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

[Meathands]

Wow, 51ma, pretty light.  Makes me think I should just get a 16VA-or-so torroid and build 8 preamps.

 

[dbeeson]

Well, it looks like I'm the third reported case to have swapped the BD140/BD139. Smoked one of them anyway.  I was wondering if I could just swap them for the NTE equivalents, as I can get them locally. Will this work all the same? 

 

[haima]

the BD140/139 are general purpose medium power transistors, nothing too fancy. i don't know what the specs of the NTE parts are, but i'd be surprised if they didn't work - providing the pinout is correct!

but those BD parts are very common - you shouldn't have tooo much trouble finding them if you want to go that way.

 

[gar381]

bdeeson

The NTE parts should work but are probably 5 to 10 times the price
of the real thing but I have never tried them.  Both mouser and digikey have the real ones.
Did you reverse them in a gar2520 or a gar1731 DOA kit??
PM me if you did.

GARY

 

[fucho!]

Hello,
I'm an enthused DIY newbie with a troubleshooting issue. I just built the first of two VP26's (from kit & caboodle packages).

With phantom power on, condenser mics seem to work, but for dynamics w/o it, the signal is just barely audible. In fact, the signal for the condenser may be fairly low too- nothing to compare it too without having built the other unit yet, but I was surprised during initial tests not to hear major clipping with the gain maxed and no attenuation.

I think I may have blown something, as I got a good signal from a Dynamic BEFORE ever having tried a condenser, but never again! Also, DMM tests (as per the assembly guide) with no power and no op amp seem to be fine. I don't have a way to power from the bench, so can't test with power but no op amp.

I've double checked the assembly. Some resistors are reading funny in the PCB (is this normal, or a terrible sign?) e.g. R4 reads a mere 12.9ohms,  R13 reads all over the place, R7 & R8 3.4K ohms (half of their rated value), R9 144ohms, and  R10 & R11 417ohms.

Everything else looks good as far as I can tell.

Can anyone point me to a particular suspect area based on this behavior?
Any help is appreciated!
Thanks!
-Ian

 

[fucho!]

Here are some pics...

 

[fucho!]

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[fucho!]

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[Infernal_Death]

I've double checked the assembly. Some resistors are reading funny in the PCB (is this normal, or a terrible sign?) e.g. R4 reads a mere 12.9ohms,  R13 reads all over the place, R7 & R8 3.4K ohms (half of their rated value), R9 144ohms, and  R10 & R11 417ohms.

Cannot help you on your main issue as i don't have a VP2X. But stuffed resistors on a pcb can always give funny readings, that's normal. If you really want to measure the resistance, you have to at least take off one leg and measure then. If not you might measure a different resistance than the one "over your resistor".
That's why you always should check resistors before soldering in.

Flo

 

[fucho!]

Thanks, Flo!
OK- I thought that would be the case. Actually I did measure before putting them in and they all read fine- so I guess there's no problem there...
I wonder if the output transformer is the culprit, but don't know how to test it. Any advice?
Thanks again,
Ian

 

[jsteiger]

Hi Ian,

Sorry I just saw this now. My notifications from this thread got messed up with all of the maintenance that Ethan was doing a little while back.

For sure as Flo said you cannot measure the R's while both ends are soldered in place.

The first thing I will ask is was the pad engaged when you were doing this testing? Make sure it is out if so. If the pad is acting more like a "mute" than a 20dB pad, double check the black bodied R's. I had a small back ordered batch from a vendor that came in as 750K instead of 750R. Like a dummy, I did not check these right away so a few kits got shipped out with these incorrect 750K's instead of 750R's. I did send an email blast out to all of my store customers but only heard back from one person.    Maybe the email ended up in everyone's spam folder. I have heard from a few guys since then. So, let me know if that is the case and I will get you the proper parts right away.

That goes for anyone else who may stumble across this too. 

Cheers, Jeff

 

[fucho!]

Thanks for getting back, Jeff!
I'm pretty sure the Mute wasn't engaged; I was trying every combination- but will test again as soon as I get a sec!

Does the fact that the dynamic worked before trying a condenser provide any clues?

It may also be possible that some solder connections aren't solid- I initially had trouble with Op amp socket test between 0 & C- then went back and retouched a sockets and a number of other points (kind of at random, as they all look good to me) and this fixed the problem. I could just retouch everything, but don't want to put stress on the PCB/ components if not necessary.

Thanks again,
Ian

 

[jsteiger]

You know Ian, I just went back and looked and I see some pins for the C&K pushbuttons that do not look soldered. This can for sure be the cause. I would double check all of those and touch them up/reflow. Especially the ones that are tied to the ground plane.

Let me know how you do!
Jeff

 

[a zombie]

Jeff, Any idea when the VP26 pcb's will be back in stock?

 

[jsteiger]

Jeff, Any idea when the VP26 pcb's will be back in stock?

I just received an email from them. Very frustrating. When I ordered (1 week after their Spring Holiday) the confirmation date was last Friday the 26th. Yesterday they told me the boards would not be done until the 8th & I would receive the 10th  ??? This morning's email says that they will be out of production the 5th. I should have them here on the 9th. Crazy.

Sorry to rant but between this and the 2503's no kits have been in stock for over 2 weeks. I hate responding to all the emails with bad news.

So, the long and short is by mid next week.  

Thanks!
Jeff

 

[a zombie]

Jeff, Any idea when the VP26 pcb's will be back in stock?

I just received an email from them. Very frustrating. When I ordered (1 week after their Spring Holiday) the confirmation date was last Friday the 26th. Yesterday they told me the boards would not be done until the 8th & I would receive the 10th  ??? This morning's email says that they will be out of production the 5th. I should have them here on the 9th. Crazy.

Sorry to rant but between this and the 2503's no kits have been in stock for over 2 weeks. I hate responding to all the emails with bad news.

So, the long and short is by mid next week.  

Thanks!
Jeff

Wow! that sounds like a royal pain in the A**!

cheers,
James

 

[Brolik]

Heyhey,

I've got this VP25 Rev A that working all smooth and shiny except for this annoying white noise/crackle when I engage phantom power. The +48v rail seems to be working fine as condensor mics do pass audio as they should, aside of course from the static. The problem exists whether a mic is attached or not. I've check the component placement and can't see anything out of order. I've switched out the 2520 for a working one, even though I'm sure this is unrelated.

Any ideas off the top of your heads? I'm going to go in and reflow all the solder joints tonight hopefully, but I thought it was worth a shot to see what you think. Thanks!

 

[jsteiger]

Hey Brolik,

Is R6 10K or 200ohm? If it's 10K, try changing it to 200ohm. Otherwise you could try the other side of the toggle switch. Might help.

Best, Jeff

 

[fucho!]

Hey Jeff,
I just wanted to say that, after being hugely sidetracked, I finally got a chance to go back over the problem unit I posted about above. After a few rounds of retouching, it's working perfectly!! Now on to some actual tracking with it... Can't wait to hear it in action. Thanks so much for the help!
Ian

 

[jsteiger]

Hey Jeff,
I just wanted to say that, after being hugely sidetracked, I finally got a chance to go back over the problem unit I posted about above. After a few rounds of retouching, it's working perfectly!! Now on to some actual tracking with it... Can't wait to hear it in action. Thanks so much for the help!
Ian

Excellent Ian. Thanks for the update.