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

[ipagel]

Just an update.
Have been testing for a couple of weeks and must say how wonderful these things really are.
They sound great for all duties.
I was using them to record a female singer using a lewitt lct 640 and everyone just stopped and was amazed how great it sounded. Only issue I have is the the led for polarity on one unit is not working, but other than that they are working perfectly. May have a look at it later.
Thanks again to Jeff for making this project possible.

M C

 

[jsteiger]

Only issue I have is the the led for polarity on one unit is not working

That LED is most likely in backwards or there may be a solder bridge around the switch pins. You can look closely at the metal innards of that LED from the cutout area of the L-bracket. See if it looks exactly like the other LED's or not.

 

[dmp]

Well I tracked down the problem with mine. It turned out to be a problem at the phase switch. I had to pull components out to find it. With that switch out and the connection jumpered, the pre is working great now. Destroyed the switch unfortunately.

 

[bartacusad]

Hey all, just finished building my new VP28 and it sounds amazing! Just have one issue though, only the green Signal LED is working. I can't get the others to work. I've flipped them around just on the off chance I got the polarity wrong and still nothing. What have I done wrong here?! I did break the red 48V LED but installed the rest of them while I'm waiting on the replacement to come in. It's not necessary to have all four LEDs in (1 red, 3 yellow) for them to work is it??

 

[jsteiger]

.....It's not necessary to have all four LEDs in (1 red, 3 yellow) for them to work is it??

Yes it is. They are all in a series string.

 

[bartacusad]

Thanks so much Jeff! You rock my friend! Can't tell ya how much it means to have the designer on here answering questions. It definitely goes on a long way in me having the confidence to encourage others to build these amazing preamps!

 

[erol]

Hi,

I am planning to build a VP28 with a gar2520 Full Kit Bundle.
This will be my first DIY project (with a lot of help from a good friend).

I've noticed there's a VP2x step-by-step guide on de CAPI website:
http://www.classicapi.com/catalog/images/gallery/VP26/VP2x-Assembly-Guide.pdf

But it seems this is all about the VP25 and VP26 am I right?

 

[jsteiger]

Go back to the beginning of this thread. All of the support docs are there along with 'Chunger's build pics.

 

[choolder]

hi guys,

I finished 2 VP28 units a few weeks ago? Both working perfectly, only minor issue was the pad led that broke (I still have to replace that).
I didn't use the vp28's for a week and today I wanted to use them and one doesn't work at all. No signal coming in.

Where do I have to start to debug the unit?


thanks!

 

[choolder]

hi guys,

I finished 2 VP28 units a few weeks ago? Both working perfectly, only minor issue was the pad led that broke (I still have to replace that).
I didn't use the vp28's for a week and today I wanted to use them and one doesn't work at all. No signal coming in.

Where do I have to start to debug the unit?


thanks!

I switched the opamps and it works again, bad contact I think!

 

[jsteiger]

Are the opamps fully seated? http://classicapi.com/catalog/DOA_Install.php

 

[verydeepwater]

Jeff, Chunger, anybody, I just completed my first VP28, a lot of fun, however it doesn't pass any signal. The LED's are lit, a minor consolence........ I can't seem to find the trouble shooting page on Jeff's site, any suggestions? Thanks much, Rich

 

[jsteiger]

All of the help is in this thread here. I would suggest scanning thru it from the beginning.

The first thing to rule out are the opamps. Who built them? If they are prebuilt they should be fine. If they are kits, they need to be checked in another module. In a VP28 there 3 main potential issues. The 2 opamps and the preamp itself.

Also, make sure the opamps are seated properly. This page is linked a few times earlier in this thread but here is the link again.
http://classicapi.com/catalog/DOA_Install.php

 

[orenradio]

Hey Jeff,

Are the pads for T3's Green and Brown leads bridged together?  For some reason after trying to put the brown lead into the PCB i noticed there is a very straight, almost purposeful bridge between Gre and Bro pads.  See the picture below.  I have a solder sucker and a desoldering wick, but nothing seems to clean it up. 

Hopefully its a purposeful bridge:

 

[jsteiger]

Yes there is a track connecting them. I don't mean to be mean but this is the VP28 thread. You should be posting in the VP2x support thread.

 

[Sansodor]

Hey guys!

I just finished building my first VP28. I was wondering if it's normal to hear a slight popping sound when engaging the mic switch? Mine gives about -20dbfs pop when pressed (gain at full, fader at unity). The same thing happens when engaging the pad but not as loud. No biggie, but just wondering if it's normal behavior?

Otherwise everything seems to be working correctly on the first try. I built my a 1731 and a 2520 for the op amps myself.

 

[orenradio]

Not a problem Jeff,

I wasn't sure if it was specific to T3 on VP28 - as the vp26 only has T1 and T2 and may have been traced differently on the PCB.  I can write a quick "fyi" post there to highlight the existence of the trace/bridge for future users.

Thanks again for your quick response, 3 Vp26s and 3 Vp28s later I'm an extremely happy DIYer; can't wait to build more

 

[brent]

Hey guys!

I finished building a couple VP28's a few days ago and they sound really great.  I'm using gar1731's on the input and gar2520's on the output, I found it to be a mellower combo for my needs than the reverse.  Before I built the op amps, I was using the 2520's from my API 2500 to test the units and those opamps actually sounded pretty good in this circuit! It's great to have multiple op amp choices and flavors.  I need to get some red dots next...

I botched up one unit temporarily when I put the 2 switches for the HPF on the wrong side of the PCB... ( not enough sleep apparently!)  I thought I was going to have to replace that PCB, but I managed to get them both out by taking the tops off, and pulling out one pin at a time while heating the respective pad.  Phew!  Ordered a couple new switches from digikey and I was back in business!  Jeff you probably have an email buried in your inbox from me about that fiasco.. you can safely disregard!

Great kit! Great guide too chunger!

Now off to contemplate some love childs...

B

 

[Pliplo]

I assembled 4 VP28's the other week and one of them has a weird issue... Super low gain, almost as u were connecting a mic in line mode... Also kinda of a Low Cut effect all the time, and mutes completely when i engage the polarity switch... Phantom works but same issues with a condenser... Any ideas?

 

[jsteiger]

Hmm, could possibly be something with the first stage output trafo. I would desolder all the leads from T2 and check DCR from one lead to all the others.