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

[jsteiger]

Error in BOM or KIT capacitors

I'm building CAPI VP28 Rev. B. A problem has arisen with capacitors C14 and C5 which are given in the BOM as 68pF and 82pF.
The only 2 capacitors I have left which have not been placed are an NC 441J and an NC112J.
Can someone help here?
/D

There is no error. The printing on those caps is very small and not super crisp. If you look close with magnification, what you think is 112 is actually 82. Not sure where you are seeing 441 but odds are that is a 68pF. I have nothing here that would be labeled 441.

 

[dubbySwords]

There is no error. The printing on those caps is very small and not super crisp. If you look close with magnification, what you think is 112 is actually 82. Not sure where you are seeing 441 but odds are that is a 68pF. I have nothing here that would be labeled 441.

My mistake, I knew I was getting old but now I know I'm up there
Thanks.
/D

 

[RekStudio]

Guys - quick question: I had to pull the brown transformer lead and unfortunately could not desolder the tiny hole so I soldered back to the top of the hole. Is this going to be a problem?

 

[jsteiger]

Guys - quick question: I had to pull the brown transformer lead and unfortunately could not desolder the tiny hole so I soldered back to the top of the hole. Is this going to be a problem?

Its not optimal but as long as the solder joint is strong it will be fine.

 

[RekStudio]

Newbie here: Seems like my first 2 VP28 builds went successfully. Quick Question...

I notice in an earlier thread Jeff says: "Lowest gain setting is knob to 7:00. Highest gain setting is knob at 6:00." Is this also true for the Channel Fader?

My rotary knobs currently stop at 11/12:00 on both so I imagine I need to realign this to have the stops at 6/7:00. Can someone kindly confirm?

 

[jsteiger]

Newbie here: Seems like my first 2 VP28 builds went successfully. Quick Question...

I notice in an earlier thread Jeff says: "Lowest gain setting is knob to 7:00. Highest gain setting is knob at 6:00." Is this also true for the Channel Fader?

My rotary knobs currently stop at 11/12:00 on both so I imagine I need to realign this to have the stops at 6/7:00. Can someone kindly confirm?

Same for channel fader. -20 is the lowest setting and +12 is the highest. There's a big blue hashmark dividing where the switch stop is at.

 

[WillDuc]

Hi guys,

I'm having a problem with a VP28 unit i built myself. When i am in line mode, pad engaged, there seems to be a substantial increase in the high end when i run tracks through it. I set up Q clone using my daw to verify that and it turns out that when the pad is engaged in line mode, there's kind of a high shelf (see picture). When i am in mic mode though, the frequency response stays flat whether or not the pad is engaged.

Is this something normal ? If not, where should i start as for as troubleshooting ? Bad solder joint, wrong capacitor or resistor value etc...

Here are my test points :
TP1=101mV
TP2=698mV
TP3=1,241V
TP4=305mV
TP5=305mV
TP6=305mV
TP7=642mV
XLR output = 1,233V

Regards,

 

[Tommmes]

Hi,

Building a pair of VP28’s. I tested the CA-0252-DIY in a other module (VP26) and 2 of them work fine. The other two are distorted(MEGA). Followed the guide step by step and measured all resistors before putting them in. Diode are in correctly. Transistor all seem to be in the right space aswell.

Where should I begin the trouble shooting?

Edit: Aah excuse me, after some extra inspection I messed up the orientation of Q7. I feel extremely stupid. Should I order two new ones?

Question number 2; I had the working VP28 with the good Op Amps running for sometime (in Line mode) with some music running through it. Everything was working fine. Then I started messing around with the gain knobs and my PSU started to catch on fire. (I test in a open Bento 2, for easy access). The Module seems to be fine.

Any guesses what the hell I did to start the fire?

Thanks for the time.

Kindly, Tom

 

[barbaroja]

Been a happy user for years. Something has always annoyed me tho. The phase is reversed. Triple checked transformer cables and everything is on position. Any other thing that could be causing phase inversion?

 

[jsteiger]

Been a happy user for years. Something has always annoyed me tho. The phase is reversed. Triple checked transformer cables and everything is on position. Any other thing that could be causing phase inversion?

