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Project Specific Discussions => Preamplifiers => Topic started by: jsteiger on April 18, 2010, 02:47:27 PM

Title: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on April 18, 2010, 02:47:27 PM
***ATTENTION!! The stepped VP312 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 build/support thread for the VP312, 500 and/or 51x series mic preamp build that can be found at our capi-gear.com (http://capi-gear.com/catalog/index.php?cPath=22_47_55_91) website. A decent amount of PCB’s have been sold so I felt it proper to start this support thread.

--------------------------------------------------------------------------------------------------------
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
--------------------------------------------------------------------------------------------------------


This is about as easy as a preamp build can get. Keep in mind, if you are using the 51x version, you must be very careful with the voltage selected and the loaded DOA. I definitely don’t want anyone to accidentally smoke a vintage API 2520 and be mad at me!

Also, if you are using the preamp in the bipolar 24V position (with an appropriate DOA), you should check the DC offset for the particular DOA you have chosen. If you have more than a few mA of DC present at the output of the DOA, you will want to use a good quality cap to block this DC from the output transformer. This cap can be positioned in place of R11, the 1 ohm R.

FWIW, PPA’s 2055E running on 24V sounds nothing short of amazing in this circuit! Kudos to Pier!  :)

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

Best regards, Jeff
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Th
Post by: [silent:arts] on April 18, 2010, 04:24:21 PM
running this on with the “VPR Mod” is childish  ;D ;D ;D
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: brichie on May 28, 2010, 07:46:13 PM
Hey Jeff!  I'm running into a slight problem with my VP312 build - using it with either a gar1731 or a stock api2520 results in low output that sounds overdriven and thin.  I just read through the VP2X thread where someone had a similar sounding issue that was eventually traced back to a cold solder joint on one of the switches.  I went back over all of my solder points and they all seem to check out.  One thing I did notice was when checking the resistance between the DOA sockets, between C and O I get 0 resistance.  All the other sockets check out with high resistance -- should this be a concern? 

I should also mention a slight f*up on my part, I followed the VP2X manual a little too closely when cutting the leads for the output transformer and thus had to extend them a little -- just the gray and yellow wires. 

BTW I have a newer API 6B lunchbox, and I did the VPR Mod as described.

Enjoyed the build immensely, I look forward to getting it up and running!
-br
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 28, 2010, 08:15:26 PM
brichie,

You should measure around 9 ohms resistance between the Com and Output DOA sockets. The Yellow transformers lead is important, I would dbl check that. It's part of the output transformer's secondary series connection. Also dbl check the t-pad wiring and connections. I have seen that be an issue for a couple of guys in the past. As you did with the switches, closely look at and even touch-up any component's solder joints to ground. These solder pads sometimes don't heat as nicely as say one only on a track. The heat dissipates out into the ground plane and can sometimes lead to a cold solder joint.

Keep us posted.

Best, Jeff
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 28, 2010, 08:57:53 PM
If the above doesn't get you there, you could also monitor the output directly from the opamp. It will be unbalanced but will bypass the t-pad, polarity switch, mute switch and the output transformer. Take this signal from the opamp side of the Zero ohm resistor. This may help you to isolate the problem.

Best, Jeff
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: brichie on May 30, 2010, 07:50:33 PM
Jeff,

Unfortunately after checking the solder points I still have 0 resistance between the COM and Output DOA sockets.

The t-pad looks pretty solid, all the leads are soldered sufficiently and they go to their respective CBA locations on the board.

Check this one out, not only had I beefed the yellow and grey wires, but it appeared I somehow confused GRY and GRE (it was about 2am when I was putting it together, guess I got a little too excited to finish) and I'm slightly concerned that maybe the initial power up in the rack may have damaged the output transformer.

I did a little search on how to pass signal and monitor the op amp but it yielded no results as far as instruction is concerned, would you mind pointing me towards a resource on how to execute?  I'm seeing a XLR connection with some alligator clips in my future. 

Thanks for the assistance Jeff, I'm a total beginner when it comes to troubleshooting electronics - hand me a bass guitar and I'll hold it down all day ;)
-br
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 30, 2010, 08:18:21 PM
Unfortunately after checking the solder points I still have 0 resistance between the COM and Output DOA sockets.
This is entirely possible depending upon the range of your DMM. It is actually a good thing. It would be a problem if it was a few ohms.

Quote
...Check this one out, not only had I beefed the yellow and grey wires, but it appeared I somehow confused GRY and GRE...
I'm thinking this is the source of your problems. If you look at the schematic and the secondary windings, well they were pretty jazzed up that way.

Quote
I'm slightly concerned that maybe the initial power up in the rack may have damaged the output transformer.
That shouldn't have happened.

I would say to fire it up and see what you've got happening now. Then report back.

Cheers, Jeff
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: brichie on May 31, 2010, 05:35:46 PM
Good news Jeff,

Fired it up and all is well! Thanks for the pointers!
-br
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 31, 2010, 05:59:02 PM
Good news Jeff,

Fired it up and all is well! Thanks for the pointers!
-br
10-4, that is good news. I will have to remember about the GRE/GRY potential switch-a-roony.  ;)

Have fun with it.
Jeff
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: letterbeacon on August 03, 2010, 03:56:51 AM
How close is does the VP312 sound to the API 3124+?

I have an API 3124+ at work and it sounds good, but not 'warm' enough for me.  Is the VP312 based on older API technology, or will it sound similar to the current API 3124+ that's in production at the moment?

Thanks a lot!

Matt
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 03, 2010, 10:26:50 AM
Matt,

My pre's do sound similar, yes. They sound like they are all related. Mine are all a little less "hard" sounding than the current production company's version. I believe this is mostly because of Ed's 2622 compared to the Jensen that they use for the input. Next important component contributing difference, the DOA's from Scott and Gary just plain sound better than a current 2520. They both sound more like their '70's counterpart.

That is just my opinion. Do a search on gs for "3124 VP26" and you will find some opinions of other peeps. Some hang here to so maybe they will have some input as well.

I have noticed on the 3124 skiz that they have a coupling cap after the opamp with a small parallel bypass cap. These components were not on the original 312 cards. I don't have them on the VP312 card either.

Best, Jeff
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: letterbeacon on August 03, 2010, 11:21:26 AM
Thanks Jeff, that's exactly what I wanted to know.  I know what you mean about the 3124+ sounding 'hard' - I'm glad to hear the VP312DI doesn't have that character to it.  

One more question - I should be able to fit two VP312DI pre amps into a 1U rack enclosure, right?
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 03, 2010, 11:57:35 AM
...One more question - I should be able to fit two VP312DI pre amps into a 1U rack enclosure, right?
Yes for sure. All remaining PCB's for the VP312DI project should be here tomorrow. I have a few outstanding parts, but 98% of the components are here already.

If you plan to mount the VP312DI in a 1RU, you will need to be very careful and meticulous with your metal work, especially where the 3-sub mini toggles are at. The back of the faceplate will need a milling in it so the switches and the Bo DI board seat properly. I have to get some up close and detailed pics of how all of that goes together. If one is not careful, nothing will fit to the faceplate or line up properly. It is not impossible, it just won't be a super easy task.

