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

Hey everyone!

Man I love these builds!  I have just a few questions, none of which are troublesome, but are nagging me none the less.

I searched this thread long and hard, and I've already reinspected the board and found no glaring issues... I will be inspecting the opamp (which is a pre-built Red Dot), and reflow solder to the switches along with other parts of the board to be sure there are no cold joints or bridges, but I figured I would ask these questions first in case there's a glaringly obvious symptom.

Before I continue I just want to say that some of these questions/issues may simply be a combination of ignorance and incompetence, so feel free to treat them that way

a) I built two VP26s and one of the attenuators is considerably more stiff than the other.  They don't behave too different from one another, if I were to quantify them the second build (the less stiff attenuator) is slightly louder by 1-2db at the same relative attenuation.  I don't know if this is simply a result of two unmatched pots, or if I may have applied the solder tip too long on the leads... just wondering if other people experience the same issue.  Not a big deal, I can match the levels by ear/sight in the DAW if needed.

b) When engaging the phase switch I notice what sounds like intermittent clipping... a sound that isn't present if the phase switch is left disengaged.  This happens with both preamps for some reason. The "clip" or distortion occurs intermittently as I am playing, and it seems to reaction to higher "electrical SPL levels" or something; it acts somewhat like a threshold, present with a louder strum/snare hit but isn't present with slighter/softer strums or hits.  Once again it does not occur when the phase switch is disengaged... its not clipping in my DAW to be sure this wasn't digital clipping, nor the Microphone (tested it with another micpre).

Is there another element in the chain that could cause higher input levels to become more distorted only when out of phase?  I don't think its the traffo, but I can ensure there are no cold joints there.  Is there perhaps another element of the board that would react this way?  It sounds beautiful without the phase switch engaged, and has helped me fine tune my mic placement skills nonetheless!

c) The Pres run hot, which is to be expected of the API style preamps, however when running the input Gain to its extremes while using the attenuator, the signal tends to break up when distorted.  Almost as if it cuts out if the gain is too hot (again the attenuator is working so it is not digital clipping, and its more than analog "distortion" as it cuts out).  Could this be related to the behavior experienced in my previous question?  Am I just ignorant of analog clipping behavior?

Thanks in advance for any responses, if I keep proper gain structures (and try not to saturate the gain too hard), and keep everything in standard phase the sound is beautiful on both preamps.  I am very pleased with the results, and hope you all can offer some guidance,  I have a few more VP26s and 2VP28s to build as well... keepin busy...

rock n roll

Hello all. I recently bought a used VP25 already built. Everything is working ok and sounds fine, but the phantom power isn't working. When I looked at the pcb last night, I noticed a few (what looks like) burnt resistors. Looked at the build guide and it looks like the phantom switch is wired properly. Would a burnt resistor cause the phantom not to work? Just trying to figure out what replacement parts to order. I've attached a pic below.

Thanks!

Yes. I would replace the 200R and the matched 6k8's.

jsteiger said:

Yes. I would replace the 200R and the matched 6k8's.

Click to expand...

Awesome, thanks for the uber fast response!

Hey Guys

Just finished my first 2 builds of a VP26.  Both sound awesome and are working like a dream.  Quick question about the op amp though.  Should i be soldering the op amp to the board or is it just a pressure fit?

Thanks

Tim

DO NOT solder the opamp to the PCB. That would defeat the simplicity of the sockets!! Take a look here. http://classicapi.com/catalog/DOA_Install.php

Hi,

I am planning to build a VP28 with a gar2520 Full Kit Bundle.
This will be my first DIY project (with a lot of help from a good friend).

I've noticed there's a VP2x step-by-step guide on de CAPI website:
http://www.classicapi.com/catalog/images/gallery/VP26/VP2x-Assembly-Guide.pdf

But it seems this is all about the VP25 and VP26 am I right?

I bought two pre built vp26s from a local engineer. He said that one or both had some problems and he thought it might have been the gar2520 opamps. I went ahead and purchased some ml2520 from whistle rock audio. When I tested the vp26s with either opamps, I would get clipping at low levels. And it's not clipping at all times..I know it's not clipping going into my converter. I read up on this thread and found out I should reflow the solder. I did that and put it all back together again, triple checking each component and solder joint...I still have clipping. Don't know what I should do now...any suggestions?

Can you test the opamps in some other module? Maybe there are issues with the new opamp builds as well.

Also, are the opamps seated fully? Take a look at this page. http://classicapi.com/catalog/DOA_Install.php

I made sure they were properly seated and I don't have any other gear with 2520 footprint opamps. You think it's the opamps?

If it is absolutely nothing external, it is most likely the opamps.

If I purchase new opamps and it still gives me the same problem, what else could it be?

Are both pre's behaving exactly the same? Maybe it's the source? Bad mic or cable maybe? Something other than the preamp itself has been the culprit countless times. What is your source?

I believe last time I checked, one was working better than the other but both were clipping..I know it's not the sound source because that was the first thing I checked. Do you think maybe there are any bad components? Nothing looks burnt or anything like that.

What is the source?

I've tried several mics: 57, d112, sm7 (not enough gain), and a stellar cm-5. Tried a couple different cables also.

OK, that said.....the very first thing that should be done in troubleshooting a build like this is to verify 100% that the opamp used is solid and working correctly. The steps to verifying that will be different from person to person.

Okay I'll buy some kits from you can give it a shot. If that doesn't work, I don't know what else I should do

Is there anyway to test the opamps without putting them in the preamp

Install them in another known to be working module. It can be a catch 22.

You can also inject a sine wave and monitor following the signal thru the preamp. See where the THD starts. It is most likely opamp related but that is a way to find out.

Can you post a pic of the top of the PCB so I can see all of the components clearly? Just do one module for now. Mark it with a piece of tape or something so you can keep it straight later. Don't want to chase your tail.