[BUILD] CAPI VP2X~500 Series~Preamp Kit~Official Support Thread

[jsteiger]

I have a VP26 with a phantom power LED out, the preamp seems to be working fine including phantom power.

Is there something I should test or would just replacing the LED be a reasonable route?

Did it ever work? They normally don't "wear out".

 

[kevinkace]

They normally don't "wear out".

That's what I was thinking! I assume I tested it, but you know what they say...

Oh wait, I'm now remembering the point about "if it doesn't work it's in wrong" from the build guide. I'll check that out.

 

[jsteiger]

Oh wait, I'm now remembering the point about "if it doesn't work it's in wrong" from the build guide. I'll check that out.

Yes that was my next reply! That's why I was wondering if it ever worked. 

 

[Z-Chord Studios]

Leave them hang temporarily and use blue for + output and black for - output. You will need to use alligator clips or solder an XLR directly to them etc.

Say I would like to bypass the T-pad and still put the unit into the 500 Rack to test it that way, is there a way to do that?

 

[Potato Cakes]

Say I would like to bypass the T-pad and still put the unit into the 500 Rack to test it that way, is there a way to do that?

There is a solder pad on the PCB that says "Opt No T-Pad-Blu". Solder the Blue wire from the transformer there.

Thanks!

Paul

 

[Z-Chord Studios]

There is a solder pad on the PCB that says "Opt No T-Pad-Blu". Solder the Blue wire from the transformer there.

Thanks!

Paul

I see that option on my Rev B. But not on my Rev C, which is the one that I would like to bypass the T-Pad on.

 

[jsteiger]

I see that option on my Rev B. But not on my Rev C, which is the one that I would like to bypass the T-Pad on.

I removed that from the Rev C board since no one really bypasses the t-pad. The only way to do it would be to route the blue wire (as Paul said) directly to gold finger #2.

 

[Z-Chord Studios]

I removed that from the Rev C board since no one really bypasses the t-pad. The only way to do it would be to route the blue wire (as Paul said) directly to gold finger #2.

If it is indeed the T-Pad that is my issue, I will order another and rewire things correctly again. I have reason to think that I may have damaged the T-Pad during installation. This is my inexpensive way of checking that. As I build more I will acquire the proper testing devices.

I greatly appreciate your patience, Jeff, as I imagine it must be frustrating repeating yourself so often and explaining things repeatedly that make perfect since to you. I know the feeling. I have years of experience remodeling bathrooms and kitchens, and every new guy frustrates me to no end, even though I know he means well and just needs to learn.

One last question and I should be good, and I'm fairly certain that I know the answer, I'm only clarifying: Gold pin 2 would be the Negative on the DOA inserts, correct? 

 

[jsteiger]

....One last question and I should be good, and I'm fairly certain that I know the answer, I'm only clarifying: Gold pin 2 would be the Negative on the DOA inserts, correct?

NO!!!! The gold fingers are the gold pads at the rear edge of the PCB that plug into the rack's card edge connector. They are labeled and start with #1 near the top edge and end with #15 near the bottom edge.

 

[Z-Chord Studios]

NO!!!! The gold fingers are the gold pads at the rear edge of the PCB that plug into the rack's card edge connector. They are labeled and start with #1 near the top edge and end with #15 near the bottom edge.

I have never been so glad to have asked a question in quite a while!!!! Thanks, dude!! whew. Glad I waited for a response.

After I run this hodge-podge test, I'll report back.

 

[Z-Chord Studios]

Yup. A bad T-Pad was my issue. All of the strange behaviors are gone. No more gain boost with the phase switch. No more low-cut on every source. Of course, now I pretty much HAVE to keep the pad on. Thus why there's attenuation on these things. 

I will be ordering a new T-Pad as soon as I have the flow.

Thank you to everyone for their patience.

And thank you to everyone for their help!!!

 

[sebperry]

Hi there,

I have a pair of VP26 that I bought pre-assembled a couple years ago. They work and sound great but I think they may be in need of a little maintenance.

On of of them in particular has a tendency to lose sound when it hasn't been passing signal for a little while. The only way to get sound back is to crank the input gain until the signal passes through. After that it's usually good for little while but will drop out again every 15 min or so.

Is there any maintenance or cleaning I can do to stop this from happening? Thanks!

 

[jsteiger]

I have a pair of VP26 that I bought pre-assembled a couple years ago. They work and sound great but I think they may be in need of a little maintenance.

On of of them in particular has a tendency to lose sound when it hasn't been passing signal for a little while. The only way to get sound back is to crank the input gain until the signal passes through. After that it's usually good for little while but will drop out again every 15 min or so.

Is there any maintenance or cleaning I can do to stop this from happening? Thanks!

