it's slightly distorted
-all switches work fine /mute/phase reverse/pad/phantom power
-all pots function fine louder/lower volume
-it sounds different than the other ones

What I have been testing:
Different Op Amp SL-2520 which worked fine with the other preamps. Problem remains.
Different microphones. Problem remains.
Different cables. Problem remains.
Different slots of the Lindell Power 506. Problem remains.


I am looking forward to any responses regarding this problem and hope for someone being able to help me out.
Thank you very much,
Mario

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mellsonic on November 06, 2013, 07:59:54 PM
(http://)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on November 06, 2013, 10:19:08 PM
I recommend skimming thru the earlier pages in this thread. You will find posts about injecting and tracing signal thru the pre. Where it stops is usually where the problem lies.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mellsonic on November 17, 2013, 07:15:46 AM
Hello everybody,

got the problem solved with the VP 26!
It was a soldering bridge with one of the parts. Everything is up and running and fine now!
First recordings sound amazing!
Thanks to everyone and especially to Jeff!

Cheers, Mario
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on December 05, 2013, 02:09:41 PM
Jeff, Can you send me the exact link for the posting or page number on this thread that involves signal injection for testing the VP26? These are the issues that I am currently having with my VP26 with prebuilt GAR2520 op amp installed:

Low signal output (not enough to reach digital 0)
Output attenuate pot works in reverse order
Phase switch kills signal

These are tests that have been run:
Testing of outboard cables, inputs and outputs,
swapping out GAR2520 for known working JH990 opamp
double checking for bridged joints
reheating all joints to eliminate cold joints as a possibility
output transformer test
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: orenradio on December 05, 2013, 06:21:27 PM
Hey everyone!

Man I love these builds!  I have just a few questions, none of which are troublesome, but are nagging me none the less.

I searched this thread long and hard, and I've already reinspected the board and found no glaring issues... I will be inspecting the opamp (which is a pre-built Red Dot), and reflow solder to the switches along with other parts of the board to be sure there are no cold joints or bridges, but I figured I would ask these questions first in case there's a glaringly obvious symptom.

Before I continue I just want to say that some of these questions/issues may simply be a combination of ignorance and incompetence, so feel free to treat them that way :)

a) I built two VP26s and one of the attenuators is considerably more stiff than the other.  They don't behave too different from one another, if I were to quantify them the second build (the less stiff attenuator) is slightly louder by 1-2db at the same relative attenuation.  I don't know if this is simply a result of two unmatched pots, or if I may have applied the solder tip too long on the leads... just wondering if other people experience the same issue.  Not a big deal, I can match the levels by ear/sight in the DAW if needed.

b) When engaging the phase switch I notice what sounds like intermittent clipping... a sound that isn't present if the phase switch is left disengaged.  This happens with both preamps for some reason. The "clip" or distortion occurs intermittently as I am playing, and it seems to reaction to higher "electrical SPL levels" or something; it acts somewhat like a threshold, present with a louder strum/snare hit but isn't present with slighter/softer strums or hits.  Once again it does not occur when the phase switch is disengaged... its not clipping in my DAW to be sure this wasn't digital clipping, nor the Microphone (tested it with another micpre).

Is there another element in the chain that could cause higher input levels to become more distorted only when out of phase?  I don't think its the traffo, but I can ensure there are no cold joints there.  Is there perhaps another element of the board that would react this way?  It sounds beautiful without the phase switch engaged, and has helped me fine tune my mic placement skills nonetheless!

c) The Pres run hot, which is to be expected of the API style preamps, however when running the input Gain to its extremes while using the attenuator, the signal tends to break up when distorted.  Almost as if it cuts out if the gain is too hot (again the attenuator is working so it is not digital clipping, and its more than analog "distortion" as it cuts out).  Could this be related to the behavior experienced in my previous question?  Am I just ignorant of analog clipping behavior?

Thanks in advance for any responses, if I keep proper gain structures (and try not to saturate the gain too hard), and keep everything in standard phase the sound is beautiful on both preamps.  I am very pleased with the results, and hope you all can offer some guidance,  I have a few more VP26s and 2VP28s to build as well... keepin busy... :)

rock n roll
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drastic on December 28, 2013, 04:25:52 PM
Hello all. I recently bought a used VP25 already built. Everything is working ok and sounds fine, but the phantom power isn't working. When I looked at the pcb last night, I noticed a few (what looks like) burnt resistors. Looked at the build guide and it looks like the phantom switch is wired properly. Would a burnt resistor cause the phantom not to work? Just trying to figure out what replacement parts to order. I've attached a pic below.

Thanks!

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 28, 2013, 04:37:51 PM
Yes. I would replace the 200R and the matched 6k8's.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: drastic on December 28, 2013, 04:47:37 PM
Yes. I would replace the 200R and the matched 6k8's.

Awesome, thanks for the uber fast response!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: timrickmann on December 28, 2013, 05:34:45 PM
Hey Guys

Just finished my first 2 builds of a VP26.  Both sound awesome and are working like a dream.  Quick question about the op amp though.  Should i be soldering the op amp to the board or is it just a pressure fit?

Thanks

Tim
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 28, 2013, 05:50:01 PM
DO NOT solder the opamp to the PCB. That would defeat the simplicity of the sockets!! Take a look here. http://classicapi.com/catalog/DOA_Install.php
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: erol on January 03, 2014, 09:35:04 AM
Hi,

I am planning to build a VP28 with a gar2520 Full Kit Bundle.
This will be my first DIY project (with a lot of help from a good friend).

I've noticed there's a VP2x step-by-step guide on de CAPI website:
http://www.classicapi.com/catalog/images/gallery/VP26/VP2x-Assembly-Guide.pdf

But it seems this is all about the VP25 and VP26 am I right?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 03, 2014, 09:53:07 PM
I bought two pre built vp26s from a local engineer. He said that one or both had some problems and he thought it might have been the gar2520 opamps. I went ahead and purchased some ml2520 from whistle rock audio. When I tested the vp26s with either opamps, I would get clipping at low levels. And it's not clipping at all times..I know it's not clipping going into my converter. I read up on this thread and found out I should reflow the solder. I did that and put it all back together again, triple checking each component and solder joint...I still have clipping. Don't know what I should do now...any suggestions?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 03, 2014, 10:04:46 PM
Can you test the opamps in some other module? Maybe there are issues with the new opamp builds as well.

Also, are the opamps seated fully? Take a look at this page. http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 03, 2014, 10:14:36 PM
I made sure they were properly seated and I don't have any other gear with 2520 footprint opamps. You think it's the opamps?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 03, 2014, 10:20:27 PM
If it is absolutely nothing external, it is most likely the opamps.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 03, 2014, 11:54:43 PM
If I purchase new opamps and it still gives me the same problem, what else could it be?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 04, 2014, 12:42:50 AM
Are both pre's behaving exactly the same? Maybe it's the source? Bad mic or cable maybe? Something other than the preamp itself has been the culprit countless times. What is your source?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 04, 2014, 02:22:18 PM
I believe last time I checked, one was working better than the other but both were clipping..I know it's not the sound source because that was the first thing I checked. Do you think maybe there are any bad components? Nothing looks burnt or anything like that.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 04, 2014, 02:28:27 PM
What is the source?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 04, 2014, 02:46:43 PM
I've tried several mics: 57, d112, sm7 (not enough gain), and a stellar cm-5. Tried a couple different cables also.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 04, 2014, 03:06:58 PM
OK, that said.....the very first thing that should be done in troubleshooting a build like this is to verify 100% that the opamp used is solid and working correctly. The steps to verifying that will be different from person to person.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 04, 2014, 03:12:16 PM
Okay I'll buy some kits from you can give it a shot. If that doesn't work, I don't know what else I should do
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 04, 2014, 03:56:22 PM
Is there anyway to test the opamps without putting them in the preamp
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 04, 2014, 04:12:33 PM
Install them in another known to be working module. It can be a catch 22.

You can also inject a sine wave and monitor following the signal thru the preamp. See where the THD starts. It is most likely opamp related but that is a way to find out.

Can you post a pic of the top of the PCB so I can see all of the components clearly? Just do one module for now. Mark it with a piece of tape or something so you can keep it straight later. Don't want to chase your tail.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 04, 2014, 04:25:48 PM
Will do. I don't have face plates on them so I already have them labeled 1 and 2. 1 is the more questionable unit. Although, as I has mentioned earlier, both units give me pproblems. I'll upload them on Monday when I go to my studio. Thanks for your help Jeff! I can't wait for these to be working 100%. I've had them for a year now!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: orenradio on January 07, 2014, 12:06:43 PM
Hello Jeff, all

Hope you had a great New Year!

I have a quick question.  I messed up the t-pad on one of my VP26 builds... and in trying to desolder the item to put in a new one, I lifted some of the pads making it very difficult (if not impossible/impractical) to insert a new t-pad.

I noticed on your website you have a t-pad pcb board.  I'm curious if this is sufficient for what I need to do to replace the tpad.  If I followed instructions wiring the t-pad A, B, and C pads with the corresponding A, B, and C pads on the PCB board, would the t-pad be "backwards" if the pcb were on the opposite (front) side of the main PCB?  Or is the board supposed to be flush with the main PCB?  Mainly curious about its alignment with the L- bracket and faceplate.

I'm not sure if its an old adapter not applicable with the new builds, or what else I can do without scrapping the board altogether.

Thanks in advance,
Oren
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 07, 2014, 12:50:17 PM
As long as the t-pad and adapter PCB does not physically interfere with the main PCB, it can be placed where ever it fits. The main thing is the wiring must go to the corresponding letters.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 07, 2014, 07:21:06 PM
Here's the unit in question.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 07, 2014, 07:42:11 PM
It appears that all R's are placed correctly. At this point, I would recommend injecting signal and following it thru the circuit to see where the problem starts. There are some steps for doing this in the first few pages of this thread.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: orenradio on January 08, 2014, 02:54:40 PM
Forgive me Jeff,

Where on the Main PCB is "A, B and C" located for the wires from the tpad adapter PCB? is that the opamp's "+ and -" on the bottom, and "c" between the +/-V?

http://www.classicapi.com/catalog/images/gallery/VP26/Rev_B/VP26-Rev-B.1-scan.jpg

Thanks in advance,
Oren
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 08, 2014, 06:43:55 PM
Oh sorry, I was thinking of a previous Rev of the preamp PCB. Maybe we should see what your board looks like now. There may be some traces to repair/jumper.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on January 14, 2014, 03:11:23 AM
I forgot I have a hairball audio Lola haha! I tested the ML2520 opamps I have in the vp26s and they appear to be working correctly with my Lola. I have to probe it now like you said. I can't imagine what it could be
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: orenradio on January 14, 2014, 02:37:27 PM
Hey Jeff,

Sorry for the delay, here's the front PCB.  As you can see a few pads have been burnt, and although I haven't completely cleared the holes of solder, I hoped there would be an alternative wiring of the tpad PCB adapter so I dont have to worry about this corner of the PCB being fried or going bad in the future.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: orenradio on January 14, 2014, 02:37:56 PM
Here's the backside PCB
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 14, 2014, 07:30:19 PM
Although the PCB doesn't look great, it does appear that all traces and pads are intact. Just follow this pic and wire A to A, B to B and C to C.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pitol678 on February 15, 2014, 05:02:40 PM
Hi,
So Im having issues with my vp26. I have built it over the last couple of months as parts have been available and finished today, minus one knob, and the volume is VERY low even when everything is all the way up. I also finished a VP28 with all the op amps etc and was successful except for a phantom power issue (it was also a lot neater than the first). This pic shows that R1 isnt in place but it was added after the pic was taken. Any help would be greatly appreciated, thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 15, 2014, 05:23:09 PM
Is the opamp prebuilt or did you build it from a kit?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: 3nity on February 15, 2014, 09:15:12 PM
The picture is from a non finished unit isnt it?
gain resistors are missing!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pitol678 on February 16, 2014, 10:37:26 AM
Jeff, I built the op amps and I switched out the ones on my vp28 and still had the same issue. I built this a little at a time so it's very possible I missed something so I need to just revisit the build guide and check into the missing gain resistors  :-[
Title: My knob is sticking out ! (so is my op amp)
Post by: jbjoubaud on February 21, 2014, 10:22:30 AM
Hey guys,

It seams like my gain knob is sticking out a little too much. Anyone ever dealt with that ?

Also, I'm not so sure about the opamp. Does it look ok to you ? (pre built 2520 red dot) It doesn't seams like it's properly secured in the sockets..

Title: pictures of things sticking out
Post by: jbjoubaud on February 21, 2014, 10:30:02 AM
here are the pics

Title: pictures of things sticking out
Post by: jbjoubaud on February 21, 2014, 10:31:08 AM
pic of the op amp
Title: Re: pictures of things sticking out
Post by: jsteiger on February 21, 2014, 10:45:11 AM
pic of the op amp
This is not at all right. Please have a look here. http://classicapi.com/catalog/DOA_Install.php
Title: Re: pictures of things sticking out
Post by: jbjoubaud on February 21, 2014, 11:15:01 AM
This is not at all right. Please have a look here. http://classicapi.com/catalog/DOA_Install.php

Thank you Jeff, and for your responsiveness as well !
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jbjoubaud on February 21, 2014, 05:00:39 PM
Guys,
I just want to make sure.
When you do the tests in section 12, which probe do you put in first ?
For instance :
12.1.d Probe between the “C” and “O”(Output) sockets for the DOA. Your reading should be a high resistance, over 200K Ω.
Is black probe on the "C" then red probe on the "O" or red probe on the "C" then black probe on the "O" ?

Either way, for 12.1.d I have the value fluctuate slowly beetween 75k and over 200K (slowly goes up, then slowly goes down, etc...)

Thanks for your help !


edit : I redid the test and if put the red prob on "O" and black on "C", I get around 6.4M ohm. If I have the black probe on "O" then I get the fluctuating thing.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 21, 2014, 06:22:47 PM
When measuring DCR it won't much matter. These results seem fine.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jbjoubaud on February 21, 2014, 06:37:38 PM
Thanks Jeff.
Just did the last test and all is working fine, I'm stoked ! Can't wait to put this baby to use.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on February 26, 2014, 06:38:10 PM
i havent been using my vp26s since my posts earlier. i used them this past session and noticed a few things. i was tracking guitar and within 5 or 6 hours of my session, one of my vp26s started sounding real thin and the output was reduced by 5-10db. i pushed in and out the switches, turned on and off my lunchbox, and checked my signal path, but still it was having that same problem. as much as i love them when theyre working, im almost fed up with these and want to sell them  :( do you think its a transformer problem?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 26, 2014, 06:40:10 PM
Sounds like a cold solder joint somewhere or maybe something opamp related.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ccstudios on February 26, 2014, 06:50:09 PM
i changed the opamps to my diy990's from hairball audio and i still get the same problem. also, i dont know if you remember, but the signal "spikes" and clips my converter on harder transients even though i have the output level real low.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: laddie.music on March 02, 2014, 04:28:38 AM
Does chunger have a VP26 build thread of pictures yet?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 02, 2014, 11:07:08 AM
Yes, he did one a few years ago. Just search "newbie builds" and you will find it. I have a link to it in the support docs email that gets sent out.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: RemcoJVG on March 08, 2014, 03:10:42 PM
Hi Jeff and other diy dudes,

a quenstion.
iN de rev b BOM there are 14 resistors listed, in the pakkage there are only 11 resistors
confused.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 08, 2014, 04:38:40 PM
a quenstion.
iN de rev b BOM there are 14 resistors listed, in the pakkage there are only 11 resistors
confused.
My guess is you are looking at the wrong parts bag. The resistor bag for a VP25 or VP26 will have 14 R's, 1 red LED and 2 4004 diodes in it. The bag with 11 R's will have a label that says VP-Gainswitch. Those are the R's for just behind the Grayhill switch, if you ordered the stepped gain kit.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: RemcoJVG on March 09, 2014, 03:03:08 PM
a quenstion.
iN de rev b BOM there are 14 resistors listed, in the pakkage there are only 11 resistors
confused.
My guess is you are looking at the wrong parts bag. The resistor bag for a VP25 or VP26 will have 14 R's, 1 red LED and 2 4004 diodes in it. The bag with 11 R's will have a label that says VP-Gainswitch. Those are the R's for just behind the Grayhill switch, if you ordered the stepped gain kit.
Yea duh... lol

OK one finished and seems to work.
i noticed that it sounds a bit lowpassed, even a slightly bright
I also noticed that i got a high reading when probing on r14 (both vp26's)
I get 14 in stead of 10. does it matter?
I now start assembling the 2nd one. see if i get simmular results

Remco
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 09, 2014, 04:12:42 PM
You cannot accurately measure the DCR of a resistor while both ends are soldered to the PCB. Measure them carefully first. If you find the need to measure them after soldering, one end should be desoldered and lifted free from the PCB.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: RemcoJVG on March 09, 2014, 04:38:39 PM
You cannot accurately measure the DCR of a resistor while both ends are soldered to the PCB. Measure them carefully first. If you find the need to measure them after soldering, one end should be desoldered and lifted free from the PCB.

jeff,

tnx for the quik response

i did me measure them before soldering. i assume it was ok sinds it was for both pre's.
anyway i'm almost done with the second pre. i'll let you know

Remco
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: RemcoJVG on March 10, 2014, 11:18:08 AM
Ok, did some quik recordings...
I tried several instruments acc guitar, vox bas direct via dibox ect. and it sounds great!!!!! i am surprised how open it sounds. a bit of level balancing and panning and it sound already halfway like a record.
One thing that concerns me is (could be operation error) that on el. guitar it starts to clip very quikly.(it is not sateration)
I mean that in the DAW the incoming signal is something like -6 and the waveform is showing clearly chopped of transient.
It is realy a nastly crackling sound.

Remco

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 10, 2014, 12:49:48 PM
On both of them or just one? This is not normal. Could it be some converter setting or something other than the pre(s)? This type of outside issue seems to happen a lot and folks always think it's the pre. Not saying it's not, but for sure rule out any and all outside possibilities.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: RemcoJVG on March 10, 2014, 01:15:49 PM
On both of them or just one? This is not normal. Could it be some converter setting or something other than the pre(s)? This type of outside issue seems to happen a lot and folks always think it's the pre. Not saying it's not, but for sure rule out any and all outside possibilities.
both pre's, and yeah good chance something else is wrong. I checked on the converter(rme 3296) and in/output is set to +4, that should be correct.
i'll check it with an other pre later. see what happens
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pitol678 on March 10, 2014, 10:28:09 PM
Hi, so I've gotten a vp26 (and 28) going within the last month or so and they are fantastic sounding. However I can get neither of them to provide phantom power for a condenser, no other issues. I'm using a radial workhorse 3-slot unit so is there a way to test the unit specifically to see if it's the rack? Otherwise I'm at a loss, and even if I did get a test jig from CAPI, I'm not sure I am capable of diagnosing the issue. Any help would be much appreciated!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: orenradio on March 10, 2014, 10:54:08 PM
Pitol,

If you have the Cube, be sure to flip the 48v phantom power switch on the back.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pitol678 on March 10, 2014, 11:30:04 PM
Oh...my...goodness...

