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

[Whoops]

did you make the opamps yourself? is there a chance both of them have a reversed component or bridged track?

A friend of mine did one of the OPamp's last week, and I did the other one sometime ago.
I re-checked the components in the OPamps, couldn't see any reversed component, the tracks and solder joints were also really clean on both OPAMPS.

what rack are you using, out of interest?

I'm using the API 500V. Rack is fine, other preamps are connected there and working fine, in the same slot I used.

thanks a lot for your help and interest

Here are some hi res shots of the solder side:

 

[jsteiger]

Yes, Haima makes good and valid points. Like he says, is it possible that both of the gar's had the same issue?

Can you check your voltage rails with power to module and no DOA? I have got into the habit of testing my projects with a bench supply before I drop an opamp in. I like to test right at the DOA sockets.

I think I can make out from the pics that you have only soldered from the bottom of the board? Like Haima says, check the bottom for a bridge or short of some kind. I also like to solder each component I can from the top and the bottom to insure there are no cold or faulty joints.

I had a similar situation once on a summing amp card. The DOA started to get real hot and smell funny. Completely smoked one of the power rail diodes. Removed it, cleaned up the board a bit, dropped in another and made damn sure it was solder very good from top and bottom. No issues and still running good right now. I can only assume I had a shoddy solder joint at the diode.

Let us know.

Jeff

 

[Whoops]

Hi Jeff,
thanks a lot for your input and Haima.

You are right I only soldered from the bottom of the board, I will solder from the top also.

Like I said, the opamps were built at different times, by different people, components all seem to be pointing in the right direction and the solder joints are really clean, so I don't think the problem is coming from the Opamp themselves but I took some pictures anyway.

I can't clearly see which component or components burned, but R11 and 12 have a different color, darker for sure.

 

[[silent:arts]]

what went wrong with the black cable of the output transformer?

 

[haima]

as jeff said - if you have a bench power supply capable of +/- 15v, power up the card using that. connecting the power to the the protection diodes where it would come in via the "finger" of the board, and a good 0v point, and measure the voltages present at DOA sockets - without the DOA installed.

if you don't have a bench supply, clear enough room to the right of the module in the rack to get your multimeter probes in to measure the voltages at the DOA socket - again, without the DOA in there.

let us know what voltages you have where.

looking at the bottom of your board, there's a few solder points that look a bit "bulge-y" - like there's perhaps too much solder there, and perhaps not enough heat... i'm looking at the secondary of the output transformer for example. not that a shorted secondary would cause the opamp to burn up - but i'm just saying, might be worth cleaning up the points a little, perhaps removing some excess solder, making sure you've got good "flow" into the joint.

** EDIT: i noticed the output transformer PRIMARY solder points look like they might be shorted due to excess solder... these are the two points near the output transformer nut. measure the resistance between them - are they shorted? **

good luck! we'll get there...

 

[haima]

some more measurements that are worth doing - with the card out of the frame, no opamp installed:

A) what's the resistance of from the opamp output pin socket to ground/0v? (related to the possibility of output transformer primary being shorted, mentioned in my previous post)

(the following stuff shouldn't be a problem given the rack seems happy with the module installed (no fuses blown etc)... but what the heck, these things are good to check

B) resistance from +ve to -ve on the opamp sockets?

C) resistance from +ve on the opamp socket to ground?

D) resistance from -ve on the opamp socket to ground?

 

[Whoops]

what went wrong with the black cable of the output transformer?

I cut it too short by mistake, so I had to extend it a bit by soldering a bit more lenght, and then used heat shrink tube over it.

as jeff said - if you have a bench power supply capable of +/- 15v, power up the card using that.

Thanks Haima,
I will do that. A friend of mine has an external Edac connector to test these modules, so I will perform the measurements and report here.
Thanks a lot for your input.

I will also do a checkup on all the solder joints.

Green and brown wires of the output transformer are not shorted, although I'm readind 13,5 ohms between Red and orange wires. Could that be right?

thanks a lot once more

 

[mus1k_freak]

I have a question about phantom power on a build i did with a vp26. I used a JLM input transformer instead of the one from jeff and a purple kdj4 op amp (i think i used a jlm99v for testing). I left out the output attenuator and added a blue led for phantom power switching, i think the led may be my problem. i i wired from the load side of the switch to a 10k resistor to the led and the other side of the led to ground (pin 1 i believe on the card) would this make my phantom power not work? The led comes on when i flip the switch and slowly fades out when i turn it off like it should. maybe the way i wired my input transformer has something to do with it? since theres only 1 primary and 1 secondary on the jlm i left pins 2 and 3 open, and just wired the primary to 1 and 4. Without phantom power everything seems to work fine, with a sm57 it sounds similar to a 512c but with a little more low end, excited to get the phantom power working and try it with the purple op amp!

also with leaving out the output attenuator, do i need to solder anything in its place?

 

[surfkat]

I just built a pair of these beauties. I ordered ready made DOAs to make it easy on myself. I put them in my API lunchbox and checked the voltage at the DOA sockets without the DOAs installed. All looks good there. #1 fired up and sounds like API Heaven. Holy Vintage, Batman!!! Pre#2 has a problem that I am unable to track down. These is audio passing thru the unit but it is very low level and sounds like it is single-ended. I am guessing that I might be shorting one side of the input before the transformer. I tried to swap the DOAs but that did not change anything. I suspected a problem with the Pad switch so I removed that, it checked out ok, then I re-soldered it. I am getting a bizarre resistance reading from the -16 input to pin 3 of the switch. 148k, like it is shorted across to the other pole. But the first 2 pins show 0 resistance to the inputs so it should work in the open position regardless. The pad switch may not be the main problem is what I am thinking.

