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

Here's a photo of the stuffed PCB(CM-75101APC input). I already have 2@VP25s(rev B) with ea2622input and CMOQ-2S for output trafos which are functional.  I have no shorts between DOA sockets. All tests in section 12.1 and 12.2 of VP2X assembly guide performed with correct results. I really hate to  start pulling functional units apart for troubleshooting. :-\

iturnknobs said:

Struggling here with output trafo.  The "tap" on the ea2503 data sheet provided does not appear to match the VP25 rev B schemo.    The "tap" colors are reversed when drawings are compared to each other. I am going to assume the cinemag literature is correct.  Any ideas?

Is there a VP25 rev C schemo anywhere... or is VP26 rev C same except for output trafo?

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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.

iturnknobs said:

I really hate to  start pulling functional units apart for troubleshooting. :-\

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Don't we all. But sometimes it's necessary.

You could start by swapping your Cinemag input transformer with an EA2622. Assuming soldering and component placement is good.

Thanks!

Paul

Just to be clear about switch function(tested in circuit)....

The "yellow" lugs should show continuity when mute switch is out and the "green" should be open. The opposite is true when the switch is engaged.  The middle, unidentified lugs show continuity in both positions. This is true for the functional units I have.

This is not the case for my non-function units. Yellow lugs always open regardless of switch position. I'm guessing I have bad switches?


-Brian

Well, it does depend on if the Polarity switch is engaged or not. If the Polarity switch is out or disengaged, for the Mute switch, in the out or disengaged position, you are measuring the output transformers primary winding DCR when probing between the lower middle lug and the green lug in your pic. This will be around 9Ω with a 2503 or 16Ω with a 2623-1 so keep this in mind if your DMM needs to be set to a particular range. Both lower or green lugs are connected to ground. The transformers primary leads are connected to the middle lugs. This can all be seen in the schematic.

The odds that you have 2 bad switches is next to impossible. I have only seen 1 or 2 in the last 15k switches.

Here goes... Couldn't get my 2@ VP25 rev C working. I have two functional VP25 rev B units. All have Cinemag output trafos (CMoQ-2 S or L).  Probing around the 2 different PCBs, I discovered that the lugs nearest the mute switch button went to the silk-screened brown and red pad for the rev B. For rev C, these mute switch lugs go to the silk-screened violet and gray, which go no where in the rev B schemo and I cannot find the rev C schemo for VP25. The circuit as stated in the rev B schemo exists physically on the rev C board, but the screening does not appear to match.

Is there and assembly thread amendment I did not find? I do have these units working now, wiring my output trafo primary to the vio and gray pads. The brown and red pads do not appear to be connected the the circuit anywhere.

Am I crazy?

I changed the wiring layout on the newer PCB's so that the transformer leads do not criss-cross if using a standard EA2503. From what I gather, the CineMag has the same wiring color code as the 2503 so you should be able to just go as normal.

I think I mentioned before that the EA2503 style transformer has 4 identical windings. There are numerous ways you can wire them up and get the exact same result.

I myself have built a new VP25 Rev C and the board is solid. I did a pictorial build for an upcoming guide. I just haven't had the time to edit the pics and create the page.

Here's a fun one...

I just finished updating my old VP25's and 26 and during testing, I noticed that when engaging the pad I would have a large audio spike engaging it and and about half of that disengaging it. I checked around for voltages and whatnot and I found that it only happens when the input is connected to a line level device. Doesn't happen with microphones or with an unterminated XLR on the input. There was no DC coming from my converter's analog output. I metered the output of the preamp for DC when these pops were being made, and there was a spike around 0.1V on the positive side (phantom off, by the way) and pretty much nothing on the negative when the Pad button is pressed. But this doesn't happen when connected to microphones, so I don't really care. I was just curious what was going on electrically as all three of them did the same thing. Frequency response, gain, etc all working perfectly. I do process recorded vocal tracks with the VP26 quite a bit, but I always have the pad engaged ahead of time.

Just curious.

Thanks!

Paul

Hey Paul, the mic pad is before the 2622 so there can be no DC present on the switch from the preamp unless phantom is engaged. The pad switch is fully galvanized from the opamp by the 2622. It must have something to do with the device feeding the preamp. I would try something else like maybe something with a transformer output into the preamp just for kicks. The pad switch is interrupting the audio path so it will never be silent but an audio spike seems odd.

Jeff,

I see that on the schematic, so there is some head scratching where the voltage is coming from if there is no DC present being feed to the input in the first place. I'll hook it up to another preamp and see if it still does it. The device it is hooked up to now is all ICs. I'll let you know.

Thanks!

Paul

So I put a Iso transformer in line and the "problem" goes away. I double checked the output of the converter and I am getting +/-0.02VDC on pins 2 and 3, but I don't see how that would cause the jump to 0.1 when engaging the pad.

It's not a big deal and I'm not going to think about it anymore. Just some fun information for others who may have this occur when doing initial testing.

Thanks!

Paul

Hello

I've built 6  VP26 pre's over the years, and I love love love them!  In the last 2 weeks, i've had a strange volume loss in one of them.  It seems to function, but i get maybe half the volume of the other pre's.  The op-amp is seated properly and nothing looks out of place.  Where would i start to look for issues?

Tim

timrickmann said:

Hello

I've built 6  VP26 pre's over the years, and I love love love them!  In the last 2 weeks, i've had a strange volume loss in one of them.  It seems to function, but i get maybe half the volume of the other pre's.  The op-amp is seated properly and nothing looks out of place.  Where would i start to look for issues?

Tim

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Sounds like a bad solder joint somewhere on the pre.

I will start there!  Thanks so much

I see the vp28 kit is out again .
Any timeline ? thanks

gevermil said:

I see the vp28 kit is out again .
Any timeline ? thanks

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I need to get all of the preamp kits setup with CA2622's for inputs and then all will be in stock. Its my main priority tomorrow morning so I'd say sometime tomorrow early afternoon or so.

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!!

c1bomber said:

(1) the pad switches are reversed, i.e. pad is engaged when the switch is out; pad disengaged when the switch is engaged.

Click to expand...

I am not even sure how this can be possible. The PCB's are all the same and the switches can't physically do this.

(2) adjacent vp26s are passing phantom power to each other. (but not to other preamps on either side)

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No modules should "pass" phantom to each other. Typically, either the phantom supply in the rack is on for all modules are off for all modules. This also doesn't make sense from a rack slot/module standpoint.

I had a polarity error at C1.  Fixed the pad issue.

c1bomber said:

I had a polarity error at C1.  Fixed the pad issue.

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C1 on a VP25 or VP26 is a 220pF ceramic cap, so non-polarized.
My bad. Corrected info comes a few posts after this.