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

[kante1603]

Actually the solder joints ....

Thank you all !!!!

Good to hear!
So all are up and running?


Best regards,


Udo.

 

[Paxkal]

Yes everything is ok !!

Thank you very much!!

 

[frenkonio]

Hi guys, got a issue with a VP28 that was made several months ago. Today the gain seems fixed. I mean, there's no change in gain using the Grayhill stepped pot. Gain is fixed. I tried to swap opamps but the issue is still there.  Pad works, HPF works, signal led is ok, Mic/Line switch works. Then, after a couple of hours, I decided to put a line signal and press MIC button. After this crazy volume rising the knob came back to work. What may have caused this?

 

[jsteiger]

Hi guys, got a issue with a VP28 that was made several months ago. Today the gain seems fixed. I mean, there's no change in gain using the Grayhill stepped pot. Gain is fixed. I tried to swap opamps but the issue is still there.  Pad works, HPF works, signal led is ok, Mic/Line switch works. Then, after a couple of hours, I decided to put a line signal and press MIC button. After this crazy volume rising the knob came back to work. What may have caused this?

This sounds exactly like the last guys problem. Bad solder joint somewhere. Things changing here and there typically points to a bad solder joint. Can't really tell you where though but I would look at the resistor network behind the gain switch as well as the 200Ω R's and the 330µF cap.

 

[cubivore]

hi everyone! just built two vp28 with red dots somewhat successfully. the first build was blotched here and there but i managed to fix a bunch of my mistakes and get it working 100%! the second build, while much more smooth and relaxing, has a minor problem. it seems like after walking on carpet (not every time, but most of the time) and simply touching the input gain knob will create a tiny burst of clicks. this doesn't happen touching the output fader or any other part of the module. i swapped mic cables, mics, output cables and it seems to only be this module. any ideas where i should start looking before i start dismantling the module?  thanks in advance!

 

[BramK]

Just successfully built 2 VP28s along with the 2520/1731 combos. Thanks Jeff for the great communication via email and everyone in this thread for sharing your experiences. For any who are thinking about building these, the biggest help for me was taking it slow, labeling and taping components down on a piece of paper, double (triple) checking each component value and placement before soldering, and using a magnifying light for the Op Amps. Check for correct placement and any solder bridges as you go along with the magnifier and you'll be up and running in no time!

 

[Catrunes]

This sounds exactly like the last guys problem. Bad solder joint somewhere. Things changing here and there typically points to a bad solder joint. Can't really tell you where though but I would look at the resistor network behind the gain switch as well as the 200Ω R's and the 330µF cap.

i ended up stupidly forgetting to solder the entirety of the push switches. derp. tends to happen when im trying to build while trying to mix a band live ha

 

[pkordel]

Quick question: Somehow R7 went missing, a 59K MF. I do have an equivalent, a 56K3 MF. OK to sub?

 

[jsteiger]

Quick question: Somehow R7 went missing, a 59K MF. I do have an equivalent, a 56K3 MF. OK to sub?

Yeah its OK temporarily but needs to be 59k. It will change the load on the input slightly and lower the operating level. Its very slight but you'll want it to match for any stereo use etc. Send me an email thru the store and I'll mail you one.

 

[pkordel]

I have an issue with the output fader grayhill switch. At the zero setting, there appears to be no attenuation and then one click to the right I end up where I'm guessing the lowest gain setting should be, then it slowly climbs to where I assume unity gain should be. I checked the resistors against the BOM and a working VP28 I have and they appear correct, also reflowed the RF resistors. It almost seems like the grayhill stops are off, have you ever experienced that? I have no previous experience with those switches, they are the variety where the stops are already set. Once the almighty desoldering tool arrives I'll redo that whole part of the PCB, just curious to hear if there have been any faulty grayhills around this thread.

I would love to know how I could troubleshoot a grayhill output fader issue with a DMM. Any pointers?

 

[Potato Cakes]

I have an issue with the output fader grayhill switch. At the zero setting, there appears to be no attenuation and then one click to the right I end up where I'm guessing the lowest gain setting should be, then it slowly climbs to where I assume unity gain should be. I checked the resistors against the BOM and a working VP28 I have and they appear correct, also reflowed the RF resistors. It almost seems like the grayhill stops are off, have you ever experienced that? I have no previous experience with those switches, they are the variety where the stops are already set. Once the almighty desoldering tool arrives I'll redo that whole part of the PCB, just curious to hear if there have been any faulty grayhills around this thread.

