SOLVED Greer Black Mountain Drive troubleshooting assistance

R

rhinoburger

New member
Hi all,

Working from this layout of the Precipice schematic. The only part substitution I used was a 1N4001 in the rectifier spot instead of the 5817.

I've tested between all the vero rows for shorts, double checked component placement and trace cuts, and I'm stumped.

IC voltages are 1:7.39v 2:7.28v, 3:7.85v, 4:0.1v, 5:0.37v, 6: 6.87v, 7:0.69v, 8:8.81v

I checked the Vref points and the clipping diodes are .317v, as is the tone control 47n cap. I think they should be closer to the 4.24v-4.27v I'm getting on the other Vref points but don't know enough to know what is going on. The R6 22k vref is 3.62v

I tried an audio-probe and I lose the signal at the 6 pin. I tried swapping the IC for different op-amps (one TL082 and a few others) I had on the bench to see if it was a bad chip but either all 4 I tested are bad - which seems unlikely - or it's the circuit somewhere.
 

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Solution
J
So I'm fairly sure your 4K7 resistor is 4R7, which would give you 1000x the gain it should, which could give you all sorts of issues.

Check these spots for solder bridges or incomplete cuts.


1722205600963.png
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looks like a solder bridge at the top right of the photo, but that could just be the angle

you didn't say what's wrong. no sound? some sound but low? whining noise?
 
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spi said:
looks like a solder bridge at the top right of the photo, but that could just be the angle

you didn't say what's wrong. no sound? some sound but low? whining noise?
Click to expand...

Bypass sounds fine, no sound with pedal engaged. Even with the amp turned up you can't hear anything (including pot sweeps).
 
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Maybe the fault is with the IC socket and not the ICs themselves.

It's the cheapo flyleaf socket, which some love, but I loath:

704238a6-ebde-4e30-96a4-18ed8e94cd04-jpeg.25753



Replace it with a proper machined socket.
 
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We have sound!

Now a different problem: there is high pitched feedback. The tone of the feedback decreases when the gain nob is increased. The level of the feedback is pretty intense.

Increasing the value of C3 does cut the squeal somewhat (I tried 1n), but what I don't understand is why the Gain pot seems to be sweeping the frequency - the higher the gain, the higher pitch of the oscillation. This effect is amplified with a higher value in C3.

Volume pot seems to be doing what it should.

Hard to tell with the tone pot what is happening.
 
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jesuscrisp said:
So I'm fairly sure your 4K7 resistor is 4R7, which would give you 1000x the gain it should, which could give you all sorts of issues.

Check these spots for solder bridges or incomplete cuts.


View attachment 79283
Click to expand...
Traces, cuts, bridges all ok. That resistor WAS only a 47 - so swapping it out fixed it. Very excited, this thing sounds sweet! Now to clean up the wiring and box it in, thanks all :)
 
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