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

[critterkllr]

I think this is the first report of this on a green PCB I have heard.

The circuit is comprised of
A2
CR3
LED5
C11
R17-R19, R27, R28

I would look for solder bridges,/cold solder joints on the amp or incorrect part placement of the above.

Great, will do. That’s for responding on your spring break, Jeff!

 

[MountCyanide]

I'm just gonna detract from the support thread to give props to Jeff for a fun and supremely well designed kit. No hiccups. It fired right up and worked as soon as I shut off my iron. Nice! Seems it's gonna pair well with my AEA Ribbon.

 

[critterkllr]

Great, will do. That’s for responding on your spring break, Jeff!

I guess it would help if I actually soldered in A2, huh? Sockets have made me lazy. Thanks again for the help!

 

[forgotteng]

I'm having some issues with my build. The pre passes audio but doesn't seem to sound like my other VP28. It seems like there is a little frequency issues with the top end and the bottom. When I engage the HPF it really sucks the bottom. on both the 40 and the 80. It seems to drop out 500 and below. (Just a guess but suffice it to say it's a lot higher than 80Hz. It looks like the caps are in the right position but am I missing something?

 

[jsteiger]

I'm having some issues with my build. The pre passes audio but doesn't seem to sound like my other VP28. It seems like there is a little frequency issues with the top end and the bottom. When I engage the HPF it really sucks the bottom. on both the 40 and the 80. It seems to drop out 500 and below. (Just a guess but suffice it to say it's a lot higher than 80Hz. It looks like the caps are in the right position but am I missing something?

The typical questions must be answered. What opamps are in there and who built them? They must be known good working amps. Short of that, I would look at all solder joints. A bad joint could easily cause this type of symptom.

 

[forgotteng]

The typical questions must be answered. What opamps are in there and who built them? They must be known good working amps. Short of that, I would look at all solder joints. A bad joint could easily cause this type of symptom.

Thanks Jeff, I did take my working opamps out of my existing working VP28 and it was the same results. Should  I be looking at solders on specifically the HPF card or on the whole card. Forgive me if these are dumb questions I'm just trying to see if there is a strategic starting point.

 

[jsteiger]

Thanks Jeff, I did take my working opamps out of my existing working VP28 and it was the same results. Should  I be looking at solders on specifically the HPF card or on the whole card. Forgive me if these are dumb questions I'm just trying to see if there is a strategic starting point.

Your best plan of attack is to use the published Test Points guide to see where things go bad. That will help narrow down where to look for trouble.

 

[tydbowl]

Hey guys... I've been trying to troubleshoot one of my VP28's that is -9db too quiet.  I checked my solder joints and re-soldered ones I thought might be questionable but I think they look good.  I have tested this in the same slot, same op amps, same converter, confirmed unity knob positions.  It sounds fine but just quiet.  I am using the Rogue Five Op Amps

I used my audio interface and a Fluke 115 Multimeter.  I tried to get it as close to 1.228 volts from the interface output but it was occasionally bumping 1.229

everything starting at TP3 and below is low

Here are my test point results...

TP1 - 111.6 mV
TP2 - .702 V
TP3 -  1.242 V
TP4 -  307.2 mV
TP5 - 307.2 mV
TP6 - 307.2 mV
TP7 - 643.4 mV

OUTPUT - .427V

Any help appreciated!
Tyler

 

[tydbowl]

Bump 

 

[jsteiger]

Hey guys... I've been trying to troubleshoot one of my VP28's that is -9db too quiet.  I checked my solder joints and re-soldered ones I thought might be questionable but I think they look good.  I have tested this in the same slot, same op amps, same converter, confirmed unity knob positions.  It sounds fine but just quiet.  I am using the Rogue Five Op Amps

I used my audio interface and a Fluke 115 Multimeter.  I tried to get it as close to 1.228 volts from the interface output but it was occasionally bumping 1.229

everything starting at TP3 and below is low

Here are my test point results...

TP1 - 111.6 mV
TP2 - .702 V
TP3 -  1.242 V
TP4 -  307.2 mV
TP5 - 307.2 mV
TP6 - 307.2 mV
TP7 - 643.4 mV

OUTPUT - .427V

Any help appreciated!
Tyler

I think the only one I would worry about is the output. How are you measuring the final output? It is floating with no reference to ground so you can only get an accurate reading between the +/- with your DMM probes or by checking the reading into PT's etc. Don't bother probing between + and ground or - and ground.

 

[tydbowl]

I think the only one I would worry about is the output. How are you measuring the final output? It is floating with no reference to ground so you can only get an accurate reading between the +/- with your DMM probes or by checking the reading into PT's etc. Don't bother probing between + and ground or - and ground.

I measured the output on pins 2 and 3 of the XLR coming out of the card slot like the daw output.  Is that correct?

Thanks!!

 

[jsteiger]

I measured the output on pins 2 and 3 of the XLR coming out of the card slot like the daw output.  Is that correct?

Thanks!!

Yes.

You will need to verify that the transformer is good. The easiest way is with some DCR measurements. The following is for a Litz 2623-1. If you have the EA version, just follow the cross reference chart on the transformers datasheet.

For the Litz 2623-1 you should have the following:
Black to Red, 15.7Ω
Pink to Gray, 31.5Ω
Violet to Orange 31.5Ω

Make sure your DMM range is set to below 200Ω. Make sure all leads are floating and not touching anything including each other.

There should be no measurable resistance between leads except for the ones shown above.

