Superfuzz - Octave Generation - Confirming oscilloscope readings

[redbagy]

Hi - I recently built a Superfuzz clone (the Uberfuzz by PedalPCB) and to confirm my understanding of the octave generation I fed a 1kHz sine wave input and probed Pin 2 at Q4/Q5 of this schematic. Using the FFT on my oscilloscope I tuned the trim pot until I saw the most magnitude for the even order harmonics (in fact the output at this point is 2kHz).

Attached please find the screenshots from my oscilloscope - my only concern is that the rectification should be full wave rather than half wave? i.e. shouldn't I be seeing positive cycles only? Rather than a positive and flat cycle? From what I read online about the octave generation, I expected that the negative cycle of the blue trace was going to be inverted to a positive cycle.

Thanks!

[Lino22]

Here are my readings from my own SF clone

Distortion at 1/4
www.hoho.cz/osobni/superfuzz/b.mp3


Full distortion

[duck_arse]

try retrimming while watching time, instead. you can trim for different things with that setup - noise or octave. (I would have expected more like Lino22's top trace.)

[redbagy]

My first image (i.e. with time) matches that of Lino22. I'm just trying to understand the output as the super-fuzz is supposed to be a full-wave rectifier (something like this).

[ElectricDruid]

My first image (i.e. with time) matches that of Lino22. I'm just trying to understand the output as the super-fuzz is supposed to be a full-wave rectifier (something like this).

I think those output waveforms look like what you might get if you feed the fullwave rectifier waveform through a hard clipper, which is what the circuit does. Plus there's probably also some distortion from the differential amp stage. I don't see anything that suggests that it's *not* doing FWR.

[idy]

You " expected that the negative cycle of the blue trace was going to be inverted to a positive cycle."
Instead the positive cycle of the blue trace has been inverted to negative. If you flipped the wave it would be what you expected.

[redbagy]

Ok got it    It might be the slight distortion of the wave (where is slowly ramps up differently than the original signal) that was confusing me unnecessarily. Cheers.