NOOB question about IC debugging

[ElectricDruid]

Just for good design practice, Tom..

LOL! Let the poor soul get it working before you start making mods to it!!

Otherwise, yes - completely agree with your reasoning.

[idy]

What the duck guy said about those red caps.... You could just tell us what is printed on them. If c7 is 1uf instead of 1nf that would do it.

[antonis]

Let the poor soul get it working before you start making mods to it!!

It can be obtained by ensuring good work of feedback/gain circuitry, I presume.. 

[half_smith]

I'd make sure that the bottom end of the gain pot is actually connected to ground. If it weren't, you'd have a unity-gain buffer, basically - somewhat underwhelming! Turn the power off, and do a continuity check from ground to the two pins on the gain knob that are connected together. I note that there's a long path from the supply ground to those on the GGG wiring diagram -

ElectricDruid thank you for the reply. I've tested good continuity throughout the grounds, reflowed and retested every wire.

C3 and C7 are both "WIMA 1000/100-" which I believe is .001uf

please, indulge me. I see your red caps with black markings, which Wima tells are FKP-2, PCM 5, from the datasheet. the 1000pF has the same smaller case measures than the 10nF, I assume your C2 is also Wima. so your C3 and C7 look "too big" to be 1nF caps, at 100V, made by wima.

also, if you had caps at much higher value than 1nF at C3 and C7, they will filter great gobs of your signal straight to ground, no matter how good your IC voltages looked.

a quick way to shut me up is to lift both those caps out of the board and see if you get full, screeching, unfiltered output.

duck_arse, I appreciate the idea. No change when i lifted C3, C7. Which is even curiouser.

And make R2 & R3 100k or better 47k..

antonis, thanks for the guidance, I will write those down and try those values to compare - once I have anything to work with!

What is the problem oh gurus of stompbox arcana?

[idy]

Signal probe... signal trace. It must die somewhere.

[antonis]

In case of Feedback/Gain loop items wiring is OK, check R4 (1M) & R5 (10k) values/ratio..
(in case of R4 too low and/or R5 too high, signal is severely dominated due to voltage dividing effect..)

[duck_arse]

thanks half, that's me out of ideas.

[half_smith]

I found the problem!

Much thanks to all who chimed in, but the credit goes to Antonis

In case of Feedback/Gain loop items wiring is OK, check R4 (1M) & R5 (10k) values/ratio..
(in case of R4 too low and/or R5 too high, signal is severely dominated due to voltage dividing effect..)

This promped me to inspect and consider trying different R values in R4, R5

what I finally discovered...

The Schematic and Wiring Diagram were not in agreement.

R4 and R6 were in opposite locations on the Diagram, putting the 1M resistor en route to the Gain pot and the 4k7 to the ground. Basically, all the juice was squeezing onto the ground and not into the effect!
I don't know if I ever would have found it if not for Antonis' comment.

Good news is, I learned how to Audio Probe, got way better at desoldering and tracing the paths of the schematic, and besides a few destroyed components (I'm still a little rough getting them off the board, worse at getting one once removed back on the board, sheesh, and then breaking wires from so much manipulation...)

Now the Pedal is all assembled with Slots in the diode spots so I can try different things. I put a random germanium diode in D1 and it really chunked up the tone awesomely!

Thanks guys.

[idy]

Congrats. What a relief.

[ElectricDruid]

I found the problem!

Excellent work!

Enjoy the pedal now it's going!

[half_smith]

And make R2 & R3 100k or better 47k..

Just to report, changed R2 and R3 from 1M to 100k.
Mostly brought the overall output level WAY down.
I ended up putting 470k in both and it seems good, that's probably where it will stay.

I also changed R6 to 47K (as suggested in the GGG Build Instructions).

Also, I've tried various Germanium Diodes, in combinations and doubled up or not.
Some of the asymmetric arrangements were cool.
But adding any diodes in D1, D2 cut the output level WAY down as well. I ended up pulling them all out.
What changes are needed to use D1, D2? (more aggressive fuzz is the idea)

[antonis]

Just to report, changed R2 and R3 from 1M to 100k.
Mostly brought the overall output level WAY down.

Are you sure we're talking about Vbias voltage divider resistors..??

[half_smith]

Per your earlier suggestion, I looked at R2 & R3

where you referencing this schem?

[antonis]

Yes, but I can't see any reason for signal output level going down with lowering R2 & R3 values..
(as far as R4 value is kept the same, there shouldn't be any input signal attenuation..)

[ElectricDruid]

+1 agree with Antonis. I'd suspect you changed the wrong 1M if the level changed. All too easily done!

[antonis]

I'd suspect you changed the wrong 1M if the level changed. All too easily done!

And a too easily obtained asymmetrical clipping effect..

[half_smith]

I'd suspect you changed the wrong 1M if the level changed. All too easily done!

And a too easily obtained asymmetrical clipping effect..

I feel dumb. The R6 and R4 are still reversed in the wiring diagram (and written on the PCB) [see OP and solution!]

I had swapped the wrong one making the route to ground 47K instead of 1M... explains the drop in output right?

With the proper substitutions I have a good signal, not necessarily better to my ears but sure why not.

Thanks again for the help.

[antonis]

I had swapped the wrong one making the route to ground 47K instead of 1M... explains the drop in output right?

Yeaapp..

You can find frequency dependent particular attenuation from the formula: R4 / [R4 + R5 + (0.159/f*C)]..
(the lower the frequency the higher the signal entering into the op-amp attenuation..)