Best, Jeff
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: letterbeacon on August 04, 2010, 06:13:50 AM
I'm planning on using switches and pots that I have lying around here so will probably just use flying leads to connect to the PCB.  That should make things a bit easier when designing the front panel too, I hope.

Thanks for your help!
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Seditionary on April 11, 2012, 08:13:59 AM
when building our vp312's... i remember there being an optional resistor?... what is the tone difference with and without this resistor?  we included it. 

thanks :)
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Knuckleduster on December 03, 2012, 08:02:47 PM
Hi Jeff, I built my vp312 a few weeks ago. After finishing building it I did a quick test and everything seemed to work with no issues. About a week later I took it on location for a session. I couldn't get much of a signal out of it. When I got home I tried it again and everything seemed to work fine. I took it to another session yesterday. Everything worked fine for the first few hours and then all of the sudden in between takes I stopped getting a good signal again. I fiddled around with some of the switches while tracking and once I flipped the phantom power off and back on again then everything worked. So I guess something isn't quite working with the phantom power. The phantom power light was still on by the way when the issue occurred (it does turns off when phantom power is in the off position though).

Any ideas on where to start looking?

Thanks

Georges
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on December 04, 2012, 02:24:29 PM
Georges

Below is some "boilerplate" help text that I send out to folks. This solves the majority of issues people have.

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 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: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Timh on August 17, 2013, 07:52:57 PM
I just got my kit in the mail, and I'm so excited to start my first preamp build, but I feel like I'm taking crazy pills. There's a 10ohm resistor in here that I don't see on the BOM. Also two 10k resistors when only one is needed for R3. I just want to be sure I'm not mixing them up before I start soldering stuff.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 17, 2013, 08:15:58 PM
Tim, you must follow the BOM that I emailed out after I shipped. The name of the BOM file will match the Rev and title on the PCB. This support docs email often ends up in spam so check there for a date about 2 days after the "shipped" order update was sent out. Of course, that may also be in your spam.  ;)
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: ruairioflaherty on August 17, 2013, 08:17:43 PM
I just got my kit in the mail, and I'm so excited to start my first preamp build, but I feel like I'm taking crazy pills. There's a 10ohm resistor in here that I don't see on the BOM. Also two 10k resistors when only one is needed for R3. I just want to be sure I'm not mixing them up before I start soldering stuff.

One very very important trick when building.  Do not go by visuals alone - measure every component on the DMM before you stuff it, this has saved my ass in the past.  Use the parts called for in the build instructions and schematic, if there are extras you can safely ignore them.

Edit - Jeff beat me to it....
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Timh on August 17, 2013, 08:36:03 PM
Tim, you must follow the BOM that I emailed out after I shipped. The name of the BOM file will match the Rev and title on the PCB. This support docs email often ends up in spam so check there for a date about 2 days after the "shipped" order update was sent out. Of course, that may also be in your spam.  ;)

Oh wow. I just now realized there were documents attached to the email. Well I feel dumb. :-[

Thanks, Jeff!
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: kato on August 18, 2013, 11:45:53 AM

Oh wow. I just now realized there were documents attached to the email. Well I feel dumb. :-[

Thanks, Jeff!

I feel even dumber.  :)  I apparently saw the attachments, saved them to my hard drive, let several months pass and forgot I had them.

Went online to look for the docs and (here's the really stupid part) started using the VP2x Assembly Guide (http://www.classicapi.com/catalog/images/gallery/VP26/VP2x-Assembly-Guide.pdf), stuffing all the resistors in blissful ignorance that the designations are different. It wasn't till I started the caps (where it called for a ceramic cap in a footprint clearly designed for an electrolytic) that I caught on. So a word of caution to others:



VP25 ≠ VP312



Just now I found this thread, looked in my API docs folder and discovered I had the documentation all along, just forgot.   :o  Time for some desoldering action...
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Timh on August 18, 2013, 04:03:10 PM
NOOOOO!! That's terrible, but hey...it happens. I'm using the VPxx guide just as an "order of operations" kind of thing since I never know what to solder next.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Timh on August 19, 2013, 01:52:16 PM
Alright. So after 12 hours of building yesterday into the wee hours of the night I finished up the DOA and plugged her in. Phantom power LED lit up so that was a good sign. I booted up my system and put my headphones on and I got sound...but then noticed something strange. Every time I took a step I could hear a fuzz. So I went to the Mic and did, "Teeeesting..." It was completely distorted. Anyone know what could be the problem? I'm glad I'm getting signal, it's just very distorted/fuzzy and it seems to be fairly sensitive to that by just distorting from my steps around the mic.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 19, 2013, 01:59:06 PM
Tim, firstly I would check a new pre build with a known good working opamp. If both are freshly built, the problem could be in either one (or maybe both). We need to be able to eliminate something from the possible issues.

Also, have you seen the DOA install page at my site? http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Timh on August 19, 2013, 02:26:46 PM
Tim, firstly I would check a new pre build with a known good working opamp. If both are freshly built, the problem could be in either one (or maybe both). We need to be able to eliminate something from the possible issues.

Also, have you seen the DOA install page at my site? http://classicapi.com/catalog/DOA_Install.php (http://classicapi.com/catalog/DOA_Install.php)

Thanks, Jeff. I did see that page before the install. There's just no way of me testing with a known working opamp. This is my first one.

Edit- My only guess is that when I was building the DOA I messed up and used the matched pair of BC550c's in the wrong spaces then had to spend a while heating them up and swapping them out. Did I fry something? Not a strong solder joint? Should I just build another DOA?
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: BenDrumRecorder on April 23, 2014, 05:09:11 PM
I just finished a 312 but am  having a problem. When I plug it into my lunchbox, the phantom power stays on all the time (w/ the LED lit) regardless of the position of the switch.  Also, when the PAD is activated, it sounds overdriven and very thin. 

I have built two of these previously without a problem.  I'm not exactly an electronics expert, but upon reviewing the VP2X testing procedure in the assembly guide, I have noticed that I have a resistance of 0.00 between my C and O connectors for my DOA...

I'm guessing the pad switch may have a cold solder joint, but I don't know how to explain the phantom power issue.

Help?

Ben
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on April 23, 2014, 07:34:16 PM
I just saw this so thought I would post my emailed reply here as well.

The test points for the VP2x yield different results with a VP312. You should have about 9 ohms. Set the range on your DMM to confirm this. I assume that the switch for phantom is wired incorrectly somehow. I also assume a cold solder joint on the Pad switch.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Rpbr on May 18, 2014, 09:02:42 AM
Hey everyone,

I'm having a few troubles with two vp312 builds I made recently..
I built them at the same time along with each-other and they share the same problem, so luckily it seems once I locate the mistake both will be up and running..!

I built them using the chungs vp26 build-thread + the vp312 BOM..

I went through Chungs guide w. pictures and every time I came to something that looked different than what I had I went into the BOM to see what went where... everything seemed to go smooth.. the checks for the +200k connections was fine.. - though the one supposed to measure 8.3 just read 0 as well - but I an pretty sure I read somewhere Jeff saying that that was ok??


