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

[jsteiger]

Are the input conditions identical when you are checking this? What is the source? Maybe there is excessive DC at the input of the module for some reason?

Popping sounds when switching usually means there is DC present on the switch contacts somewhere. Maybe there is a solder bridge or short somewhere with phantom or something? If it where me, I would measure for DC at gold fingers #8 and #10 with phantom off. There should be none. Then check again with phantom on.

 

[Commander Fluffypants]

Thanks, Jeff!

Where are gold fingers 8 and 10? On the card edge?

And I guess I'll need the jig to test this thing. I messed up the build on the jig twice! It's the receptacles on the cable; I keep breaking them when trying to put them on. This sounds crazy, but can I buy a length of cable with the connectors attached?

 

[kante1603]

Thanks, Jeff!

Where are gold fingers 8 and 10? On the card edge?

And I guess I'll need the jig to test this thing. I messed up the build on the jig twice! It's the receptacles on the cable; I keep breaking them when trying to put them on. This sounds crazy, but can I buy a length of cable with the connectors attached?

Hi,


pin 8 is before pin 9,pin 10 after it (couldn't resist  ;D ).
Here's the pinout for both 51x and 500 series.
With the module held in normal upright position (the way it is mounted in a rack) pin 1 is on top.


http://www.51xaudio.com/alliance/pinout.html


How do you manage to break the receptacle (pics please)?


Best,


Udo.


Edit: If you're unsure on finding the goldfinger pins you can measure the dc on the corresponding female xlr (input) too.Just measure dc between pins 2 & 3.Make sure the module is fully and correctly seated,phantom off.
This is a very first step to sort things out,a working test jig is most helpfull,you'll need it for other modules anyway.

 

[Commander Fluffypants]

Thanks Udo!

At the risk of sounded totally lame, that chart doesn't help me...  I'm trying to figure out where these things are on the unit... and I'm assuming these are the contacts on the back of the card that slide into the receptacles on the lunchbox... ?

As for the jig, I must not be squeezing the parts together correctly because I crack them every time. I'm sure this is also a very silly mistake. I tried very hard to duplicate what's going on Jeff's photos.

As I've stated before, I really appreciate all the help I get from you guys and I'm grateful to Jeff for putting these things out into the world. I've built six of these things with remarkable success (just the troubles with this one) because of the help of this forum. I am careful and follow directions well... however, I am still truly a neophyte in terms of understand exactly what goes on with this stuff, so some of my problems and questions may make me seem far more hopeless than I really am.

 

[kante1603]

Hahaha.....well,we all started as newbies,didn't we?
O.K.,yes the goldfingers are the ones on the back of the unit,so the part that slides in the rack connector.
Btw,if you have Jeff's test extension jig it's easy to figure out which pin number is where- some are printed on the small pcb.


Best,


Udo.

 

[aaronnewberry]

I have a simple question but has anyone encountered a kit where C12 is not the correct value?
The directions indicate a 1uf, 100 v and I receive a 1u0-m, 36v
Any help would be much appreciated.

 

[jsteiger]

I have a simple question but has anyone encountered a kit where C12 is not the correct value?
The directions indicate a 1uf, 100 v and I receive a 1u0-m, 36v
Any help would be much appreciated.

Yes this is a forced change since BC discontinued the previous 1µF/100V. The replacement part is also from BC and is blue instead of white and is a 1µF/63V cap.

 

[hamlyf]

Hey guys, just noticed I may have had a bridge in one of my Grayhill switches. Wondering if that has caused any issues with the rest of the circuit?

 

[jsteiger]

Hey guys, just noticed I may have had a bridge in one of my Grayhill switches. Wondering if that has caused any issues with the rest of the circuit?

No. It will just cause that particular switch to not fully function.

 

[Golgoth]

Hello everyone,

What is the testing procedure for the VP-28. Which values should I read and where?
I can't find any guide for that.

Thank you!
G.

 

[jsteiger]

With no discrete opamps installed and no power connected, just check for a direct short from both V sockets to ground. I then would make sure your +/-V's are near 16V at the opamp sockets. That is done under power with no discrete opamps installed.

 

[Golgoth]

Hello,

I finished my first VP28, test is done and I get around 15.8V at the +/- V sockets when powered on. I don't know how to check for shorts Jeff.
But I have a major problem : NO SOUND AT ALL, only a white noise / hum sound that increases from 0 when I turn the channel fader up and decreases by the same amount when I turn it down... The preamp gain switch has no effect on the level of that noise.
The green signal LED pops (lights for a microsecond) when I turn the module on and pops again when I turn it off but even when talking into a mic it doesn't light on again so I guess no signal is coming in. Also a crazy loud pop buzz sound when turning on/off.

I encountered one problem during the bulding process which was implanting C12 in the wrong direction, I fixed that before connecting the VP28 to DC but maybe I burned it down when de-soldering?

I also built the 501 power rack unit from Soundskulptor to power my VP28, tests on this unit all gave perfect voltages.
By the way I don't have another 500 module to test the power unit or another power unit to test the VP28 module. I don't have any other opamps either...



EDIT : I switched the Opamps position (2520 / 1731) and now I get a signal ONLY with the 2520 in A3 and the 1731 in A1. SIG LED works. Still a tremendous amount of noise anyway...

Is it an opamp problem?

Thank you,
G

 

[jsteiger]

Yes this sounds like opamp(s) problems. It is nearly impossible to test a fresh preamp build (especially 2-stage) with freshly built opamps. There are too many variables and we don't know where to start looking. You either need to test the opamps in something else or you need 2 solid, good, known to be working opamps to test the VP28.

 

[Golgoth]

Yeah I get the point, I should have thought about that before ordering but, hey, this was my first build ever ahah.
I see you provide assembled gar's with kits only, where can I order some otherwise?

Anyway I'd like to thank you Jeff for all the help I got from you from the beginning.
G

 

[gar381]

Yeah I get the point, I should have thought about that before ordering but, hey, this was my first build ever ahah.
I see you provide assembled gar's with kits only, where can I order some otherwise?

These guys sell them 

http://www.customanalogservices.com/?t=doas

GARY

 

[Golgoth]

I finally identified the problem. The 2520 is faulty, I didn't check for NPNs / PNPs. De-soldering failed so I just ordered another 2520 kit from you Jeff. Everything should be fine this time.

 

[Golgoth]

Alright I will stop spamming the thread after this message ahah.

My VP28 is finally perfectly working!

I received my 2520 replacement kit this morning and carefully built it right away. In fact NPNs / PNPs were not the problem, Q5 was soldered backwards on my first 2520!

Note to every first timers/DIY beginners like me : CHECK TWICE, SOLDER ONCE. These wise words are not mine, they're Jeff's. I made 4 stupid (but hopefully fixable) mistakes building this kit because I wanted to finish quickly and have fun recording... Take your time.

Shout out to Jeff, Gary, Chunger and everybody on the forum!
G

 

[northamrec]

Hi everyone, I'm almost finished building my first CAPI VP28 but I broke the green LED (Panasonic LN382GPX). Does anyone know where I can get a replacement? I also need a couple pieces of the clear tubing. Thanks!

 

[jsteiger]

You can get them at Rapid if you are in the UK. The are Kingbright 2mm Lighthouse LED's now since Panasonic discontinued the original line I used. If you are domestic, shoot me an email and I'll mail you one.

 

[discord]

It seems these new C12 caps (the blue ones) have no positive or negative markings. Anyone know how to tell which way is which?