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

[Potato Cakes]

Just completed my first two vp26.  They sound amazing! thanks for the great work Jeff.  I have two problems:

(1) the pad switches are reversed, i.e. pad is engaged when the switch is out; pad disengaged when the switch is engaged.
(2) adjacent vp26s are passing phantom power to each other. (but not to other preamps on either side)

where should I look to fix these problems?

op-amps are 1 Red Dot and 1 gar 2520
rack is Purple Audio Sweet Ten.

thanks for your help!!

Do you have other modules to test the phantom power issue? Separate the modules in the rack and see if the problem persists. My guess is you have a build issue where the phantom is bypassing the switch and going the XLR input. Like Jeff said, phantom is not going to "jump" from one module to another. It comes down the 48V rail in the rack then the module sends it out the XLR input when activated by the module.

For the pad, unless you have a switch that operates backwards (highly unlikely if you purchased a kit), there is something off with the build. You can test continuity between the top terminals of the switch and compare to the other switches.

Thanks!

Paul

 

[c1bomber]

Hi Jeff and Paul,

The speed of your responses is just amazing!  C1 on vp26 Rev C is 33uf, 25V.  I flipped it and the pad issue went away.  Phantom power issue turns out to be a problem with my Sweet Ten rack.  Channel 2 is passing 48v to Channel 3.  For some reason I hadn't noticed it until I put the vp26s in those slots.  I just tried it out and a 512c passed power to a vp26.  Pair of vp26s in any two other slots have no issues.

thanks again!

 

[jsteiger]

Hi Jeff and Paul,

The speed of your responses is just amazing!  C1 on vp26 Rev C is 33uf, 25V.  I flipped it and the pad issue went away.  Phantom power issue turns out to be a problem with my Sweet Ten rack.  Channel 2 is passing 48v to Channel 3.  For some reason I hadn't noticed it until I put the vp26s in those slots.  I just tried it out and a 512c passed power to a vp26.  Pair of vp26s in any two other slots have no issues.

thanks again!

Oops my bad. Yes you are correct about C1. Either way though, there is very little to no DC present on that cap so its polarity will not change anything especially with the pad situation as mentioned.

Still not following your phantom issue since. I also have never seen a Sweet 10 in person.

 

[c1bomber]

Hi Jeff,

Yes, turned out flipping the polarity did not solve the pad issue.  I think it's all an issue with my Sweet Ten rack.  512c just gave me the same pad problem in a different slot

 

[c1bomber]

wow, got it figured out.  I was testing the vp26s with a mic I don't use very much.  A stereo mic where the stock capsules ship with flipped-from-standard polarity.  The circuit employed to correct the polarity causes this PAD flip with a few (mostly 500 series) pre-amps.  Weird.  And I was running the stereo mic into the two mono vp26 which I guess explains the 48V being shared across both pre's.  Lesson is always test the gear with stuff you know like the back of your hand.  Thanks for you help Jeff.

 

[c1bomber]

on another topic, I need to change out a bad API 2520 op amp in a 512c (probably with a gar2520).  Anyone know the Mill-Max pin length so as not to crush the ceramic capacitor underneath?

 

[Whoops]

on another topic, I need to change out a bad API 2520 op amp in a 512c (probably with a gar2520).  Anyone know the Mill-Max pin length so as not to crush the ceramic capacitor underneath?

not exactly the same answer but you can replace that ceramic cap with one that you has longer legs and then you can bend it horizontally and don't worry about crushing it, it can fit flat on the pcb

 

[JBHamby]

Hello everyone. Hopefully you guys can help me with a problem. I have 2 VP25's that I have had for over a year. Both preamps have worked fine with no issues what so ever. Yesterday during a session one of them stopped passing phantom power. The 48volt light switch would still power on but it would not power any condenser microphone I tried. The preamp still would work wth  dynamic mics. I tried several different cables and several different microphones and it seems that the preamp is the issue. Thanks for any possible help!

 

[TillM]

look at the resistors R6,R7,R8 and capacitor C9.
Maybe something there is leaking.

