My weird take on the Harmonic Percolator

[edvard]

It's been a long while... I started experimenting with this idea probably 15-20 years ago, then put it away for a few years, then made a board and put it in a box, then forgot about it for a few more years and re-discovered it last week after I got some new tubes for my '52 Deluxe. For lack of a more clever name, I call it the "Blergholator".

Anyways, here's the gist; take a Percolator circuit, flip the chain so the input goes to the NPN, make the PNP and diodes silicon, and buffer the output with a FET.  I don't know what possessed me to try this, but I'm glad I did; the sound can go from breathy overdrive to broken and spitty with a twist of the guitar volume.  Schematic:



I don't remember why I put a 33k resistor between the Q1 base and the 50nf cap coming from the input, but I remember it was helpful; maybe for better input impedance?  I don't remember.  I also don't remember why I used an audio-taper pot for the input, maybe it's all I had at the time I built it. It works, and I'm not sure a linear pot would work better. I also don't remember exactly why I initially put the FET buffer on the end, but I remember keeping it because it made a drastic change in the output, making the tone much more present, with more top end and higher gain. The diodes are 1N4148 because (if I recall correctly) Germaniums lowered the output volume and didn't contribute anything interesting to the sound.

Let me try do describe how it sounds, as I don't have a Soundcloud account (maybe some day soon).
All my tone tests were made using my Squier Strat tuned normally with Wilkinson single-coil-sized rail humbuckers, going out to either my computer interface or my Deluxe.  My descriptions may be different from how you'd describe the tones, but at least I didn't say "haunting mids"     
- With both the Harmonics control and guitar volume full up, it sounds thick and smooshy and splatty with that classic fuzz-pedal buzzy grind mixed in, but not gated. Curiously, the background noise doesn't go up as the Harmonics control is turned up.
- Back the guitar volume down to 7 or 5 and I get a nice tone that seems to me more like a smooth overdrive rather than distortion, but I'll let you try it and judge for yourself.
- Turning the Harmonics knob down a bit (maybe 50-60%) gives my guitar volume more control range, but that's with my pickups. I hear only a small difference between 50-100%, so I can afford to back off the redline. Your setup may be much different; classic single coils may need that whole range, and full-size humbuckers may work better with the Harmonics control backed down a little further. YMMV, twiddle until you get good results.

Anyways, that's my take on the classic Percolator circuit.  Give it a shot.  Tell me what you think, even if you think it sucks.

[patricks]

I like it!
I've been looking for something to use some spare Si PNPs, this looks like a fun way to do it