I put them in my 51x rack, fired them up - nothing burning, popping or anything..
BUT I get no signal through them with any mic.
phantompower light comes on
I get pops on my daw-tracks when I press any of the three push-buttoms on the vp's but still no signal.

Problem is I am far from a geniuous with these things - I kinda jumped into it cause it seemed interesting and fun - still is, but just get a little complicated when I build mostly from "picture guides" and the build doesn't work, since I have no clue where to dive in regarding checking whats wrong..

Do any of you who's build it perhaps have an idea what might have gone from seeing as how I followed Chungs vp26 build - using the vp312 BOM.. any "rookie" traps I've stumbled into?

I hope some of you have hint or advice since I'm really looking forward to trying these on drum-overheads

have a very nice day!

all the best
Rasmus
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 18, 2014, 11:40:57 AM
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 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 Toneluck 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: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: bleedingears on May 30, 2014, 11:54:08 AM
Hi,

I built a VP28 and a VP312 a few months ago. Both worked fine when I had finished building them.
Now, the VP312 has stopped passing audio. The phantom power light still comes on, but can't get a signal at all. I took it to a tech as I didn't have time to fix it. I know that the DOA's were fine as I swapped them out when testing.

Anyway I got it back from my tech (who said I had a resistor in the wrong place - I doubt this but hey) and the pre worked, but not the DOA. So I had a spare kit and built another gar1731 for it which got it back up and working.

A month later, and its stopped working again. LED still comes on when you give it phantom power though. DOA's tested and are fine.

Don't really want to pay a tech again, when i wasn't fixed properly in the first place. Any ideas? I guess its a cold solder joint, but could I have damaged it by leaving it in the rack, powered up when its not passing audio?
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 30, 2014, 08:55:05 PM
Skim back thru this thread for some pointers.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: walkz187 on July 05, 2014, 10:14:05 AM
Hi All

I'm new to this DIY community and the DIY electronics. however i have always been tech minded person. So i was considering taking the plunge on VP312 pre as my first project. I did some soldering years ago. Not sure how my skills remain. I have lots of old junk that i will start to practice on first. alarm clocks, modems web cams etc.
i have a few questions:
Can i loosely following the FREE, Step-by-step, VP2x Assembly Guide for VP 312? or is this dangerous or confusing for a newbie?
Should i buy a completed DOA or are the DOA at the same level as the rest of the pre-amp? i do not want to bite off more than i can chew for my first project? however would feel good knowing i built the entire kit.

Also what should a newbie consider before taking such a project?

Thanks
Sean


Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: gabygab on July 19, 2014, 01:53:15 PM
Hello,

I'm almost done my 2 VP312s but I seem stuck at a very silly spot. I'm trying to install SW1(the toggle one for phantom power) and I can't seem to tighten it. Does anyone have pointers for this?

Thanks!


Gab
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on July 19, 2014, 02:08:20 PM
Hello,

I'm almost done my 2 VP312s but I seem stuck at a very silly spot. I'm trying to install SW1(the toggle one for phantom power) and I can't seem to tighten it. Does anyone have pointers for this?

Thanks!


Gab
Gab, the hex nut and lock washer should be on the threaded bushing behind the faceplate. You can adjust the hex nut out a little so the trim nut can fully tighten to the faceplate. Chung has some excellent pics in this post that will help. http://groupdiy.com/index.php?topic=41741.msg520553#msg520553
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: gabygab on July 19, 2014, 02:27:22 PM
Thanks for the reply Jeff!

I seem to have assembled them in the proper order. However, the switch is still loose. I must have cross threaded it (on both haha). I tightened them by hand so I will try to undo it. Now, just to be sure, can the "pretty" nut be tightened with a hex ratchet. I can't seem to find one that fits.

Edit: Do NOT bother responding. Gaby is very silly. Thanks for the help!
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: zaiata on July 24, 2014, 11:06:39 AM
Thanks for the reply Jeff!

I seem to have assembled them in the proper order. However, the switch is still loose. I must have cross threaded it (on both haha). I tightened them by hand so I will try to undo it. Now, just to be sure, can the "pretty" nut be tightened with a hex ratchet. I can't seem to find one that fits.

Edit: Do NOT bother responding. Gaby is very silly. Thanks for the help!

I had the same issue.
Just add a lock washer, one before you tread the included nut in the switch and one after for the switch to be a little farther back. The front nut will be very tight.   
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: zaiata on July 24, 2014, 11:26:27 AM
Success!!!

(http://groupdiy.com/gallery/0/thumb_54613-240714112031.jpeg) (http://groupdiy.com/index.php?action=gallery;sa=view;id=249)
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: gabygab on July 25, 2014, 02:30:39 PM
Thanks a lot for the reply Zaiata. I finally managed to get it on. The nut has a few battle scars on it now. It's a bummer but I figure there are worst parts that I could have screwed up haha.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Edward on September 03, 2014, 08:42:08 AM
Just wanted to say thanks for a great project with the VP312 :D

Took me about 3 hours to put togehter and works like a clock. Really happy with it.

/Edward
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Prophotographer on November 14, 2014, 03:56:10 AM
Hey guys, for anyone looking for complete build instructions, all in one place and with every step laid out, I made this build tutorial video. Could be a big help for someone new starting to put these together!

http://youtu.be/VsOgoayrr4s
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: miscend on February 04, 2015, 05:36:44 PM
Hi everyone. Just a quick question. Is the short burst of noise when you press the pad switch on the VP312 normal?
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on February 09, 2015, 12:47:49 PM
It is possible especially with phantom on. There will be a pop as well. This is fairly common.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on February 10, 2015, 01:17:03 PM
Just ordered two of these, will be my first preamp build.

Looking at the BOM:

http://www.classicapi.com/catalog/images/gallery/VP312/1_VP312-xxx-BOM.pdf

and the pcb:

http://www.classicapi.com/catalog/images/gallery/VP312/VP312-VPR-Rev-A-PCB.jpg

there is something I don`t understand. Where is R13? And there is no part for R14?
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on February 10, 2015, 01:29:09 PM
Just ordered two of these, will be my first preamp build.

Looking at the BOM:

http://www.classicapi.com/catalog/images/gallery/VP312/1_VP312-xxx-BOM.pdf

and the pcb:

http://www.classicapi.com/catalog/images/gallery/VP312/VP312-VPR-Rev-A-PCB.jpg

there is something I don`t understand. Where is R13? And there is no part for R14?
That's an early scan of the PCB. On the production boards, what you see here as R14 is now labeled R13. I don't recall what/when I caught and made that change. I don't even remember it, its been so long.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on February 10, 2015, 01:38:11 PM
Ah that clears things up. Now just the wait for my kits to arrive  8)
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on February 25, 2015, 12:16:53 AM
My kits arrived earlier today, and I`ve just built my first pre-amp!

However, during the quick startup test, while probing my DOA-sockets, I get 0r between C and O. Have I shorted something somewhere?

