Harmonic Percolator is one the coolest vintage dirtboxes out there with its simple yet unique design, its odd even order harmonics texture, odd mojo parts and it is also a very good overdrive with the gain control rolled back.
But using mostly humbucker equipped guitars nowadays it tend to be overly compressed and a bit muddy and dull. Started to tinker with it tso it would suit hot humbuckers but no dice. As it is an unique circuit like no other, the usual mods didn't work out very well like reducing input cap or add a resistor in line with the input signal.
But I stumpled upon Dead End Fx Splinter project whcih offers a sollution for this namely reducing the coupling cap value between the transistors and adding a cap across the base of Q1 and ground.
Later on I added a "Texture" control which techically is a resostat which alters the resistanse to ground for one of the clipping diodes. Most stock HP's has 4,7k resistor here for some assymetric clipping. I used a 10k pot so stock setting is at noon, turn it up and you get a more open and wide distortion, roll it back for some glithy compreesed sounds with sub octaves jumping around.
And I added a two band gyrator tonestack at the end with values not to far away from Boss HM2. The result is a quite lo-fi, fat, industrial and grim fuzz.
