ramtazz

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1060 on: February 27, 2020, 11:00:05 PM »
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

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1061 on: February 27, 2020, 11:54:30 PM »
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!
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Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1062 on: March 28, 2020, 11:26:34 PM »
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

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1063 on: March 29, 2020, 03:25:53 PM »
@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.
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CAPI is not affiliated with, endorsed by, or sponsored by API.

iturnknobs

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1064 on: March 29, 2020, 04:36:39 PM »
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.
Election 2020.  For the people, not the money.

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1065 on: March 30, 2020, 04:35:45 PM »
Well... it works now :D  I basically went through @ 800 and sucked out any excess solder and retouched every point. Thanks guys!!

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1066 on: March 31, 2020, 06:53:32 AM »
Hi there  8)
Someone saved the  pictures of Chunger's build guide ?
They are no longer displayed on the thread  :-\
Thanks,
Stay safe !

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1067 on: April 13, 2020, 01:01:00 PM »
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 sh*tty 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.

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1068 on: May 23, 2020, 09:58:11 PM »
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

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1069 on: May 23, 2020, 11:21:15 PM »
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....?
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CAPI is not affiliated with, endorsed by, or sponsored by API.


Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1070 on: May 24, 2020, 01:19:22 PM »
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

Re: [BUILD] CAPI VP28~500 Series~2-Stage Preamp~Official Support Thread
« Reply #1071 on: May 24, 2020, 02:35:00 PM »
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.
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CAPI is not affiliated with, endorsed by, or sponsored by API.


 

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