All the other socket-probing turned out fine (over 200)

All transformer wiring is correct. I`m not sure about all the soldering, altough I gave it my best try  :P

Should i try it in the rack? Do I have to do the voltage check before I try it with an opamp? I don`t have the breakout-bracket that makes it easy, so I`m afraid to go poking in the rack while it`s on, afraid of not hitting the right pins straight away...
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on February 25, 2015, 12:28:25 AM
It could be an auto-range function on your DMM. The resistance should be around 9 ohms so make sure your meter is set for less than 200 ohms.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on February 25, 2015, 12:32:53 AM
Getting about 10ohms, should be good to go?
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on February 25, 2015, 12:50:16 AM
Ok fired it up in the rack, did the voltage testing and it checks out fine. +48V lights up when asked to. No funny smell.

Am I good to to put in the OpAmp ? Wow I might have gotten it right on the first try, fingers crossed!

Edit: So I plugged it in... and guess what... it works beautifully. Great sound! Can`t wait to play more with it! So happy!  ;D
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on February 26, 2015, 02:48:40 PM
Made the second one today, much quicker this time around. Works right away!

So... do you think I`m ready for a couple of 553f`s? What is the "preferred" advancement through the capi line, in terms of build difficoulty? Something like (from easy to hard):

312/VP25/VP26 - 312di - VP28/553f - LC53A/VC528 ?

Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on February 26, 2015, 03:11:59 PM
I would put the 553F's as a little easier than a VP28. You should be fine moving up to the next level. Many folks have built the 553F as their first project.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on February 26, 2015, 03:34:26 PM
Cool, I`ll keep that in mind! Now im hoarding parts for 2x EZ1084, but like Scwharzenegger says....


I`LL BE BACK
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on March 02, 2015, 07:21:17 PM
Just wanted to chime in and say that I just built my two GAR2520. Both worked straight away! First took me a good few hours, but the second one was much faster.

I kinda bought them as training-kits, and was really preparing myself for the beginning of my DIY adventure to be alot of troubleshooting and maybe a few non-working projects to start with; but so far my rate has been 100% working. Kinda scary, hope I don`t get too discouraged when the inevitable hits!

Anyways, the GAR2520 sound great. A bit hard to to compare to my SL red dot`s, as I can only use my 312`s with a mic/my voice, that is hardly the same every time. Maybe when I get a DI, so I can run pre-recorded audio through them, a comparison might be easier.

Now I need to get something to stick my GAR`s in!!
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: Greg on March 20, 2015, 11:58:11 AM
After having spent years away from DIY and tech work...

I built 6 VP312. The build went fine. I didn't use the output attenuator; rather, I simply hard wired a DPDT to select between 1:2 (normal) and 1:1 (the extra secondary winding).

Thanks for doing the leg work on this one. Sorry for the poor quality of the picture.

Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: samguaiana on May 13, 2015, 09:48:33 AM
I bought three VP312s from a guy, but funny enough, each one has some sort of issue. One's Grayhill step switch goes all the way around, one has a blown cap from what I think is a resistor wired the wrong way, and one is fine, but has all white buttons (the other two with full black buttons haha.) My plan is to make them all right again. Just a few quick questions though.

One, the steps, there should be 11 clicks right? On the one without the step pin, is there a way to fix that easily?

Two, I posted some photos of the one with a blown cap next to one without, I see one resistor with the orange stripe in a different spot, is that the problem? Check it out http://imgur.com/a/sMehZ (http://imgur.com/a/sMehZ) This one also has a recessed LED, but I'm not too concerned.

Three, the pushbutton caps, are they easily removable? My money is on no. If not, are they easy to snap off and replace with ones of the right colour?

Thanks guys! Really stoked to use these pres all the time, just want them all nice and healthy first!!
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on May 13, 2015, 10:23:37 AM
I have a question regarding the output attenuator. In some designs the attenuator is placed after the output transformer, so you can drive the op tx for added saturation. Afaik in this 312 design it is before the TX, so all saturation by driving the input and backing off on the output is from driving the components in the circuit inbetween the two transformers.

Why is it designed this way, and what are the benefits/caveats of the two ways of doing this?
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on May 13, 2015, 12:06:57 PM
Afaik in this 312 design it is before the TX
Is it? No. Look at the schematic (http://www.classicapi.com/catalog/images/gallery/VP312/Classic-VP312-schemo.pdf)
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on May 13, 2015, 01:01:37 PM
I have a question regarding the output attenuator. In some designs the attenuator is placed after the output transformer, so you can drive the op tx for added saturation. Afaik in this 312 design it is before the TX, so all saturation by driving the input and backing off on the output is from driving the components in the circuit inbetween the two transformers.
As Volker stated, the t-pad attenuator comes AFTER the output transformer in all of my single stage preamps.
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on May 14, 2015, 07:49:42 AM
My bad then. I`m pretty new to reading schematics so it`s not so easy for me to see. What is the T-Pad marked as on the schem?
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: [silent:arts] on May 14, 2015, 08:35:48 AM
What is the T-Pad marked as on the schem?
R1 (-A / -B / -C)
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: fragletrollet on May 14, 2015, 08:50:11 AM
Thanks for confirming, I thought so but thinking ain`t knowing.  8)
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: New Soul Rebel on August 05, 2015, 04:13:35 AM
Hi Guys

I am stumped. Which is a first on this build (as I have built many). I'm trying to repair a build that someone else had a go at, but made a complete hash of in every possible sense.

The preamp (with one of my opamp builds - his one was shot to bits and was promptly thrown in the bin!) passes audio cleanly:

output attenuator works
phantom works
-10 and phase, mute all work.
25k reading from outer and inner pin of grayhill

but no gain.

Basically the soldering on the build was so bad, that I have had to desolder most of the board.

I can get the schemo out and start testing, but I just wondered if anyone here has experienced the 'no gain, such a pain' problem, and can get me route one to the heart of the matter.

Cheers Matt
Title: Re: classicapi.com *VP312, 500/51x Series Mic Pre Kit* Official Build Support Thread
Post by: jsteiger on August 05, 2015, 10:21:29 AM
Matt, no gain tells me that there is a cold solder joint in the inverting opamp to ground string. I suggest following the schematic and looking at the 200Ω R, the 330µF cap, the string of Grayhill resistors and the switch. If something in there is floating, the gain switch will not function.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Capturedsound on November 02, 2015, 09:15:56 AM
Hey Jeff and  all you good people ,
      I built a 312 and 312DI ..Both with the GAr2520 DOA. I thought they were great..but lately something is a miss...I noticed the sound to be quite thin after recording drum overheads. That sparked me to do some testing. Talking into and using an array of mics and comparing to a UA 610 pre and my console pres, I found they do not have much gain and lacking any sort of low end to the sound. Also to get the required gain , it  brought up a good bit of noise too .. As I was turning knobs and testing the buttons, this is what I noticed ..
 
 A) The output pot all the way to the left ( towards infinity symbol) passed sound just as loud as being all the way to the right but warmer ..as you turn it to 9 o'clock ( from far left ) the sound disappears and as you continue to turn it to the right the sound comes in on a gradual slope ( as one might expect) 

B) If you push in the  polarity switch, the output knob acts in reverse. And I tended to like the sound better with it pushed in.

