# Captain Bit Low Volume



## UnusedPortion (Apr 28, 2020)

I just built a Captain Bit, and I am having an issue where the volume is very low, even with the Level Pot at 100%.  I have already done the following:

double checked the values of all resistors and capacitors
swapped out the TL072 IC
used an audio probe to track the issue to somewhere between pin 1 of the TL072 and leg 3 of the "Level" pot
replaced the 1uf capacitor at C14 (which is between pin 1 of TL072 and the Level pot)
confirmed continuity between pin 1 of TL072 and positive leg of C14 and continuity between negative leg of C14 and leg 3 of the level pot
The audio probe confirms that I am getting loud signal at pin 1 of TL072 and signal is already low at leg 3 of the Level pot.  I haven't replaced the pot, since the signal drop is already present at the input of the pot.  Am I thinking about that correctly?  Any other suggestions?

Thanks in advance, 
JB


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## Ratimus (Apr 28, 2020)

**Edited to remove question I wouldn't have asked if I had read OP more carefully.


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## Ratimus (Apr 28, 2020)

That's a sneaky bug you've got! Everything seems to be pointing to C14, but I think you've eliminated that as your problem. Have you got continuity from pin 1 of the pot to ground?


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## UnusedPortion (Apr 29, 2020)

I just checked.  Interestingly, I have continuity between pin 1 of the pot and ground, but I also have continuity between pin 3 and ground, which seems like it might be the problem.  Is it possible I have a bad pot?


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## Ratimus (Apr 29, 2020)

That's a possibility, but it's much more likely you've got a bit of solder where it shouldn't be or somewhere that the solder mask is scratched off or burned through and something is shorting to ground. If the lugs of that pot are right on the board, there's a chance one of them is also making contact with ground so that might be something to check out. If that's the case, maybe try individually heating each lug and pulling them up by about 1/16 of an inch (but still connected to the pads).

Do you have continuity from pin 2 to ground at both extremes of rotation? If pin 2 is short to ground directly or through pin 1 and you have the level cranked, that would make pin 3 look guilty when he isn't really the problem. You can measure resistance between pin 1 and pin 3 with nothing plugged into the output. Check from pin 2 to each of its neighbors as well.


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## UnusedPortion (Apr 29, 2020)

All 3 pins of the pot have continuity to ground, and the level of the pot doesn’t change that.  I measured the resistance between pins 1 and 3 at ~1.5 ohms (basically nothing), and when I measure between pin 1 or 3 and pin 2, it’s ~3 ohms at each extreme and maxes out at ~30K ohms somewhere in the middle.


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## Ratimus (Apr 29, 2020)

Ah, so the 30k you're seeing is the upper half of the pot in parallel with the lower half, which tells us pin 2 is fine. I would guess there's a solder bridge between ground and either the negative side of C14 or pin 3. Try desoldering pin 3 and bending it all the way up and out of the board, then measuring from that pad on the pcb to ground. If it's not short, that was your problem, otherwise suspect C14.


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## Ratimus (Apr 29, 2020)

Heck, at this point you might benefit from just removing that pot. While you've got it out, you can check resistance from each of the traces on the pcb to ground, and you can test the pot as well.


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## UnusedPortion (Apr 29, 2020)

I removed the pot and C14, and I still have continuity between negative side of C14 and pins 1 and 3 for the pot.  Here are some photos:


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## Ratimus (Apr 29, 2020)

First pic shows negative side of C14 might have a solder bridge? Try cleaning up all the lands for the components you removed. You're so close to getting this thing working!


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## Ratimus (Apr 29, 2020)

Here's the part I'm talking about:


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## UnusedPortion (Apr 29, 2020)

Thanks.  I went back and cleaned that with IPA, but I'm still having the same grounding problem.  In fact, I'm pretty sure the messiness you see is caused by the rework that I did earlier (replacing C14 in this case), so I don't think it is the cause of the problem.  I am pretty stumped at this point.


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## zgrav (Apr 29, 2020)

you circuit seems to have a connection to ground somewhere between the negative side of C14 and the hole in the PCB for lug 3 of your pot.  take a good luck at the area where IC1 is soldered in to the board, since it looks like the connection from C14 base goes under that chip on the way to the level pot.  maybe there is a damaged trace that has a solder bridge to ground or something similar.


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## UnusedPortion (Apr 29, 2020)

Thanks, zgrav.  I pulled out the CD4024BE chip from the socket and looked at the traces that go under that socket, but I'm not seeing anything problematic there.  For good measure, I went ahead and cleaned in there with IPA, but still having that grounding problem.


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## zgrav (Apr 29, 2020)

still sounds like you have a short in the board to ground somewhere between the base of c14 and lug 3.  that is the only way I can see that you would end up with continuity to lug 1 as well.  

if you can't find a spot with a solder bridge or a shorted trace between those two points and they are connected to lug 3 for the pot (and that means to ground as well, right?), you could try disconnecting the base of c14 from the board and not connecting lug 3 to the board, then wire those two points directly to see if that bypasses the problem.  that should ensure your audio signal reaches the level pot without losing volume.


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## bengarland (Apr 29, 2020)

A bad pot wouldn't be out of the question. I use the standard Alpha pots from Tayda and found a bad one a week ago -- I was building the Hydra, and the output was inexplicably staticky / distorted. I could hear the delays but it sounded like garbage. I finally traced it back to the volume pot and and pulled it. Put a new pot in, works great.


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