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

[jsteiger]

Hey! Done building 1 VP28, im getting sound and all the buttons are working functionally, LEDs working, phantom working etc.
have some test results. But the signal is very weak, measuring somewhere -70 to -30 db on my audio interface, with a sm57 and fader and pre gain all the way max. Testpoints 1-5 seem to measure values that are good. but 6-7 not really anything there.

1. 109mA
2. 696mA
3. 1.26V
4. 307mA
5. 309mA
6. 0
7. 0

Hope someone could help! Thanks.

Between TP5 and TP6 is the HPF PCB so check that along with the 5-pin header and the mini toggle switch as signal passes thru it.

 

[mariush]

Looks good there, reflowed the solder joints, could it be the op amps? Whats between tp6&7?

 

[jsteiger]

Looks good there, reflowed the solder joints, could it be the op amps? Whats between tp6&7?

If its down at TP6 most likely the issue is between TP5 and TP6.

The fader amp is between TP6 and TP7.

If you aren't testing with 2 known good working opamps then trying to "fix" the module is like a dog chasing its tail.

 

[mariush]

If its down at TP6 most likely the issue is between TP5 and TP6.

The fader amp is between TP6 and TP7.

If you aren't testing with 2 known good working opamps then trying to "fix" the module is like a dog chasing its tail.

Ah ok, too bad. Might have to buy some preassembled opamps then!

 

[jsteiger]

Ah ok, too bad. Might have to buy some preassembled opamps then!

You can remove the fader amp and check for ACV at that opamp's non-inverting input socket. If there is not signal then the issue is previously where I said to look. I would dbl check TP5 and TP6 at the same time.

 

[mariush]

How would I measure that socket? The + & - ?

 

[mariush]

Everything works PERFECTLY! Thanks so much for the help! And it sounds really nice!! So good on snare & kick so far tested, driving the preamp and backing off the fader, really makes them pop!
now gonna build another one! at least I know what went wrong for next time =)

 

[jsteiger]

How would I measure that socket? The + & - ?

Same as you are measuring the other test points. + socket to ground looking for ACV.