C) As I stated earier, The gain seems really low. The design boasts 60dbs in gain , which is comparable to the UA, but no where close to the gain I get from the UA or my console pres for that matter...I need to turn the gain almost all the way up to get a usable signal. Introducing a lot of noise too... And this is vocal testing with a Blue Bottle Rocket, an Octova ribbon ( which i couldn't even get the gain needed ) , and a Seinnheiser MD421 ...

The weird thing is that both pres , the 312 and 312DI ,  behave the same. I have them mounted in a Radial Engineering Powerstrip. I could of swore they operated much better than this when I built them months ago. 
     Has anybody else had these issues? Do the pres behave this way by design ? Do you think I could have an issue with power from the 500 series rack? Or is something wrong with the pres? 
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 02, 2015, 10:16:28 AM
It is very strange to me that this could happen with both preamps at the same time. This is far from being normal. I would first rule out any potential problems with the opamps. Also make sure the opamps are seated correctly.
http://capi-gear.com/catalog/DOA_Install.php

The next thing I would do is check and reflow for bad solder joints. The symptoms you describe to me sound like bad solder joints.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Capturedsound on November 02, 2015, 11:45:00 AM
Hey Jeff,
    Tis really strange.  I will get to trouble shooting this evening.

 Just to be clear though,  the output knob " should not"  behave that way?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 02, 2015, 06:57:17 PM
Just to be clear though,  the output knob " should not"  behave that way?
No, definitely not.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Capturedsound on November 03, 2015, 12:44:43 PM
Hi Jeff,
    So I went thru and took a magnifying glass to all soldier joints and even reflowed the soldier joints. I checked for the proper positions of all components . All good . I did the testing at the end of the VP26 build instructions and came up with 9.5ohms between  C and O . It states there should be over 200k.. I did see in an earlier post from 2012 where you stated it should be about 8.5ohms so I guess this is fine? I won't be able to test it tonight due to destroying the gain pot trying to remove it to isolate where O was shorting to ground..( before I found the 2012 post)..ugh..

  I also went thru the Opamp in the same way..all looks good..

Well I need to jump on your site and order a gain pot..I am also going to order a ready built opamp just in case..

Thanks!!
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Capturedsound on November 09, 2015, 09:23:07 AM
Soooo..update...I went thru the 312  replaced gain pot , resoldered, ran tests, said prayer and all is good except for C8 which I had backwards which maybe is why it was noisy.. Installed in rack and still had the same issue...with both the 312 an 312DI..SO I started looking else where..I had recently wired up an extensive patch bay network. Before I had been using mic cables and crawling behind the gear to make connections. So I disconnected it from the patch bay and tested with mic cables..THEY WORK RIGHT AGAIN!! So thru further troubleshooting, and this is where I become a dumb ass , I discover I had yet to connect the sleeve and ring on the TRS connections going into my "unbalanced" line ins on the console. Thus I was not properly converting the out going balanced signal from the pres to an unbalanced signal for the line ins..Ugh...Well..at least I know the pres are working and kick ass. Moral of the story ; don't forget about proper cable connections, and patch bays always will be a menace..At least my knees and back are getting a respite ..Thanks Jeff for the help and making great DIY kits.
 
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Houstnwehavuhoh on January 08, 2016, 06:55:23 PM
Hey Jeff,

Just received two 312 (w/Litz) kits today! I noticed on the BOM for them though, that R2 is marked with an asterisk which stated

 "optional loading resistor, not typically found on a vintage 312 card"

Please excuse my ignorance, but what does this mean? I'm assuming I do not have to solder in this resistor if I do not want to? How would this affect the sound/performance, and is it ideal to leave it out or solder it in?

Thanks


***EDIT***
So I just finished one of the kits and I simply left the resistor at R2 out. I went to measure the resistance at the sockets for the DOA and I want to confirm some measurements:

-V and +V read "Overload" (pass)

-V and C read "Overload" (pass)

+V and C read "Overload" (pass)

C and O read 9.5 Ohms. I read in an earlier comment in this thread it should be about 8.4 ohms? So does this pass?

+V and O read "Overload" (pass)

-V and O read "Overload" (pass)

SO assuming C and O reading is okay, I should be fine going to testing with power?
Just want to confirm so I dont end up cooking anything!

Thanks again
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 09, 2016, 04:37:48 PM
..... R2 is marked with an asterisk which stated "optional loading resistor, not typically found on a vintage 312 card"

Please excuse my ignorance, but what does this mean? I'm assuming I do not have to solder in this resistor if I do not want to? How would this affect the sound/performance, and is it ideal to leave it out or solder it in?
Installing R2 with lower the input impedance of the preamp to around 1k. Leaving it out will yield appx a 1.2k input Z. The pre will sound a little more "open" without R2.

Quote
C and O read 9.5 Ohms. I read in an earlier comment in this thread it should be about 8.4 ohms? So does this pass?
This is perfectly fine. Possibly just a slight difference in DMM tolerances.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Houstnwehavuhoh on January 09, 2016, 08:45:16 PM
..... R2 is marked with an asterisk which stated "optional loading resistor, not typically found on a vintage 312 card"

Please excuse my ignorance, but what does this mean? I'm assuming I do not have to solder in this resistor if I do not want to? How would this affect the sound/performance, and is it ideal to leave it out or solder it in?
Installing R2 with lower the input impedance of the preamp to around 1k. Leaving it out will yield appx a 1.2k input Z. The pre will sound a little more "open" without R2.

Quote
C and O read 9.5 Ohms. I read in an earlier comment in this thread it should be about 8.4 ohms? So does this pass?
This is perfectly fine. Possibly just a slight difference in DMM tolerances.

Thank you !
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Blackdawg on January 11, 2016, 11:12:19 PM
Jeff,

Im very excited to have two of the VP312 kits! I got them for Christmas from my Dad. I requested them after hearing them at my School, Webster University.

Im about half way through my first one. About to do the power transformer. I've just been using a combination of the VP2x guide on your site as well as the BOM on the site to hash out what componets go where. But I'm not sure what the RG slots are for? I am out of componets so I am not totally sure what they are for.

I've read in this thread you generally email a build guide for the 312 after one purchases the kit. Could I get a copy of that just so I know I'm doing everything right? I'm very certain i have all the resistors and capacitors in the right spots. But couldn't hurt to double check. I think I am missing some washers too for the Power Transformer. I just have lock washers.

My other question is the op amp. My Dad didn't get my any so I am going to get some. My question is, are there any big differences? I am a student so the cheaper ones are tempting, but I also know you get what you pay for generally especially in audio gear. So basicially are the VF600s you sell worth it? Or should I go with an SL2520 or a gar or ML, JLM, John Hardy? There are so many. How different are they?

Thank you!

Monte
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 12, 2016, 10:37:17 AM
Monte, the RG positions are for the resistors required if you are building a stepped gain module with a Grayhill switch. I assume you have a Bourns pot for variable gain so no VP-Gainswitch R's were shipped.

