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

[ramtazz]

Thank Jsteiger for the nudge in the right direction.  I borrowed 2 J Hardy Ops from another project and then verified the main board was sound. Then by solder sucking and resoldering a few connections on both of the 2520 op amps one by one I got both to work. Great sounding preamp.  Bill

 

[jsteiger]

Thank Jsteiger for the nudge in the right direction.  I borrowed 2 J Hardy Ops from another project and then verified the main board was sound. Then by solder sucking and resoldering a few connections on both of the 2520 op amps one by one I got both to work. Great sounding preamp.  Bill

That's great Bill. Congrats!

 

[FivePointsRecording]

Hey guys, I am having some strange high pitched whistle sounds come from the VP28 I built, as well as no signal. Unfortunately, I mismatched the Q7 and Q8 transistors (#139 & #140) which caused a little smoke and burnt the PR2 & PR4 resistors. I’ve replaced those resistors and actually built a whole new Gar1731 but there is noise from the pre, as well as no audio from the microphone.  There also seems to be some small sparking happening near the connection point (UNDER J3-12) when I insert the pre into the rack, whereas none of my other pres do so.

The make things short, I’ve checked:

*Made new Gar 1731, tested on Capi Vp312 and VP25 pre and worked fine
*Gar 2520 opamp also works fine
*went thru and reconnected all solder points for gray hills and resistors
*Filter PCB no cold solder joints
*All LEDs are working correcting

As for testing points:
—I was able to run a sine wave thru the preamp (WITH THE MIC BUTTON ENGAGED?) successfully BUT the preamp stepped gain switch seems to be stuck in a specific location, as it has no change when adjusting. The fader knob works fine, but the preamp knob might be in a more gain-forward state, as you can hear the harmonics very clearly.
—Even though the sine wave is coming thru with MIC engaged, the preamp still passes no microphone signal when connected to a mic.
“With nothing connected to the output of your generator, assuming a balance device with an XLR, connect your red probe to pin 2 and black probe to pin 3. Your DMM should read 1.228V AC. “
—Read 0.000000 v  so I didn’t continue on this path yet as the instructions are a bit difficult for me to follow.

I’ve included a couple of pictures, any help would be greatly appreciated! Excuse my amateur soldering!

 

[jsteiger]

@FivePointsRecording

I'm not trying to be mean but in looking at the bottom of that board, your problem could be almost anywhere and in more than 1 spot. I see multiple solder joints that look cold. Also, many spots where there is way to much solder than could potentially be shorting out to the ground plane.

 

[iturnknobs]

I believe in the past, Jeff had said he solders around 800F.  I took his advice and haven't had any issues since(minus dirty solder tips). Using chore boy combined with a wet sponge in between each use has helped me out also. Reflow all your points as recommended by Jeff. You should see the solder "flash" shiny silver and it shoud simultaneously adhere to the component and pcb trace/hole. As soon as that occurs, remove the iron. Also, I'm not sure what "common" practice is, but I always turn off power when inserting modules to the rack/chassis.

 

[FivePointsRecording]

Well... it works now   I basically went through @ 800 and sucked out any excess solder and retouched every point. Thanks guys!!

 

[AttamanuBe]

Hi there  8)
Someone saved the  pictures of Chunger's build guide ?
They are no longer displayed on the thread  :-\
Thanks,
Stay safe !

 

[deep_transmissions]

Took me a 6months to get approved for this board ... yes 6 months! Dude.

Anyways, so I'm just now able to add some thoughts here after building 2 CAPI VP28's back in 2019. My previous experience was pretty limited, I built a DIYRE summing mixer, and that's about it. A few wees ago I just finished a Hairball 1176 Rev D for my 500 rack. Totally worth it!

My VP28's worked without any troubleshooting, so if you're worried about being able to do this I'll say that if you take your time and don't rush anything, go slowly, follow the intructions in this thread carefully, make notes to yourself of any conflicts in parts, or potential confusions so you can track possible errors, I think you'll do just fine!

In fact, I bought a Hakko FX-888D knowing I was going to build these pre-amps, since the passive summing mixer I built requires amplification. These 2 togetehr are a pretty killer way of getting analog console mixing sound in your home studio. I cannot put into words how good they sound. Smokin'. And running my analog gear through the CAPI's into the 1176, forget it. So good.

