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

[frenkonio]

A VP28 I built more than a year ago is showing this issue: when you switch it on, after for example a couple of days not using it, the input knob stays at fixed value and if you move the knob ccw or cw it doesn't change the gain. If you press the MIC switch one second and depress it to let it come back to Line mode the knob works perfectly and so it does for short periods of time. I checked all the solder joints and repassed everyone with fresh solder. Opamp have been changed with several types, it doesn't change the issue. Anyone could help me?

 

[jsteiger]

A VP28 I built more than a year ago is showing this issue: when you switch it on, after for example a couple of days not using it, the input knob stays at fixed value and if you move the knob ccw or cw it doesn't change the gain. If you press the MIC switch one second and depress it to let it come back to Line mode the knob works perfectly and so it does for short periods of time. I checked all the solder joints and repassed everyone with fresh solder. Opamp have been changed with several types, it doesn't change the issue. Anyone could help me?

Classic signs of a cold solder joint somewhere on the build. Hard to say where exactly at this point. The physical jarring action of engaging the switch doesn't necessarily mean its one on that switch but it could be.

 

[frenkonio]

Solved Jeff. Don't know how but the 330uF cap near the input trafo was a bit moving. Desoldered and resoldered did the job. Thanks!

 

[forgotteng]

Does anyone know what the part number for the IC socket at A2 is I somehow can't find the socket and need to order another one.

 

[jsteiger]

Does anyone know what the part number for the IC socket at A2 is I somehow can't find the socket and need to order another one.

The IC socket has not been supplied with the VP28 kit for a few years now. They are not required for operation. If you want to grab one, I have them at the store. The Mill-Max part # for the ones I have is listed on the product page here.
http://capi-gear.com/catalog/product_info.php?cPath=71_77&products_id=331

 

[forgotteng]

The IC socket has not been supplied with the VP28 kit for a few years now. They are not required for operation. If you want to grab one, I have them at the store. The Mill-Max part # for the ones I have is listed on the product page here.
http://capi-gear.com/catalog/product_info.php?cPath=71_77&products_id=331

That's awesome Jeff. That explains a lot. I was looking all over the place for that bugger. I think the toughest part for me has been keeping all the versions and revisions of the instructions and BOM's  separate and organized. It's been a learning process but so good. Thanks.

 

[adamhall202020]

Hey guys could you please help me a bit. Im struggling with the last thing. Is it placing op-amps about using quite a force to push them deeper? Even if im trying to push them a bit harder they wont go any deeper and the thing is that they feel loose im even afraid they could fall off.  Op-amps are quite high above board. I have pre-build red dots, only about to insert them

 

[kante1603]

Hey guys could you please help me a bit. Im struggling with the last thing. Is it placing op-amps about using quite a force to push them deeper? Even if im trying to push them a bit harder they wont go any deeper and the thing is that they feel loose im even afraid they could fall off.  Op-amps are quite high above board. I have pre-build red dots, only about to insert them

Welcome to the forum,


have you read Jeff's instructions?


http://capi-gear.com/catalog/DOA_Install.php


Best regards,


Udo.

 

[IndietownRecording]

Hey guys could you please help me a bit. Im struggling with the last thing. Is it placing op-amps about using quite a force to push them deeper? Even if im trying to push them a bit harder they wont go any deeper and the thing is that they feel loose im even afraid they could fall off.  Op-amps are quite high above board. I have pre-build red dots, only about to insert them

A good trick is to use a paper clip to insert in the sockets to "break them in" a bit. It helps.

 

[IndietownRecording]

So, I've got a VP28 here with the mic signal present LED constantly on. These are the earlier black board versions. I got these from someone else, and cleaned up the build substantially. I went through the BOM and verified all components are correctly placed. Been looking at it for a couple weeks now and can't figure it out. Thought it's time to reach out to you guys on here to see if you might be able to give me some pointers on where to look.

 

[jsteiger]

So, I've got a VP28 here with the mic signal present LED constantly on. These are the earlier black board versions. I got these from someone else, and cleaned up the build substantially. I went through the BOM and verified all components are correctly placed. Been looking at it for a couple weeks now and can't figure it out. Thought it's time to reach out to you guys on here to see if you might be able to give me some pointers on where to look.

I know this happened to a couple of folks but I've never seen one in person so not sure what the cause is. You can try putting an R around 1k to 2k across the pins of the LED header to see if that handles it.

 

[IndietownRecording]

I know this happened to a couple of folks but I've never seen one in person so not sure what the cause is. You can try putting an R around 1k to 2k across the pins of the LED header to see if that handles it.

Just tried a 1k2 with no luck.

 

[IndietownRecording]

Anyone have any other ideas before I throw in the towel on this one?

 

[jsteiger]

Anyone have any other ideas before I throw in the towel on this one?

What are the opamps and who built them? Have you tried swapping them around? Maybe there is some noise or something present at the output of the first amp that is triggering the sig present circuit?

 

[IndietownRecording]

What are the opamps and who built them? Have you tried swapping them around? Maybe there is some noise or something present at the output of the first amp that is triggering the sig present circuit?

Hey Jeff, they’re red dots. I’ll try swapping them.

 

[jsteiger]

Hey Jeff, they’re red dots. I’ll try swapping them.

They should be fine.

This is the main reason why I simplified that part of the build for the Rev B version. A handful of folks had trouble and I could never reproduce the problem on our end.

 

[critterkllr]

I just finished a VP28 and the green signal led is stuck on. Everything else works as it should. It’s not a big deal, but I’d like to fix it. I’m at the mercy of this thread since schematics aren’t available. What should I look at to fix the signal LED?

 

[jsteiger]

I just finished a VP28 and the green signal led is stuck on. Everything else works as it should. It’s not a big deal, but I’d like to fix it. I’m at the mercy of this thread since schematics aren’t available. What should I look at to fix the signal LED?

Which Rev PCB is it? Green or black?

Have you made sure its not opamp related?

 

[critterkllr]

Which Rev PCB is it? Green or black?

Have you made sure its not opamp related?

It’s the green pcb. I just received it yesterday. It doesn’t matter if the opamps are in or out. And I’ve also switched them around with known working opamps. There was no change in performance.

 

[jsteiger]

It’s the green pcb. I just received it yesterday. It doesn’t matter if the opamps are in or out. And I’ve also switched them around with known working opamps. There was no change in performance.

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.