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 !


 

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