Um yeah that was it. Im not sure if I am relieved or embarassed  :o On the bright side I put together the units correctly, on the other hand, its like saying saying "my car wont start" and someone asking "did you put gas in?" Then Im like "are you kidding me, of course I...oh wait" As a disclaimer, this is my first 500 rack  :-[

Well thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on March 12, 2014, 11:45:35 PM
Jeff, Can you post the instructions for testing these pres with an injected sine wave signal? Your posts say that it's available on the first few pages, and I've looked, but it's a bit of a goose chase on here.

Thanks,

-Pittsburgh
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 13, 2014, 10:15:49 AM
I am out of town for a few days so won't be able to post any full details like that until next week.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Houstnwehavuhoh on March 24, 2014, 04:13:07 PM
Hey there,
So I built a few of these a couple weeks ago and all of them were working perfectly, however today I went recall a session from yesterday and ended up just switching the order of two of the pres and noticed the ones I used today on a particular instrument was about 4db quieter than the other I had used. I double checked the pres against each other and it was in fact quieter. I checked all cables, level settings, mics, knobs were aligned correct, etc etc so I know it is the preamp thats causing the signal different.

So I was wondering what I should check? I thought it was the opamp because I had one start making some noise before but that was just from a bad solder joint that was fixed. Thanks for the help
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 24, 2014, 05:48:26 PM
Is it variable or stepped gain?

If stepped, I would first compare all the R's behind the GH switches. And if stepped, I would check the 2 pre's against each other at all preamp gain settings.

Next check all other R's. Maybe something got switched around accidentally.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on April 26, 2014, 02:42:43 PM
Jeff, I'm not getting adequate signal from my VP26. There are three issues here. Sending a mic level signal through my lunchbox only comes through when my gain pot is set to full, and does not result in enough gain, the phase switch kills all signal, and the attenuate pot works in reverse where the pot set to 0 on the face plate results in a fully attenuated signal, and 0 passes signal. I have passed all tests listed at the end of the install guide, and am passing signal with both dynamic and condenser microphones, but the signal is distorted and requires the stepped gain as well as the input attenuate pot, (in reverse,) to be set to full. The output transformer is wired to the PCB properly, and I have also swapped out the pre built GAR op amp with a JH990C that I know is in good working order. I also know my lunchbox and the connections from it to my UA Apollo to be tested and in good working order.

Can you send me the exact link for the posting or page number on this thread that involves signal injection for testing the VP26? What other suggestions do you have for getting this unit to go?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on April 26, 2014, 02:43:26 PM
  Picture two.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 27, 2014, 09:58:40 AM
Some of these symptoms combined makes me wonder about the output transformer. Desolder all of the leads and measure DCR between them. Set your DMM to a range of less than 100 ohms. Start at one end of the colored leads and measure each lead to all of the others. You should have DCR between only 3 sets of windings.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on April 30, 2014, 05:57:51 PM
Jeff, measuring the output transformer leads has me slightly concerned. For this measurement I have to say that my DMM never quite settled on any of the measurements, and every time I measured I noticed significant changes compared to the last test. I also noticed that the orange and red was the most significant/solid reading by my DMM, but moving the red lead, (without touching or allowing any of the other connections to touch one anther), caused my resistance level reading to change significantly beyond the less than 30 ohm level.  If I had to average my findings I would say the following:

BLACK   BROWN   36 Ohms
GREEN   BLUE   26.6 Ohms
ORANGE   RED           21.7 Ohms

After your last suggestion to test the output transformer I realized that I had done this at your request months ago, these are the numbers that I came up with then. I didn't document it, but I suspect that my measurement numbers were inconclusive then too, and that these numbers were taken as an average.

Black & Brown: 22.7 Ohms
Red & Orange: 14.4 Ohms
Green & Blue: 23.4 Ohms

-P
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on April 30, 2014, 06:10:24 PM
Was your DMM set to a low range like less than 50 ohms? Depending on the DMM, the readings should not change when moving them around. Make sure you are not touching the leads with your fingers.

Otherwise these results are correct. That tells me the polarity switch is most likely a bad solder joint. All that switch does is flip the red and orange leads to the 2623-1. My guess tells me that it could also be a bad solder joint on the t-pad.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on May 01, 2014, 12:55:52 PM
Jeff, My DMM is a full auto sensing meter. I'm using an ideal 61-312. If I need something that tracks in a lower range to perform this test with better accuracy I might be able to borrow one.

I checked and reheated all t-pad and switch terminals with the same results. I see no bridged connections, and have ruled out cold joints.

I'm running out of ideas here for how this unit continues to not function. Please advise on how I can get it to go.

-P

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 01, 2014, 12:59:53 PM
You can scroll back and find the injecting signal pointers. It is pretty easy to do. You need to send a sine wave tone into the pre (-40dBu @ 400Hz) and use the schemo as a road map to "follow" the signal and see where it stops.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on May 14, 2014, 07:27:34 PM
While doing some testing posted by Haima on this forum with my signal probe I was able to determine some questionable connections at the output section. See below:


F) now test the output all the way to the end - with your signal generator still connected as before, connect your probe "0v/sheild/ground" to the "black" lead on the output transformer or card edge pin 4.

G) probe the "blue" lead of the output transformer - got signal? if so,

I get no signal at this point.

H) probe the card edge pin 2 - turn the output attenuator - got signal? if not look at the attenuator wiring, everything on the output transformer secondary.
 
The turning of the output attenuator in any direction makes no difference.

Suggestions?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 09:39:03 AM
Do you have good signal at the primary of the 2623-1? That would be the red lead of the 2623-1 with the polarity switch out or disengaged.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on May 15, 2014, 12:06:13 PM
Jeff, With my signal entering at the O socket of the op amp and my probe set at the red lead of the output transformer I get good signal with the phase switch disengaged and no signal with the phase switch engaged. This is done without an opamp in circuit and the pre disconnected from the power supply.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 12:22:28 PM
OK this is good. With the phase switch engaged, the signal should be flipped over the orange lead.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on May 15, 2014, 12:24:26 PM
Yes, that's correct. Flipping the phase flips the output to the orange lead. Ideas?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 12:29:02 PM
Pardon me but it's hard to remember, have you fully desoldered the 2623-1 to test for internal shorts and open windings?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on May 15, 2014, 12:31:48 PM
Yes, I have done that. Our back and forth about this is actually on the last page of this support forum.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 12:39:48 PM
OK I just found that. Did you measure each lead to all of the other leads or only verify the winding pairs?

Right now we are at the t-pad and output transformer. There is nothing left it can be and I highly doubt its the t-pad.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on May 15, 2014, 01:31:50 PM
  Jeff, I checked all leads to one another and posted only the resistances that were noticed. Here's what I found:

BLACK   BROWN   36 Ohms
GREEN   BLUE   26.6 Ohms
ORANGE   RED           21.7 Ohms
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 01:51:54 PM
OK, well next remove the t-pad. Move the blue wire from the 2623-1 over to the hole near the gold fingers that says opt no t-pad. You can just splice/solder a short lead on if its too short.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on May 15, 2014, 07:28:49 PM
Jeff, removing that T-Pad is realistically going to destroy it, or remove traces from the board from my end. Without a desoldering iron I'm faced with the reality of reheating 13 joints and getting lucky with a pump, or cutting off leads from the top of the board and getting rid of the remaining leads. If that is absolutely the way to go I'm ok with this, but that T-Pad will never work again if that does indeed turn out to not be the case.

I'm not understanding why what seems like a failed transformer test by not getting signal when placing ground at the black lead of the OT and the probe at the blue wire seems to not make a difference here. If the writing made earlier by Haima is correct than I should be getting signal at this point, but I am not. 



G) probe the "blue" lead of the output transformer - got signal? if so,

I get no signal at this point.

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 07:35:57 PM
Well, its because the DCR measurements reported earlier tell us that the 2623-1 is fine.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 07:37:47 PM
Just humor me and move the blue 2623-1 lead over to the opt-blue pad near the gold fingers. I forgot that on this Rev of PCB that will bypass the t-pad.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 07:52:14 PM
Also, not sure what device you are using for a signal generator but you should have the opamp installed and inject signal into the pre's input, not the opamp sockets. The output transformer in an API mic pre circuit is a pretty heavy load that should be driven by a 2520 or similar. In your test scenario, it is most likely too much of a load since you are essentially connecting whatever you are using as a signal generator directly to the 2623-1's primary winding.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: pittsburgh on May 15, 2014, 07:55:38 PM
I'm having the same issue with the transformer blue lead going to the optional no tpad point. The problem must be related to the output transformer. My tests with an auto sensing DMM must be the weak link here, as I have no way to put my tester into a setting into the >50 ohm band.

I say this while testing with my pre assembled GAR 2520 in place and running signal through a powered lunchbox.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 15, 2014, 08:08:16 PM
Send me an email thru the store and I'll get a new 2623-1 out to you. Please include your full name.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Anacondaq on May 16, 2014, 11:36:01 PM
Hi jeff, i have had 2 kits of VP26 for quite some time now with gar2520 op amps. I built the first one and although it passes audio it seems its not quite right, there seems to be no low end and it sounds overly bright and buttons do not work correctly. Ie. the phase button changes the gain applied. I have gone over the whole board and preamp for dry solder joints and checked polarities. I'm pretty sure that theres nothing on the 2520 that is short circuiting, this is quite a fine circuit and i did my best! i do need an iron with a smaller tip though.

Unfortunately this is where my trouble shooting knowledge ends and sifting through this long forum, although it probably already has the answers im looking for, begs the question of what to check next and how to test it?

Thanks in advance

Ben 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Reverend on May 28, 2014, 12:17:28 AM
Hello to all. Does anyone have any idea when Jeff is going to have more VP26 kits available? Floor PSU for the 51x too?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mhuss on June 20, 2014, 10:36:15 AM
I have a pair of stepped VP26s I built a while ago, but just started using them as a pair, and noticed their gain is mismatched a lot, perhaps 20-30db! I carefully checked that all the resistor color codes match on both units and I'm pretty sure I measured them all when I built the preamps as a safety check.

I swapped 2520s but it made no difference. Can you suggest anything else I can check? Is there any way a transformer could be bad?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 21, 2014, 04:36:15 PM
It could be a cold solder joint. It will not hurt to reflow the solder joints real quick. The next step will be injecting a sine wave and seeing where the levels change from pre tp pre. There are some steps earlier on in the is thread on how to do this.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: mhuss on June 22, 2014, 12:19:27 AM
Arrgh. I need a couple of those 500 'extender' boards, troubleshooting these 500 modules in the rack is a pita...

--mark
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: gabygab on August 20, 2014, 09:54:37 AM
Hello! I just wanted to take a second to thank Chunger and Mr.Steiger for the great support and great products!

To all the lurkers around here that might be afraid to jump on the DIY bandwagon, take it from me. DO IT! These builds are fun and straightforward. I feel great now that I've finished them and I only want MORE! Also, they sound amazing!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: midnitestudios on September 05, 2014, 01:24:42 AM
Where can I get the bom for the new vp25?
thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 05, 2014, 09:30:30 AM
Where can I get the bom for the new vp25?
thanks!
Support doc emails have been sent out for all open orders. They often end up in spam/junk folders for some reason.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: burglar on September 18, 2014, 05:35:27 PM
Hi folks,

I have a strange problem.  I've recently built x2 sound skulptor MP 12 api clones with EA2622's, EA2503's & GAR2520's.   Upon firing them up I had EXACTLY the same distortion as is in the soundcloud link below.  The problem was identical.  Fizzy distortion that reacts to input (is only audible with signal) and increases when I turn the output pad up.  If I bring the output pad down and increase the gain, things begin to clean up (example in clip). This distortion does not always start with power up, it can take 10-20 seconds to creep in.

After the opamp in the sound skulptor builds there is a Servo / DC offset option including jmp3, P3, U1 & JMP4 as per this schematic http://www.soundskulptor.com/pdf/mp12-schematic.pdf (http://www.soundskulptor.com/pdf/mp12-schematic.pdf) I omitted this option under the advice of Jean Pierre, set the GAR's to +/- 15.5v & rubbed down the underside of the GAR's with isopropyl.  Since then the preamps have been working fine so I thought all was cured.

Just last night I built a VP26, stole a gar from one of my sound skulptor modules, installed it in the vp26, installed the vp26 in a lindell 510 and powered up.  I was surprised to hear exactly the same distortion as I had mith the Mp12's !!

The only conclusions I have been able to draw are that the lindell rails are +\- 16v ass opposed to 15.5 which should no difference really?

The problem is opamp based even though they appeared to work fine in the other pre's.

I used the same kettle lead from the same socket as the sound skulptor pre's so if there is some AC problem it could have been that?

I have built a new computer recently but this doesn't sound like interference?

Any help is much appreciated.  I am a newb and am vexed at this stage : /

https://soundcloud.com/overtoneuk/vp26-distortion/s-ysRkP

Ed
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: clearkutz on September 22, 2014, 03:16:17 PM
Hello i am in the middle of my first build i am a newb but i have have took on this with having researched for quite a while and i have to other people to rely on that have some experience with building electronics as well as standard equipment for compiling these preamps together. after carefully going over the instructions provided for the build both of the preamps are together and when powered up everything is ok (nothing is blowing up or burning out but there is no audio :( when pushing in the mute and polarity buttons there is a spike in the channel metering ..this does get louder when the gain is increased but there is still no audio being passed .. the pots do nothing as far as audio is concerned I'm also not sure if i am getting power to the led as it doesn't work either for phantom  i have used two mic to test phantom (one that requires and one that doesn't ) and still nothing … i have place pics below am i missing something ?? what should i do to trace where there is a problem ?? thanks in advance for any advice …

this is my first build but i feel if i can get one to work i will know how to ensemble them from here on out
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on September 22, 2014, 03:39:35 PM
The phantom LED is most likely in backwards. Is the opamp a kit or prebuilt? If a kit, I would suspect it is not working properly.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: clearkutz on September 22, 2014, 05:34:48 PM
i thought that maybe the led is in backwards and the op amp is a kit that i built  and i am willing to by a prebuilt one to test .. i built the opamps first before buying the kit just to see if i could get it down and honestly they went pretty smooth how do you test to make sure it is operating correctly ??  i have a multi meter   also the problem sounds like it stems for the opamp and not anywhere else ?? here is a pic of the op amp
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: midnitestudios on September 23, 2014, 02:06:16 AM
Just finished building my vp25 but i am not getting any sound. The led turns on when i flip the 48 switch.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: midnitestudios on September 23, 2014, 02:29:40 AM
I switch the red dot opamp with gar2520 and it started working. Any ideas?
Thanks!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: clearkutz on September 26, 2014, 12:54:11 PM
so here is a little update i was able to get the preamps working Success!! i didnt put the 10 k resistor in the r1 spot on the pcb it does say it in the instructions but in the pictures it is not populated so i didnt put that resistor in ..this also solved my problem with the led and everything is working great !!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: weiss on November 29, 2014, 06:58:59 AM
done :)
(http://i62.tinypic.com/5v98g7.jpg)
but still got problems fitting the push buttons between the two metal plates.. seems like i have to resolder them
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on November 29, 2014, 10:57:46 AM
.....but still got problems fitting the push buttons between the two metal plates.. seems like i have to resolder them
The only thing that explains this is the switches are not soldered tightly down to the PCB. There is a small flat spacer on each end of the PC pins. Use a magnifying glass to make sure both of those on each switch are tight to the board.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: weiss on November 29, 2014, 11:23:25 AM
.....but still got problems fitting the push buttons between the two metal plates.. seems like i have to resolder them
The only thing that explains this is the switches are not soldered tightly down to the PCB. There is a small flat spacer on each end of the PC pins. Use a magnifying glass to make sure both of those on each switch are tight to the board.

Actually not. They are completely on the pcb. And when i tighten the screws of the potentiometers the L-Plate does not correctly align with the front plate and so the buttons stick together with the metal framework. Buttons and potentiometers show into slightly different directions
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on November 29, 2014, 11:46:00 AM
It must be the alignment of the pots then. The PCB, L-bracket and faceplate should be assembled together before the pots are soldered.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: gunner666 on December 23, 2014, 05:40:11 PM
Hi All-

   First post here but there's a ton of great knowledge on this forum I've been checking out.  I built a VP26 stepped gain pre over the past few weeks.  Super fun to build and everything is super high quality.  Nice work Jeff.

  I'm having one problem.  Recording into a DAW and looking at the waveform reveals that half the wave has considerably less amplitude than the other half.  This reverses with the phase switch and is clearly audible.  Both the VP26 and the Gar2520 (and the 51x rack and power supply) were new builds so I ordered a Gar1731 to see if the problem went away.  It didn't, so unless I made the exact same mistake on two different opamps the problem must lie with the VP26.  I've reflowed every joint and inspected everything with a magnifying glass and don't see any bad joints or solder bridges.  I pulled the output transformer and it measured with correct resistance and no shorts. 

  Anyone have any ideas what else I might look for?  I just ordered a cheap signal generator to go with the scope my grandfather gave me a few years ago, I figure this problem is a good exercise to learn how to troubleshoot with a scope if no one has a quick solution.  Does anyone have any tips for using a scope?  I gather the general idea is to hook the signal source to the input and then trace the circuit with the scope to see where the waveform gets distorted.

  Attached is a photo of the wave in logic swapping the phase a few times during an acoustic guitar part. 

  Thanks in advance for any advice!

-mike
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: weiss on December 24, 2014, 05:41:26 PM
I experienced a massive distortion when going out of my RME interface into the preamps and back to my DAW. i have to lower the send gain to about -60dB to prevent distortion but then the output signal is very low again.
Is this normal? what can i do if i want to integrate the preamps as an external effect on a buss and not as a gain stage?

thanks for your answers
weiss
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Dr Gris on December 24, 2014, 06:02:19 PM
I experienced a massive distortion when going out of my RME interface into the preamps and back to my DAW. i have to lower the send gain to about -60dB to prevent distortion but then the output signal is very low again.
Is this normal? what can i do if i want to integrate the preamps as an external effect on a buss and not as a gain stage?

thanks for your answers
weiss

For connecting line level into a micpre I've built pads. Have a look at this:
http://www.uneeda-audio.com/pads/

Best
//M
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: weiss on December 24, 2014, 06:07:59 PM
For connecting line level into a micpre I've built pads. Have a look at this:
http://www.uneeda-audio.com/pads/

Best
//M

unfortunately, lowering the signal from +4 to -10dB does not make any change, as well as enabling the "pad" mode on the preamps. Still distorting.. I never had any problems with my other 19" gear in my studio, so that's basically why i ask.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 24, 2014, 07:11:14 PM
Just build a simple u-pad with 4k99 series R's and a 160R shunt.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: weiss on December 24, 2014, 08:48:33 PM
Just build a simple u-pad with 4k99 series R's and a 160R shunt.

Ah okay. Did you guys integrate this into your modules or outside the lunchbox?
sorry but i am completely new to this..
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 24, 2014, 09:41:08 PM
They can be built into Switchcraft XLR tubes like these http://classicapi.com/catalog/product_info.php?cPath=84_85_165&products_id=336
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Dr Gris on December 25, 2014, 03:09:35 AM
Just build a simple u-pad with 4k99 series R's and a 160R shunt.

Ah okay. Did you guys integrate this into your modules or outside the lunchbox?
sorry but i am completely new to this..

