Harmonic Percolator

The Harmonic Percolator challenge. What should it sound like? How much should it clean up? Does that high pitch Velcro noise at the top of the note when backed off make the Jerkulator unusable? Should the input volume be left off? Is a clone made from more commonly available parts a clone at all? What means good when a pedal at its best sounds "bad"?

The lore of the Percolator is all over the place out on the web. Clones are commonly available. Devi Ever came up with some values that would work well with commonly available parts. Her version (the Jerkulator) uses two Silicon transistors and eliminates the hard clipping diodes. This is the version with the high fizz when input volume is backed off. Full up it sounds explosive and delightfully broken and over the top. With certain bridge humbuckers it delivers a delightful kerrang with the strumming of an E major cowboy chord.

My recent attempt to breadboard the circuit (as it may be as there are a variety of schematics on the web) with a NPN Silicon (2N4401) and a PNP Germanium (AC128) transistor resulted in a backed off sound without the fizz, bright and raspy. Full on it has that exploding thing but raspy, not as bright and biting. It has more of a lo-fi edge. I'm not really getting that E chord tastiness and single notes sound weak and uninspiring. The resistance between the collectors and voltage and between the bases and collectors of the transistors can be tweaked for gain and texture.

I am going to end up using pots to dial in those resistor values and going with what sounds best bad or worst good and be happy with it. Hopefully I can hang on to that kerrang with enough gain for tasty single notes. Hopefully I can back off the input and get a sparkly clean.

Here is a phone video of a Firebird through a "stock" ish Percolator with a variety of guitar settings through a modded Valve Junior.

Here is the Jerkulator with and without Germanium clipping diodes engaged.

Here is me dialing in what I would hope to be the ideal tone with these particular transistors. 1M pots instead of the resistors between the collectors and bases. 100k pots from collectors to v+ and ground.

I basically ended up with the same tone but with more squish. Somewhere in there there is a bright tone with less squish but still very transistorish. What to choose!

Here is the schematic for the squishier sound:

If you flip the values of the resistors form base to collector it is much tighter and brighter. Also, I discovered that with the tone rolled back, things get very interesting. Super saturated and bright.

Update: I think I nailed it! A 220k resistor replacing the 750k and a 500k pot in series between the base and collector of the silicon transistor. This allows me to adjust from raucous and open sounding to squishy and exploding!