[BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Good back!
Change the burnt resistors of the VP28, verify that everything is in order and we tried with a friend, the two preamps worked very well for now!. If something happened to us and I would like you to guide me, because we are new with this. We had the box turned on and we took out one of the cards to put them in another slot, but when we moved it, PR1 and PR3 burned again, I changed the resistors again and they didn't burn anymore. It could have been caused by the fact that the box was turned on?

Regards!
Burned up 10Rs is a result of a respective opamp problem.
 
Burned up 10Rs is a result of a respective opamp problem.
But when changing the resistors again, using the same op amp, it no longer burned again. When changing the card while the lunch box was on, that happened, it could have been the cause that the lunch box was on and we changed places like that
 
But when changing the resistors again, using the same op amp, it no longer burned again. When changing the card while the lunch box was on, that happened, it could have been the cause that the lunch box was on and we changed places like that
Was the amp properly seated? Classic Audio Products, Inc.

Hot swapping should be no problem.
 
Hello! I have a VP28 that’s quite low in level to others.
I got the output reading 1.22vAC with gain/fader set to unity and here are the measurements:

1 - 419 mVAC
2 - 1853 mVAC
3 - 1.17 VAC
4 - 291 mVAC
5 - 291 mVAC
6 - 291 mVAC
7 - 613 mVAC
As you can see the TP1/2 are the ones that are quite far off!

Any idea where to look based on this?

Cheers!
May I bump this in case it has been missed!
 
I put my DIY Vp28 into my chassis, The green signal light is keep tuning on even i didn't connect the microphone. And their is not signal pass through. Can anyone know whats wrong with my build.
Thank you so much
 

Attachments

  • IMG_5142.jpg
    IMG_5142.jpg
    3 MB · Views: 2
  • IMG_5143.jpg
    IMG_5143.jpg
    2.5 MB · Views: 1
  • IMG_5144.jpg
    IMG_5144.jpg
    2.4 MB · Views: 0
What are the opamps and who built them?

They're both CAPI 0252 built by myself! I built 2 VP28s and the other one works fantastic!

Further testing today - I switched the preamp/fader DOAs to see if that opamp was the issue and both the preamp and fader gain seemed work great, but the Q8 and Q10 transistors on the dodgy DOA were getting REALLY hot - definitely feels like a problem with that specific op amp
 
I would make sure all diodes are facing the proper direction.
They're both CAPI 0252 built by myself! I built 2 VP28s and the other one works fantastic!

Further testing today - I switched the preamp/fader DOAs to see if that opamp was the issue and both the preamp and fader gain seemed work great, but the Q8 and Q10 transistors on the dodgy DOA were getting REALLY hot - definitely feels like a problem with that specific op amp
I would make sure all diodes are facing the proper direction.
 
I not sure if this is a problem or not. However my builds output levels are really hot. Need to use the pad to get it close to line level. Everything is working that I see of. Any ideas?
 
A while ago now I got some VP28’s - all worked great except one which had a lower output.

I measured the windings and one transformer reads 31.20ohms between purple and pink. And the other is open between purple and pink. Wondering whether this might be an indication of a faulty transformer?

Cheers!
 

Latest posts

Back
Top