If you scroll down in the link I posted, there's a little picture tutorial.

Best//M
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: weiss on December 25, 2014, 06:59:18 AM
Thanks guys, this is what i searched for ;)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: weiss on December 25, 2014, 04:33:26 PM
Okay, now i lowered the input signal so i can pull it up afterwards in the DAW (works as well).
But apparently i have some strange distortion anyway on either of the two preamps. Just hear for yourself..
(rename txt to zip first) :)
Numbers are the relative positions of the knobs
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: gunner666 on December 27, 2014, 10:41:20 AM
Hi all-

  Hope you're holidays were good!  Just bumping post #645.  I think it got buried by all that useful u-pad info.

-mike
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: [silent:arts] on December 27, 2014, 11:00:32 AM
Hi Mike,

this is normal. nothing wrong.
most acoustic signals ARE asymmetric  ;)

do you have any other preamp to compare?
you will see  :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: gunner666 on December 27, 2014, 11:09:20 AM
I wondered that at first so  I also tried the same source/mic/cable/converter with my vintech x73 and didn't have the audible change in sound when I used the polarity switch.  The audible difference when using the polarity switch on the VP26 is very pronounced, one setting is very bass heavy and on the other the bass nearly disappears and the the mids are very pronounced. 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on December 27, 2014, 11:15:46 AM
The polarity switch should not make a drastic tonal change. I imagine you have a cold solder joint on either the mute and/or the polarity switch. Also double check you wiring for the output trafo as well as the soldering on the t-pad.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: gunner666 on January 01, 2015, 03:16:30 PM
Hi All-

  Thanks for the help so far.  A quick update.  I reflowed all the joints again, then desoldered, removed and tested the Tpad and replaced it (not fun, wow).  I checked for bridged connections as best I could with a multi meter and triple checked the output transformer wiring and component values and placement.  No luck yet.

  I did learn to use my scope and signal generator though, so even if this pre never works I've gained a bit of knowledge.

  Here's what my scope shows, and please feel free to correct my beginner mistakes.

  I connect the scope and signal generators ground wires to pin one on the card connector.  With the other lead of the signal generator I inject a 1K sin wave at R3.  The scope probe shows the sin wav makes it all the way to the Opamp with no issues.  Post Op amp the amplitude of the sin wave grows as I expected.  With the phase switch out the sin wave shows up at the red lead of the output transformer and not at the orange, phase switch in shows the opposite.  The mute switch eliminates the sin wave at both the orange and red leads.  Unless I'm missing something this all looks good.

  Where it starts to look funny is with the phase switch out the sin wav shows up at the Brown, Green and Black leads at about half the amplitude of the red but the blue lead shows a slightly higher amplitude than the red lead.  The phase switch moves the larger amplitude sin wav to the black lead.  The Tpad has no effect on the sin at the green or brown leads but both the black and blue lead's sin waves are slightly higher amplitude at the extremes of the Tpad and slightly lower amplitude at the center of it's travel.

  At pin 2 of the edge connector you get a large amplitude sin wav with Tpad fully up.  As you turn the Tpad down the sin diminishes to zero amplitude and then back up to half amplitude when the Tpad is all the way down.  Pin 4 on the edge connector shows a similar phenomenon except the amplitude is not as high as pin 2 when the Tpad is all the way up and it doesn't diminish all the way to zero amplitude.  If you reverse the phase switch Pin 2 does the same thing but opposite and pin 4 does the same thing except with a large amplitude sin wav.

  I am now stuck,  thanks so much to anyone that has any ideas.  If anyone can confirm I'm using the scope right I'm thinking I'll post a few photos of how to hook things up and trace the signal.  Might be a useful post for some other guys.

-mike
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jeid on January 01, 2015, 05:26:51 PM
Just wanted to thank Jeff for providing such a great product. Got my pair of VP26's yesterday and I put one together then and another one together today (with a hangover, so it shows how simple it is to do!)

I got the Gar2520 kits as well and they were a bit easier than I expected. A little fiddly but both great.

Chunger's guide was so helpful, the only thing missing from it was the LED install, but I managed to figure that out myself. I'll be looking to get a couple more in the next couple of months I suspect.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: epresalex on January 15, 2015, 12:29:24 AM
Hey guys and Jeff,
Was all excited to get my vp26 built up and running the other day once I finally got the free time, made sure to read through the addendum as suggested and was following 'chungs  incredible documentation quite attentitively, when I got a little cocky (and perhaps overly buzzed) and made the wonderful mistake of soldering the t-pad pretty much flat to the board...

Can't say I know what I was thinkin, lined both pots up to the L bracket before hand and believed I knew what I was doing but for whatever reason didn't flatten the pcb front end with the side of the L bracket/ front end screws and nuts. So I've been trying to think of a clever way to inch the tpad from the board without ruining everything, but there are so many legs on the thing it seems pretty impossible. Just wondering if anyone might have any miraculous ideas before I just snip and desolder all the leads and order a new $30 attenuator.

Thanks guys,

-E
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 15, 2015, 09:25:42 AM
Desoldering the t-pad is the only choice you have. The cheapo desoldering pumps from Rat Shack are not great but should get this done and save you from buying a new t-pad. Otherwise invest in a Hakko desoldering tool and have some fun. They are awesome and if you do a lot of DIY it will be a great tool.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: epresalex on January 17, 2015, 02:47:33 PM
Used a slightly better quality sucker from work with a little bit of added patience and was able to get it free enough from the pads to align pretty well. And according to my meter it still works!!! Doesn't look quite as nice as I'd like on the board (flux city) but after taking some alcohol to it it should be a bit more presentable. Thanks for the vote of confidence Jeff, I guess I just got a little over frustrated.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Flukes on January 21, 2015, 03:32:22 AM
Hi guys,

Just finished building a pair of VP26's and I'm having an issue with noise. Let me add that I am most certainly  new to DIY electronics (first build) and pro audio.

Is this normal? Could it be a grounding issue?

I've tried to attach an mp3 sample of the noise but the file format isn't accepted? Anyway around it? Clearly also new to forums!

Chung thanks for the guide and fun build Jeff!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Flukes on January 22, 2015, 07:18:32 PM
Hey fellas,

Giving this a cheeky bump.

Here is the noise sample. Dropbox Link [https://www.dropbox.com/s/v5zcgkd2p6r9x1p/VP26%20%281%29%20Noise.mp3?dl=0]

Any help tracking this bad boy down would be much appreciated.

Thanks!



Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Flukes on January 23, 2015, 10:04:46 PM
Some additional info.

a) I have made two of these pre's both of which are making the same noise.
b) Both are fitted with pre assembled GAR2520 DOA's bought from Jeff.
c) I have ruled out the following:
- Rack slot
- Cabling
- MR816X audio interface (noise still apparent when VP output goes direct to Monitor ins)
- Mic (noise still apparent with SM57 and Rode NT1A)

Notes:
- The MR816X pre's do not make the same noise
- I placed all transformers away from the mic cable and Lindell 10 cable but this does not diminish the noise
- During testing the amount of noise increases as the preamp gain and output attenuator increase
- The audio sample was achieved by Rode NT1 > VP26 > Interface. The phantom power was not engaged on the NT1A and both VP26 knobs were fully cranked.

Let me know if you have any ideas!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on January 24, 2015, 12:08:59 PM
Well, seeing as how you have 2 pre's that are both behaving the same exact way, I would look at an outside cause. Under normal gain conditions, the pre's are very quiet. If you crank the input gain wide open, there will be some noise. Is there unacceptable noise at normal operating conditions?

I am not a DAW guy but have heard reports from a few customers with similar issues and then later report back that it was some setting on their convertor or something.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: burglar on February 03, 2015, 02:44:06 PM

Hi Folks,

I built my VP26's about 2 months ago.  I only had a chance to test that they passed audio quickly and last night got my first opportunity to do some tracking.

On power up I noticed the attached noise.  This is high enough in the noise floor to be a problem.  It is present in both pre's though one a little brighter than the other.  It sounds like oscillating.

I'm using a Lindell 510, I don't have any other 500 series modules to test. however, when I heard the noise I pulled the leads and plugged them into two other pre's and the noise was gone so I have narrowed it down to the pre's or the lunchbox.

Have you guys any thoughts?

Channel 1 - https://soundcloud.com/sdosuk/noise-1 (https://soundcloud.com/sdosuk/noise-1)

Channel 2 - https://soundcloud.com/sdosuk/noise-2 (https://soundcloud.com/sdosuk/noise-2)
   
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Flukes on February 03, 2015, 08:21:34 PM
Hi Burglar,

I'm having the exact same issue (see above). I'm using a Lindell 10 Slot for power and the noise I'm getting sounds very close to channel 1.

I'm going to try one of the VP26's today in a different power supply. I'll let you know how it goes!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: burglar on February 04, 2015, 05:43:51 AM
Folker,

Very intrigued to hear your findings!

B
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Flukes on February 04, 2015, 06:15:32 AM
Hey burgler, didn't end up happening today. When it does I'll let you know!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: burglar on February 04, 2015, 01:30:59 PM
Flukes (sorry about previous typo)

Do you have any other 500 modules to test?  I wonder if it's a bad batch of 510's?

Anyone else have any thoughts on the noise?  Today I have tried one module @ a time, straight into a monitor speaker, both pre's exhibit exactly the same noise. 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Flukes on February 04, 2015, 07:54:06 PM
Not to worry mate.

No I don't have any other units to try it out with.

I have run the same test as you (VP's straight into monitors) with identical results, leading me to think that perhaps it's not the 510 anyway?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: burglar on February 05, 2015, 08:35:41 AM
I live near Absulote music where I bought it,  I'm heading in on Saturday with said lunchbox & pre's.  I'm going to try some other modules in my lunchbox & also try my vp26's in some other lunch boxes, hopefully this will expose the root of the problem :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Flukes on February 06, 2015, 02:17:30 AM
Let me know how you go burglar!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: chuckj on February 06, 2015, 04:04:48 PM
I recently built a pair of VP26s with the SL2520 Red Dots and stepped gain. They seem to function fine and sound really good and they both pass clean sine waves until the gain is pushed, no level jump with the phase switches etc. However one is about 6-7 dB louder than the other at the same gain and attenuation setting. This discrepancy is fairly consistent with most any gain stage variation.

Any ideas? I can compensate by running test tones and checking meters in my DAW, but it would be nice to be able to use these quickly as a pair without the extra calibration step.
Thanks!
chuck
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: burglar on February 07, 2015, 09:21:11 AM
Let me know how you go burglar!

Unfortunately can't make it there this weekend, have you had any joy your end?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Flukes on February 07, 2015, 10:02:12 AM
Dang I might be able to try the VP's in a workhorse on Wednesday.

Will let you know. Did you get your LED's working?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: burglar on February 07, 2015, 11:22:32 AM
Yeah, rookie move, wrong polarity, hasn't helped the noise any though :(
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: weiss on February 22, 2015, 10:25:36 AM
I bought two pre built vp26s from a local engineer. He said that one or both had some problems and he thought it might have been the gar2520 opamps. I went ahead and purchased some ml2520 from whistle rock audio. When I tested the vp26s with either opamps, I would get clipping at low levels. And it's not clipping at all times..I know it's not clipping going into my converter. I read up on this thread and found out I should reflow the solder. I did that and put it all back together again, triple checking each component and solder joint...I still have clipping. Don't know what I should do now...any suggestions?

having the same problems, distortion on lower levels (sounds grainy and stuttered). when input is increased to almost 12 o clock it goes away and "normal" coloration begins..

how did you solve the issue?
tested with gar 2520 and red-25 opamps

is it normal that the input gain knob is very noisy when turned?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OrganizedKonfusion on February 22, 2015, 09:18:47 PM
Just finished my VP26 last night! It sounds great! I really dig the layout and simplicity of this kit.  My only confusion is with the Grayhill pot. When I put the knob on where it made sense to me (pointing at the first marker on the faceplate) in the fully attenuated position, the set screw isn't lined up with the flat detented side of the pot. So after adjusting the gain for a little while, the knob will slip until it catches that part. Is there a way to adjust the stops of the Grayhill so that the knob lines up with the flat side of the pot and matches. I feel like I'm missing something obvious, but this is my first experience with  a Grayhill knob so maybe this is a just a quirk I have to live with? Or maybe I just need to really crank down harder on the set screws?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on February 22, 2015, 09:24:01 PM
Sadly, neither of the setscrews line up with the flat on the shaft. Its a bit of a bummer but par for the course with the Grayhills. I did check into full round shafts and the increase in cost was absurd. I line them up so that fully CW (wide open) is pointing down or 6:00. It may take a little fiddling your first time but very doable.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: OrganizedKonfusion on February 22, 2015, 11:01:25 PM
That seems to have done the trick! Thanks ! Great kit, cant wait to pick up some more in the future! :D
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Neil T on March 05, 2015, 11:53:41 PM
Hi Folks, just completed my first build of the Rev B VP26.  All is well other than no LED for 48v.  I have 48v, just no LED.   

Is the LED in backwards then?  Is there any documentation for the LED install?  I couldn't find it.

Huge thanks to CHUNG for his pics, can't wait for the updated detailed instructions from Jeff.

Thanks for any help on the LED.

Neil 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Neil T on March 06, 2015, 01:02:20 AM
OK happy to answer my own question on the correct LED install.  The LED is indeed polarised (long leg positive, short leg negative), meaning the long leg goes at the 'base' of the arrow on the PCB.

Best to all.

NT
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jonesey013 on March 06, 2015, 08:18:41 PM
Hello all,

I am almost through my first vp26 build. I noticed that in the new guide (on this forum), resistor R1 doesn't appear to have been installed. Should it be? I'm not totally clear on that. Thanks in advance for the help!

P.S., having a blast putting this thing together. Can't wait to hear it :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 07, 2015, 10:29:12 AM
R1 must be installed for the LED to work.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jonesey013 on March 07, 2015, 05:01:23 PM
Thanks for the quick reply Jeff. So, if I am not using the LED (which I think requires drilling a new hole for it), it should not be installed, or does it still need to be in the circuit?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 07, 2015, 06:10:16 PM
All kits come with the LED. It has been that way for some years now, so yes install that 10k R.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Neil T on March 07, 2015, 06:11:09 PM
Jonesey, check your faceplate. If you received a recent kit from Jeff you will have a hole already pre-drilled next to the hole for the 48v switch. 

Note my posts regarding correct install of the LED above.

Get to it!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jonesey013 on March 07, 2015, 10:42:49 PM
Gotcha! Thanks :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jeid on March 14, 2015, 08:07:50 AM
Hello, I got another two of the VP26's and managed to put them together rather quickly.  Was more sure of what I was doing this time.

I turned on one of the previous VP26's I have and it was making a horrible noise https://dl.dropboxusercontent.com/u/3526809/noise.mp3 (you might need to turn it up for the first bit, but it's very obvious towards the end)

I decided I'd try some trouble shooting. I tried the pre in a different slot to rule out the cabling/slot and the pre carried the noise to the other slot. I thought I'd swap the opamps over before looking for bad solder joints and the noise carried over to the other pre, so I'm narrowing it down to the opamp (self built Gar2520's). When I turn my lunchbox on, there's a very prominent pop from that one pre, but not the others.

Upon closer inspection, there's solder running down one of the millmax pins on the opamp. Trying to remove it has been tricky. I've managed to get the pin off but I can't get the solder off of the pin as it's wrapped right round it.

Is there a part number for the pins so I can order some from Mouser? I'd get them from Jeff, but I live in the UK so figure it would be quicker this way.

Failing that, I anticipate I'll be ordering another couple of pres, so I could just get a new Gar2520 kit then. I'll likely get a new socket for it to sit in, just in case any of the solder has scraped off.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 14, 2015, 10:41:07 AM
jeid, it sucks you are having the trouble but I am happy you are sorting it out. Sounds like you are close!

The part for the opamp pin is Mill-Max #3103200210000080
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jeid on March 14, 2015, 01:24:08 PM
Looks like Mouser are out of stock and it'll be another two weeks before they have any. I'm not in a huge rush, so I'll just get some when I order a couple of new pres.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jeid on March 14, 2015, 02:21:02 PM
Hmmm, after carrying out a further test, I swapped the opamp around and the original card made noise. Typically, after I just made an order for another opamp kit. Going to reflow the solder joints and test again.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 14, 2015, 02:26:44 PM
Are the opamps fully and properly seated? http://classicapi.com/catalog/DOA_Install.php
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jeid on March 14, 2015, 03:07:23 PM
Yup, looks good and I can't push it in any further. I'm confident it's not the opamp now as the same card was causing an issue with a different opamp. I've just reflowed the solder over everything and will test again. Cheers.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jeid on March 14, 2015, 03:46:17 PM
I retract my previous statement. Opamp to blame. I ordered one this afternoon so I'll get it built when it arrives in a couple of weeks :)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Jumpybuns on March 29, 2015, 03:08:15 AM
Hello,
I just put together my first vp26 but eveytime I try to plug it in to my lunchbox R6 starts to smoke and melt. Everything looks good and seemed to test as normal. Any idea what could be causing this?
Thanks for your time!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on March 29, 2015, 10:38:59 AM
Hello,
I just put together my first vp26 but eveytime I try to plug it in to my lunchbox R6 starts to smoke and melt. Everything looks good and seemed to test as normal. Any idea what could be causing this?
Thanks for your time!
R6 is the 200R for the phantom supply. I would look for a direct short or solder bridge.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: soundvscience on May 03, 2015, 12:13:38 AM
Jeff,

Just ran into my first problem with one of the VP26s I ordered from you. I'm building a full rack of VP26s as my first attempt at soldering (I'm probably a glutton for learning through mistakes) and actually have made it through the Floor Box PSU, 11 space rack and 8 preamps before encountering a problem. But still, I'm learning the ropes of PCBs and solder and I've no real idea how to troubleshoot this unit beyond what I've read in the past posts.

The VP26 I'm building right now appears to be set up correctly, however I'm getting a very low signal from the output and none of the pots or buttons on the front have any affect on the outputted signal. Phantom works just fine, but none of the pots add gain or attenuate the signal, the mute switch doesn't mute, and the pad switch doesn't pad. Not sure how that happens but I'm at a loss as to what it could be.

I took it apart and checked all my solder connections, fixed what may or may not have been cold solder joints, and touched up most of the solder joints just in case, but no change in behavior.

Any guidance would be much appreciated!

Andrew

P.S. - The 8 that I have finished sound absolutely fantastic. I'm using the stepped gain models with Scott's SL2520s and I'm beyond thrilled with them. I'm recording drums Monday through the lot and I couldn't be more excited!!!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on May 03, 2015, 10:06:47 AM
Using the schematic, inject a signal and follow it thru the preamp to see where it stops. The good thing is you have other working units to compare to. There is no magic bullet per se. It will require a bit of tech detective work on your end to sort it out.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: soundvscience on May 03, 2015, 05:54:52 PM
Looks like no signal injection will be necessary. It required very basic troubleshooting. Same problem occurred on the next unit I made so I swapped channels on a rack I had borrowed to test them at my house with and they work great. Something is up with my friends first channel, which is weird since its what I've tested the first 8 with.