I would love to know how I could troubleshoot a grayhill output fader issue with a DMM. Any pointers?

Have yet to encounter a faulty gray hill switch of any kind, but that doesn't mean it is impossible. To test turn the switch all the way CW or CCW, doesn't matter which. One probe of DMM on the pole (the connection by itself) and the other on one end of the row of pins, depending on your switch position. Once you find that out, turn the switch one click and you should have continuity on the next pin in on the row of pins and the pole. Rinse and repeat. You should not have continuity between any of the pins in the row of pins on a Grayhill switch (at least in this design).

And just to clarify, when you say the "zero setting," do you mean in the middle (0=unity gain=no attenuation) or do you mean fully CCW?

Thanks!

Paul

 

[pkordel]

Have yet to encounter a faulty gray hill switch of any kind, but that doesn't mean it is impossible. To test turn the switch all the way CW or CCW, doesn't matter which. One probe of DMM on the pole (the connection by itself) and the other on one end of the row of pins, depending on your switch position. Once you find that out, turn the switch one click and you should have continuity on the next pin in on the row of pins and the pole. Rinse and repeat. You should not have continuity between any of the pins in the row of pins on a Grayhill switch (at least in this design).

And just to clarify, when you say the "zero setting," do you mean in the middle (0=unity gain=no attenuation) or do you mean fully CCW?

Thanks!

Paul

Thanks Paul! Yes, by zero I meant unity gain. So to be even more specific on this issue: imagine the unity gain position being the most gain available, then going CCW arriving at close to where unity should have been. So in essence, a mirror reverse scenario. Going one step CW from the unity gain position seems to be what the lowest gain setting of the switch should be, i.e. fully CCW on a working switch and then it increases normally CW to what I imagine the gain of the position just one step CCW from the unity setting should be. So it's like the throw of the switch is split in two and mirror reversed. Interesting indeed.
Not sure I'm explaining this well...

 

[jsteiger]

As history has it, your issues are likely not the Grayhill switch. Can you post a pic of the bottom side of the board where the fader switch and resistors are?

 

[pkordel]

As history has it, your issues are likely not the Grayhill switch. Can you post a pic of the bottom side of the board where the fader switch and resistors are?

Sure Jeff, here is the bottom.

 

[pkordel]

Sure Jeff, here is the bottom.

And here's the top...

 

[pkordel]

OK guys, here it is:

Even though there's no evidence on this thread of a faulty grayhill switch, I have the dubious honor of finding the first! I desoldered and resoldered everything related to the switch, no change. I finally removed the switch (love the new Hakko FR300!!!)
Fully CCW, I measured continuity between pole and pin 7!! Not pin 1 seen from the bottom as in a functional switch I got. This confirms my hunch in the thread above. I will open up the switch and see what I can see.

Goes to show you that eventually every component can and will fail, even a brand new one.

Cheers and thanks for the pointers

 

[Potato Cakes]

Can you do a test of all the switch positions? It may just be the factory stop is in the wrong the place. The switch itself may be fine. You can actually fix that yourself if you want to as I have had to open up several of the continuous rotation versions and install my own stop pins.

Thanks!

Paul

 

[pkordel]

Can you do a test of all the switch positions? It may just be the factory stop is in the wrong the place. The switch itself may be fine. You can actually fix that yourself if you want to as I have had to open up several of the continuous rotation versions and install my own stop pins.

Thanks!

Paul

Sure Paul,  I suspect the factory stops as well...
Yes indeed, it was the factory stops. Now to open up the switch.

 

[pkordel]

Sure Paul,  I suspect the factory stops as well...
Yes indeed, it was the factory stops. Now to open up the switch.

Well, opening it was fairly easy, not sure if I'll be able to re-assemble it haha! Gotta work now, glad I had a spare switch to get back up and running.

 

[Potato Cakes]

Well, opening it was fairly easy, not sure if I'll be able to re-assemble it haha! Gotta work now, glad I had a spare switch to get back up and running.

The trick to keeping all the wafers together for this and other rotary switches is to remove one of the bolts, re-insert it backwards with the threads facing forward, then do the same for the other bolt. It will keep it the wafers from falling apart, which I learned only doing it the hard way several times. When it's completely disassembled, the tiny bent piece of metal that makes contact between pole and the positions will fall out of place. That is when the real fun begins.

Glad you're up and running.

Thanks!

Paul