Interfax Harmonic Percolator working circuit DANTONE Pastry Chef

There's a lot of "information" out there about the Harmonic Percolator.

Here is one I spent a few days on working out the kinks that works as it should.

I started out with Iviark's nice small layout (posted below) but I found some problems.

The two blue additions to the schematic drawn below are my fixes, and had to be manually added to the existing layout.  I haven't had time to draw a new layout yet.

The diode lift switch works fine, and is a recommended mod.

The first problem was a fizzy/crackly/velcro kind of decay on the fuzz mode.  Adding the 1 nF capacitor parallel to the clipping diodes near the output solved this problem.  You could experiment with other values maybe in the pF range.  This cap shows up on some of the traced schematics out there.  In my case, it was needed.

I also added a 1 nF cap from the collector of Q1 to ground.  Parallel to the 20K resistor.  This cap is present in the MadBean schematic, as well as a few others.  It increased the transistor fuzz/gain of the circuit and generally made the fuzz sound better.  Without it, the fuzz setting was sort of "insane, bogus" and "fucked up" sounding.  I wasn't too thrilled about it.  With the cap in place, it's a huge, usable fuzz tone.  "Why doesn't my pedal sound like the videos."  In my case, this cap was the answer.

I also experimented with adding 220 uF filter capacitor to the 9V rail, then I tried 47 uF with 100 nF in parallel.  BOTH OF THESE ADDED EXTRA NOISE.  Not what I'd expect, but the filtering actually made the pedal noisier!  I could swear it sounded a little worse that way too.  Not recommended.  I would recommend building with shielded I/O cable from the jacks and circuit board if you have the time and patience.  That might help the hiss a little bit.  You could almost think of it as a pleasant hiss but if I'm being perfectionist I'd rather it not be there.

I used 1N695 diodes with a forward voltage of about 290-350 mV.

You could use 1N4148 if you want the fuzz to be louder.

My Q1 was a 2N404A of 186 hFE.  Q2 was a silicon 2N222 of about 150-180 hFE.  I could have gotten away with a little less gain I guess but these values work fine, they just are a little fuzzier at lower settings on the Harmonics knob.  Doesn't quite work as a "clean boost" it's more of a "dirty boost" with the diode switch lifted.

This pedal does clean up exceptionally well with the guitar's volume knob, like a Fuzz Face.

Diode lift sounds great on this pedal, giving a warm fuzz/boost/overdrive.  Be careful though because it can get dangerously loud.  Watch those cilia.

This is the "stock" or "collective" version.

If you want to build the "Albini" version, check out the MadBean pedals PepperSpray2018 PDF file for the correct values.  I think the "Albini" version is a little lower gain and a little less wild and crazy.  I'd like to build that one too just to see.