At any rate, thanks for the help Jeff!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Eymi on May 22, 2015, 11:33:19 AM
Hi,

I'm just building my second VP312 (the first one worked fine right from the start - great kit by the way :) ) and i have got a question concerning one of the Capacitors:

The reading says 330uf 16V, but according to the BOM that came in the email form Jeff,  it should be 330uf 25V (the one in the first kit also says 25V). As far as my knowledge goes, i could use a capacitor if the voltage is higher, but i'm not sure if everything will be working correct if the voltage is 16V instead of 25V.

Does anyone can comment on this?

Greetings form Austria,
Chris
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Potato Cakes on May 22, 2015, 08:37:08 PM
If you are doing the VPR version you would probably be fine with 16V, but it would be safer to stick with 25V as it is in the instructions. I think the BOM says 25V to accommodate 51X builds which runs on +/-24V. Probably makes it easier when packaging kits.

Paul
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Eymi on May 25, 2015, 07:01:37 AM
Thanks for your response Paul,

I'm doing the VPR version of the VP312, so i guess using the16V cap in C8 will be just fine.

I found someone in the VP28 thread having the same problem with the cap in C12 and Jeff himself replied that he swapped out the   25V cap with a 16V cap, as the voltage in C12 is just around 100mV. However I can not find a schematic of the VP28 so i'm not shure where C12 in the VP28 is located, and if it is equivalent to C8 in the VP312.

Chris
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Potato Cakes on May 28, 2015, 12:35:00 AM
Well, to be absolutely certain, measure the voltage the voltage on C8 on your other 312 and that will probably give you your answer.

But since it is the VPR version, I can't think of any reason why 16V wouldn't work.

Let us know how it goes.


Paul
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 01, 2015, 02:44:57 PM
Sorry for the slow response. I was away for 10 days.

I have made a few small adjustments to the kits lately. The main thing is a decrease in voltage for the 330uF caps as well as the  470uF coupling caps. In typical operating conditions, neither cap should see more than 100mV across it so all is good here.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 10, 2015, 05:32:25 AM
Hi,

Just built my first VP26 and it actually works. Having a slight issue though, at high gains I'm getting a high pitched ringing at 6k and 12k, whether a mic is connected or not. Any tips on tracking the issue down?

Thanks,
Phil
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 10, 2015, 09:41:11 AM
What is the opamp and who built it?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 10, 2015, 11:41:07 AM
It's a pre-built GAR2520 direct from you....
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 10, 2015, 01:47:39 PM
It's a pre-built GAR2520 direct from you....
OK well not that then....is the opamp fully seated? http://classicapi.com/catalog/DOA_Install.php

I have never experienced this so I suppose I would inject a sine wave and probe thru the signal path to see where this oscillation starts.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 10, 2015, 03:04:37 PM
thanks Jeff, much appreciated
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 11, 2015, 10:38:36 AM
I think I may have put some resistors in the wrong place. Now...it's going really well, built a 2nd one, everything works, no funny noises.....except the gain pot doesn't do anything, only a slight issue. Any suggestions for that?

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 11, 2015, 10:47:16 AM
I think I may have put some resistors in the wrong place. Now...it's going really well, built a 2nd one, everything works, no funny noises.....except the gain pot doesn't do anything, only a slight issue. Any suggestions for that?
Most likely a bad solder joint somewhere between the 200R, the 330uF cap and the pot itself. Not seating the opamps fully can also be the cause.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: SoundOfRolf on June 12, 2015, 07:06:10 AM
EDIT: FIXED IN POST #728

Hello folks!

First of all great kit, documentation and all!

I have two VP26 kits and decided to build one at a time so if I made a mistake I wouldn’t double it. The first one worked perfectly except that the phase button seemed to change the sound somehow. I re-read this thread and noticed that other had had the same issue.
I have two Red dots so the problem shouldn’t be in them. Before I started to build the second one I checked the output transformer with a DMM as described in an earlier post. It was OK. Now I’ve finished the second one and the results are the same. Everything works great, but the phase button changes the sound. I’ve must have messed up somewhere again. :) I’ve triple checked component values, and gone through soldering every joint again, but no change.

To exclude external issues I’ve tried different slots in the Lindell 510.
Different cables and audio interface inputs.
When I fed the preamps sine wave or pink noise there weren't any notable difference, but when I fed them some music everything cancelled out except a bump peaking about 4k. See the attached picture. The music level was at about -20db. It was same in both units.

So any idea where I should start looking for a mistake or is this a feature of the output transformer? Or am I just too paranoid…

Thanks for the help!

EDIT: I think I'm suffering the issue as gunner666 states in post#645. I've sifted through the posts, but it seems that it never got resolved?

-Tony
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 12, 2015, 12:56:40 PM
....or is this a feature of the output transformer?
No this is not a "feature". Something is wrong somewhere. The most common issue folks have is bad solder joints. Since you are repeating the result with 2 different units, I am thinking there is something else going on with the test rig setup. I am no DAW guy but have had folks with similar issues report that is was some software setting or active plug-in that they didn't know was on. I would not test them this way but I have an AP rig. Doing phase sweeps in the past shows nothing more than a near identical inversion of polarity.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: [silent:arts] on June 12, 2015, 01:53:34 PM
When I fed the preamps sine wave or pink noise there weren't any notable difference, but when I fed them some music everything cancelled out except a bump peaking about 4k. See the attached picture. The music level was at about -20db. It was same in both units.

May I guess: the sine wave / pink noise signal generated in your DAW is Mono, and cancels out.
But the music is a stereo signal (at least I see stereo tracks in the screenshot)?
Low end is often near mono, this is why it cancels out much better.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 12, 2015, 02:24:59 PM
May I guess: the sine wave / pink noise signal generated in your DAW is Mono, and cancels out.
But the music is a stereo signal (at least I see stereo tracks in the screenshot)?
Low end is often near mono, this is why it cancels out much better.
Ah ha. Seems logical to me. Thanks Volker.  ;)
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: SoundOfRolf on June 12, 2015, 05:08:43 PM
Quote
May I guess: the sine wave / pink noise signal generated in your DAW is Mono, and cancels out.
But the music is a stereo signal (at least I see stereo tracks in the screenshot)?
Low end is often near mono, this is why it cancels out much better.

Nope. Pink or white won't cancel either.. The audio file is stereo. Track is mono. Feeding mono into the pre.
And I'm talking about the cancellation of recorded phase on and phase off tracks. Not canceling to the original track.
So no user error there. I first noticed this using just a mic and the sound difference was big.

Well no can do.I'll take them apart and solder the joints the third time :)


Thanks for the input!

-Tony
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 13, 2015, 06:57:15 PM
I think I may have put some resistors in the wrong place. Now...it's going really well, built a 2nd one, everything works, no funny noises.....except the gain pot doesn't do anything, only a slight issue. Any suggestions for that?
Most likely a bad solder joint somewhere between the 200R, the 330uF cap and the pot itself. Not seating the opamps fully can also be the cause.

Hi, I've resoldered all those bits and checked the op-amp, also tried different op-amps. any suggestions?

Thanks,

Phil
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 13, 2015, 07:58:52 PM
Hi, I've resoldered all those bits and checked the op-amp, also tried different op-amps. any suggestions?
Post a pic or 2 of the top of the PCB so I can see the colors on the resistors.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 14, 2015, 04:35:06 PM
Hi, I've resoldered all those bits and checked the op-amp, also tried different op-amps. any suggestions?
Post a pic or 2 of the top of the PCB so I can see the colors on the resistors.

Here's one....
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 14, 2015, 04:35:58 PM
and the other...
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 14, 2015, 06:40:31 PM
The R's look correct as far as I can tell in the pics. Either the gain is really low or really high. Do you know which?

What is your test rig?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 15, 2015, 05:13:38 AM
The R's look correct as far as I can tell in the pics. Either the gain is really low or really high. Do you know which?

What is your test rig?

It's a low gain setting, although the output is 6dB quieter than the other one I've built.  I think there is a dodgy connection in there somewhere, the signal occasionally dies and bumping the level of the test tone up and down brings it back to life. Not much of a test rig, just a multimeter and DAW. I'll sort a way of doing a signal inject.

Thanks.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on June 15, 2015, 10:15:13 AM
Sound like a bad solder joint. That is still my feeling for why the gain pot is not working. There is really not much to that part of the circuit. Are you sure the middle 3 leads for the gain pot are soldered? You would not be the first to have forgotten this.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: SoundOfRolf on June 15, 2015, 12:24:38 PM
OK. Phase button problem described in post #716 FIXED !!!

The error was so stupid I’m ashamed to tell you, but if this helps anyone in a similar situation this might save them some time, sweat and tears.

I first noticed the HUGE difference in sound depending on the phase testing with a mic and HEADPHONES. That’s the clue. The phase change cancels audio inside your head!!! I’d never thought of that. I’ve worked in studios for over 20 years and never ever tried changing phase with my own voice and headphones on. There’s never been need for that. We’ll after some great help from Gunner666 and studying the matter that was it. Live and learn. BTW different phase can help singers performance as they hear themselves better.

Well how does this explain the phase canceling effect I clearly was able to record?
Because I was sure I had made a mistake I never thought about an other more plausible reason. Now I’ve tested several mic pres high and low end stuff and they all have this same feature. Some more than others. Then it hit me. It’s the bloody self noise that’s never the same even if your audio is……

So sorry for the trouble.
Again great pre, great documentation, super support.

Next time I’ll think before I’ll post. :)

Yours,
Tony

Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: bulley on June 15, 2015, 02:57:11 PM
Sound like a bad solder joint. That is still my feeling for why the gain pot is not working. There is really not much to that part of the circuit. Are you sure the middle 3 leads for the gain pot are soldered? You would not be the first to have forgotten this.

Ha, my stupidity is probably at the root of all this but I did remember that bit. I think you're probably right though, I did a resolder and the gain pot works occasionally now so I just need to get it right
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Andersson on July 04, 2015, 12:38:00 AM
   Hi! I just finished my first ever build (VP 26) and I'm having a bit of trouble.

   The fuse on my power supply blew twice when I tried to test my new preamp. I haven't used anything in the lunchbox before so I don't quite know if it's an issue with the supply or the preamp.  The power supply/lunchbox is a Fredenstein Bento 6.

   I couldn't find any visual evidence of shorting (no smell either) and my solders look ok and without bridges.Is there anything you would suggest that could be the cause of it in case the problem lies with my build ?

   Other than that I had a great time putting it together and would like to thank Mr. Steiger for making me take the leap into DIY'ing!  :)

   Cheers!

  Andersson

   
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 04, 2015, 12:54:22 AM
What is the opamp and who built it? Is it installed correctly? http://classicapi.com/catalog/DOA_Install.php
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Andersson on July 04, 2015, 01:05:58 AM
   Thanks for your reply!

   It's the pre-built 2520 Red Dot. It's seated like the install guide says it should be. I have another unbuilt VP 26 kit with another Red Dot DOA that I will try as soon as I can get my hands on new fuses for the lunchbox.

   

 
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 04, 2015, 01:24:02 AM
If its a red dot then the opamp is most likely not the issue. I would think that only a direct short on the build would be tripping the PSU fuse. With the module loose, remove the opamp and check DCR from +V and -V opamp sockets to ground.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Andersson on July 04, 2015, 02:08:01 AM
  I went through the testing list yesterday and went through the whole list again right now and all measurements are above 200K Ohms. I don't have any power supply to complete the test list.

   I'll get new fuses today and I'll see if I can borrow a 500 series pre from my local music gear shop. That way I'll at least be able to find out wether it's my lunchbox or my build that's at fault.

   Thanks again and I appreciate all the help! 

   
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Andersson on July 04, 2015, 06:34:05 AM
   FIXED!  :)

   I got some new fuses and voila! Preamp works perfect with both DOAs and sounds great! Tested on different channels in my lunchbox to be sure and no issues what so ever!

   I guess I'll just have to do a shootout with the Lindell Pre-82 I borrowed from the local gear store. ;)

   
Quote
I first noticed the HUGE difference in sound depending on the phase testing with a mic and HEADPHONES. That’s the clue. The phase change cancels audio inside your head!!! I’d never thought of that. I’ve worked in studios for over 20 years and never ever tried changing phase with my own voice and headphones on. There’s never been need for that. We’ll after some great help from Gunner666 and studying the matter that was it. Live and learn. BTW different phase can help singers performance as they hear themselves better.

   You just made my life so much easier with that post (I'm a singer who records himself). Thanks SoundOfRolf!

   On top of it all, I got a message that my VP-26 Litz's have arrived aswell! This is the best weekend ever!  :D

   I forgot to thank Chunger for his wonderful guide that I used extensively for this build. Thank you Chunger!
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jgmille on July 05, 2015, 06:18:19 PM
Hey everyone, brand new to this board and the world of DIY mic pre's.  Just finished a VP26 with the Gar op amp.  Feel pretty good about my build and plugged it in with smoke and a burned out resistor in the R14 placement.  I may have had a short created with the solder from the op amp millmax pin that is right next door to it. 

Really not sure how to proceed with testing, etc - I have zero experience troubleshooting this type of thing.  Any step in the right direction would be appreciated.

Jason
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 05, 2015, 06:56:08 PM
R14 on the VP26 PCB smoked? The 1/2W 10R? That's kinda strange.

There are a few tips in the first post of this thread. I would start there.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jgmille on July 05, 2015, 07:00:53 PM
thanks Jeff,  I double checked and its the R14 10r.  I'll check the whole thread more thoroughly tonight.

Jason
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jgmille on July 05, 2015, 07:01:51 PM
actually to clarify, its the R14 spot on the GAR1731 op amp..
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 05, 2015, 08:52:05 PM
actually to clarify, its the R14 spot on the GAR1731 op amp..
Ah ok.

Best thing is to have a look at that specific support thread. I would look at the larger BD transistors though. Most common error on the opamp builds is turning and/or swapping those with each other by accident. They are NOT interchangeable.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Trench Studio on July 06, 2015, 04:18:47 PM
Hello All. Not sure if this question has been asked prior or not. I was curious if a stock 2520 DOA from a 3124 would work properly in the vp26? I noticed the pins on the api op amp were a lot longer than the purchased red dot. I didn't check for clearing issues yet either. Thanks in advance.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 06, 2015, 06:04:39 PM
Electronically, yes no problem. You will have to check the physical attributes though. You can trim those pins if need be.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: wirehair on July 15, 2015, 02:22:15 AM
Hello,

Testing my first build (a Classic API vp26) and I think that I have a problem.  When testing the voltage with no DOA installed I  get +16v at the v+ but at the v- I get -22v.  Should I be concerned about this?

 While setting up to test voltage with No DOA in using the test jig from Classic API I accidentally hooked up the header upside down and applied power.  I know….. totally newbie mistake I don't know how I missed it.  Would that cause a problem?  If so what might I have damaged?   I did test my API luchbox and it is putting out +16v and -16v. 

Thanks for the help
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: [silent:arts] on July 15, 2015, 06:07:54 AM
Are you sure your lunch box is putting out -16V?
If yes there would be magic involved having -22V in the VP26 module.

Sounds more like a blown -16V rail, which would be in the lunchbox, which for sure could have caused by powering the module upside down.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: wirehair on July 15, 2015, 12:54:34 PM
Ok, so with fresh morning eyes I figured out my voltage problem but I have one more question for some peace of mind.

So having hooked up the header upside down if I look at the schematic I see that I sent the +48v to the chassis ground which I don't think I need to be worried about.   But I also see that the mistake sent the the +16v and -16v through RV1 the output potentiometer and in to the output transformer.   Do I need to worry about having damaged the output transformer, output potentiometer, or any of the components that follow? 

Thanks for the help.  This is not a mistake I will make again…..I guess that's how you learn.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 15, 2015, 01:02:59 PM
If it was just for a short second or two I think you will be fine. I guess the true test will be once you get it up and running.
Title: Profile 4804 color code ?
Post by: okgb on July 20, 2015, 01:47:14 PM
 Profile 4804 A.P.I. type output transformer color code ?
any one have the diagram or know it ?

I'm building up a vp25 and using some profile output xmfrs ,
Does anyone have or can post the windings color code for the profile ?
I need to translate it to Jeff's vp25 board
I did get it working based on some info here, , but unsure it is correct
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ILR on July 24, 2015, 09:43:57 PM
Hey everyone, I just recently finished my build on a pair of VP26 pre's. They fire up fine and pass audio, but am running into an odd problem that two different users also seemed to have happen. The issue is, all functions work fine, pad works as it should, phantom, etc. But, the phase invert switch, when pushed, sounds as if some comb filtering is happening. It changes a normal sounding source into a mid rangy mess. There is also a significant jump in gain (volume) when the button is pushed. I went through all my solder points on one module and made sure everything looks clean. I do not see and solder bridges or dry sockets. Any suggestions or solutions are very welcome. I am new to DIY kits, but am having a friend that builds amps and pedals guide me and fix and bad joints. I am running them off a brand new Fredenstien Bento 10. Heres a picture.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 29, 2015, 11:39:14 AM
I did not check them but have you followed the wiring guide for the Litz 2623-1? The polarity switch is merely flipping the 2 wires of the 2623-1's primary so I would look for a solder issue with that switch or the mute switch or the 2623-1.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ILR on July 29, 2015, 07:46:52 PM
Yes, I followed the color to color swap and checked those solder joints as well. Everything on the main board looks good and have gone over it twice, could the problem be with in the DOA? I built the Gar2520 kit.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 29, 2015, 07:52:53 PM
Yes, I followed the color to color swap and checked those solder joints as well. Everything on the main board looks good and have gone over it twice, could the problem be with in the DOA? I built the Gar2520 kit.
Yes I think that has been the case before. Is it fully seated? http://classicapi.com/catalog/DOA_Install.php I have mentioned it a million times, it is very hard to troubleshoot a fresh module build with a fresh opamp build.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ILR on July 29, 2015, 08:15:19 PM
Yes sir. I have seated the doa completely, clicked and locked into place. I have read through most of this forum and have gone through most of the suggestions that seem relevant. As I have the new rev B with the new transformers and myself being a new diyer, I was not expecting a flawless success. I am at a bit of a loss after trying to clean up all my solder joints and double checking values and assembly instructions. It seems like it should be a fairly simple fix, but am unsure where the most likely foul up would be.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on July 29, 2015, 08:18:58 PM
Do you have another 2520 style amp around?
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: ILR on July 29, 2015, 08:30:45 PM
Not as of now, I left the preamps at my friends shop until Friday, when I'll be able hopefully sort out the issue and use them.  this is a pic from above.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: Trench Studio on August 10, 2015, 03:46:31 PM
I'm curious in what position should the output attenuator be If I wanted it fully open? I'd assume full throttle? And If I chose to bypass the attenuation entirely how would I do that on the PCB? And does bypassing it sound much different? I'd assume it reduces a little of the load on the transformer allowing it to breathe a bit more?

I'm sure this has been explained in this post somewhere and I apologize if so... but I was hesitant to scan 38 pages for it. Thanks in advance.
Title: Re: [BUILD] classicapi.com *VP2X, 500 Series Mic Pre Kit* Official Support Thread
Post by: jsteiger on August 10, 2015, 04:06:44 PM
Yes fully clockwise is wide open for the attenuator.

