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

[mrmike186]

Here's another.

 

[mrmike186]

Just in case. Thanks again.

 

[jsteiger]

All R's look to be properly placed so next I would think bad solder joint since you ruled out the opamp and rack slot etc.

The next step would be to inject signal and trace it thru the circuit to see where the change happens. The good news is you have a good working unit as a benchmark.

 

[mrmike186]

Thanks Jeff for looking at the pics. I will look at the solder joints again and hopefully find the culprit. Not sure how to inject a signal into the circuit to test but I'll look at the solder joints first.

 

[mrmike186]

Update!

After inspecting the solder joints and not finding anything obvious I decided to swap output transformers and sure enough, the low output followed the transformer. There is one difference and I'm not sure why but the low output transformer is now very distorted when before it was just lower output.. Hopefully a new output transformer is the cure.

 

[pkordel]

Hi guys, new capigear fan here.

I just finished building a VP26, a VP312DI and a grouipdiy 511 rack to house them in. After a false start where I fixed my backwards wiring of the PSU to rack connection everything fired up and passes audio.

Results:

The VP26 worked flawlessly at first (more on that later). The VP312DI exhibits noise, a low level crackling and a very noisy Pad switch - likely a cold solder joint somewhere. The DI part has no issues and sounds amazing to my ears. I have the IC module installed.

The VP26 took a hit when I removed it to experiment with another DOA. With all power off I reseated it and when I applied power, it caught fire. More precisely, R14, the carbon film 10R resistor next to the OT. Not seated properly or at an offset is my guess. I do have a spare in my workshop but it's a 1W instead of the 1/2W included in the kit. OK to substitute?
Hoping that the resistor was meant to burn in order to protect the OT...

Seems like the rack slot where the fire occurred stopped passing audio as well. I measured voltages on the 18 pin and all checks out. I guess I'll have to break it down to peek behind the backplane.

Any tips and insights are welcome, cheers!

 

[jsteiger]

Hi Peter

The 10Ω 1/2W R cooking sounds like a possible rack wiring problem. All that R does is connect the pin-1 card edge gold finger to pin-5 card edge gold finger. Its a safety feature in case a rack has the pin-1 card edge floating in the rack.

The VP312DI questions would be better served if you post on that specific support thread.

 

[TRevMFB]

I was thinking of posting this in the Lab, yet this forum page appears to be the larger for the VP2x series stuff. Over a year ago I purchased a pair of used prebuilt VP2X with the VP26 RevA.2 board. Tested them, and did notice a slight difference in audio figured this was do to the different opamp in the unit. Unit A has a 2521 opamp. Unit B doesn't have a specific model marking on the board.

Over the next few months I mainly used Unit B for snare drum and a few occasional other sessions, yet hardly used the other unit. Well today I was going through my outboard gear just making sure everything is still up to par. Unit A had a major issue, a very low output and was extremely distorted. I decided to check the opamp and swapped them. Unit A then fired right up. Great, I figured it would be an easy fix and I'd had to only replace the opamp. Just to be certain I tested to "faulty" opamp  (2521)from Unit A in to Unit B, and it worked just fine. I decided to compare to 2 units, and Unit A was still thinner and more aggressive sounding than Unit B. Proceeded to swap the opamp back into their original units and the issue was still the same. Unit A sounding thinner and more aggressive. I left my 500 chassis powered on for an hour, went back to test them again and the output of Unit A had dropped significantly.

Is this an issue with the output transformer or do I have a larger issue at hand?

 

[jsteiger]

Is this an issue with the output transformer or do I have a larger issue at hand?

I would first look for shoddy/cold solder joints. Buying used DIY can be tricking. You may not know the credentials of whomever built it.

Also, are those amps seated fully? http://capi-gear.com/catalog/DOA_Install.php

 

[TRevMFB]

I would first look for shoddy/cold solder joints. Buying used DIY can be tricking. You may not know the credentials of whomever built it.

Also, are those amps seated fully? http://capi-gear.com/catalog/DOA_Install.php

I’ll have the double check the unit in question to see if the oamp isn’t seating all the way down with the paperclip trick.

Does anyone happen to have the DIY schematic for the vp26 just to ensure everything is where it should be?

 

[jsteiger]

Does anyone happen to have the DIY schematic for the vp26 just to ensure everything is where it should be?

Send me an email thru the store. I'll dig one up for you. The good news is you have a good one to compare to. It'll be easy to scan part by part to see if something is not the same. Keep in mind you cannot measure R's with both ends soldered in circuit. Just use the color codes for a quick visual scan.

 

[TRevMFB]

Send me an email thru the store. I'll dig one up for you. The good news is you have a good one to compare to. It'll be easy to scan part by part to see if something is not the same. Keep in mind you cannot measure R's with both ends soldered in circuit. Just use the color codes for a quick visual scan.

 

[mrmike186]

Update!

After inspecting the solder joints and not finding anything obvious I decided to swap output transformers and sure enough, the low output followed the transformer. There is one difference and I'm not sure why but the low output transformer is now very distorted when before it was just lower output.. Hopefully a new output transformer is the cure.

UPDATE #2

After a couple of weeks trying to figure this out it appears the problem has been the DOA's I've been building myself and not the tranformer.  It can be tricky tracking down the problem in a 500 rack because if one unit is not working properly then it affects the other units in the rack . 

My appolgies to Jeff and the manufacture of the output transformer. Jeffs customer service is second to none!

 

[kevinkace]

Reading the VP26 Rev B/C instructions: "...solder from the bottom and trim the leads. Leave the top of the PCB as is."

This goes for all components?

 

[jsteiger]

This goes for all components?

Yes indeed. All of the holes are plated thru so they internally connect top to bottom.

 

[kevinkace]

Yes indeed. All of the holes are plated thru so they internally connect top to bottom.

Thanks!

 

[drew571]

just finished a vp26 build .  if done a lot of these before but this one passes audio but at very low volumes.  i've switched out the opamp with two different working opamps that have been tested in another preamp to make sure they are working.  i've also went back through and resoldered all the points to make sure there's no cold solders.  still low output.  background noise also has a weird "ticking" going on.  recorded a snippet so you can hear. 

any suggestions?

https://www.dropbox.com/s/ts9f65rkf1mqcml/vp26%20issue.mp3?dl=0

 

[jsteiger]

Sean, wrong build thread but this is normal from my experience.

 

[seanweaverguitar]

Oh shoot, sorry. Total accident! Just noticed while checking back in here this evening. I'll remove the original post and re-post on the proper thread. Thanks for understanding (I'm normally with it; insomnia last night may well have led to not reading the proper thread title!) Best wishes.

 

[albertoaudioengineer]

just finished a vp26 build .  if done a lot of these before but this one passes audio but at very low volumes.  i've switched out the opamp with two different working opamps that have been tested in another preamp to make sure they are working.  i've also went back through and resoldered all the points to make sure there's no cold solders.  still low output.  background noise also has a weird "ticking" going on.  recorded a snippet so you can hear. 

any suggestions?

https://www.dropbox.com/s/ts9f65rkf1mqcml/vp26%20issue.mp3?dl=0

Im having a similar problem. Built 3 - VP26, they pass audio but at low volume. Gain needs to be cranked all the way up.
Went over all the solder points and the issue is still there. Not sure where to go from here.