Troubleshooting simple tape-saturation pedal

[robthequiet]

Channel 1 AND Channel 2 NJM2068 (both measure the same):
Pin 1, 2,  3:  .02v
Pin 4: -15.08v
Pin 5, 6, 7:   .02v
Pin 8: +14.98

This looks healthy. Maybe re-check but the op amps are probably not bad if these readings hold.

[Flynn]

Left lug ground (zero volts connected to it from the PS).
Center - output jack.
Right lug - Pin7 output.

No sound.

Touching the circuit board i do get a report on the return signal to the DAW.

Will try bypassing the last pair of diodes and going over the circuit with a fine-tooth comb again next.

[robthequiet]

Sounds like something may have worked its way loose. Do you have signal from IC1A to IC1B?

Another diagnostic I would try would be to gently disconnect the diode array and make sure signal is getting through the 820R resistor R3. Have to isolate the fault to a section of the circuit.

[pinkjimiphoton]

be aware also of phase.

i didn't really look at the schematic cuz its kinda small and i don't have my glasses on.

but if you get signal dry, and signal wet, and it dissappears in the middle, that is classic phase issues. the signal is cancelling itself in the middle.

i may be wrong, but i have encountered that on a few things in the past, including the fender ic fuzz from the old fuzz wah gus helped me with years ago. the clean blend, if inverted should bring it back in phase again.

generally every stage will invert the signal output from the signal put into it. in most cases, it won't matter, but when trying to blend a clean signal with distortion, shit can get dodgy.

electronics engineering generally focuses on avoiding distortion and often don't come to the same conclusions us fuzz mongers seem to arrive at. ymmv, just a thought. good luck man!

[ElectricDruid]

It is basically a 3V clipper. You need to hit it with signal MUCH higher than guitar level.

"Guitar level" is a bit of a movable feast, more's the pity. My recent Digidelay pedal has 3.3V headroom, but I got several reports from people who'd managed to make the processor chip reset by overloading the input. So some guitars can blast a signal hotter than 3V. Humbuckers and "Metal" pickups (which are designed for particularly hot output apparently) it seems. At the same time, I got a lot of complaints from people with low output pickups who weren't getting a decent signal-to-noise ratio, and had to come up with a modification to boost the input for them. Guitars vary a *lot*.

And that makes designing something that produces *just a hint* of soft saturation a pretty tricky business! For some people, it won't do anything, and for others, it'll be full-on distortion. Levels are everything...

Tom

[pinkjimiphoton]

i think even more so, its the player. if you took 10 guys and made them all play the same guitar thru an identical rig, they'd all sound different. too many variables sometimes. thank god for knobs

[Flynn]

Thanks a lot for the input everyone!!

Sounds like something may have worked its way loose. Do you have signal from IC1A to IC1B?

Another diagnostic I would try would be to gently disconnect the diode array and make sure signal is getting through the 820R resistor R3. Have to isolate the fault to a section of the circuit.

I have only checked voltages on the ICs.  I need to whip out the signal tracer and try this.

Regarding the diodes, can i simply alligator-clip it to ground or should it be disconnected?

thank god for knobs

FOR SURE!!!!   


As I mentioned, i did have one half of this working a couple months back, and the mix pot was working at least, but i definitely do recall some phasing going on.  Will definitely keep that in mind for after i get this thing online.

"Guitar level" is a bit of a movable feast

Well said and love the Paris/Hemingway reference!

[robthequiet]

Regarding the diodes, can i simply alligator-clip it to ground or should it be disconnected?

I think the best way would be to gently desolder the top of the array. Bypassing to ground may have drastic consequences.

[Flynn]

Ok, well I had to move to another country and just got my electronics stuff unpacked and setup.  Back to futzin with this thing!

Used a basic signal tracer (capacitor going to an amp) and got signal on all the opamp ins and outs, at R3, etc.   

Can't hear any effect.

I detached the diodes from the circuit.  No change.

I removed the 'mix' pot from the circuit.  No change.

Only place i can hear any effect with the signal tracer is if i go down to near the last diodes before ground.

I also cranked up my output volume going into the circuit (from out of my soundcard).

It's as if the the two opamp stages (which i believe are both acting as buffers?) are working fine, but the signal just isn't getting any action from those diodes.