To bypass it, the best way is to remove the t-pad and then move the specific lead for the output trafo over to the pad near the edge connectors. It will be labeled [Opt no t-pad xxxxx] and then the color of lead to move.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: ninopelo29 on October 10, 2015, 11:32:14 PM
Hi All,

I've just completed building 2 VP26's and, wow, what a great build. The guide was great and the new site is super helpful. Such a good time to build!

My question is I am getting this crazy crackle when I engage phantom power on one of the units. The other is perfectly quiet.

I've changed the 200 ohm resistor, swapped out the switch, tried different cables and changed slots but still the crackle persists. 

I saw some posts by Brolik from back in 2011 in which he had the same problem but there were no posts about what he discovered the problem to be.  I sent him a message but he hasn't been active since 2014 so I'm not sure I'll get a response.

Has anyone had this same problem and, if so, how did you fix it?

Any help would be much appreciated!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on October 11, 2015, 12:30:12 AM
Sounds like a bad solder joint somewhere. Check the PB switch as well as the 120µF cap.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: ninopelo29 on October 11, 2015, 10:50:10 AM
Hey Jeff, thanks for the quick response!

So now I've reseated and resoldered:
• the LED,
• the phantom power switch
• the pushbutton Pad
• all 3 resistors in the phantom power line and
• the 120µF cap. 

I've tried it with two different red dot DOA's (both working fine in other units), I've tried the phantom power without the LED and switch in the circuit (direct wire between the switch solder pads) and I've tried it in different slots with different (good) cables. I even put the unit on a soft pillow to try to eliminate any stray vibrations in case a component was shaking in there!  :o

I can't get the noise to stop.

I've tried wiggling components to see if I can make it sound better/worse, but it just seems to fluctuate on its own independent of what I do.

Is there a component that could be failing or a part you'd recommend I change out? Maybe the 120uF cap? It's perfectly quiet with the phantom power off.

Thank you for all your help!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on October 11, 2015, 11:48:49 AM
Could it be an outside the module issue? Have you tried a different rack slot, cabling, mic etc?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: ninopelo29 on October 12, 2015, 04:07:26 PM
The sound happens without a mic or mic cable connected.  The only cable I have connected is the output 1/4" which makes no noise when connected to the second module.

I've tried every slot in my Radial Workhorse and the good module makes no noise in any slot and the bad one makes noise in every slot.

The noise only happens when the phantom power is on. When I initially powered the cards up, there was no noise, tho. It started making a slight crackle after about 10 minutes and then got full blown crazy after 15 minutes and hasn't stopped since.  It makes me feel like a part went bad...I'm gonna replace the phantom components and eliminate that as a possibility.

Can I order the components in the phantom power circuit from you?

...and thanks again for all your help Jeff! You rock, sir!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on October 12, 2015, 04:33:20 PM
The sound happens without a mic or mic cable connected.  The only cable I have connected is the output 1/4" which makes no noise when connected to the second module.

I've tried every slot in my Radial Workhorse and the good module makes no noise in any slot and the bad one makes noise in every slot.

The noise only happens when the phantom power is on. When I initially powered the cards up, there was no noise, tho. It started making a slight crackle after about 10 minutes and then got full blown crazy after 15 minutes and hasn't stopped since.  It makes me feel like a part went bad...I'm gonna replace the phantom components and eliminate that as a possibility.

Can I order the components in the phantom power circuit from you?

...and thanks again for all your help Jeff! You rock, sir!
For kicks, just try removing the 120µF cap ands see if that does it. If so I can send you a replacement.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: ninopelo29 on October 13, 2015, 02:44:38 PM
Hey Jeff (and All),

I'm stumped. I removed the 120uF cap and the noise is still there.

I resoldered all the components again and tested for continuity point-to-point across the whole pcb. Everything checked out ok, but the noise persists.

Here is a sample of the noise (I had to record it with my phone, so please turn down your speaker):
https://soundcloud.com/ninopelo29/api-noise-sample

Any other recommendations?

Thanks again for all your help, Jeff
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jeroberts on October 18, 2015, 10:41:34 PM
Hi all --

I am about to start my first VP-26 build and was wondering what the best kind of lab power supply is for testing them. 

I was looking at the one below, but I'm a newbie to DIY and I'm not sure if it could deliver enough voltage.

http://www.amazon.com/gp/product/B000CSQK5E?psc=1&redirect=true&ref_=oh_aui_detailpage_o02_s00
Title: VP2X~500 Series~ odd problem
Post by: okgb on November 02, 2015, 05:23:28 PM

 Having strange problem where polarity switch , seems ........... to either dim the signal or full waveform on one side of output ?
it's a pretty straight ahead circuit and I've built plenty before so this must be something stupid simple,  all resisters are correct
I'll pull the switch and check it out of circuit ,

Does this ring any bells with anyone ?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jeroberts on November 18, 2015, 11:01:07 PM
Hi All,

I am working on my first VP-26 build.  I finished my build and plugged the unit into my 500 series rack.  Everything was working perfectly for a few minutes, then there was a pop and the VP-26 started producing smoke.  Now it isn't working at all.  After a quick inspection, it looks like the one of the connections on the gain knob is the thing that blew.  Has anyone had this happen to them?  If so, what can I do to fix it?

Josh
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 19, 2015, 09:51:04 AM
Hi All,

I am working on my first VP-26 build.  I finished my build and plugged the unit into my 500 series rack.  Everything was working perfectly for a few minutes, then there was a pop and the VP-26 started producing smoke.  Now it isn't working at all.  After a quick inspection, it looks like the one of the connections on the gain knob is the thing that blew.  Has anyone had this happen to them?  If so, what can I do to fix it?

Josh
I myself have never heard of such a thing. Are you sure it was on the gain pot? I'm not imagining a way this could happen.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jeroberts on November 19, 2015, 11:04:33 AM
Hi Jeff,

I'm not 100% sure, but to me it looked like some of the plastic on the PCB was burnt around the gain pot.  Also, the smoke was coming out from that area.  I will take another look at it tonight and let you know if I find anything else.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 19, 2015, 11:18:15 AM
It was most likely the opamp.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jeroberts on November 19, 2015, 01:34:34 PM
It was most likely the opamp.

Ok.  How could I check to make sure it's the opamp?  Also, would that entail getting a new opamp or do you think I could fix it?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 19, 2015, 01:44:10 PM
It was most likely the opamp.

Ok.  How could I check to make sure it's the opamp?  Also, would that entail getting a new opamp or do you think I could fix it?
If you smoked something it should be kinda easy to spot. My age old rule of thumb, never start with a fresh preamp kit and a fresh opamp build. Too many variables to trouble shoot. You need to have one or the other in known to be good working condition. If its the opamp, its best to post in the respective opamp build thread.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jeroberts on November 19, 2015, 02:30:39 PM
Thanks, Jeff.  That's good advice to follow.  I'll take a look at the op amp to see if it blew.  I'm actually using the SL Red Dot op amp though, so is it possible that soldering it into the PCB the wrong way could result in smoke?  I messed up soldering the op amp standoffs and wound up resoldering them a few times.  There was some solder stuck in the bottom of one of the standoffs so the op amp actually wasn't going down all the way and I soldered a few of it's legs to the standoffs to keep it in place.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jeroberts on November 19, 2015, 11:32:09 PM
Quick update: I cleaned up the connections on the op amp and everything is working now.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: phanlon on January 15, 2016, 10:51:06 PM
Hi there,
Looking for some help. I just built a pair of vp-26s. Fired them up and one works perfectly. The other seems to be working but the volume is very, very low. With the gain cranked all the way talking into a 58 hits -38 in pro tools. Switched cables and its definitely the pre.

Want to know where I should start to look. I should add that the gain pot on the quiet pre doesn't feel smooth when it's turned.

Thanks
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 16, 2016, 12:37:01 AM
Rule out the opamps first. Are they fully seated? http://capi-gear.com/catalog/DOA_Install.php
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: phanlon on January 16, 2016, 12:58:32 AM
Swapped them between units. The quiet pre is still quiet. I have also double checked all of the resistor values. They are all as they should be. Not sure where to check next.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 16, 2016, 10:44:38 AM
At this point, you will have to inject a -40dBu sine wine and see where the signal stops. You will need to use the schemo as a road map. You should use the good working unit as your benchmark.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: phanlon on January 16, 2016, 05:36:59 PM
Got it. Just ordered the test Jig from your site today.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: bulley on February 16, 2016, 11:43:59 AM
Hi,

I'm having an issue with a VP26 that I built about 6 months ago. It's been working fine but the sound now distorts at low levels. If I bang a loud signal through it the sound briefly becomes undistorted again before the distortion fades back in. There's obviously a dodgy connection somewhere but I've re-soldered everything and haven't got anywhere. Any ideas what might be causing it?

Edit: I've also found now that with this module in the +16V light is blinking when I power up my lunchbox (Lindell 506). I think this is some kind of protection so there's something bad happening somewhere. It powers on properly after about 10 seconds.

Edit: SOLVED! One of the capacitors was shorting. Why it's taken 6 months to decide it's a problem I don't know but everyone relax, you can all stand down.

Thanks,
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: shaun_curran on February 17, 2016, 02:10:22 PM
I just recently built 4 vp26 pre amps.  One of them the output attenuater isn't doing anything.  It passes signal fine and the stepped gain input knob works fine.  Any Thoughts.  I switched out the DOA with one of the pres that worked perfect and it still doesn't work.  Where should I start my search for the problem?

Also, I have an issue with all 4 pres that sounded common to other people in this forum but I haven't seen any solution.  The phase switch seems to cut all the low end and does something with the mid range.  It's very obvious and I would never track anything with the phase button flipped with it the way it is.  Not a huge deal but kind of a bummer.

These things sound so great though.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on February 18, 2016, 12:07:10 PM
I would guess a bad solder joint on the t-pad or output transformer? The polarity switch will not change the frequency response at all if everything is built correctly.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: shaun_curran on February 26, 2016, 06:10:16 PM
T pad?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on February 26, 2016, 08:37:44 PM
t-pad = output attenuator
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: shaun_curran on March 01, 2016, 04:02:03 PM
Clearly I'm a newby.  I figured that out.  I resoldered everything on the board paying close attention especially to the output transformer and the t-pad everything looks good.  I'm gonna order another couple of kits.  So maybe I'll try to replace the t-pad with a new one.  Maybe I have a bad one.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on March 01, 2016, 04:17:46 PM
So maybe I'll try to replace the t-pad with a new one.  Maybe I have a bad one.
Very highly unlikely its the t-pad.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: shaun_curran on March 01, 2016, 06:45:58 PM
Maybe I have c10 backwards.  It doesn't have the bar indicating the negative side but I have it so the two ridges are one the bitten towards the ea2622.  This is how It was in all of the pictures I saw.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on March 01, 2016, 07:37:01 PM
Maybe I have c10 backwards.  It doesn't have the bar indicating the negative side but I have it so the two ridges are one the bitten towards the ea2622.  This is how It was in all of the pictures I saw.
That will not make a difference either but, they are marked. If you look closely, there are some "-" going down the body inside of a larger arrow(s) that point to the negative end. Also the groove is nearest the positive end.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Sinkia on April 08, 2016, 01:46:20 PM
Hi there !

We have ordered 3 Capi VP26, done the build, and had our first session today !

Upright piano -> schoeps (AB mode) & U87 below the keys -> CAPI VP26..

The sound of those units are really great !!!

Thank for it !
Cheers up to you !
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Spino on April 18, 2016, 07:07:14 AM
Finally had the time to build the VP26 and the GAR2520. It was great fun. Obviously enough (any tip here suggest not to go with both things built from scratch), the preamp would not work correctly. The closest 2520 that I could borrow is many kms away, so I thought I could try temporarly with a 2132 I had around. And it works! As suspected, the 2520 build got my eyes crossed :). But at least now I know where to look for.

Once again: great fun building it, great forum to read through.

Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on April 20, 2016, 05:42:30 PM
Finally had the time to build the VP26 and the GAR2520. It was great fun. Obviously enough (any tip here suggest not to go with both things built from scratch), the preamp would not work correctly. The closest 2520 that I could borrow is many kms away, so I thought I could try temporarly with a 2132 I had around. And it works! As suspected, the 2520 build got my eyes crossed :). But at least now I know where to look for.

Once again: great fun building it, great forum to read through.

It's really just practicing building the opamps. My first 3 or 4 attempts where failures because I went faster than I should have and didn't pay close enough attention to component placement, orientation, and had some solder bridges, which as you know is easy to do since you're cramming a bunch of stuff in a tiny space. My suggestion if you aren't already, is to use a fine solder tip and the thinnest solder possible. Give it a couple more tries and I'm sure you'll nail it.

No, Jeff does not pay me to tell other people to buy more stuff from his store.

Thanks,

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jaminem on April 22, 2016, 09:09:56 AM
Cleaning:

I have 2 x VP28,26 & 312 and they all are suffering from a sort of reddish tarnish on the front panels, making them look dull. Any idea how I can clean them safely to bring them back to their black/white/blue former glory?

Was thinking about lighter fuel but I don't want to burn the silk screening off....

Thanks
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: slangrj on May 08, 2016, 01:08:50 PM
Newbie question:
I just got my VP26 kit and I've got the REV B.1 - is it the same as REV B?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: 59flame on May 28, 2016, 03:34:11 PM
have a vp28  that the green signal light stays on constantly. Unit works fine other then that.   signal Light did not light constantly when first built but has started recently. Again all else works fine.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: savingpandas on July 16, 2016, 11:58:01 PM
Alright gents hopefully someone can help me out. I just built the VP26 Rev B.1 variable gain with litz transformer and the red dot DOA and during the 12.1 Tests from the general assembly guide I got these readings on the respective sockets for the DOA (which should have been over 200 kOhm)
- and O 20 kOhms 
+ and C 150 kOhms
all the others are over 200 kOhms though. I debugged every component to make sure they were in the right slot or orientated correctly, made sure there were no bridges and no cold solders, and made sure the switches were done as described in the trouble shooting tips along with the rest of the suggestions and am still at a loss. Anyone think they can point me in the right direction or share their unforseen errors? Thanks!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on July 17, 2016, 12:04:02 PM
Alright gents hopefully someone can help me out. I just built the VP26 Rev B.1 variable gain with litz transformer and the red dot DOA and during the 12.1 Tests from the general assembly guide I got these readings on the respective sockets for the DOA (which should have been over 200 kOhm)
- and O 20 kOhms 
+ and C 150 kOhms
all the others are over 200 kOhms though. I debugged every component to make sure they were in the right slot or orientated correctly, made sure there were no bridges and no cold solders, and made sure the switches were done as described in the trouble shooting tips along with the rest of the suggestions and am still at a loss. Anyone think they can point me in the right direction or share their unforseen errors? Thanks!
I think you are checking between opamp input - and O. That will be 20k since there is a 20k feedback R between those pins. The tests were described as +V and -V. Those are the voltage supply pins NOT the audio input pins.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 01, 2016, 05:10:26 PM
have a vp28  that the green signal light stays on constantly. Unit works fine other then that.   signal Light did not light constantly when first built but has started recently. Again all else works fine.

Do you have another IC to use for the LED control? Is it oriented correctly? Does it go away if you pull the IC? If everything is working correctly then I would see if the chip has not somehow gone bad. I had something like this when I first built one, but it was a faulty DOA I believe.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: rshake87 on August 18, 2016, 08:37:14 PM
Hi guys! I too have the green light problem happening. When I power up the unit, it passes signal perfectly with good tone, however the green light stays lit until the gain knob is turned to the center position. It then turns off and functions normally. Is there any way to remedy this? Thank you.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: blackartmixing on August 20, 2016, 08:21:25 AM
can someone help me with the transformer wiring for a Rev C VP26 please?  the wires don't match up with the PCB or the support documents.  i have, from left to right, black, red, grey, pink, purple, orange.  photo  attached
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 20, 2016, 10:29:30 AM
Those markings are for the Ed Anderson transformer. You have to go to Jeff's site and look at the table on Litz product page that shows which color lead of the transformer you have matches the label on your PCB.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on August 29, 2016, 11:06:33 AM
Finished up putting together a few VP25 kits, but I decided to use the Cinemag 3301 for output. I had seen a few people mention using this transformer in 312 builds. Builds went smooth,  but they are lower output, than my other CAPI modules. Basically, they are the same max gain as my others get with the pad switch engaged. Switch still works and pads further. Swapped between the GAR1731s that I built for the project and some Red25s that I keep as my tested opamps, to make sure it's not a build error on the opamp. Pretty much identical output, either way. The units sound good, but super low output.

So, Jeff suggests checking the transformer wiring, between the 2503 and the 3301. Unfortunately, there's no datasheet available for the 3301, on the Cinemag site, but Dave says it is directly swappable with a CMOQ-2 transformer, though.  The CMOQ datasheet is available, so I'm putting it below. The datasheets definitely look different, but I had always thought that the CMOQ and EA transformers all followed the same wire color. If anyone could take a look at them and tell me how to read it or what wires need to be swapped, I'd really appreciate it.

2503 datasheet
http://www.capi-gear.com/catalog/images/gallery/2503/2503-specs.pdf

CMOQ-2 datasheet
http://cinemag.biz/output/PDF/CMOQ-2.pdf

I just put the wires into the circuit, as labeled on the CAPI board. Skipped the T-Pad. Looking at the datasheets, I'm thiunking the problem might be elsewhere. Kinda strange that both modules ended up with the same error. I'm gonna check resistor bands to the BOM, this evening. Any help is much appreciated!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on August 29, 2016, 04:17:57 PM
Well, as far as I can tell, transformers are properly installed/leads soldered to correct pads. I'm gonna start checking to make sure I didn't swap a resistor. It would be weird, since both modules are giving the same low output. Totally possible, though! It's always like one little thing.

I've attached a photo of the top of one of the cards. It's a pretty clean build. No solder bridges, underneath. Anybody spots the boo boo, I'd appreciate the help. Kind of stumped, since everything seems to be where it should be going. One of the things I love about CAPI is the ease of building the units.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 30, 2016, 12:13:16 PM
You it seems that you have the T-Pad installed (the bourns potentiometer is a 600 ohm T-Pad attenuator). Move your blue transformer wire to other solder pad marked Blue.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on August 30, 2016, 05:38:14 PM
Just to make sure that I'm understanding correctly. With the T Pad installed, you can't just solder the wire to the optional pad, to skip it?

I installed the T Pads for cosmetic reasons (ie looking good when in the rack, but thought that wiring into the other pad would still skip it. Turning the T Pad has no noticeable effect on output. I had originally thought that might be the culprit, but since there didn't seem to be an effect from turning the T Pad, I figured that it wasn't interacting with the circuit.

Darn. I was hoping to not have the T Pads on these, but I have no idea how I could possibly unsolder tham.  Guess I should've done more research, before soldering them together. :(

I'll try moving that wire and see if this gets them operational!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 30, 2016, 09:13:51 PM
If that doesn't do it, and assuming all solder joints, component placement, orientation, etc are good, then send some tone through it and measure what you're getting at the +/- input of the DOA. If the above statement is true, then it has to be at the input transformer, the DOA, or the output transformer. It's a pretty simple circuit, so finding the problem should be easy.

Let us know.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 30, 2016, 10:04:55 PM
After taking a second look, the problem is your output transformer wiring.

