Timh

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!


kato


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, 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...

Timh

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.

Timh

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.

jsteiger

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
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Timh

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

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?
« Last Edit: August 19, 2013, 02:57:25 PM by Timh »

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

jsteiger

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.
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CAPI is not affiliated with, endorsed by, or sponsored by API.

Rpbr

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

jsteiger

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.
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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?

jsteiger

Skim back thru this thread for some pointers.
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CAPI is not affiliated with, endorsed by, or sponsored by API.

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



gabygab

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

jsteiger

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
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CAPI is not affiliated with, endorsed by, or sponsored by API.

gabygab

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!
« Last Edit: July 19, 2014, 02:53:42 PM by gabygab »

zaiata

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.   

zaiata

Success!!!


gabygab

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.

Edward

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


 

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