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

[tctonn]

Howdy world,

I just finished building my first VP28 and all looks good to the eye. However, when I plugged it into my Chameleon Labs CPS 501 chassis it killed the chassis. The power LED on the chassis came on, the signal LED on the VP28 flashed and then they both went out. Now the chassis power LED won't light up at all. I am waiting to hear back from Chameleon Labs but am note holding out great hope. I've done this with two of those chassis now and the same thing happened with both.

I'm no expert at this but I've done some pretty complicated builds before and had no issues. Anyone have any ideas where I might start troubleshooting?

TT

PS- thanks to Jeff for a great kit and Chunger for an amazing build doc. I can't wait to sort out my idiocy and get this guy fired up.

 

[jsteiger]

Please scroll thru this thread and you will find things to look at starting with the opamps.

 

[zaiata]

Complete my first two VP28s. Every thing worked, first try ....... The build was fun. But the sound is just awesome, Wooooooo!
Installed on a Purple Sweet Ten.

 

[okgb]

Nice first post !
They're good enough and different enough that I think everyone should have a pair
in their arsenal !

 

[zaiata]

Thank you.
Now I realize... the photos are too big. 
I am waiting for Jeff to come back from Nashville to get some VP312......

I am reading so much good information on this forum... just awesome.
Need to decide on a good kit for a Neve flavor preamp.

 

[tctonn]

UPDATE-

No surprise that my problem was simple and Jeff was right on track: all works perfectly with two Red Dots from Scott Liebers.

I love this thing. All of the VP28s virtues have been well documented but to add to the praise- I use this primarily for long form narration and VO and was looking for a pre with a low sound floor and lots of clarity. I couldn't have asked for more. I think I like it more than the Hardy M-1 that we were using previously. Guitar tests coming today. 

For any novices who may have run into similar issues: it looks like I had a short on one of the GAR1731's that I built that somehow killed the Chameleon Labs power supply. Once I replaced those with the Red Dots and slotted it into my Lindell rack it worked flawlessly.

Next up- a pair ofVC528s.

Thanks again Jeff.

 

[j_fraser]

So after making up a fresh pair of Gar2520s both VP28s power up, test and run perfectly.  The anomaly with the phantom, was as Jeff predicted, embarrassingly traced to a niggling earth fault in one of the multi-pin connectors behind the rack.

Have thus far only strapped the pair of VP28s across an existing mix, but wow!  I can see these units seeing a lot of use…

Once again, many thanks to Jeff for yet another great pair of mic amps, and also for his knowledgeable insight and support in getting this build up an running.  It is very much appreciated.

Many Thanks & Best Wishes

Justin

 

[TheGiantLie]

Hello, my signal indicator led isn't working. Everything else is perfect! I was hoping someone could give me an idea on where to check.

*its worth noting that I had originally had the ic chip in backwards. Of course it popped when I turned the unit on. I replaced the ic chip and the unit works perfectly other than the signal indicator.

Thanks in advance guys

 

[kante1603]

Welcome to the forum,

Led is backwards too?

Best,

Udo.

P.S.:The chip does not like reverse supply voltage,so it is 99% sure it doesn't survive.Swapping it to a new one was correct.

 

[TheGiantLie]

Thank you for the quick reply. When I say the ic chip popped, I mean it was in pieces. So I had no choice but to replace haha. The led tests fine, and I have double checked that it was in correctly.

I'm fine with leaving well enough alone for now (the pre works great) but if anyone has anything else that I should check I'm all ears.


ps: I have successfully built a second vp28, complete with a working signal indicator led!!

 

[kante1603]

Hello,

we don't have the schematics here,but with a working second unit you can do some comparisons.
Here's the chip datasheet taken from Jeff's site:

http://www.classicapi.com/catalog/images/gallery/opamps/IC/RC4558-datasheet.pdf

Best to use extension cables or - jigs and lay them side by side.Feed them with the same signal and compare the signals entering and leaving the chip,I thinks it's somewhere around there.

As always check for cold solder joints and/or shorts.

Best,

Udo.

 

[blackbird]

Hey guys.
Just finished my first VP28, and 2 x gar1731's.

Plugged it in, and no signal comes in. Powers up fine, but it appears the input isn't getting in. When I switch phantom on, I can see a flicker in the converters which hints the output stage is ok, so I was thinking perhaps my issue is something to do with the input stage?

I have no idea what I'm talking bout really, so any advice on where to start checking would be lovely.

Thanks!
Dave

 

[jsteiger]

Dave, I would suggest scrolling thru this thread starting at the beginning. Ruling out the opamps is always the first step.

 

[blackbird]

Hey Jeff.

I'll scroll through it all tonight, but I'll have a go at putting some reddots in it I already have.