Comparing the two data sheet, they have the same colors, but you'll notice that the 2503 has a single set of primaries and three secondaries, while the CMOQ-2 has dual primaries and secondaries. So when you solder the same color leads on your CMQ-2 to the labels on the VP25, you are actually putting one of the sets of primaries where secondaries are supposed to go, so all the electrons are getting very confused, hence, the lower output.

Go look at the schematic on Jeff's website for the VP25. It shows how the transformer should be wired. It is in a 1:2 configuration. Then look at the CMOQ-2 data sheet. Wire your primaries on your Cinemag parallel, with the + polarity going to Red on the PCB, the - side to Brown. The series connection for the output already in the VP25 circuit. The Cinemag green goes to PCB blue, blue to green, violet to yellow, and gray to orange. The PCB violet and gray will be unused.

The T-Pad can stay in place as you had it. That was bad information on my part.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on August 31, 2016, 10:47:21 AM
I really don't understand how to read the transformer schematic, apparently. Just trying to make sure I understand. In the end, I'll need to:

A. Leave Red and Brown where they are, but wire orange to brown pad and yellow to red, as well
B. Swap Blue and Green wires
C. Move Violet to Yellow
D. Move Grey to Orange

Is that right?

Because I'm trying to learn: Looking at the schematic, wouldn't this flip the phase? It would seem that I need to swap the above wires to Red and Brown pads, if blue and green are swapping?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 31, 2016, 12:32:56 PM
It seems it was late and my eyes were getting crossed looking at the schematic.

So, 50%  yes.

http://www.capi-gear.com/catalog/images/gallery/VP26/VP25-Rev-B-schematic.pdf

The polarity dots on the Cinemag and EA transformers line up per color, and on the VP25 schematic they are all opposite of both of those transformers.
 
Cinemag Brown and orange to PCB Brown. Red and Yellow to PCB Red. THEN, Green to green, blue to blue, violet to PCB orange and gray to PCB yellow.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on August 31, 2016, 01:16:24 PM
Thanks! Having the outputs and inputs seeming to flip sides really threw me, but these instructions seem right on, and with a little less soldering!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on August 31, 2016, 02:22:15 PM
Well, having tried it on one, this doesn't seem to be the culprit. Red and Yellow to PCB RED. Orange and Brown to PCB BRN. Green and Blue stay put.  Violet to PCB ORG and Grey to PCB YEL.

Strangely there's no change, as far as I can tell. Even with these wires changed, it seems that I have the same amount of gain, compared to the unit I haven't rewired and still far below the vp25 that I've already had. Even tried swapping OpAmps, again. Oh well, I'll try and get back to these in the next few days. I had gotten all hopeful, too!

It's kind of weird That the wire swaps seems to have no real difference in output.  Could it be that Red and BRN always went to the 1:2 wired BLU and GRN, making the wire changes unnecessary? Just spitballing, here.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 31, 2016, 03:05:41 PM
Okay, one more time. I need more sleepy time...

If you look at the schematic versus the 2503 data sheet, you'll noticed that the the secondaries are flipped in relation to polarity, but the connection for the center is still the same. So, look at it being rotated on that center line, then do the same for the Cinemag and line it up with the schematic.

Starting with the top of the secondaries per the schematic.
Cinemag - PCB
Gray - Blue
Violet - Green
Blue - Yellow
Green - Orange

Primaries still as previously discussed.

If that doesn't work then I'll get out my VP25 and do some voltage tests.

Let me know.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on August 31, 2016, 05:04:11 PM
Bizarrely, still no change, even with all the output wires swapped to these different pads. It wold seem like something should make some kind of difference.

Looking at the schematic, I'm even more confused. Then I thought back to the time I made some whistle rock 312s and my 2503-Ls worked perfectly fine, following the color codes marked for the Cinemag (obviously after following the 2503 to 2503-L conversion chart on the schematics. Taking that into account, the more I look at the schematic, the more it looks like your first suggestion was right, Leaving blue/green pair, moving violet and gray over to orange and yellow. Grey and Violet pads are obviously not in the circuit. It seems that this last wire swap would've flipped the phase, but I think that's pretty much it.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 31, 2016, 05:11:44 PM
Weird. You should be all even Steven. I've used these Cinemags in a similar circuit and it worked like a champ.

One of the things I did notice earlier is you mentioned that the problem preamps had the same output as the other ones with the pad engaged. That seems to me that there is something else going on. I'll pull out one of my VP25's and see if can get some voltages for you to check.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on August 31, 2016, 05:32:17 PM
Thanks a ton. I'll have to order the test jig, but I shouldn't have deleted it from my cart, anyway. This weekend, I'm gonna check all of the resistor bands, too. Caps are all where they're supposed to be.

I'm really just amazed that all of the wire flipping and no audible change as a result. I thought that I had the transformer going out 1:1, which seemed to be a rational explanation, especially with the pad functional. Was also what Jeff recommended looking at.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on August 31, 2016, 06:48:41 PM
Yeah, going from 1:1 to 1:2 isn't the same difference as the pad being in/out.

Okay, party time.

Generate a .775 VAC signal at 1k. If you're using a DAW, fire up its test generator and turn it up till the output is approximately -18dBFS. To be sure, take a mulitmeter and put it on pins 2 and 3 and see if you're getting about .775VAC. Some converter boxes are spot on and some aren't, so unless you know that you're I/O box is telling the truth, you need to meter it. Engage the PAD on the preamp before connecting signal to the preamp, with gain all the way down and attenuator all the way up. 

All measurements are with the -/COM side of the multimeter attached to one of the nuts holding the PCB to the L bracket. DOA used was a GAR2520, but they should be similar to a 1731. Set meter for VAC.

DOA In +/-  -  .409 for both
DOA out - .705
Pad - starting top row, closest to the faceplate - .320, .033, .030
Pad - bottom row, closest to faceplate - .320, .033, .030
Middle row resistors (R6-12) starting top left (R6) - 0, .322, .320, .320, .033, .322, .400, .705
Same row, bottom left - R6-R10 - all .030, .402, 0
C10 - both sides - .705
Output transformer
Red - .705
Brown - 0
Orange - .659
Yellow - .049
Green - .049
Blue - .676
Blue Bypass - .676

These are the easiest values you can test with the module fully built. Everything after brown is with a properly wired transformer installed.

Hope this helps.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on September 02, 2016, 02:17:50 PM
Test gig ordered. Thanks for all of the help, I really appreciate it!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on September 02, 2016, 03:27:53 PM
No worries. Let us know how you go.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on September 12, 2016, 10:21:45 AM
Well, turns out the mess up was simple. I accidentally printed out the Rev C BOM, instead of Rev B. The main difference is which resistors are listed as R2-4. After I swapped those to the correct positions and wired the transformers per your instructions, these seem to be 100%.

Thanks for all the help!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on September 12, 2016, 05:28:23 PM
Excellent!

It seems it is mostly something simple like that. Glad I could help.


Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: dissonantdissident on September 19, 2016, 08:29:31 PM
Turns out that the final issue I was dealing with was PSU noise, from my 500 rack. Now that I've got that diagnosed, I'm totally happy with these units. Thanks for the help!

ps- After looking at numerous sites/schematics, it seems that the quadfilar transformers can be wired different ways, but it also makes the schematic confusing. If they can be wired all those different ways that means the second primary wind can be a third secondary wind, like the 2503 schematic shows. I don't really understand how this would work, but if anyone cares to explain it, I'd appreciate the knowledge.

Check out these schematics to understand what I mean about primary moving to secondary:
http://layeredaudio.com/support/index.html
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: IndietownRecording on November 10, 2016, 02:20:40 PM
Hi, I'm having an issue with a VP26 I recently built.

The T-Pad output is least attenuated with the output knob in center position, with the output attenuation increasing as I move the knob left and right. It acts like the taper is wrong. It attenuates on both ends, and is loudest in the middle position.

The overall output is still really low, even at the center position.

I've double checked my transformer wiring and swapped out my opamp to a working SL2520 Red Dot.

Anyone have any ideas?

(http://i475.photobucket.com/albums/rr113/ajoel23/VP26_TOP_zpszlyvwden.jpg)

(http://i475.photobucket.com/albums/rr113/ajoel23/VP26_BOTTOM_zpsnpnmpld1.jpg)
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 10, 2016, 07:10:22 PM
Hi, I'm having an issue with a VP26 I recently built.

The T-Pad output is least attenuated with the output knob in center position, with the output attenuation increasing as I move the knob left and right. It acts like the taper is wrong. It attenuates on both ends, and is loudest in the middle position.

The overall output is still really low, even at the center position.

I've double checked my transformer wiring and swapped out my opamp to a working SL2520 Red Dot.

Anyone have any ideas?
I would desolder the leads for the 2623-1 and check to make sure nothing is shorted. Measure DCR of each lead against all others and report which colors have resistance. All values should be less then 50Ω so set your DMM accordingly.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: IndietownRecording on November 12, 2016, 03:36:20 PM
I would desolder the leads for the 2623-1 and check to make sure nothing is shorted. Measure DCR of each lead against all others and report which colors have resistance. All values should be less then 50Ω so set your DMM accordingly.

Thanks Jeff. Two questions: 1) should I measure resistance with the transformer leads in circuit? 2) should I apply power to the circuit when taking these measurements?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: IndietownRecording on November 12, 2016, 03:38:47 PM
Oh, and that's less than 50R? Not 50K or 50M?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 12, 2016, 03:40:59 PM
I will quote myself. Seems weird to say  :o

I would desolder the leads for the 2623-1 and check to make sure nothing is shorted. Measure DCR of each lead against all others and report which colors have resistance. All values should be less then 50Ω so set your DMM accordingly.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: IndietownRecording on November 12, 2016, 03:49:43 PM
I will quote myself. Seems weird to say  :o

Ha! Super sorry. I wasn't getting a lot of readings on my DMM and was second guessing myself.

Here's what I got:

Red against Green = 14.5
Blue against Green = 23

That's it. The rest were 0.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: IndietownRecording on November 12, 2016, 10:31:41 PM
I would desolder the leads for the 2623-1 and check to make sure nothing is shorted. Measure DCR of each lead against all others and report which colors have resistance. All values should be less then 50Ω so set your DMM accordingly.

Ok, so I just threw in a litz 2623 from another project, and the pre works normal. I just got finished putting the EA2623 back, and I'm back to the same issue.

Sounds like a bad transformer.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 12, 2016, 10:37:10 PM
Well, with the measurements on a 2623-1 you should expect something like this;

Red-->Orange=14.5Ω
Blue-->Green=23Ω
Brown-->Black=23Ω

Make sure no leads are touching each other when taking the above DCR measurements. You should have an open reading or no resistance on any combinations EXCEPT what is shown above. My meter reads "OL" in this situation.

0Ω tells me its a direct short which is very opposite of open or OL.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: IndietownRecording on November 13, 2016, 02:29:58 PM
Well, with the measurements on a 2623-1 you should expect something like this;

Red-->Orange=14.5Ω
Blue-->Green=23Ω
Brown-->Black=23Ω

Make sure no leads are touching each other when taking the above DCR measurements. You should have an open reading or no resistance on any combinations EXCEPT what is shown above. My meter reads "OL" in this situation.

0Ω tells me its a direct short which is very opposite of open or OL.

You're right, I misinterpreted my meter. I'm getting no resistance on all combinations except:

Red-->Orange=14.5Ω
Blue-->Green=23Ω

Brown-->Black=no resistance. I made sure that none of the leads were touching to eliminate the possibility of any shorts.

Do you think this means the transformer is bad?

Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 13, 2016, 02:42:27 PM
Red-->Orange=14.5Ω
Blue-->Green=23Ω

Brown-->Black=no resistance. I made sure that none of the leads were touching to eliminate the possibility of any shorts.

Do you think this means the transformer is bad?
Yes indeed. Please send me an email and I'll take care of sending you a replacement.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: IndietownRecording on November 19, 2016, 03:31:07 PM
Yes indeed. Please send me an email and I'll take care of sending you a replacement.

Just installed the replacement transformer. Works like a champ.

You rock, Jeff!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: AudioHak on November 24, 2016, 02:01:50 PM
Hi guys! I too have the green light problem happening. When I power up the unit, it passes signal perfectly with good tone, however the green light stays lit until the gain knob is turned to the center position. It then turns off and functions normally. Is there any way to remedy this? Thank you.

Hey Jeff and everyone else,

I too am experiencing a similar problem on a new build. I searched, but was not able to find any responses to this problem.  The green signal led stays lit when I first power up the module, but strangely, when I turn on phantom power, the signal led functions as normal. Turn phantom back off, the signal led goes back to constantly lit. Another odd behavior I have noticed is that around 30 minutes of use, the signal led begins to function as normal, regardless of the 48v phantom switch position. Kinda stumped on this one. Everything looks like its correct. Signal passes fine and the preamp sounds fantastic.

Things I have tried:
     Changing the op-amps for known working op-amps.
     Reheating connections that are in the path.
     = Same behavior.

Could this be a faulty chip? What would cause it to function normally once heated and running for 30ish minutes?

Note: I do have plenty of experience with electronics, worked with Keeley Electronics for years. Still stumped. Any help is appreciated.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 25, 2016, 10:58:21 AM
I think your post belongs in the VP28 support thread?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: AudioHak on November 26, 2016, 03:33:22 PM
I do agree, however, this thread had someone posing the same problem I had. I can post again, or the mods can move my post. Whatever we think is best.

Just looking for some answers.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on November 30, 2016, 12:34:48 PM
Hi guys!

I've build hundreds of VP26s by now, and probably nearly as many VP28s, as well as a handful of other CAPI preamps and modules.
In the past I've had only a handful of issues, every time it was either faulty input or output transformers.

I recently built a set of 4 VP26s with SL2520 red dot op amps and Litz output transformers.  3 of them sounded perfect but one has VERY low signal output.  When I attach a mic I do get signal, but it's far too low in level.  I have tried various mics and slots in my chassis and there is no issue with the mic/cable/chassis, it is definitely something with the VP26 itself.

I have quadruple checked each component (there aren't that many) and am positive that there is no build error.  I also tried de-soldering the Litz output transformer leads and checked the windings.  Cross checking the Litz data sheet I only see resistances between leads of the same windings, so that looks good.  That's about as far as I have gotten in troubleshooting.  I could de-solder the input transformer but that is quite a bit of work.

I do have a decent digital multimeter, a function generator and also the extension jig (that I got for building/tuning VC528s).  I can inject a signal and measure it at points using my DMM.  Is there are place in particular that I should try?  Any help here would be great!

MZ 
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on December 01, 2016, 12:05:01 PM
The best way to proceed and find out where the problem starts is to inject signal and "follow" it thru the circuit with an audio probe, a scope or DMM set to ACV.

I would inject a 400Hz tone at -40dBu. You will have to use the schematic as a "road map" of sorts probing along the way to see where the first large difference shows up. The good news is you have 3 good units to get some benchmark readings from. There are really only a few spots to check. I do publish the schemo for this preamp so everything you need is on there.

First would be the 1k R. Pick an end and stay consistent. This is just after the 2622 input so differences here would point to the 2622.

Next would be at the 470µF coupling cap. Differences here would likely indicate the opamp but could also be something with the output transformer. Swapping opamps around would rule those out.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on December 02, 2016, 02:25:46 PM
Jeff,

I've got things set up now.  I am using SL2520 red dots for these so I assumed there would not be an op amp issue... Just to be sure I took swapped op amps from one of the working units, no change.

I next injected the AC signal as you described (though I'm not positive of the input signal level from my function generator). 

I first checked at the R3 1k position.  Both good and bad modules read the same ~22mV.

Then I moved onto the 470uF coupling cap C10.  I tried checking both sides of this cap, and here I noticed a slight difference.

On the good module I see the same ~22mV on the negative side, but ~28mV on the positive side.

On the bad module I see ~22mV on BOTH the negative and positive side of C10.

Any ideas on what could be going wrong?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on December 05, 2016, 12:17:43 AM
OK I've got an update.

I poked around both the good and bad VP26s some more and found some interesting things.  I had to reset my function generator as the last time I ran these tests the good unit was clipping.  Here are the test points and values I measured in VAC with my DMM (admittedly not the nicest DMM fyi)

GND=R14 (bottom)
                                              Good   Bad
In High (J1-10)   11.7mV   11.7mV
In Lo (J1-8)         11.6mV            11.7mV
R11 (top)                   11.4mV    11.6mV
C10 (pos-bottom) 4.2mV       4.0mV
C10 (neg-top)            4.2mV               4.0mV
Out Hi (J1-2)             5.1mV       3.0mV
Out Lo (J1-4)              1.8mV       3.0mV

Here's something else that's interesting, when I use the phase invert switch on the bad unit all signal cuts out.  When I do this with the good unit the signal level doesn't change.  The mute switch works in the same way on both units as does the pad switches and phantom power settings have no effect on the signal.  Seeing the exact same values on Hi and Lo outputs for the bad unit seems strange, like there could be a phase problem with the differential outputs. 
Would this mean there is wrong with the output transformer?  I did desolder those leads once already and checked for shorts or open circuits in the windings.  Everything looked OK to me.  There were low DC resistances between leads of the same winding, and open circuit to the leads of the other windings.  Still at this point I'm not sure what else it could be?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on December 13, 2016, 09:01:19 PM
I haven't gotten a response here in a little while.... but I did just get some new parts in and tried swapping out the output transformer for a new one.  Still no dice, same behavior.  I would love some advice on what to try now, I'm stumped as to what could be going wrong here...
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on December 15, 2016, 03:00:22 PM
From what you have posted, the audio levels seem extremely low on both units. It may be a DMM thing. Possibly rigging up a probe so you can "hear" at the test points may be a better way. Either that or get a good Fluke with true RMS.

The fact that the signal cuts out completely when engaging the polarity switch is a problem. That makes me think bad solder joint at the switch, bad switch, problem with the t-pad or output transformer. By looking at the schematic you can see exactly whats happening when that switch is depressed. It is simply swapping the primary leads of the output transformer.

You can easily lift the output leads from the secondary of the transformer and check the output there. This will bypass the t-pad.

Maybe probe the pins on the polarity switch to make sure both poles are making proper contact in both positions.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on December 17, 2016, 02:23:33 PM
I would certainly believe that my DMM isn't giving accurate AC readings.  However, the readings are very consistent, so while accuracy is in question the precision not so much.  I wouldn't trust the exact voltage levels, but I do trust the discrepancies between good/bad modules that I measured.  I went over those test points several times and got the same exact values on each board each time. 

I don't really have a way to rig an audio probe unfortunately.  I wish I had the budget for a Fluke right now, but I don't just at the moment.

It is strange, and maybe telling, that the polarity switch cuts out the signal completely. 

I am convinced that this is not an issue with the output transformer.  I tried swapping it out with another and there was no change in the bad module's behavior whatsoever.

I checked the solder joints on the polarity switch and they looked fine.  I re-heated them again anyway but got no change.

I'll try measuring the signal at the secondary of the transformer, I haven't done that yet.

I did probe the pins on the polarity switch and they seem fine. 