I spent much time examining parts placement and soldering, checking for shorts and comparing things to the working pre, all to no avail. All resisters and caps appear correct, and polarities look good. I hope someone can point me to a few test procedures to narrow the problem. I do not have a test jig to power the pre on the bench while plugged into the Lunchbox. I do have a 16 volt supply that I can power it on the bench without audio I/O.

I saw Haima's post #85 and was going to try these but he does not say what they should read. Any signs pointing in the right direction would be appreciated.

Happy Holidays to all.

 

[jsteiger]

I have a question about phantom power on a build i did with a vp26. I used a JLM input transformer instead of the one from jeff and a purple kdj4 op amp (i think i used a jlm99v for testing). I left out the output attenuator and added a blue led for phantom power switching, i think the led may be my problem. i i wired from the load side of the switch to a 10k resistor to the led and the other side of the led to ground (pin 1 i believe on the card) would this make my phantom power not work? The led comes on when i flip the switch and slowly fades out when i turn it off like it should. maybe the way i wired my input transformer has something to do with it? since theres only 1 primary and 1 secondary on the jlm i left pins 2 and 3 open, and just wired the primary to 1 and 4...

Did you try completely removing the LED and see about the phantom? If all is fine like that, which it should be, try connecting the LED to the PSU common-pin #13 instead of pin #1. Not sure what if anything pin #1 is connected to on your rack. Sounds like the input iron wiring is fine to me.

also with leaving out the output attenuator, do i need to solder anything in its place?

No, it has been taken care of on the PCB. You will just need to connect the output transformer's secondary to the holes labeled "Opt-(whatever color)" right near the gold fingers for pins #2 and #4. The color's are output transformer dependent.

 

[mus1k_freak]

ah right i do remember moving those two wires on the output transformer, that makes sense, thanks jeff! i haven't had a chance to try it without the led yet, but hopefully ill have some free time in the next day or two and try pulling it out and see what happens, thanks! and merry christmas!

 

[djmukilteo]

I need to build one of these

 

[jsteiger]

Hey Surfkat,

Double check your wiring on the t-pad and output transformer. I had a guy who described similar problems before. Turns out he made a small error when wiring the attenuator.

Cheers, Jeff

 

[haima]

OK, here's some clarification on the basic troubleshooting tips above. i'm hoping this is all correct - i can't verify exactly as - my units are "permanently borrowed" right now...  


with the card out of the frame, no opamp installed:
---------------------------------------------------------

A) what's the resistance of from the opamp output pin socket to ground/0v?

should be "SOME RESISTANCE" (i.e. not a short)

B) resistance from +ve to -ve on the opamp sockets?

should be VERY HIGH

C) resistance from +ve on the opamp socket to ground?

should be VERY HIGH

D) resistance from -ve on the opamp socket to ground?

should be VERY HIGH


now with the card in a rack or connected to a bench power supply, no opamp:
---------------------------------------------------------------------------------------

E) check +ve and -ve power supplies are at the correct pins - both voltages are present and not reversed etc


if all these checks are positive, install the opamp and test for audio


--
mus1k_freak: if you were using a JLM99v to test, was it the  +/-16v version? i'm not sure how happy the standard one is at +/-16v - it's more designed for +/- 24v to 34v as far as i know...

 

[mus1k_freak]

mus1k_freak: if you were using a JLM99v to test, was it the  +/-16v version? i'm not sure how happy the standard one is at +/-16v - it's more designed for +/- 24v to 34v as far as i know...

yup its the 16 volt one, it actually sounds pretty good! i also tested it in another vp26 i have thats built to spec and i like it alot, not as much as the gar2520 though! but i think it sounds better in the vp26 then it does in the eisen i pulled it out of, maybe next ill try the gar2520 in the eisen and see what happens! purple kdj4 on its way for the new vp26 with the jlm input transformer ;D

 

[Whoops]

Hi,
after carefully re-checking every component in the Gar2520 opamps I realized that the BD140 and BD139 are swapped with each other.
So this might be the cause for the burning Opamps and not the mic pre board.

What do you think?

thanks

 

[jsteiger]

Hi,
after carefully re-checking every component in the Gar2520 opamps I realized that the BD140 and BD139 are swapped with each other.
So this might be the cause for the burning Opamps and not the mic pre board.

What do you think?...

Well, the BD139 is NPN and the BD140 is a PNP so I would agree that this is a/the smoking problem.

A friend built one and you built the other right? Odd that both of you guys made the same error but I guess "shit happens" as they say.

It is as clear as day in your first pic. I was so worrying about think of the preamp board that I didn't look real close at your DOA pics.

The preamp is a pretty simple build. Much easier than the gar2520.

Cheers, Jeff

 

[haima]

that sounds like the problem (or at least A problem!) ;D

i'd replace those BD140 and BD139 & probably those higher wattage output resistors... hopefully you'll be good to go! not having the schem, it's hard to say - but hopefully that's the only parts that would be damaged.

be careful removing components from a double sided board like these - best to snip the transistors off and then pull out each leg individually - otherwise you run the risk of overheating the board and lifting traces.

 

[jsteiger]

...be careful removing components from a double sided board like these - best to snip the transistors off and then pull out each leg individually - otherwise you run the risk of overheating the board and lifting traces.

A very nice tip indeed! Thanks haima! 

 

[Whoops]

Thanks a lot for the tips,
I will replace the transistors.

The resistors don't seem Burned out, the look fine, should I replace them also?


Do I need to buy a specific brand , or that is not really important?


Yes Jeff, it's a shame that we both did the same mistake when building the OPamps, it's my fault because I did the first one, and he used the one I built as a reference for the second one. And what a bad reference it was!!!

thanks, once more