So the Hakko blew a capacitor right when I started installing the first resistors. The unit had to get shipped to the company for a repair which they did fo free under warrantee and you know what? I used my ****** Radio Shack wand soldering iron for the entire of both the VP28's! It was probably not the best decision, but just shows if you work carefully you don't necessarily need pro grea to get this stuff done.

My Advice:

- Read through this whole thread. I did that while waiting for my VP28 kits, it went pretty fast, you'll have a good idea of what you're going to be doing and you'll also see where other people had problems, and you can then work sensitively around those trouble areas.

- Definitely read through the whole build thread at the beginning. You want to knwo wahts' coming before you get there.

- Test every component you can, I didn't have any problematic parts but if you do, finding them at the beginning and re-ordering instead of going through your entire build is a huge time saver.

- Do the LEDs very carefully.

- Wire the transformers very carefully. Get a good wire splicer that won't cut extra wire, if you cut those too short you're going to have a hell of a time fixing that problem.

- Be sure you have the right diameter wrench for the knobs before you start. You'll be bummed if you can't finish your build with the knobs on when you rack em.

That's it! This was such a good project. I feel like doing these 2 was equal to years of therapy. I learned to be confident in myself, to slow down and pace and breathe and just focus on quality and not speed. And it then led me to have the confidence to build that 1176 compressor which is just the absolute cats meow on drums.  My next project is a Syncussion drum machine, this one has a lot of SMD parts so it's going to be a toughy.

Good luck and you'll be blown away by the thump these things bring your mix.

 

[fancytimestudio]

Hi all,
I have two VP28 preamps on my bench here. One is quite a bit louder at line level (unity gain).

I swapped opamps and the issue followed the PCB. I reflowed solder and still have the same issue. So I started probing around and found the following:

I have a signal generator suppling 1.212v at 400Hz. At the +/- points on the first opamp socket I'm getting different readings on the two preamps. Preamp 1 has .706v and Preamp 2 has .110v.  I'm unsure if either of these are correct but I know they aren't the same! Any ideas?`

 

[jsteiger]

Hi all,
I have two VP28 preamps on my bench here. One is quite a bit louder at line level (unity gain).

I swapped opamps and the issue followed the PCB. I reflowed solder and still have the same issue. So I started probing around and found the following:

I have a signal generator suppling 1.212v at 400Hz. At the +/- points on the first opamp socket I'm getting different readings on the two preamps. Preamp 1 has .706v and Preamp 2 has .110v.  I'm unsure if either of these are correct but I know they aren't the same! Any ideas?`

Misplaced resistors....?

 

[fancytimestudio]

Misplaced resistors....?

Hi Jeff, Thanks for the quick response. I went through and confirmed all resistors were in their correct places this morning. Thought I had a 70k at R34 so I removed it, tested and it tested at 20k as it should (the red looked very purple, my daughter confirmed). So I re-soldered it in place.  I should mention that when I have the "mic" button depressed, they function identically. It is only when in line mode that they differ that one is quite a bit louder than the other. Not sure if that helps

 

[jsteiger]

Hi Jeff, Thanks for the quick response. I went through and confirmed all resistors were in their correct places this morning. Thought I had a 70k at R34 so I removed it, tested and it tested at 20k as it should (the red looked very purple, my daughter confirmed). So I re-soldered it in place.  I should mention that when I have the "mic" button depressed, they function identically. It is only when in line mode that they differ that one is quite a bit louder than the other. Not sure if that helps

Post a pic of the resistors that are just behind the switches and below the T2 output transformer.

 

[mcdavis]

Hey all! I just built a vp28, everything seems to be working fine though when I turn the preamp on I get a click, and when powering it off I get a bit of a zap sound. My vp26s I built don't do that and are quiet powering up and down. Just want to make sure this is normal? or if I should investigate something. thanks!

 

[Brinporter]

Hey Everyone. I ran into a problem (that i think i solved) but wanted to put it up on the forum incase it helps any one in the future.

I made a vp28 about 8 months ago and LOVE it. Use it for everything. So what comes next? Another one of course!

