Great Cheddar feedback loop + curds = fuzz factory-ish sounds

[Processaurus]

This definitely isn't rocket science, but worth noting, I just tried this with my great cheddar/big cheese clone, to try and coax some of the Fuzz Factory category glitchy, note skipping arpeggio type sounds out of it, and it works great,  definitely gets you in the ballpark, though its a totally different circuit and method of introducing instability.  I just stuck a 1M pot set as a variable resistor from the output (pre vol knob) to the input.  That worked with just the guitar feeding the pedal, if there is another buffered pedal or active electronics in the guitar, I bet it would work better to have the 1M pot go from the output of the last opamp (before the output cap) directly to the input of the first opamp.  That way the series 1K resistor from the input would make it so the low impedance of the preceding effect wouldn't load it down totally.

Without the curds switch on (the misbiased setting, I think that's what its called on the BC) it just squeals. 

Another thing I tried was using DPDT center off toggle switch to connect the .0068 (C8) in one position, and on the opposite position switching in a .020uF cap in parallel with the .01 to ground in the tone control (C10), a la the Swollen Pickle, its a caricature of the mid scooped sound, 700Hz begone.   So its the flat mids setting, and in the center its the stock (1kHz) mid scoop, and then the stupid deep midscoop @ 700Hz.  Its nice to be able to go too far.

[Processaurus]

To try and get less gain when the fuzz pot was turned all the way down, I tried a 5K linear pot for the fuzz as well, and changed the collector resistor (C8) to 33K, to bias that section to the 2.8v RG notes in the Great Cheddar PDF, anywhere from 2v to 4.5v sounds about the same, there isn't really a sweet spot, it just gets misbiased if the collector resistor is too large, and quieter if its too small.  Though I didn't have a easy way to compare, it seemed like it worked.  Still sounds good turned all the way up.  I'm digging the sound of this pedal for sure, it gets such a nice transition from kinda overdive where you can still hear the character of your instrument, to super squished transistor fuzz that makes you feel like you aren't even playing guitar anymore.  The opamp buffers are nice too, because it makes it compatible with situations other than a guitar plugged straight in.

I also made a switchable boost (which you'll be needing to get the squished out sound, if you use single coils) on the input that somewhat resembles the Proco Rat's noninverting gain stage, except I used a 20 to 1 gain rather than a jillion to 1 and there's more high frequency rolloff to try and control noise.  Now I'm thinking it would be really great to make a sweepable band pass filter on the input, to get lots of colors of funky narrow 70s midrange.

Thanks alot to Dan Coggins for the original BC design and RG Keen for the Great Cheddar page.

[Processaurus]

I was having trouble with oscillation in my finished pedal with my extra gain, I thought it was because of recklessly running wires all over tied to my opamps inputs, but no, it only would happen when a guitar was plugged directly into it, and the output was turned up.  I tried everything, and got it a tiny bit better every time (but I wasn't surrendering the gain... it neeeeds it), shielded input wire to footswitch, shielded input wire to board, changing the footswitch around so the in and out where on the outside lugs of my 3pdt, less highs from the first stage, bleeding highs in the output, bleeding highs on the input, lowered input impedance to 75K, everything. 

What actually undeniably cured the problem, opposed to all these things, was making the output stage an inverting amplifier.  Now cranked it just has random crazy noise instead of an uncool steady squeal.  This opened up a new batch of worms, because now the feedback knob didn't sound fun anymore.  So the new (and even more animated sounding) version of this mod is to hook a pot up as a voltage divider (I used 1M, but it could be lower), top lug to the C7 R11 junction, bottom lug to ground, and the wiper goes to a .01 cap, which then goes back to the noninverting input of the input opamp, like the original mod.  I thought it would short out the input when it was all the way to ground, but it doesn't, it sounds to me the same as not having it in the circuit. Mine goes through a DPDT switch to disconnect it simultaneously when the curds setting is disconnected.

It even has a spot where it squeals just when you're playing, and this gets gated when you stop.  Yummy.

I learned a lot from diddling with this pedal, that a lot of noise from distortion is high end, if you limit that (especially if you can cut it as the gain is increased/only apply gain to the midrange, with noninverting opamp gain stages, Rat and TS style) you can get gobs of gain and sustain with manageable noise.