[BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread

[jsteiger]

Hello,
I just put together my first vp26 but eveytime I try to plug it in to my lunchbox R6 starts to smoke and melt. Everything looks good and seemed to test as normal. Any idea what could be causing this?
Thanks for your time!

R6 is the 200R for the phantom supply. I would look for a direct short or solder bridge.

 

[soundvscience]

Jeff,

Just ran into my first problem with one of the VP26s I ordered from you. I'm building a full rack of VP26s as my first attempt at soldering (I'm probably a glutton for learning through mistakes) and actually have made it through the Floor Box PSU, 11 space rack and 8 preamps before encountering a problem. But still, I'm learning the ropes of PCBs and solder and I've no real idea how to troubleshoot this unit beyond what I've read in the past posts.

The VP26 I'm building right now appears to be set up correctly, however I'm getting a very low signal from the output and none of the pots or buttons on the front have any affect on the outputted signal. Phantom works just fine, but none of the pots add gain or attenuate the signal, the mute switch doesn't mute, and the pad switch doesn't pad. Not sure how that happens but I'm at a loss as to what it could be.

I took it apart and checked all my solder connections, fixed what may or may not have been cold solder joints, and touched up most of the solder joints just in case, but no change in behavior.

Any guidance would be much appreciated!

Andrew

P.S. - The 8 that I have finished sound absolutely fantastic. I'm using the stepped gain models with Scott's SL2520s and I'm beyond thrilled with them. I'm recording drums Monday through the lot and I couldn't be more excited!!!

 

[jsteiger]

Using the schematic, inject a signal and follow it thru the preamp to see where it stops. The good thing is you have other working units to compare to. There is no magic bullet per se. It will require a bit of tech detective work on your end to sort it out.

 

[soundvscience]

Looks like no signal injection will be necessary. It required very basic troubleshooting. Same problem occurred on the next unit I made so I swapped channels on a rack I had borrowed to test them at my house with and they work great. Something is up with my friends first channel, which is weird since its what I've tested the first 8 with.

At any rate, thanks for the help Jeff!

 

[Eymi]

Hi,

I'm just building my second VP312 (the first one worked fine right from the start - great kit by the way ) and i have got a question concerning one of the Capacitors:

The reading says 330uf 16V, but according to the BOM that came in the email form Jeff,  it should be 330uf 25V (the one in the first kit also says 25V). As far as my knowledge goes, i could use a capacitor if the voltage is higher, but i'm not sure if everything will be working correct if the voltage is 16V instead of 25V.

Does anyone can comment on this?

Greetings form Austria,
Chris

 

[Potato Cakes]

If you are doing the VPR version you would probably be fine with 16V, but it would be safer to stick with 25V as it is in the instructions. I think the BOM says 25V to accommodate 51X builds which runs on +/-24V. Probably makes it easier when packaging kits.

Paul

 

[Eymi]

Thanks for your response Paul,

I'm doing the VPR version of the VP312, so i guess using the16V cap in C8 will be just fine.

I found someone in the VP28 thread having the same problem with the cap in C12 and Jeff himself replied that he swapped out the  25V cap with a 16V cap, as the voltage in C12 is just around 100mV. However I can not find a schematic of the VP28 so i'm not shure where C12 in the VP28 is located, and if it is equivalent to C8 in the VP312.

Chris

 

[Potato Cakes]

Well, to be absolutely certain, measure the voltage the voltage on C8 on your other 312 and that will probably give you your answer.

But since it is the VPR version, I can't think of any reason why 16V wouldn't work.

Let us know how it goes.


Paul

 

[jsteiger]

Sorry for the slow response. I was away for 10 days.

I have made a few small adjustments to the kits lately. The main thing is a decrease in voltage for the 330uF caps as well as the  470uF coupling caps. In typical operating conditions, neither cap should see more than 100mV across it so all is good here.

 

[bulley]

Hi,

Just built my first VP26 and it actually works. Having a slight issue though, at high gains I'm getting a high pitched ringing at 6k and 12k, whether a mic is connected or not. Any tips on tracking the issue down?

Thanks,
Phil

 

[jsteiger]

What is the opamp and who built it?

 

[bulley]

It's a pre-built GAR2520 direct from you....

 

[jsteiger]

It's a pre-built GAR2520 direct from you....

OK well not that then....is the opamp fully seated? http://classicapi.com/catalog/DOA_Install.php

I have never experienced this so I suppose I would inject a sine wave and probe thru the signal path to see where this oscillation starts.

 

[bulley]

thanks Jeff, much appreciated

 

[bulley]

I think I may have put some resistors in the wrong place. Now...it's going really well, built a 2nd one, everything works, no funny noises.....except the gain pot doesn't do anything, only a slight issue. Any suggestions for that?

 

[jsteiger]

I think I may have put some resistors in the wrong place. Now...it's going really well, built a 2nd one, everything works, no funny noises.....except the gain pot doesn't do anything, only a slight issue. Any suggestions for that?

Most likely a bad solder joint somewhere between the 200R, the 330uF cap and the pot itself. Not seating the opamps fully can also be the cause.

 

[SoundOfRolf]

EDIT: FIXED IN POST #728

Hello folks!

First of all great kit, documentation and all!

I have two VP26 kits and decided to build one at a time so if I made a mistake I wouldn’t double it. The first one worked perfectly except that the phase button seemed to change the sound somehow. I re-read this thread and noticed that other had had the same issue.
I have two Red dots so the problem shouldn’t be in them. Before I started to build the second one I checked the output transformer with a DMM as described in an earlier post. It was OK. Now I’ve finished the second one and the results are the same. Everything works great, but the phase button changes the sound. I’ve must have messed up somewhere again. I’ve triple checked component values, and gone through soldering every joint again, but no change.

To exclude external issues I’ve tried different slots in the Lindell 510.
Different cables and audio interface inputs.
When I fed the preamps sine wave or pink noise there weren't any notable difference, but when I fed them some music everything cancelled out except a bump peaking about 4k. See the attached picture. The music level was at about -20db. It was same in both units.

So any idea where I should start looking for a mistake or is this a feature of the output transformer? Or am I just too paranoid…

Thanks for the help!

EDIT: I think I'm suffering the issue as gunner666 states in post#645. I've sifted through the posts, but it seems that it never got resolved?

-Tony

 

[jsteiger]

....or is this a feature of the output transformer?

No this is not a "feature". Something is wrong somewhere. The most common issue folks have is bad solder joints. Since you are repeating the result with 2 different units, I am thinking there is something else going on with the test rig setup. I am no DAW guy but have had folks with similar issues report that is was some software setting or active plug-in that they didn't know was on. I would not test them this way but I have an AP rig. Doing phase sweeps in the past shows nothing more than a near identical inversion of polarity.

 

[[silent:arts]]

When I fed the preamps sine wave or pink noise there weren't any notable difference, but when I fed them some music everything cancelled out except a bump peaking about 4k. See the attached picture. The music level was at about -20db. It was same in both units.

May I guess: the sine wave / pink noise signal generated in your DAW is Mono, and cancels out.
But the music is a stereo signal (at least I see stereo tracks in the screenshot)?
Low end is often near mono, this is why it cancels out much better.

 

[jsteiger]

May I guess: the sine wave / pink noise signal generated in your DAW is Mono, and cancels out.
But the music is a stereo signal (at least I see stereo tracks in the screenshot)?
Low end is often near mono, this is why it cancels out much better.

Ah ha. Seems logical to me. Thanks Volker.