All of the support docs are published on my site. You will find a hardware BOM that shows how to install the output transformer (its not a "power" transformer) with the split lockwashers that were provided. http://capi-gear.com/catalog/support_docs.php

As for the opamp, it depends on what you want to do. If this is your first DIY build, I would suggest a prebuilt opamp so you know its working, in case there is trouble at startup. I would go with the tried and true so a red dot or a gar2520. The 990 is not the best match for the EA2622 transformer so I never recommend using them in a 312 style circuit.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Blackdawg on January 12, 2016, 02:00:32 PM
Monte, the RG positions are for the resistors required if you are building a stepped gain module with a Grayhill switch. I assume you have a Bourns pot for variable gain so no VP-Gainswitch R's were shipped.

All of the support docs are published on my site. You will find a hardware BOM that shows how to install the output transformer (its not a "power" transformer) with the split lockwashers that were provided. http://capi-gear.com/catalog/support_docs.php

As for the opamp, it depends on what you want to do. If this is your first DIY build, I would suggest a prebuilt opamp so you know its working, in case there is trouble at startup. I would go with the tried and true so a red dot or a gar2520. The 990 is not the best match for the EA2622 transformer so I never recommend using them in a 312 style circuit.

Correct! No stepped Gain pots. Good to know! Thank you.

ah output transformer, thank you again. It seems very straight forward with the nice labeling of the PCB, just wasn't totally sure if the lock washers should go in between the transformer and the PCB. Thank you for confirming!

I was going to go with a prebuilt one for this pair of pres, as you said to just simply things. Its not my first build, but its my first mic pres. Im still curious about the VF600, is that a modified 2520 or a 990? Im assuming 990. what, if any, are the sonic differences between the gar and SL?

Thank you for your quick reply! Very nice to beable to ask the maker himself questions! Love the kits. Really dig the new face plates too.

Monte
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on January 12, 2016, 02:12:01 PM
The VF600 is Steve Firlotte's (Inward Connections and Tree Audio) amp block. Its his own design.

The red dot and gar2520 are pretty similar. Both are nearly identical in sonics to mid '70's Huntington's and Melville's. Some folks prefer the red and some the gar. Neither is a bad choice.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Blackdawg on January 12, 2016, 03:03:53 PM
The VF600 is Steve Firlotte's (Inward Connections and Tree Audio) amp block. Its his own design.

The red dot and gar2520 are pretty similar. Both are nearly identical in sonics to mid '70's Huntington's and Melville's. Some folks prefer the red and some the gar. Neither is a bad choice.

Cool thank you again! My Schools has the Sl2520, so I think I will opt for the Gar2520 and compare the two for myself! Maybe try a VF600 at a later time or another build.

Thanks again Jeff!

Monte
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: samguaiana on March 01, 2016, 11:58:02 PM
Still a bit curious as to why this cap blew. Was it because those two resistors seem soldered in the wrong spot? Is it as easy as swapping them and grabbing a new kit? Any help is appreciated!
 http://imgur.com/a/sMehZ
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on March 02, 2016, 10:15:26 AM
I would just replace the 120µF cap. Should be no biggie. Not sure why it failed.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: samguaiana on March 08, 2016, 11:20:39 AM
I would just replace the 120µF cap. Should be no biggie. Not sure why it failed.

Ok will do. I think two resistors are in the wrong spot. On the pre without the blown cap, two resistors are one way, on the other they're another way. I should probably swap those two right? I am so bad at this DIY business haha
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on March 08, 2016, 01:39:54 PM
I think two resistors are in the wrong spot. On the pre without the blown cap, two resistors are one way, on the other they're another way. I should probably swap those two right? I am so bad at this DIY business haha
No don't bother. Resistors are not directional so rotating them will make no difference.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: samguaiana on March 08, 2016, 11:01:53 PM
I think two resistors are in the wrong spot. On the pre without the blown cap, two resistors are one way, on the other they're another way. I should probably swap those two right? I am so bad at this DIY business haha
No don't bother. Resistors are not directional so rotating them will make no difference.

Sorry, I think I worded it wrong. It's not that they're wired backwards, I think two are soldered in the wrong location. Would that cause the cap to blow? If you look at the pic, you can see that two of the resistors I think are in the wrong spots (R6 and R7). I'm not totally sure, as I said, I got them from someone in the shape they're in, so I don't have any frame of reference.
Thanks for the responses!
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on March 09, 2016, 12:25:30 AM
R6 and R7 both look to be 6k8's which is correct.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: samguaiana on March 11, 2016, 06:43:11 PM
R6 and R7 both look to be 6k8's which is correct.

Holy crap you're totally right. I didn't notice both had the orange dot on them!

Thanks so much, stoked to get them back in my rack and party with some 312s
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jaminem on August 01, 2016, 09:26:41 AM
Hi There, I have 2 of the original Rev A VP312's without the LED, pretty sure I saw a mod to include one - can someone help or point me in the right direction - Jeff?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: hydnwllms on September 10, 2016, 05:03:54 PM
Hey all,

I've just built my first VP312 (new rev. with Litz transformer).
Have just done opamp socket testing and all the tests are coming up with resistance in the megaohms.
I thought C and O was meant to be lower on these than VP26, etc. - is having all reading so high OK (new revision or Litz xformer?)

Thanks so much guys!
Hayden
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on September 10, 2016, 07:21:19 PM
Hayden, for a VP312, C to O should be around 9Ω no matter the Litz or standard 2503. Make sure your DMM is set to that range, if its a manual type.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: plevine on September 23, 2016, 02:18:18 AM
Hey Jeff,
     So stoked to have finally built my 312! Unfortunately, I'm having some issues and I'm wondering if you could shed some light on the problem.

I'm getting fairly strong level out of the pre, but along with some buzz, it looks as if there's distortion (or perhaps DC offset?) on the signal. Please see the attached picture. Do you know what could be causing this? I've done the pre-start checklist, checked my component values and direction, and checked the leads of the output transformer (litz) multiple times (and with multiple people ;) ).

Attached is a picture of a waveform recorded through the pre. The phase flip in the the middle corresponds with me hitting the phase flip button.

Any help appreciated!
Thanks,
Phil
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on September 23, 2016, 02:44:28 PM
There should be no DC present after the 2503 since the transformer would block it.

What is the opamp and who built it?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: plevine on September 23, 2016, 04:05:52 PM
I believe the opamp is an SL-2520 (Scott Leiberman). This one was borrowed for testing purposes, so I can't vouch for it's condition. Does this seem like a problem with the op amp itself?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on September 23, 2016, 04:14:53 PM
I believe the opamp is an SL-2520 (Scott Leiberman). This one was borrowed for testing purposes, so I can't vouch for it's condition. Does this seem like a problem with the op amp itself?
Highly unlikely for a red dot. It is Liebers BTW  ;) Is the amp fully seated? http://capi-gear.com/catalog/DOA_Install.php

If so I would next look for bad solder joint.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: plevine on September 25, 2016, 01:20:52 AM
I reflowed the opamp connections and it works! Thanks Jeff. I had already done that at one point, but I suspect I seated the opamp when the pcb was already mounted on the metal frame (gingerly..), and that pressure probably lifted something. Anyway, it sounds wonderful - really appreciate you making yourself available to help!
All the best
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: geardude on December 24, 2016, 12:35:07 AM
I'm having an issue with my latest 312 build- the phase invert DRASTICALLY alters the sound when engaged. Sucks up all the bass when engaged.