There is no maintenance involved in a properly built preamp. To me, this sounds like bad solder joint that is getting worse.

 

[mxz174]

Well guys you might have thought I figured out my misbehaving VP26 since I haven't posted in quite a while, NOPE!
I've just been incredibly busy with a new job, but tonight I finally got a change to work on this again.

I started from scratch once more.  Hooked up the signal generator to run ~400Hz sine wave at the max amplitude of the generator.

I desoldered the output transformers completely on both a known working board and the bad board (for anyone that doesn't remember, this bad VP26 is giving me very very low signal output).  I then connected each module to my 500 series rack (via extension cable) and checked voltages on each one to compare them.  Same exact settings on both modules.  ALL of the voltages matched for each module along the signal path up to, and including, the red and orange pads at the output transformer.

While the output transformers were still disconnected I measured the resistances of all of the leads relative to one another.  I found no shorts between windings or open circuits across any particular winding.  The resistances for the winding pairs matched up almost perfectly with one another as well.  SO FAR SO GOOD

Then I soldered in the red and orange leads for the output transistors (as labeled on the PCBs, I am using Litz transformers).  Now I hooked these back up and checked the voltages across the outputs from the transformer as they were dangling (disconnected from the board), and here I found a big difference!  The bad module had voltages between output winding pairs that were HALF of that from the good module.

Now to remind everyone again, I have already tried swapping output transformers on this bad module and it made no difference.

If the output transformer itself isn't bad, and the signal level up to the red and orange pads isn't bad, then what on Earth could be causing this problem?  I'm definitely still perplexed and have had a bum VP26 kicking around my studio for far too long now...

 

[mxz174]

So far the only major component I have not tried to replace is the input transformer.  Now, this would really seem to make no sense since the audio signal beyond this component lines up nicely between the bad unit and a known good unit.  Still, I'm about at my wits end with this module and would be up for trying just about anything by now.

I've swapped output transformers, no difference.  I've swapped op amps, no difference.  Again, the audio signal traced through the circuit looks good (nearly identical to a good unit) all the way up to the output transformer.  Once I attached the input winding of the transformer then both windings on the output of the transformer have low voltage, about half of what they should be.  It looks like a bad output transformer, except I've already tried swapping them with no change!

If anyone has any other suggestions I would be very grateful.  I may just go ahead and buy another input transformer and try swapping it out for kicks...

I've built hundreds of VP26s and VP28s now and out of all of those only about 3 or 4 ever had any issues whatsoever.  In each of those cases it was either a bad input transformer or output transformer.

 

[Winetree]

I have some Version  A-2  VP 25s & 26s with out phantom L.C.D.s
Is there a picture how to wire the L.C.D.s on the early P.S.B.s?

 

[jsteiger]

@ Michael, I would not bother with the input transformer. There is no way that could have anything to do with this. This is a bit odd.

Does flipping the polarity have any major impact? Besides hopefully flipping the polarity?

With no transformer leads connected, no power to PCB, does the DCR from the Red pad to the Orange pad match? And also after engaging the polarity switch?

There are no black art things here so we should be able to figure this out. In the same way that 1+1 is always 2 and never occasionally 3 ;-)

 

[jsteiger]

I have some Version  A-2  VP 25s & 26s with out phantom L.C.D.s
Is there a picture how to wire the L.C.D.s on the early P.S.B.s?

There maybe a pic around from someone. I have not had any of those modules for ages. All you need is the LED with the anode connected to the switched side of the 48V toggle to a 10k R that goes to ground.

 

[mxz174]

Jeff, I agree that the input transformer seems like a very unlikely culprit, I'm just sort of at my wits end here!

The polarity switch does act peculiar.  I wrote about this on the very thread if you scroll up.  Engaging the polarity switch on the bad unit drops the signal to basically zero. 

I've checked the DC resistant between red and orange pads with the transformers completely taken out of the circuit and there is certainly a difference.  The good module shows 20k Ohm between those pads, the bad one shows OL (overload), basically an open circuit or at least up into the tens of mega ohm region.

 

[jsteiger]

Jeff, I agree that the input transformer seems like a very unlikely culprit, I'm just sort of at my wits end here!

The polarity switch does act peculiar.  I wrote about this on the very thread if you scroll up.  Engaging the polarity switch on the bad unit drops the signal to basically zero. 

I've checked the DC resistant between red and orange pads with the transformers completely taken out of the circuit and there is certainly a difference.  The good module shows 20k Ohm between those pads, the bad one shows OL (overload), basically an open circuit or at least up into the tens of mega ohm region.

Maybe there is an internal problem with the polarity switch. You can check continuity between the solder lugs to make sure its ok. Continuity between the top 2 pins when out and the bottom 2 lugs when its engaged. Both "sides" should work the same.