 

[PerspectiveSound]

Hey everyone, my first post here, I came looking for support as my first foray into diy audio has not gone as planned, there were clouds of smoke involved... I built a CAPI 511 rack and vp28 preamp, was pretty careful to follow the proper build and leave no obvious bad soldering points on either piece, but I finished the pre up, plugged it in the rack, and I started smelling smoke... 

I immediately cut the power to the rack, I did however notice that the power link switch for that rack space was on which made me want to test a different rack space, after powered everything down I switched the rack space and the pre powered on, leds working, no smoke, but no audio signal either, just some faint noise that clicks when phantom power is engaged.

It seems likely that the rack is fine and the pre was also fine until I set it up wrong. My question would be if there is a way to pinpoint which components might have failed and might be replaced, also to make sure the rack is OK and won't damage other gear since I planned to build other pieces.  I'm sure this looks like a newbie story, any help y'all could give me would be much appreciated!

 

[jsteiger]

The obvious way is to look for charred parts. You never mentioned if the opamps were kits you built or pre-built from the store.

We should only handle VP28 questions here. Testing the rack is simple but should be handled on the respective rack support thread. Please skim it before posting as I am sure it has been covered before.

 

[PerspectiveSound]

Oh yes I should have said, I built the opamps GAR2520, I didn't see any burned parts but I just checked and the transformers have a strong burnt odor, I will look through the power rack forum for testing as you suggest but is it possible the power link issue cause the transformers to burn out on an otherwise well built pre-amp? Thanks so much for your quick response

 

[jsteiger]

Oh yes I should have said, I built the opamps GAR2520, I didn't see any burned parts but I just checked and the transformers have a strong burnt odor, I will look through the power rack forum for testing as you suggest but is it possible the power link issue cause the transformers to burn out on an otherwise well built pre-amp? Thanks so much for your quick response

It will not be the transformers. It will likely be on the opamps or the 10Ω damping resistors that are inline for each opamp's power rails.

A golden rule has been broken...do not try to test a fresh preamp build with fresh opamp builds. There is truly no way of knowing where the problem is at. It could be one amp, both amps, the preamp or any combination of the above which is WAY too many variables.

There is no gold finger for pin-6 so the DC-Link switches in the rack are irrelevant to the VP28.

 

[tydbowl]

Yes.

You will need to verify that the transformer is good. The easiest way is with some DCR measurements. The following is for a Litz 2623-1. If you have the EA version, just follow the cross reference chart on the transformers datasheet.

For the Litz 2623-1 you should have the following:
Black to Red, 15.7Ω
Pink to Gray, 31.5Ω
Violet to Orange 31.5Ω

Make sure your DMM range is set to below 200Ω. Make sure all leads are floating and not touching anything including each other.

There should be no measurable resistance between leads except for the ones shown above.

Thanks Jeff,

Here are my measurements on the output transformer leads...

Black to Red, 15.7Ω
Pink to Gray, 32.8Ω
Violet to Orange 31.1Ω

I went ahead and measured other colors together after you mentioning there should be no measurable resistance between the other colors. I am getting resistance between these other leads..

Grey and Orange 33.3
Grey and Violet 63.7
Pink and Violet 31.1

 

[jsteiger]

Thanks Jeff,

Here are my measurements on the output transformer leads...

Black to Red, 15.7Ω
Pink to Gray, 32.8Ω
Violet to Orange 31.1Ω

I went ahead and measured other colors together after you mentioning there should be no measurable resistance between the other colors. I am getting resistance between these other leads..

Grey and Orange 33.3
Grey and Violet 63.7
Pink and Violet 31.1

It looks like there is an internal short with this transformer. Send me an email thru the store referencing this post and I will get you a replacement.

 

[onss13]

Hey all/Jeff,  I’ve read through this thread because of a similar issue and was hoping to find the solution here.  I have two VP28s in a Capi 11 space rack and both sound perfect but one is having the signal present led issue others have had. It stays on with no signal actually present but turns off when 48v is switched on. Makes no sense.
I’ve ran a few pure sine waves  into it from a calibrated generator I borrowed from work. Both pres look damn near identical in PT.
Doesn’t have any noise on the output when not sending tones through it. The led seems to have no discernible effect on the sound whatsoever.
Switched the placement in the rack as well as having it in there by itself. No change.
It’s on with or without opamps installed.

For years I was a bench tech as well as building custom effects. I have appropriate tools and supplies but as I am human, I did reflow every things on the board as a precaution. Again, no change at all.

Anyone have some pointers. Or a partial schematic to start tracing.

 

[jsteiger]

Hey all/Jeff,  I’ve read through this thread because of a similar issue and was hoping to find the solution here.  I have two VP28s in a Capi 11 space rack and both sound perfect but one is having the signal present led issue others have had. It stays on with no signal actually present but turns off when 48v is switched on. Makes no sense.
I’ve ran a few pure sine waves  into it from a calibrated generator I borrowed from work. Both pres look damn near identical in PT.
Doesn’t have any noise on the output when not sending tones through it. The led seems to have no discernible effect on the sound whatsoever.
Switched the placement in the rack as well as having it in there by itself. No change.
It’s on with or without opamps installed.

For years I was a bench tech as well as building custom effects. I have appropriate tools and supplies but as I am human, I did reflow every things on the board as a precaution. Again, no change at all.

Anyone have some pointers. Or a partial schematic to start tracing.

What version of PCB is this?

The 48V switch has literally nothing to do with the signal present circuit.