Never encountered this with the 26,or 28 and I've built dozens of them however this is my first 312 so maybe this is normal? But I doubt it.

I've touched up all three button switches & tried a different xlr just to see if a cheap chord was the suspect and I'm still seeing this issue.

Any advice & happy holidays
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on December 29, 2016, 08:56:01 PM
Check the output transformer wiring as well as solder joints on the t-pad.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: geardude on December 29, 2016, 11:19:03 PM
Check the output transformer wiring as well as solder joints on the t-pad.

Well hope the holidays are treating you well. Perhaps I really made a glaring and obvious mistake, I've attached a picture below. I just did the litz transformer in order down the line....so this is probably it?! facepalm I realize now after checking the hardware page for the litz it states the correct order now so I guess I'll whip out the desolder tools
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on December 30, 2016, 07:18:22 PM
I just did the litz transformer in order down the line....so this is probably it?! facepalm I realize now after checking the hardware page for the litz it states the correct order now so I guess I'll whip out the desolder tools
Yeah that is the situation for the smaller 2623-1 Litz option but due to the winding process, the colors for the 2503 need to be swapped around a bit. I try to keep it simple. You HAVE to follow the color code chart on the bottom left of the 2503-Litz datasheet here http://www.capi-gear.com/catalog/images/gallery/2503/2503-Litz-specs.pdf
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Santos76 on January 23, 2017, 10:54:49 AM
Hey there, I just built 2x 312's and the pre sounds fantastic. I love it! I feel like it has way more mojo somehow than my VP26's & VP28's to my ears although I love the like hell too. With my Lovechilds it's bliss. However, on one of the two 312's  I built the phantom isn't working. I examined both pres and they are identical and were built side by side simultaneously. When I engage the phantom on the unit in question there is a loud pop & then a powering up noise that leads to dead silence and no signal. I have been using the unit with the phantom disengaged and getting great sounds with dynamics but the phantom is a no go right now.

The leads on the phantom switch are in the correct position. The solders on the PCB connected to the switch look good. Before I start de-soldering and re-soldering the whole thing,  are there any dead giveaways/go to's I can try first?

Thanks,

C
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on January 23, 2017, 12:35:01 PM
Without seeing it, I don't know if there are any dead giveaways. You'll just have to meter where phantom power comes in the module and make sure it is evenly distributed across the In Lo and In Hi as shown on the schematic. There's only a handful of components to check, so you should see pretty quickly who the culprit is. No need to resolder the whole thing if it works properly with a dynamic microphone.

Thanks!

Paul
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: rwrwrw on March 16, 2017, 12:33:47 PM
Hi, I've successfully built 2 of the vp312 litz stepped gain modules and I really like the way they sound. However, the phantom power LED doesn't work for either of them - is this a big issue? I currently don't have any mics that need phantom power, but I want to make sure that I'm not going to somehow fry the board if one of the switches get flipped. The modules were built at different times. I'm guessing I may have put the LED in backwards?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on March 16, 2017, 01:08:34 PM
.....I'm guessing I may have put the LED in backwards?
This is most likely the problem.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: rwrwrw on May 06, 2017, 07:44:57 AM
This is most likely the problem.

Yep that was it. Phantom power works fine.

On another note, I'm finding that I like the tonal variations that the optional resistor adds. Would it be hard to wire a switch into the vp312 so the user can choose whether they want the optional resistor in or out on the fly? An air switch I guess?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on May 06, 2017, 03:17:01 PM
Yep that was it. Phantom power works fine.

On another note, I'm finding that I like the tonal variations that the optional resistor adds. Would it be hard to wire a switch into the vp312 so the user can choose whether they want the optional resistor in or out on the fly? An air switch I guess?
Yeah for sure. Super easy. And after all its DIY!
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: rwrwrw on May 07, 2017, 12:21:00 PM
Cool. Unfortunately I'm a bit of a noob when it comes to figuring out how to mod something like this on my own... Whats the best way to go about adding a switch? Do I need a SPST switch?

Thanks for your help! Feel free to point me in the direction of any literature if that would be easier. Or if anyone else has any suggestions that would be greatly appreciated!

Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on May 07, 2017, 02:38:59 PM
Yes a SPDT switch is all you need. Either the 150k R gets connected to ground or it floats. Its pretty east once you wrap your head around what is happening.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: rwrwrw on May 07, 2017, 05:53:22 PM
Hm alright I've got some spdt switches, lemme see if I've got this right - I've attached a photo of a possible diagram... It is the same wiring as the phantom power switch?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on May 07, 2017, 05:56:12 PM
Hm alright I've got some spdt switches, lemme see if I've got this right - I've attached a photo of a possible diagram... It is the same wiring as the phantom power switch?
Bingo! You got it!
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: rwrwrw on May 07, 2017, 05:59:55 PM
Sweet, thanks for your help! Excited to try this out now
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: rwrwrw on May 08, 2017, 09:34:47 PM
Got em modded up now (the 312 on the left was the guinea pig...)! The difference is subtle, but its a nice option to have. I find that if I want something to cut more in the mix, then I don't want the resistor in there. But if I need a track to sit back in the mix, then that's when I want the resistor.  Thanks again for your help jsteiger! Now heres one of the things I can't wrap my head around yet... Why does this resistor effect the high frequencies?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on May 08, 2017, 10:05:13 PM
The 150k load R increases the load the mic sees from around 1k2 to 1k.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 09:28:48 AM
Hi Jeff!
I finish soldering 2 VP312, now I believe I have about 25 of your preamps! Thanks for your Job!
One is OK an the other is OK to,  but the output pot doesn't work.... it let the signal pass but I can't push down the output level?
All your Quick Startup Testing Procedure is ok for me, I read all the posts on this blog and don't find why this output level doesn't work? Can you help me?
I change the amp op... I've the same problem...
Thanks
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 09:58:23 AM
some picture
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 09:59:32 AM
some picture
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 10:00:33 AM
the last
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on July 15, 2017, 10:04:41 AM
The output pot is a connection between the output transformer and the Bourns T-pad. If you are getting full signal all of the time then there is a short or bad connection on the transformer leads PCB connection points or the T-pad solder points. You could pull the Bourns pad and measure resistance to see if changes when you turn it to verify it is good.

It has to be related to one of those things assuming it is passing full signal.

Thanks!

Paul
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 11:53:02 AM
Thanks Paul,
I do all the point welding around the output transformateur, and the output pot RV1... I still have the same problem!
I try to make continuity test between the output transformateur and RV1, to try to understand but I don't really now which point is which bourn, (I don't know if it's clear...)
your believe you can help me or must I wait Jeff answer me?

Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 11:54:00 AM
Could RV1 be broken?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 12:13:34 PM
I mesure between "out Hi" and the blu green yellow & orange bourns of the out put transformer, the value is moving so RV1 is Ok but why the sound does not fall?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on July 15, 2017, 12:40:23 PM
Go to CAPI's website and pull up the VP312 schematic:

http://www.capi-gear.com/catalog/images/gallery/VP312/VP312-VPR-Rev-B-Schematic.pdf

You should be able to trace where you should be getting continuity.

You can also just pull Bourns T-Pad and see if you are still getting signal to the output.

Either you have a bad T-Pad (possible, but unlikely) or there is a short between the Blue transformer solder pad and Out Hi (pin 2 on the edge connector).

Thanks!

Paul
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 01:17:07 PM
Thanks again Paul!
I Pull RV1 and there is a very very little sound which pass again! Is it normal? or should it have no sound?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on July 15, 2017, 01:33:41 PM
The Out Lo is still connected (see schematic) so there will be something, but it should be very low output and possibly sounding very thin.

Take your meter and one at a time measure resistance for the wiper and CW for all three sections of the T-Pad while turning it. Then do the same for the wiper and CCW. If the resistance changes for each one then it should be good and there is a soldering issue.

Thanks!

Paul
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 15, 2017, 01:54:40 PM
Ok Thanks Paul!
It's wright it's a very little sound very thiny...
I must soldering again RV1, if I understand! Cause it is a little bit damage, I prefer get a knew one! Can I buy it in France do you know?
And my family arrive I must welcome them.... so sorry.... But very thanks about all this advice! I give you some news when I have a new RV1!
Very thanks!
read you
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on July 15, 2017, 02:49:43 PM
In the meantime you can swap it with one that is working to verify.

Thanks!

Paul
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Winetree on July 15, 2017, 03:18:15 PM
Is there any known way to replace or repair the 51X (24 volt) tab that has be removed from the P.S.B.?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: the new frenchy on July 21, 2017, 08:23:07 AM
Hi Paul! With a new output pot, the problem is gone! All my preamp is Ok! thx a lot for your help!

Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on July 21, 2017, 08:54:13 AM
Hi Paul! With a new output pot, the problem is gone! All my preamp is Ok! thx a lot for your help!

You are welcome! Enjoy that sweet preamp.

Thanks!

Paul
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: haselnusse on November 02, 2017, 02:31:17 PM
Hi all,

i just finished builing 4 VP312s and by accident noticed a small amount of microphonics on all 4 units when tapping at the knobs with no mic connected and max gain, anybody experienced that before? all components are mounted tight to the PCBs...

cheers
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on November 02, 2017, 03:46:21 PM
Hi all,

i just finished builing 4 VP312s and by accident noticed a small amount of microphonics on all 4 units when tapping at the knobs with no mic connected and max gain, anybody experienced that before? all components are mounted tight to the PCBs...

cheers
I have never checked this way but not sure its relevant since the input should be terminated in some way. What rack is this BTW?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: haselnusse on November 03, 2017, 06:55:22 AM
A Lindell 510 (the old rev without the D-sub connectors on the back). Never noticed any microphonics before with the two VP28 and some homebuilt modules... i will do some more testing today.

thanks for the fast reply!
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: haselnusse on March 21, 2018, 03:56:50 PM
Hi,

i recently encountered a problem with one of my VP312s, it started making weird wind-like noises and crackled from time to time. When i engage the pad or switch the polarity there is a loud pop which almost clips my AD - way louder than on any of the other VP312. Also there is some microphonics when i lightly hit the frontplate with my finger. What could the problem be?

Here is what i did:

- carefully reflowed all solder joints, especially around the switches, trying not to overheat them
- checked all traces for continuity
- measured DCR as mentioned in the VPXX build assembly guide

The opamp checks out fine, works like a charm in any other of my Pres.

Any help would be much appreciated!
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on March 21, 2018, 04:31:20 PM
Hi,

i recently encountered a problem with one of my VP312s, it started making weird wind-like noises and crackled from time to time. When i engage the pad or switch the polarity there is a loud pop which almost clips my AD - way louder than on any of the other VP312. Also there is some microphonics when i lightly hit the frontplate with my finger. What could the problem be?
Sounds like a bad solder joint to me.

Could also be a rack issue. What rack is it?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: haselnusse on March 22, 2018, 06:22:18 AM
Thanks for the fast answer!
It is a Lindell 510 (the first version without the sub25 connnectors).
Could it be that i overheated the Pad switch when soldering it in or reflowing the solder joints?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: jsteiger on March 22, 2018, 09:43:25 AM
Thanks for the fast answer!
It is a Lindell 510 (the first version without the sub25 connnectors).
Could it be that i overheated the Pad switch when soldering it in or reflowing the solder joints?
Unlikely. I would honestly try another rack especially if you have an early version. Many reports of similar behavior with those racks and a few other Asian models.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: haselnusse on March 23, 2018, 06:48:16 AM
Thanks, i tried the Pre in different slots of that same rack but will try to get my hands on another rack to try them in. Cheers for all the help!
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Mole-man on November 19, 2018, 12:05:26 PM
Hello,

I recently purchased an unused vp312 rev a kit second hand and it's missing resistor R9. Can any resistors with the same spec (160r, 1%tolerance, 0.25watt,metal film) be used?

Thanks.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: [silent:arts] on November 19, 2018, 12:12:33 PM
Yes  8)
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Potato Cakes on November 19, 2018, 12:54:44 PM
Thanks for the fast answer!
It is a Lindell 510 (the first version without the sub25 connnectors).
Could it be that i overheated the Pad switch when soldering it in or reflowing the solder joints?

I had a Lindell 510 (first version) and it would power some pres but not others and had trouble with most compressors. I contacted my gear dealer and sent mine back and they sent me a new one with an external power supply. My recommendation would be to get it swapped out. I think they will just do it since that first design is plagued by a bad power scheme.

Thanks!

Paul
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Mole-man on November 26, 2018, 08:51:16 AM
Hello,

I accidentally soldered the bourns t-pad too close to the board. I have managed to re-soldered and get it into the correct position but am wondering whether all the soldering may have overheated it and caused some damage..
Should I complete the rest of the build and test it or could a faulty t-pad cause damage to other components?

Thanks in advance :)
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: [silent:arts] on November 26, 2018, 09:42:20 AM
A broken T-Pad won't damage anything.
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Mrosso on April 24, 2019, 11:32:34 AM
I have just finished one of two VP312DI pres for 24V 51X. The pre seems to be functioning  as expected; however, the phantom LED is not working. The first time I fired up the pre and flipped the switch for +48V, the LED flashed for a second then went dark. The phantom power is working, but the LED is dark. Double-checked polarity. Is there anything special about the LED contained in the kit? I used a generic old red LED I had laying around instead. Shouldn't all  3mmred LED be same specs?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Walrus on April 24, 2019, 12:12:49 PM
You have got the 10kOhm resistor in series with the LED haven't you?
Title: Re: [Build] CAPI VP312~500/51x Series~Preamp Kit~Official Support Thread
Post by: Mrosso on April 24, 2019, 06:18:12 PM
Kevin,
No, I do not. I thought that the Rev D boards didn't need resistor on the LED.
Thanks!