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

[pittsburgh]

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[qmp audio]

Do you have a solder bridge between the two resistors above T1?
can't tell but looks like thats possible from the photo in post 518 http://groupdiy.com/index.php?topic=33501.msg688331#msg688331

 

[pittsburgh]

I know what your saying. It was just a piece of flux left over. No bridged connection there.

 

[Harpo]

Sounds like you might have connected the transformer balanced preamps output  (signal is across XLR-pins2/3, XLR-pin1 is only shield) to a following stage with unbalanced input, only sensing XLR-pin2/XLR-pin1 ?

 

[pittsburgh]

How do I check the path of the T2 windings?  Is it possible that the colors from the output transformer are not correct? Jeff's first suggestion was to check the wiring of the output transformer, but I know, and have posted pictures of this wiring termination and know this is right. I've found another posting on here with a output transformer that needed to be swapped out, is it possible that mine may need to be swapped out as well?

 

[jsteiger]

I don't recall having a bad 2623-1 since we switched to this new winder a while ago but you can check. You will need to desolder all 6 transformer leads and make sure they are not touching anything. Then measure DCR between red->orange, green->blue then black->brown. You can also make sure one lead is not internally shorted to any other lead this way. Report the results here.

BTW, like Harpo said, make sure this is not a converter, rack slot or cabling issue of any sort. Read Chuck's last post on the VP28 thread to see what I mean.

 

[pittsburgh]

Jeff, This is what I'm getting. Can you also send a link to the post that you mentioned?

Black & Brown: 22.7 Ohms
Red & Orange: 14.4 Ohms
Green & Blue: 23.4 Ohms

 

[jsteiger]

Those results are as expected so I would guess that the 2623-1 is fine. I would investigate what devise you have following the pre.

Here was Chuck's post http://groupdiy.com/index.php?topic=48610.msg688337#msg688337

 

[Triscuit]

Hello everyone! I need some help troubleshooting. Just completed the VP26 kit Rev B.1 and the gar2520 opamp kit last evening. I put it into my Lindell rack to test this morning and ... you guessed it ... nothing.

Here's what I've done:
1. Checked the resistance in the millmax pins per the directive - all checked out fine.
2. Scanned and reflowed solder on components where it looked a bit weak; I admit, there are some more spots that I could probably go over, but nothing looked offensive per se (I won't take it personally if you tell me otherwise).
3. Checked that I placed the resistors in correctly; I am 99.99% certain I did. I sorted them pre-install and measured each with a DMM.
4. Cleaned the board with some flux cleaner and a toothbrush to make sure I didn't leave any grossness on there.

Here's what I see may be a problem:
1. I only soldered from the bottom of the board; I notice at a lot of the pads on the top that the solder hasn't come through. Will this cause a problem?
2. I didn't have double face tape to attach the 2622 - I rolled some duct tape and used that to insulate between the board and the transformer. This doesn't SEEM to be problematic, but am I wrong?
3. I haven't checked resistance at the output transformer yet - sort of waiting on that because .. (see 4).
4. I may have done a terrible job at completing the opamp. I have attached photos. Maybe I need to go back and reflow some solder on the top of the board? I do not have a preassembled opamp to test, and sort of wanted to avoid this because I really wanted to nail that kit. 

Here's what's happening in the rack:
1. When I power on the rack with the VP26 in, I do get a pleasant "pop" - nothing LOUD or OFFENSIVE .. just a little "poof" that lets me know something's happening.
2. The 48v LED comes on appropriately with the flick of the switch, and then fades nicely as it drains when I turn it off.

That's pretty much it. Tried an SM57 and a frankenstein condenser. No output sound.

I won't take anything personally - please take a moment if you can to see the photos. Tell me what your thoughts are. I obviously want to get this VP26 up and running, but I also want to learn here because I want to do more!

Thank you all in advance! I am new to the forums here, so this is my first post. Sorry to bring a problem to the table.  :-\ (Will post additional pics consecutively)

 

[Triscuit]

Bottom of board:

 

[Triscuit]

gar2520 bottom of board (I can take this to the official thread if necessary):

 

[jsteiger]

I would reflow the bottom of the opamp. It is hard to tell in the pic but a few pads look like they may be cold or not have enough solder. You should be careful when doing this. It is not a problem to only solder from the bottom. The holes are plated thru and connect the top layer to the bottom layer.

It is very hard to test a fresh pre build with a fresh opamp build. The issue could be in one or the other or both.

 

[Triscuit]

Thank you, Jeff!

It's apparent now when I have a full-res photo on my laptop - there are some rough spots there! Also, I know it's hard to test with a fresh build on both; that's what's sort of frustrating me.

Donny

UPDATE: problem was with the opamp; we're up and running! Long live VP26!

 

[pittsburgh]

Is there a compatibility issue that I'm missing in trying to get my VP26 to run on my system? I'm attempting to run this pre on a new API 6b lunchbox over XLR connections. I know that VP26 units can be used on the 51X systems. As of right now I'm using my lunchbox with a UA Apollo running TRS to XLR connectivity, where the mic pre is fitted into a slot that I have used before with a different pre running properly.

 

[jsteiger]

The VP26 is 100% VPR or 51x compatible.

 

[mellsonic]

Hello everybody,

I need to consult those of you who possibly have any idea of what could be the solution to the technical problem I'm having.


What I have:
-4xvp26 Capi Preamp
-4xOp Amp SL-2520 Red Dot
-1xLindell Audio Power 506

The problem with one of the pre amps is:

Half of the waveform is missing/much lower than the other one. When I reverse the phase it switches from the bottom up, as you can see in the screenshot.

-basically audio can pass through
-it's slightly distorted
-all switches work fine /mute/phase reverse/pad/phantom power
-all pots function fine louder/lower volume
-it sounds different than the other ones

What I have been testing:
Different Op Amp SL-2520 which worked fine with the other preamps. Problem remains.
Different microphones. Problem remains.
Different cables. Problem remains.
Different slots of the Lindell Power 506. Problem remains.


I am looking forward to any responses regarding this problem and hope for someone being able to help me out.
Thank you very much,
Mario

 

[mellsonic]

 

[jsteiger]

I recommend skimming thru the earlier pages in this thread. You will find posts about injecting and tracing signal thru the pre. Where it stops is usually where the problem lies.

 

[mellsonic]

Hello everybody,

got the problem solved with the VP 26!
It was a soldering bridge with one of the parts. Everything is up and running and fine now!
First recordings sound amazing!
Thanks to everyone and especially to Jeff!

Cheers, Mario

 

[pittsburgh]

Jeff, Can you send me the exact link for the posting or page number on this thread that involves signal injection for testing the VP26? These are the issues that I am currently having with my VP26 with prebuilt GAR2520 op amp installed:

Low signal output (not enough to reach digital 0)
Output attenuate pot works in reverse order
Phase switch kills signal

These are tests that have been run:
Testing of outboard cables, inputs and outputs,
swapping out GAR2520 for known working JH990 opamp
double checking for bridged joints
reheating all joints to eliminate cold joints as a possibility
output transformer test