I want to take a single opamp circuit and get as close to a square wave as possible. Originally I was thinking about putting a 308 (cause I like Rats) in it and using germanium diodes. I've started to wonder if using a cleaner opamp, like a tl071, and let the diodes do the work would lead to a better result. What do you guys think? I'm sure they would be pretty different, but I think the 308 doing more clipping work might actually make thing less like a square wave.
If you want a square wave, you might consider setting the opamp up as a comparator. This will just slam the output voltage to the positive rail when the input signal exceeds the bias voltage and slam it to the negative rail when it fall below the bias voltage. Darkglass' Duality encorporates this idea. Something like the attached, which is take from Aion FX's Binary Dual Fuzz. If you take this approach the "squareness" will be improved by a nicer opamp because the higher slew rate will allow it to move between extremes faster. I'm not sure there would be an appreciable diffence in the sound between a TL072 and a 308, or which one I'd expect to sound better. It's probably worth trying both if you have them at hand.
with the 308 I'm thinking expandora's forbidden mode