From the schematic and what you've told me thus far I'm starting to think it might be the T-pad.  Besides lifting those leads from the output transformer (which I will try) is there anything else I can do to check the T-pad?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on December 17, 2016, 03:27:07 PM
.....From the schematic and what you've told me thus far I'm starting to think it might be the T-pad.  Besides lifting those leads from the output transformer (which I will try) is there anything else I can do to check the T-pad?
The best and most accurate way is to lift the blue/black output transformer leads from the PCB and take your balanced output signal from those leads.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on December 17, 2016, 06:59:34 PM
This is a Litz transformer so I take it that you mean the gray and orange leads?

I will try that out as soon I get a chance, thanks!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on December 17, 2016, 07:17:08 PM
Either way, the pad labels on the PCB will be Blue and Black.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on January 11, 2017, 07:09:21 PM
Sorry it's taken me so long to get back to this!

Ok I checked out the VAC between the black and blue leads and here's what I've found:

Good unit:  12.9mV

Bad unit:  4.4mV

Quite a difference!  Does this point to the T-pad as the problem component?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 12, 2017, 10:41:10 AM
The best and most accurate way is to lift the blue/black output transformer leads from the PCB and take your balanced output signal from those leads.
To quote myself, desolder the 2 leads and use those for your balanced output. This will eliminate the t-pad from the circuit.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on January 12, 2017, 03:42:07 PM
Oh I see, so then since I am seeing the level difference at that point that tells me it is NOT the T pad.

I've already verified that it isn't the output transform either by swapping.  What else is there?  Could it be th input transformer?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 12, 2017, 08:09:40 PM
Well, did you physically desolder both of those leads from the board? If so, the next previous spot to measure for a difference is just before the opamp which is at the 1k R.

I can't recall if you found a dif just after the opamp or not?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on January 13, 2017, 01:19:37 PM
Sorry if that wasn't clear.  Yes, I de-soldered those leads and took the measurements from the leads.

I don't believe I checked the 1k resistor you are referring to (is that R2?).

I did make a handful of measurements comparing good and bad modules.  Here are those measurements again:

In High (J1-10)   11.7mV   11.7mV
In Lo (J1-8)         11.6mV            11.7mV
R11 (top)                   11.4mV    11.6mV
C10 (pos-bottom) 4.2mV       4.0mV
C10 (neg-top)            4.2mV               4.0mV
Out Hi (J1-2)             5.1mV       3.0mV
Out Lo (J1-4)              1.8mV       3.0mV

I'll do a similar comparison for R2 later tonight and post the results.

Thanks for all your help Jeff!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on January 13, 2017, 07:03:12 PM
OK, so the voltage across R2:

Good unit: 3.2 mV
Bad unit:  3.2 mV

No difference.  You said that point is before the op amp?  So then that maybe points to the op amp.  But that doesn't make sense to me.  These are SL2520 red dots, and I did already try swapping the op amp with another one and it made no difference.

Now I'm really stumped!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on January 16, 2017, 12:51:31 PM
I spent some more time with this last night, going through the schematic and probing a good unit and the bad unit back and forth.

The two units have identical measurements through the entire circuit until you get up to the output transformer.  If I compare measurements taken at any point before that transformer I find no difference at all.  However, after the output transformer, right from the transformer leads and in the final output on the card's edge, there is significantly less voltage on the bad unit.

What has me stumped is that I have already pulled the output transformer off of the bad board and replaced it with another, with no change whatsoever.  I used the output transformer that I pulled on another module and it works fine.  So it would appear that the issue isn't in the transformer itself. 

I touched up the solder points from the transformer leads to the board but got no change.  However, I'm starting to think that for some reason the connections into the output transformer from the board might be messed up.  I have had many PCBs of all shapes and sizes made myself and have never had a single issue, but do you think there could possibly be a defect in the board itself?  Somehow I think some trace is mistakenly connected to ground, or traces/leads shorted together where they shouldn't or open where they should be shorted.  But I can't find any spot on the board where that is happening due to soldering.  The VP26 is not that complicated of a circuit, there aren't very many solder junctions or components so it's easy to check each one, still I can't find a mistake anywhere.

I'm still pretty stumped at this point :(
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on January 16, 2017, 03:03:42 PM
Just to confirm, when you run signal to both units, the AC measurement for each connection point for the output transformer primaries (Red and Orange solder pads) are the same, correct?  If this is true it can only be a handful of issues:

Bad solder joint(s) on pads to transformer leads

Broken transformer lead

Incorrectly wired transformer leads

Bad solder joints on output attenuator

Bad Output attenuator

Like you said, it's a pretty easy circuit. So unless something else is causing a short on the transformer secondaries between themselves or ground or a copper trace has been broken, I don't see how it can be anything else.


Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 24, 2017, 08:10:31 PM
 I have read through this entire thread and have not found a solution to my particular issues. Before I bother anybody for advice on how to track down my problem, firstly I want to try one thing.

What is the method for bypassing the T-Pad on the Rev C VP26?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 24, 2017, 08:20:43 PM
What is the method for bypassing the T-Pad on the Rev C VP26?
It is just above here post #845 https://groupdiy.com/index.php?topic=33501.msg821820#msg821820
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 24, 2017, 08:34:25 PM
It is just above here post #845 https://groupdiy.com/index.php?topic=33501.msg821820#msg821820

I guess what confused me there is that you said to desolder the blue and black and use them as the output.

I assumed it was pertaining to something else. As I said I've read this entire thing, and I think I may have been a bit hazy towards the end.

 After I take them off of the PCB, what do I do with them at that point? Leave them hanging? I guess I don't know what you mean by using them as my output.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 24, 2017, 08:48:51 PM
Leave them hang temporarily and use blue for + output and black for - output. You will need to use alligator clips or solder an XLR directly to them etc.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 24, 2017, 09:00:00 PM
Leave them hang temporarily and use blue for + output and black for - output. You will need to use alligator clips or solder an XLR directly to them etc.

Oh I see. Yes yes.

I meant permanently though. It sounds like you were talking about just to run the tests?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 24, 2017, 09:05:55 PM
I don't have the cash to afford to put together a test rig. So for now I just want to do a hard bypass on the attenuator so that I can put it back into my rack and see if it works.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 24, 2017, 09:18:15 PM
I do get what you were saying, and I suppose I could sacrifice an XLR cable and just plug it straight in to my converter, see what happens.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: kevinkace on January 25, 2017, 01:44:49 AM
I have a VP26 with a phantom power LED out, the preamp seems to be working fine including phantom power.

Is there something I should test or would just replacing the LED be a reasonable route?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 25, 2017, 02:14:08 AM
I have a VP26 with a phantom power LED out, the preamp seems to be working fine including phantom power.

Is there something I should test or would just replacing the LED be a reasonable route?
Did it ever work? They normally don't "wear out".
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: kevinkace on January 25, 2017, 02:46:09 AM
They normally don't "wear out".

That's what I was thinking! I assume I tested it, but you know what they say...

Oh wait, I'm now remembering the point about "if it doesn't work it's in wrong" from the build guide. I'll check that out.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 25, 2017, 10:53:50 AM
Oh wait, I'm now remembering the point about "if it doesn't work it's in wrong" from the build guide. I'll check that out.
Yes that was my next reply! That's why I was wondering if it ever worked.  ;)
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 25, 2017, 07:10:29 PM
Leave them hang temporarily and use blue for + output and black for - output. You will need to use alligator clips or solder an XLR directly to them etc.

Say I would like to bypass the T-pad and still put the unit into the 500 Rack to test it that way, is there a way to do that?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on January 26, 2017, 03:26:53 AM
Say I would like to bypass the T-pad and still put the unit into the 500 Rack to test it that way, is there a way to do that?

There is a solder pad on the PCB that says "Opt No T-Pad-Blu". Solder the Blue wire from the transformer there.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 26, 2017, 05:43:03 PM
There is a solder pad on the PCB that says "Opt No T-Pad-Blu". Solder the Blue wire from the transformer there.

Thanks!

Paul

I see that option on my Rev B. But not on my Rev C, which is the one that I would like to bypass the T-Pad on.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 26, 2017, 05:51:54 PM
I see that option on my Rev B. But not on my Rev C, which is the one that I would like to bypass the T-Pad on.
I removed that from the Rev C board since no one really bypasses the t-pad. The only way to do it would be to route the blue wire (as Paul said) directly to gold finger #2.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 26, 2017, 06:08:49 PM
I removed that from the Rev C board since no one really bypasses the t-pad. The only way to do it would be to route the blue wire (as Paul said) directly to gold finger #2.

If it is indeed the T-Pad that is my issue, I will order another and rewire things correctly again. I have reason to think that I may have damaged the T-Pad during installation. This is my inexpensive way of checking that. As I build more I will acquire the proper testing devices.

I greatly appreciate your patience, Jeff, as I imagine it must be frustrating repeating yourself so often and explaining things repeatedly that make perfect since to you. I know the feeling. I have years of experience remodeling bathrooms and kitchens, and every new guy frustrates me to no end, even though I know he means well and just needs to learn.

One last question and I should be good, and I'm fairly certain that I know the answer, I'm only clarifying: Gold pin 2 would be the Negative on the DOA inserts, correct?   
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 26, 2017, 06:16:28 PM
....One last question and I should be good, and I'm fairly certain that I know the answer, I'm only clarifying: Gold pin 2 would be the Negative on the DOA inserts, correct?
NO!!!! The gold fingers are the gold pads at the rear edge of the PCB that plug into the rack's card edge connector. They are labeled and start with #1 near the top edge and end with #15 near the bottom edge.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 26, 2017, 06:19:34 PM
NO!!!! The gold fingers are the gold pads at the rear edge of the PCB that plug into the rack's card edge connector. They are labeled and start with #1 near the top edge and end with #15 near the bottom edge.

I have never been so glad to have asked a question in quite a while!!!! Thanks, dude!! whew. Glad I waited for a response.

After I run this hodge-podge test, I'll report back.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Z-Chord Studios on January 26, 2017, 06:57:39 PM
Yup. A bad T-Pad was my issue. All of the strange behaviors are gone. No more gain boost with the phase switch. No more low-cut on every source. Of course, now I pretty much HAVE to keep the pad on. Thus why there's attenuation on these things. 

I will be ordering a new T-Pad as soon as I have the flow.

Thank you to everyone for their patience.

And thank you to everyone for their help!!!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: sebperry on February 27, 2017, 04:05:22 PM
Hi there,

I have a pair of VP26 that I bought pre-assembled a couple years ago. They work and sound great but I think they may be in need of a little maintenance.

On of of them in particular has a tendency to lose sound when it hasn't been passing signal for a little while. The only way to get sound back is to crank the input gain until the signal passes through. After that it's usually good for little while but will drop out again every 15 min or so.

Is there any maintenance or cleaning I can do to stop this from happening? Thanks!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on February 28, 2017, 09:30:48 AM
I have a pair of VP26 that I bought pre-assembled a couple years ago. They work and sound great but I think they may be in need of a little maintenance.

On of of them in particular has a tendency to lose sound when it hasn't been passing signal for a little while. The only way to get sound back is to crank the input gain until the signal passes through. After that it's usually good for little while but will drop out again every 15 min or so.

Is there any maintenance or cleaning I can do to stop this from happening? Thanks!
There is no maintenance involved in a properly built preamp. To me, this sounds like bad solder joint that is getting worse.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on April 04, 2017, 10:05:49 PM
Well guys you might have thought I figured out my misbehaving VP26 since I haven't posted in quite a while, NOPE!
I've just been incredibly busy with a new job, but tonight I finally got a change to work on this again.

I started from scratch once more.  Hooked up the signal generator to run ~400Hz sine wave at the max amplitude of the generator.

I desoldered the output transformers completely on both a known working board and the bad board (for anyone that doesn't remember, this bad VP26 is giving me very very low signal output).  I then connected each module to my 500 series rack (via extension cable) and checked voltages on each one to compare them.  Same exact settings on both modules.  ALL of the voltages matched for each module along the signal path up to, and including, the red and orange pads at the output transformer.

While the output transformers were still disconnected I measured the resistances of all of the leads relative to one another.  I found no shorts between windings or open circuits across any particular winding.  The resistances for the winding pairs matched up almost perfectly with one another as well.  SO FAR SO GOOD

Then I soldered in the red and orange leads for the output transistors (as labeled on the PCBs, I am using Litz transformers).  Now I hooked these back up and checked the voltages across the outputs from the transformer as they were dangling (disconnected from the board), and here I found a big difference!  The bad module had voltages between output winding pairs that were HALF of that from the good module.

Now to remind everyone again, I have already tried swapping output transformers on this bad module and it made no difference.

If the output transformer itself isn't bad, and the signal level up to the red and orange pads isn't bad, then what on Earth could be causing this problem?  I'm definitely still perplexed and have had a bum VP26 kicking around my studio for far too long now...
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on April 05, 2017, 11:28:18 AM
So far the only major component I have not tried to replace is the input transformer.  Now, this would really seem to make no sense since the audio signal beyond this component lines up nicely between the bad unit and a known good unit.  Still, I'm about at my wits end with this module and would be up for trying just about anything by now.

I've swapped output transformers, no difference.  I've swapped op amps, no difference.  Again, the audio signal traced through the circuit looks good (nearly identical to a good unit) all the way up to the output transformer.  Once I attached the input winding of the transformer then both windings on the output of the transformer have low voltage, about half of what they should be.  It looks like a bad output transformer, except I've already tried swapping them with no change!

If anyone has any other suggestions I would be very grateful.  I may just go ahead and buy another input transformer and try swapping it out for kicks...

I've built hundreds of VP26s and VP28s now and out of all of those only about 3 or 4 ever had any issues whatsoever.  In each of those cases it was either a bad input transformer or output transformer.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Winetree on April 06, 2017, 06:25:16 PM
I have some Version  A-2   VP 25s & 26s with out phantom L.C.D.s
Is there a picture how to wire the L.C.D.s on the early P.S.B.s?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 07, 2017, 10:58:19 AM
@ Michael, I would not bother with the input transformer. There is no way that could have anything to do with this. This is a bit odd.

Does flipping the polarity have any major impact? Besides hopefully flipping the polarity?

With no transformer leads connected, no power to PCB, does the DCR from the Red pad to the Orange pad match? And also after engaging the polarity switch?

There are no black art things here so we should be able to figure this out. In the same way that 1+1 is always 2 and never occasionally 3 ;-)
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 07, 2017, 11:00:12 AM
I have some Version  A-2   VP 25s & 26s with out phantom L.C.D.s
Is there a picture how to wire the L.C.D.s on the early P.S.B.s?
There maybe a pic around from someone. I have not had any of those modules for ages. All you need is the LED with the anode connected to the switched side of the 48V toggle to a 10k R that goes to ground.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on April 07, 2017, 11:56:54 AM
Jeff, I agree that the input transformer seems like a very unlikely culprit, I'm just sort of at my wits end here!

The polarity switch does act peculiar.  I wrote about this on the very thread if you scroll up.  Engaging the polarity switch on the bad unit drops the signal to basically zero. 

I've checked the DC resistant between red and orange pads with the transformers completely taken out of the circuit and there is certainly a difference.  The good module shows 20k Ohm between those pads, the bad one shows OL (overload), basically an open circuit or at least up into the tens of mega ohm region.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 07, 2017, 12:19:06 PM
Jeff, I agree that the input transformer seems like a very unlikely culprit, I'm just sort of at my wits end here!

The polarity switch does act peculiar.  I wrote about this on the very thread if you scroll up.  Engaging the polarity switch on the bad unit drops the signal to basically zero. 

I've checked the DC resistant between red and orange pads with the transformers completely taken out of the circuit and there is certainly a difference.  The good module shows 20k Ohm between those pads, the bad one shows OL (overload), basically an open circuit or at least up into the tens of mega ohm region.
Maybe there is an internal problem with the polarity switch. You can check continuity between the solder lugs to make sure its ok. Continuity between the top 2 pins when out and the bottom 2 lugs when its engaged. Both "sides" should work the same.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on April 07, 2017, 01:32:32 PM
Jeff, I did already check the polarity switch (you can see this in my post on the previous page of this thread.  It's been a while so I could certainly go over those again for good measure, but I recall checking the continuity on the pins in both engages and disengaged states and it looked like it was working perfectly.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 07, 2017, 01:50:21 PM
Jeff, I did already check the polarity switch (you can see this in my post on the previous page of this thread.  It's been a while so I could certainly go over those again for good measure, but I recall checking the continuity on the pins in both engages and disengaged states and it looked like it was working perfectly.
10-4. Well, there is nothing else between the opamp and output transformer but the polarity switch, mute switch and some PCB tracks. Have you check the mute switch out? I don't see how the 20k R or the 100pF cap could have any affect like this.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on April 07, 2017, 01:58:12 PM
I have not checked out the mute switch yet.  I'll do that and go over the polarity switch again to see if I may have missed something

thanks again for your help Jeff!  I'll report back once I've checked those out
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 07, 2017, 02:03:53 PM
I have not checked out the mute switch yet.  I'll do that and go over the polarity switch again to see if I may have missed something

thanks again for your help Jeff!  I'll report back once I've checked those out
If it were me and those 2 switches look OK, I would lift the - end of the 470µF cap from the PCB and solder the primary lead of the transformer directly to it. Solder the other primary lead to a ground ref on the PCB. Do not use the standard transformer pads for this. Make sure the proper 2 secondary leads are soldered together (not to the PCB) and then take your final output from the remaining 2 secondary leads, again not connected to the PCB. Hope this makes sense. This will hard bypass everything in question between the opamp and the output transformer, as well as the t-pad.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: mxz174 on April 09, 2017, 10:35:48 PM
WOW, after all this time I FINALLY found the problem.  It's the mute switch.  I had checked that polarity switch inside and out but never tested the mute.  The pins do not show continuity for the appropriate switch state.  I double checked this against a known working module and indeed it is the switch that is faulty.  It looks fine from the outside and feels OK when you engage it, but it's not making connections on one side...
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 09, 2017, 10:41:15 PM
WOW, after all this time I FINALLY found the problem.  It's the mute switch.  I had checked that polarity switch inside and out but never tested the mute.  The pins do not show continuity for the appropriate switch state.  I double checked this against a known working module and indeed it is the switch that is faulty.  It looks fine from the outside and feels OK when you engage it, but it's not making connections on one side...
Well sonuva b!tch. Glad that is sorted and major sorries for the faulty switch.

A lesson for all though, the schematic holds the key. Everything else was checked. The only other possibility was the Mute switch. Electrons flowing down the roadmap highway.....
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: rocka on April 26, 2017, 02:27:40 PM
Hi! New to the forum and new to the diy world here!

First build is a vp25... I checked everithing, and seems to be ok!, the test points on the assembliy guide meassure ok, all the switches work ok, it sounds really nice, but it have low gain... really low gain... with all the pots open, i still get moderated to low input.

Any clue where i can check if i made some mistake in the building stage?

thanks!

bests

N
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 26, 2017, 02:38:43 PM
Hi! New to the forum and new to the diy world here!

First build is a vp25... I checked everithing, and seems to be ok!, the test points on the assembliy guide meassure ok, all the switches work ok, it sounds really nice, but it have low gain... really low gain... with all the pots open, i still get moderated to low input.

Any clue where i can check if i made some mistake in the building stage?

thanks!

bests

N
First rule for posting about these types of module builds....what opamp is it and who built it?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: rocka on April 26, 2017, 02:45:07 PM
sorry! neewbie here....