Thanks!
Dave

 

[blackbird]

Hi guys.

I tried the unit with a pair of red dots I use everyday, and no change on the no signal issue.
I've read through this thread start to end, and saw one person with a similar issue, ( no signal) but no solution. There was a mention to check the preamp section, but I confess, I'm not sure where to start..

All LEDs work, obviously not the green gain light, as I have no gain. The rack is a radial rack, and is all good. Swapping leads over to the preamp next to it works fine, so that eliminates leads  mic, and converters.

Thanks in advance.

Cheers
Dave

 

[kante1603]

Hello,

so you have just swapped the DOAs,right?
Next step as usual would be voltage checking at their sockets.But I don't feel like this is the issue.
You say the green light is not working.That leads me to something else.Look here,this is the description from Jeff's site:

The only green LED on the faceplate. This is a full wave rectifier circuit feed from immediately after the 1st EA2623-1.

So since this is prior to the second stage (fader/amplifier/output) it seems to happen somewhere in the preamp.

I'd check if either a signal enters the transformer as well as leaving it.If there's a signal at the input but not on its' output then you might have

a)a broken transformer
b)wires misplaced
c)wires shorted or open condition(s) within the windings
d)a combination of them

If so measure the transformer dcr,you can find the info for wire colours on Jeff's site.
If the transformer is o.k. you can check the in- and outputs of the driving DOA.

http://www.classicapi.com/catalog/images/gallery/2623/2623-1-specs.pdf

If all fails you might want to post some clear and well-focused pics from the pcb,both sides.

Hope to have helped and good luck,

Udo.

 

[jsteiger]

Also, if you scroll thru this thread from the beginning, you will find a pdf with test points and some instructions on how to try and isolate where your problem is.

 

[blackbird]

Hello,

so you have just swapped the DOAs,right?
Next step as usual would be voltage checking at their sockets.But I don't feel like this is the issue.
You say the green light is not working.That leads me to something else.Look here,this is the description from Jeff's site:

The only green LED on the faceplate. This is a full wave rectifier circuit feed from immediately after the 1st EA2623-1.

So since this is prior to the second stage (fader/amplifier/output) it seems to happen somewhere in the preamp.

I'd check if either a signal enters the transformer as well as leaving it.If there's a signal at the input but not on its' output then you might have

a)a broken transformer
b)wires misplaced
c)wires shorted or open condition(s) within the windings
d)a combination of them

If so measure the transformer dcr,you can find the info for wire colours on Jeff's site.
If the transformer is o.k. you can check the in- and outputs of the driving DOA.

http://www.classicapi.com/catalog/images/gallery/2623/2623-1-specs.pdf

If all fails you might want to post some clear and well-focused pics from the pcb,both sides.

Hope to have helped and good luck,

Udo.

Thanks udo.

I will order a extender thingy for the 500 rack from jlm ( I'm in Australia) to be able to test voltages and signal. Too hard to reach in there...

When talking transformers, are you talking about the output trafos? You mention wires, so I thought that might be what u mean to check.

I did notice aft testing it yesterday, one of the opamps came out warm. Not hot, just warm. Whilst the other was cold. Hmmm. Mabey I can reach in enough to check opamp pin voltages. Will give it a go tonight..

Thanks again for your help.

Cheers
Dave

 

[blackbird]

Also, if you scroll thru this thread from the beginning, you will find a pdf with test points and some instructions on how to try and isolate where your problem is.

Hi Jeff.

I just went back through it to find the PDF. Came up empty. I swear I'm not just being lazy. Can u direct me to the post or the page it's on?

Cheers
Dave

 

[kante1603]

I will order a extender thingy for the 500 rack from jlm ( I'm in Australia) to be able to test voltages and signal. Too hard to reach in there...

Cool,a must-have when doing a lot of 500/51x stuff.

When talking transformers, are you talking about the output trafos? You mention wires, so I thought that might be what u mean to check.

Yes,because it is easier to reach.I just thought it was a good point to start and sort things out.You can of course start at the iput transformer too,but I haven´t heard from a broken 2622 so far,it is sealed while the o/p transformer has an more open structure with wires.Therefore easier to break something.The results of dcr measurings will lead you to where to look next anyway,either before or behind it.

I did notice aft testing it yesterday, one of the opamps came out warm. Not hot, just warm. Whilst the other was cold. Hmmm. Mabey I can reach in enough to check opamp pin voltages. Will give it a go tonight..

Be patient.Don´t try to do voltage checks when you can´t reach the pins safely.Too easy to cause a short.Wait for the extender cable.
About the opamps,it´s pretty normal that they get warm,especially the big o/p transistors.While it is not normal that they stay completely cold.....which one was cold,which one went warm?

Best,

Udo.