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 (https://docs.pedalpcb.com/project/Uberfuzz-PedalPCB.pdf). 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!
(https://i.postimg.cc/p5vKPzbp/fft.png) (https://postimg.cc/p5vKPzbp)
(https://i.postimg.cc/tnzWJJpD/time.png) (https://postimg.cc/tnzWJJpD)
Here are my readings from my own SF clone
Distortion at 1/4
www.hoho.cz/osobni/superfuzz/b.mp3 (//www.hoho.cz/osobni/superfuzz/b.mp3)
(https://i.postimg.cc/ykX7Jc85/A-trimr-skoro-na-pulce-red-Q4b-blue-Q4-5c-druha-harmonicka-je-silna.jpg) (https://postimg.cc/ykX7Jc85)
Full distortion
(https://i.postimg.cc/cKPpkLJw/c.jpg) (https://postimg.cc/cKPpkLJw)
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.)
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 (https://www.circuits-diy.com/wp-content/uploads/2021/08/Fullwave-Bridge-Rectifier.jpg)).
Quote from: redbagy on December 29, 2023, 08:53:39 AMMy 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 (https://www.circuits-diy.com/wp-content/uploads/2021/08/Fullwave-Bridge-Rectifier.jpg)).
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.
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.
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.