I bought it (watched the website like a hawk as it sold out in less than 3 days), and got it built. Upon trying it out for the first time it sounded like the 160hz was stuck on. My first move was to try the DOA’s (all 4 are self built 0252’s) from my first successful build in the new module... no good.

Then I tried my new DOA’s in the old module and got vastly smaller signal than it should with or without the 160hz drop. I thought strange but... ah- ha?

So i put the old DOA’s back on the old module and back in the capi 511 rack. There want really any reason to, but i tried it out anyways. Low and behold my previously working vp28 and DOAs had super low signal. I wasnt stoked.

I started with troubleshooting my new build. I could go on in detail about what i tried (rack spots, cables, reflowing, resistor checks, voodoo), but in the end I found that my output transformers blue and green cables didnt have any continuity when all the others did. I find it weird that that would just cause the low end to drop out, but im just a stubborn dude with a soldering iron.

The first module wasnt working because one of the feet for the opamps lost their connection to the PCB when i swapped the DOA’s. they all felt solid, but when i reflowed the solder it worked again.

I just ordered another transformer (and an extender kit) about half an hour ago, but ill let you know if it doesnt work.

I read all 54 pages of this thread and although read ALOT of useful info, thought this little anecdote might help someone down the line.

Thanks for designing such killer stuff guys. Cant wait to have my 2nd vp28 up and running!

 

[resilient]

Hey Everyone. I ran into a problem (that i think i solved) but wanted to put it up on the forum incase it helps any one in the future.

I made a vp28 about 8 months ago and LOVE it. Use it for everything. So what comes next? Another one of course!

I bought it (watched the website like a hawk as it sold out in less than 3 days), and got it built. Upon trying it out for the first time it sounded like the 160hz was stuck on. My first move was to try the DOA’s (all 4 are self built 0252’s) from my first successful build in the new module... no good.

Then I tried my new DOA’s in the old module and got vastly smaller signal than it should with or without the 160hz drop. I thought strange but... ah- ha?

So i put the old DOA’s back on the old module and back in the capi 511 rack. There want really any reason to, but i tried it out anyways. Low and behold my previously working vp28 and DOAs had super low signal. I wasnt stoked.

I started with troubleshooting my new build. I could go on in detail about what i tried (rack spots, cables, reflowing, resistor checks, voodoo), but in the end I found that my output transformers blue and green cables didnt have any continuity when all the others did. I find it weird that that would just cause the low end to drop out, but im just a stubborn dude with a soldering iron.

The first module wasnt working because one of the feet for the opamps lost their connection to the PCB when i swapped the DOA’s. they all felt solid, but when i reflowed the solder it worked again.

I just ordered another transformer (and an extender kit) about half an hour ago, but ill let you know if it doesnt work.

I read all 54 pages of this thread and although read ALOT of useful info, thought this little anecdote might help someone down the line.

Thanks for designing such killer stuff guys. Cant wait to have my 2nd vp28 up and running!

I actually came here to ask about this very issue... my VP28 recently lost all the low end.

jsteiger:  Should I check the transformer first?  I've tried every possible combination of pad settings and nothing changed... just sounds low passed at like 200Hz or so.  Not sure what to do.  It had been working perfectly. I do have Litz transformers, if that makes a difference.  Red dot op amps, so I don't think that would be the issue. 

Brandon

 

[Brinporter]

It was my middle 2 wires from my T3 tranny that lost continuity. I havnt got my new one to know if it fixes the problem yet, but im curious to know if youre tranny’s in the same boat.

 

[resilient]

It was my middle 2 wires from my T3 tranny that lost continuity. I havnt got my new one to know if it fixes the problem yet, but im curious to know if youre tranny’s in the same boat.

I haven't had mine out yet.  Working on building a pair of C12s.  Did you get your extender yet?

Brandon

 

[Brinporter]

Replaced the tranny, thing works like a hawt damn.

 

[resilient]

Nice!  Pulled mine out and checked it today... transformers still have continuity... so that's not it.  :-/

Brandon

 

[resilient]

Well, I found some flux I hadn't cleaned previously... so I cleaned it.  Put it back in and the thing sounds killer!  Hopefully that's all it was.  Can't wait to order another one or three!

Brandon