 

[JBHamby]

Thank you so much for the reply! I have just checked R6, R7, R8 and then C9. R6 was 198r which is good but R7 and R8 both came in at 3.4k, with both should be 6.8k. C9 was good with no leaks. Could the drop in the value of the resistors for R7 and R8 be the cause of my problems? Thank you again for the help

 

[[silent:arts]]

With a transformer balanced input those measured values are fine (in circuit).
Resistors don't change their values anyway (if it burned you would see and smell it).
The 2nd VP25 is still working fine in the same slot with the same cables with the same microphone?

My guess is more to your PSU. The phantom power LED often don't use the 48V rail.
Don't know how Jeff is doing it, my VP26 is old enough for having no LED 
EDIT: found the rev B schematic, the LED is using the 48V, it is a real 48V indicator  8)

 

[JBHamby]

I had not checked it another slot in the power supply yet. I’m going to do that now and see if that’s the issue. I wouldn’t have thought if that! Thanks

 

[jsteiger]

I had not checked it another slot in the power supply yet. I’m going to do that now and see if that’s the issue. I wouldn’t have thought if that! Thanks

That would be my suggestion as well. As Volker has kindly pointed out, the 48V indication LED runs from the 48V rail so if it is illuminated then the module is getting 48V power. If you check the schematic, there are only 4 other components related to phantom power.

There is also this which is helpful
http://www.shure.com/americas/support/find-an-answer/how-to-test-phantom-power-voltage-and-current

 

[Zingg]

Not exactly what you mean by "tap" but the 2503 is a quadfilar device with 4 identical windings. There are many different ways to connect it to get the exact same result.

The VP25 is identical to the VP26 with the exception of the output transformer. The VP312 schemo can be used for help with the output transformer wiring.

I have never used that specific CineMag part but when comparing datasheets, the wire color code is the same as the EA2503.

Hi

I'm assembling the first VP25 and got stuck on the output transformer. The colors of the transformer leads do not correspond with the color labels on the VP25 rev. "C" PCB. Any help appreciated Thanx

 

[jsteiger]

I'm assembling the first VP25 and got stuck on the output transformer. The colors of the transformer leads do not correspond with the color labels on the VP25 rev. "C" PCB. Any help appreciated Thanx

This is posted at the store on all product pages that use the Litz wire transformer. The cross reference table is on the 2503-Litz wire transformer datasheet.
http://www.capi-gear.com/catalog/images/gallery/2503/2503-Litz-specs.pdf

 

[Zingg]

This is posted at the store on all product pages that use the Litz wire transformer. The cross reference table is on the 2503-Litz wire transformer datasheet.
http://www.capi-gear.com/catalog/images/gallery/2503/2503-Litz-specs.pdf

Stupid me Sorry for bothering and Thanx for the super fast response

 

[Tiotever]

This is posted at the store on all product pages that use the Litz wire transformer. The cross reference table is on the 2503-Litz wire transformer
datasheet.
http://www.capi-gear.com/catalog/images/gallery/2503/2503-Litz-specs.pdf

Is there another chart for 2503 L in place of the EA 2623 -1 for the VP 26 rev c?  The VP 26 Rev C PCB doesn’t have violet.
Thanks in advance.

Nevermind. I found the data sheet I was looking for.  Thanks again!

 

[mrmike186]

I just finished  three vp26's and one vp25. One of the vp 26's has substantially lower output than the other two and sounds a little different.

It passes all the tests on the assembly guide.

I am able to test the stepped gain resistors with a multimeter  but the others don't give an accurate reading, maybe because they are now connected to the board.  It looks like the resistors are in the correct place by the color coding.

I tried switching out doa's  and changing position on the 500 rack.

Added some solder to anything that looked like its possibly not a good connection and scrutinized any bridges.

Any ideas on how to troubleshoot this problem? 

 

[jsteiger]

I just finished  three vp26's and one vp25. One of the vp 26's has substantially lower output than the other two and sounds a little different.

It passes all the tests on the assembly guide.

I am able to test the stepped gain resistors with a multimeter  but the others don't give an accurate reading, maybe because they are now connected to the board.  It looks like the resistors are in the correct place by the color coding.

I tried switching out doa's  and changing position on the 500 rack.

Added some solder to anything that looked like its possibly not a good connection and scrutinized any bridges.

Any ideas on how to troubleshoot this problem?

You cannot accurately measure R's when they are soldered in circuit. Post a clear pic of the low output VP26 PCB so I can see the color codes.

 

[mrmike186]

Thanks Jeff!