The op amp is a SL2520 red dot, i bought it with the vp25 kit... the opamp came already asembled

thanks for your reply jeff

Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 26, 2017, 07:05:06 PM
sorry! neewbie here....

The op amp is a SL2520 red dot, i bought it with the vp25 kit... the opamp came already asembled

thanks for your reply jeff
OK good to know. Is it fully seated? http://capi-gear.com/catalog/DOA_Install.php

The biggest issue folks have with these builds are faulty solder joints. I run my iron at 800˚F.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: rocka on May 02, 2017, 11:57:38 AM
I rechecked everithing... and the only thing i noticed is when i make the testing procedure, without the opamp, and without a power source, i dont have the 600Kohms measurment... all the other procedures are ok, i have +/- 16 volts...

i rechecked the solder points and they are ok...

bad opamp could be?

thanks!!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on May 02, 2017, 01:11:40 PM
bad opamp could be?
No it won't be that. Scott burns in and checks each and every opamp before he ships to me.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: TillM on May 02, 2017, 03:35:54 PM
seams to me, that you insert a wrong resistor or maybe a electrolytic capacitor has the wrong polarize.
Check your resistors first. Its easy to confound a 10R with a 10k resistor.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: rocka on May 02, 2017, 05:25:45 PM
thanks! will re check that!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: PetezaSlice on May 05, 2017, 09:01:54 AM
Accidentally mixed 750r resistors on a dual VP26 build... This matter? Possible to rematch using a DMR-4200 DMM?

Doh whops

Thanks

*edit*

Also, if I'm doing two preamps, am I then taking 1 resistor from each taped pair, and putting it into each preamp? ie, the orange dotted 6k8 (R7, R8) - am I splitting a taped pair for R7 in each, and splitting a second taped pair for R8 in each?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on May 05, 2017, 09:27:18 PM
Accidentally mixed 750r resistors on a dual VP26 build... This matter? Possible to rematch using a DMR-4200 DMM?

Doh whops

Thanks

*edit*

Also, if I'm doing two preamps, am I then taking 1 resistor from each taped pair, and putting it into each preamp? ie, the orange dotted 6k8 (R7, R8) - am I splitting a taped pair for R7 in each, and splitting a second taped pair for R8 in each?
No worries with matching. All of the supplied parts are more than precision enough for their respective uses.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: iturnknobs on May 23, 2017, 08:37:58 PM
Anybody know if a Cinemag  CM75101-APC will work as an input trafo for the VP25? I just did  a build(2) that do not work. I have used  CMOQ-2S and CMOQ-2L for output trafos.

PCB color      ---------   CM color

   red                                           brn
   brn                                           yel
   blu                                            grn
   grn                                            blu
   yel                                             vio
   org                                            gry
                                               red &org tied together

Any help is appreciated.

Thanks.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: iturnknobs on May 24, 2017, 01:49:28 PM
...I do believe my secondaries(CMOQ-2) are phase reversed, but I should still have something...
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on May 24, 2017, 02:04:53 PM
If your transformer wiring is correct, it's either a bad DOA or the eternally classic bad solder joint/misplaced component combination.

The spec sheet for the CM75101-APC has a higher secondary impedance than the EA2622, but sound in some type of form should still be happening.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: iturnknobs on May 26, 2017, 11:05:08 AM
Struggling here with output trafo.  The "tap" on the ea2503 data sheet provided does not appear to match the VP25 rev B schemo.    The "tap" colors are reversed when drawings are compared to each other. I am going to assume the cinemag literature is correct.  Any ideas?

Is there a VP25 rev C schemo anywhere... or is VP26 rev C same except for output trafo?


http://www.capi-gear.com/catalog/images/gallery/2503/2503-specs.pdf
http://www.capi-gear.com/catalog/images/gallery/VP26/VP25-Rev-B-schematic.pdf

http://cinemag.biz/output/PDF/CMOQ-2.pdf

DOA is fucntional
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: iturnknobs on May 26, 2017, 12:30:31 PM
(http://)

Here's a photo of the stuffed PCB(CM-75101APC input). I already have [email protected](rev B) with ea2622input and CMOQ-2S for output trafos which are functional.  I have no shorts between DOA sockets. All tests in section 12.1 and 12.2 of VP2X assembly guide performed with correct results. I really hate to  start pulling functional units apart for troubleshooting. :-\
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on May 26, 2017, 09:00:12 PM
Struggling here with output trafo.  The "tap" on the ea2503 data sheet provided does not appear to match the VP25 rev B schemo.    The "tap" colors are reversed when drawings are compared to each other. I am going to assume the cinemag literature is correct.  Any ideas?

Is there a VP25 rev C schemo anywhere... or is VP26 rev C same except for output trafo?
Not exactly what you mean by "tap" but the 2503 is a quadfilar device with 4 identical windings. There are many different ways to connect it to get the exact same result.

The VP25 is identical to the VP26 with the exception of the output transformer. The VP312 schemo can be used for help with the output transformer wiring.

I have never used that specific CineMag part but when comparing datasheets, the wire color code is the same as the EA2503.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on May 26, 2017, 10:54:05 PM
I really hate to  start pulling functional units apart for troubleshooting. :-\


Don't we all. But sometimes it's necessary.

You could start by swapping your Cinemag input transformer with an EA2622. Assuming soldering and component placement is good.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: iturnknobs on June 01, 2017, 05:55:20 PM
Just to be clear about switch function(tested in circuit)....

The "yellow" lugs should show continuity when mute switch is out and the "green" should be open. The opposite is true when the switch is engaged.  The middle, unidentified lugs show continuity in both positions. This is true for the functional units I have.

This is not the case for my non-function units. Yellow lugs always open regardless of switch position. I'm guessing I have bad switches?


-Brian
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on June 01, 2017, 09:26:32 PM
Well, it does depend on if the Polarity switch is engaged or not. If the Polarity switch is out or disengaged, for the Mute switch, in the out or disengaged position, you are measuring the output transformers primary winding DCR when probing between the lower middle lug and the green lug in your pic. This will be around 9Ω with a 2503 or 16Ω with a 2623-1 so keep this in mind if your DMM needs to be set to a particular range. Both lower or green lugs are connected to ground. The transformers primary leads are connected to the middle lugs. This can all be seen in the schematic.

The odds that you have 2 bad switches is next to impossible. I have only seen 1 or 2 in the last 15k switches.

Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: iturnknobs on June 06, 2017, 01:35:15 PM
Here goes... Couldn't get my [email protected] VP25 rev C working. I have two functional VP25 rev B units. All have Cinemag output trafos (CMoQ-2 S or L).  Probing around the 2 different PCBs, I discovered that the lugs nearest the mute switch button went to the silk-screened brown and red pad for the rev B. For rev C, these mute switch lugs go to the silk-screened violet and gray, which go no where in the rev B schemo and I cannot find the rev C schemo for VP25. The circuit as stated in the rev B schemo exists physically on the rev C board, but the screening does not appear to match.

Is there and assembly thread amendment I did not find? I do have these units working now, wiring my output trafo primary to the vio and gray pads. The brown and red pads do not appear to be connected the the circuit anywhere.

Am I crazy?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on June 06, 2017, 03:00:47 PM
I changed the wiring layout on the newer PCB's so that the transformer leads do not criss-cross if using a standard EA2503. From what I gather, the CineMag has the same wiring color code as the 2503 so you should be able to just go as normal.

I think I mentioned before that the EA2503 style transformer has 4 identical windings. There are numerous ways you can wire them up and get the exact same result.

I myself have built a new VP25 Rev C and the board is solid. I did a pictorial build for an upcoming guide. I just haven't had the time to edit the pics and create the page.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on June 25, 2017, 12:55:59 AM
Here's a fun one...

I just finished updating my old VP25's and 26 and during testing, I noticed that when engaging the pad I would have a large audio spike engaging it and and about half of that disengaging it. I checked around for voltages and whatnot and I found that it only happens when the input is connected to a line level device. Doesn't happen with microphones or with an unterminated XLR on the input. There was no DC coming from my converter's analog output. I metered the output of the preamp for DC when these pops were being made, and there was a spike around 0.1V on the positive side (phantom off, by the way) and pretty much nothing on the negative when the Pad button is pressed. But this doesn't happen when connected to microphones, so I don't really care. I was just curious what was going on electrically as all three of them did the same thing. Frequency response, gain, etc all working perfectly. I do process recorded vocal tracks with the VP26 quite a bit, but I always have the pad engaged ahead of time.

Just curious.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on June 25, 2017, 11:00:33 AM
Hey Paul, the mic pad is before the 2622 so there can be no DC present on the switch from the preamp unless phantom is engaged. The pad switch is fully galvanized from the opamp by the 2622. It must have something to do with the device feeding the preamp. I would try something else like maybe something with a transformer output into the preamp just for kicks. The pad switch is interrupting the audio path so it will never be silent but an audio spike seems odd.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on June 25, 2017, 12:59:18 PM
Jeff,

I see that on the schematic, so there is some head scratching where the voltage is coming from if there is no DC present being feed to the input in the first place. I'll hook it up to another preamp and see if it still does it. The device it is hooked up to now is all ICs. I'll let you know.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on June 25, 2017, 01:15:24 PM
So I put a Iso transformer in line and the "problem" goes away. I double checked the output of the converter and I am getting +/-0.02VDC on pins 2 and 3, but I don't see how that would cause the jump to 0.1 when engaging the pad.

It's not a big deal and I'm not going to think about it anymore. Just some fun information for others who may have this occur when doing initial testing.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: timrickmann on August 08, 2017, 08:39:24 PM
Hello

I've built 6  VP26 pre's over the years, and I love love love them!  In the last 2 weeks, i've had a strange volume loss in one of them.  It seems to function, but i get maybe half the volume of the other pre's.  The op-amp is seated properly and nothing looks out of place.  Where would i start to look for issues?

Tim
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on August 09, 2017, 12:56:22 AM
Hello

I've built 6  VP26 pre's over the years, and I love love love them!  In the last 2 weeks, i've had a strange volume loss in one of them.  It seems to function, but i get maybe half the volume of the other pre's.  The op-amp is seated properly and nothing looks out of place.  Where would i start to look for issues?

Tim
Sounds like a bad solder joint somewhere on the pre.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: timrickmann on August 09, 2017, 04:59:36 PM
I will start there!  Thanks so much
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: gevermil on August 09, 2017, 08:51:35 PM
I see the vp28 kit is out again .
Any timeline ? thanks
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on August 09, 2017, 09:47:39 PM
I see the vp28 kit is out again .
Any timeline ? thanks
I need to get all of the preamp kits setup with CA2622's for inputs and then all will be in stock. Its my main priority tomorrow morning so I'd say sometime tomorrow early afternoon or so.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: c1bomber on October 03, 2017, 11:22:34 AM
Just completed my first two vp26.  They sound amazing! thanks for the great work Jeff.  I have two problems:

(1) the pad switches are reversed, i.e. pad is engaged when the switch is out; pad disengaged when the switch is engaged.
(2) adjacent vp26s are passing phantom power to each other. (but not to other preamps on either side)

where should I look to fix these problems?

op-amps are 1 Red Dot and 1 gar 2520
rack is Purple Audio Sweet Ten.

thanks for your help!!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on October 03, 2017, 12:43:43 PM
(1) the pad switches are reversed, i.e. pad is engaged when the switch is out; pad disengaged when the switch is engaged.
I am not even sure how this can be possible. The PCB's are all the same and the switches can't physically do this.

Quote
(2) adjacent vp26s are passing phantom power to each other. (but not to other preamps on either side)
No modules should "pass" phantom to each other. Typically, either the phantom supply in the rack is on for all modules are off for all modules. This also doesn't make sense from a rack slot/module standpoint.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: c1bomber on October 03, 2017, 01:19:30 PM
I had a polarity error at C1.  Fixed the pad issue.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on October 03, 2017, 01:25:54 PM
I had a polarity error at C1.  Fixed the pad issue.
C1 on a VP25 or VP26 is a 220pF ceramic cap, so non-polarized.
My bad. Corrected info comes a few posts after this.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on October 03, 2017, 01:34:29 PM
Just completed my first two vp26.  They sound amazing! thanks for the great work Jeff.  I have two problems:

(1) the pad switches are reversed, i.e. pad is engaged when the switch is out; pad disengaged when the switch is engaged.
(2) adjacent vp26s are passing phantom power to each other. (but not to other preamps on either side)

where should I look to fix these problems?

op-amps are 1 Red Dot and 1 gar 2520
rack is Purple Audio Sweet Ten.

thanks for your help!!

Do you have other modules to test the phantom power issue? Separate the modules in the rack and see if the problem persists. My guess is you have a build issue where the phantom is bypassing the switch and going the XLR input. Like Jeff said, phantom is not going to "jump" from one module to another. It comes down the 48V rail in the rack then the module sends it out the XLR input when activated by the module.

For the pad, unless you have a switch that operates backwards (highly unlikely if you purchased a kit), there is something off with the build. You can test continuity between the top terminals of the switch and compare to the other switches.

Thanks!

Paul
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: c1bomber on October 03, 2017, 02:00:39 PM
Hi Jeff and Paul,

The speed of your responses is just amazing!  C1 on vp26 Rev C is 33uf, 25V.  I flipped it and the pad issue went away.  Phantom power issue turns out to be a problem with my Sweet Ten rack.  Channel 2 is passing 48v to Channel 3.  For some reason I hadn't noticed it until I put the vp26s in those slots.  I just tried it out and a 512c passed power to a vp26.  Pair of vp26s in any two other slots have no issues.

thanks again!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on October 03, 2017, 02:23:25 PM
Hi Jeff and Paul,

The speed of your responses is just amazing!  C1 on vp26 Rev C is 33uf, 25V.  I flipped it and the pad issue went away.  Phantom power issue turns out to be a problem with my Sweet Ten rack.  Channel 2 is passing 48v to Channel 3.  For some reason I hadn't noticed it until I put the vp26s in those slots.  I just tried it out and a 512c passed power to a vp26.  Pair of vp26s in any two other slots have no issues.

thanks again!
Oops my bad. Yes you are correct about C1. Either way though, there is very little to no DC present on that cap so its polarity will not change anything especially with the pad situation as mentioned.

Still not following your phantom issue since. I also have never seen a Sweet 10 in person.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: c1bomber on October 03, 2017, 02:51:28 PM
Hi Jeff,

Yes, turned out flipping the polarity did not solve the pad issue.  I think it's all an issue with my Sweet Ten rack.  512c just gave me the same pad problem in a different slot :(

Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: c1bomber on October 04, 2017, 10:39:02 PM
wow, got it figured out.  I was testing the vp26s with a mic I don't use very much.  A stereo mic where the stock capsules ship with flipped-from-standard polarity.  The circuit employed to correct the polarity causes this PAD flip with a few (mostly 500 series) pre-amps.  Weird.  And I was running the stereo mic into the two mono vp26 which I guess explains the 48V being shared across both pre's.  Lesson is always test the gear with stuff you know like the back of your hand.  Thanks for you help Jeff.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: c1bomber on October 04, 2017, 10:41:47 PM
on another topic, I need to change out a bad API 2520 op amp in a 512c (probably with a gar2520).  Anyone know the Mill-Max pin length so as not to crush the ceramic capacitor underneath?
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Whoops on October 05, 2017, 09:51:33 AM
on another topic, I need to change out a bad API 2520 op amp in a 512c (probably with a gar2520).  Anyone know the Mill-Max pin length so as not to crush the ceramic capacitor underneath?

not exactly the same answer but you can replace that ceramic cap with one that you has longer legs and then you can bend it horizontally and don't worry about crushing it, it can fit flat on the pcb
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: JBHamby on November 19, 2017, 07:19:20 AM
Hello everyone. Hopefully you guys can help me with a problem. I have 2 VP25's that I have had for over a year. Both preamps have worked fine with no issues what so ever. Yesterday during a session one of them stopped passing phantom power. The 48volt light switch would still power on but it would not power any condenser microphone I tried. The preamp still would work wth  dynamic mics. I tried several different cables and several different microphones and it seems that the preamp is the issue. Thanks for any possible help!
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: TillM on November 19, 2017, 07:44:47 AM
look at the resistors R6,R7,R8 and capacitor C9.
Maybe something there is leaking.
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: JBHamby on November 19, 2017, 10:06:30 AM
Thank you so much for the reply! I have just checked R6, R7, R8 and then C9. R6 was 198r which is good but R7 and R8 both came in at 3.4k, with both should be 6.8k. C9 was good with no leaks. Could the drop in the value of the resistors for R7 and R8 be the cause of my problems? Thank you again for the help
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: [silent:arts] on November 19, 2017, 10:38:08 AM
With a transformer balanced input those measured values are fine (in circuit).
Resistors don't change their values anyway (if it burned you would see and smell it).
The 2nd VP25 is still working fine in the same slot with the same cables with the same microphone?

My guess is more to your PSU. The phantom power LED often don't use the 48V rail.
Don't know how Jeff is doing it, my VP26 is old enough for having no LED  ;)
EDIT: found the rev B schematic, the LED is using the 48V, it is a real 48V indicator  8)
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: JBHamby on November 19, 2017, 11:11:50 AM
I had not checked it another slot in the power supply yet. I’m going to do that now and see if that’s the issue. I wouldn’t have thought if that! Thanks
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 19, 2017, 12:46:51 PM
I had not checked it another slot in the power supply yet. I’m going to do that now and see if that’s the issue. I wouldn’t have thought if that! Thanks
That would be my suggestion as well. As Volker has kindly pointed out, the 48V indication LED runs from the 48V rail so if it is illuminated then the module is getting 48V power. If you check the schematic, there are only 4 other components related to phantom power.

There is also this which is helpful
http://www.shure.com/americas/support/find-an-answer/how-to-test-phantom-power-voltage-and-current
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Zingg on November 25, 2017, 04:12:16 PM
Not exactly what you mean by "tap" but the 2503 is a quadfilar device with 4 identical windings. There are many different ways to connect it to get the exact same result.

The VP25 is identical to the VP26 with the exception of the output transformer. The VP312 schemo can be used for help with the output transformer wiring.

I have never used that specific CineMag part but when comparing datasheets, the wire color code is the same as the EA2503.

Hi

I'm assembling the first VP25 and got stuck on the output transformer. The colors of the transformer leads do not correspond with the color labels on the VP25 rev. "C" PCB. Any help appreciated :-) Thanx
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 25, 2017, 05:07:15 PM
I'm assembling the first VP25 and got stuck on the output transformer. The colors of the transformer leads do not correspond with the color labels on the VP25 rev. "C" PCB. Any help appreciated :-) Thanx
This is posted at the store on all product pages that use the Litz wire transformer. The cross reference table is on the 2503-Litz wire transformer datasheet.
http://www.capi-gear.com/catalog/images/gallery/2503/2503-Litz-specs.pdf
Title: Re: [BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread
Post by: Zingg on November 25, 2017, 05:20:12 PM
This is posted at the store on all product pages that use the Litz wire transformer. The cross reference table is on the 2503-Litz wire transformer datasheet.
http://www.capi-gear.com/catalog/images/gallery/2503/2503-Litz-specs.pdf

Stupid me :-) Sorry for bothering and Thanx for the super fast response :-)