No. I would swap 2 leads on one of the transformer primaries. Like Red and Orange on T3.

 

[barbaroja]

No. I would swap 2 leads on one of the transformer primaries. Like Red and Orange on T3.

Thanks. I will. Any idea on why this could happen?

 

[jsteiger]

Thanks. I will. Any idea on why this could happen?

Maybe one of the transformers was internally wired that way.

 

[barbaroja]

Thanks!

 

[barbaroja]

Ok, polarity inverted. I just noticed a bulging capacitor. Kind of weird since it is not that old. Do you think I should replace ASAP? What is its function?

 

[andYz00m]

Hey there, just built a fresh unit and when I went to test in a known good rack with known good op amps (Jeffs 2520s), everything is working properly but the output is very low. Tested against a known working unit and the output is significantly lower at the same settings with the same test.

Test points all show the correct voltage (near enough) but when the gain pot is at unity and the fader is at 0 in line mode with a +4dBu 400Hz test tone, the output is more like 420mV instead of the correct ~1.29V.

Ive checked my components, triple checked for funky solder joints and build errors and im stumped.

Any ideas? Could an output trafo be the culprit? I dont see the schematic in the support docs (I think this is on purpose so people dont copy the sexy circuit) but I cant troubleshoot any further.

 

[jsteiger]

Hey there, just built a fresh unit and when I went to test in a known good rack with known good op amps (Jeffs 2520s), everything is working properly but the output is very low. Tested against a known working unit and the output is significantly lower at the same settings with the same test.

Test points all show the correct voltage (near enough) but when the gain pot is at unity and the fader is at 0 in line mode with a +4dBu 400Hz test tone, the output is more like 420mV instead of the correct ~1.29V.

Ive checked my components, triple checked for funky solder joints and build errors and im stumped.

Any ideas? Could an output trafo be the culprit? I dont see the schematic in the support docs (I think this is on purpose so people dont copy the sexy circuit) but I cant troubleshoot any further.

If the TP just before the final output is correct then I would desolder the transformers leads and check DCR looking for possible shorts between windings.

 

[andYz00m]

If the TP just before the final output is correct then I would desolder the transformers leads and check DCR looking for possible shorts between windings.

Both output transformers are showing the same readings and the primary and both secondaries are continuous. I compared to the other two trafos in the other kit and all 4 are the same.



Another point of interest is the voltages on the test points were about 20% higher than in the test point guide. The test signal was a little bit hotter than exactly 1.228 (1.3ish) as I did it quick and dirty with my daw.

TP1: 133mV
TP2: 841mV
TP3: 1.49V
TP4: 369mV
TP5: 369mV
TP6: 369mV
TP7: 770mV
Output: 426mV

 

[jsteiger]

Both output transformers are showing the same readings and the primary and both secondaries are continuous. I compared to the other two trafos in the other kit and all 4 are the same.

View attachment 99236

Another point of interest is the voltages on the test points were about 20% higher than in the test point guide. The test signal was a little bit hotter than exactly 1.228 (1.3ish) as I did it quick and dirty with my daw.

TP1: 133mV
TP2: 841mV
TP3: 1.49V
TP4: 369mV
TP5: 369mV
TP6: 369mV
TP7: 770mV
Output: 426mV

You also need to make sure there's no connection between windings. Black should only have DCR to Red and no other colors. Gray should only have DCR to Pink and no other colors etc.

 

[andYz00m]

You also need to make sure there's no connection between windings. Black should only have DCR to Red and no other colors. Gray should only have DCR to Pink and no other colors etc.

ANDDDDD there it is... Secondaries are shorted together on T3 (Gray shows continuity with all 4 secondary leads.)

That would explain the drop in signal right? As the resistance in doubled on the output signal?

 

[jsteiger]

ANDDDDD there it is... Secondaries are shorted together on T3 (Gray shows continuity with all 4 secondary leads.)

That would explain the drop in signal right? As the resistance in doubled on the output signal?

Yes. Please send an email to the store with order # and description of the transformer issue and we'll get it sorted.