I recently came across a video featuring one of my favorite producers of all time, Steve Albini where he talks about his use of the harmonic percolator guitar pedal. I always wondered how he got his guitar sound. I dont think for a second that this magical box is his secret, but hey if he uses it, why not build one and see what its like? I did a prototype on a perfboard last week and I must say, it has
become one of the most useful boxes in my pedal chest (yes, I have a pedal chest). This thing is phenomenal! Seriously, not only does it work as a great fuzz at full whack, but at lower gain levels it works really, really well as a driver / booster that makes just about any overdrive pedal sing with dynamic glee! I'm now running this thing before just about everything, can I make a line level one for mixing?. It seems to improve the sound of most things I put it in front of and it has become my favorite pedal of the moment.
The Harmonic Percolators secret (Apparently) is its ability to pass only even order harmonics (the good ones) and reduce odd order harmonics (The bad ones) resulting in a utility fuzz pedal that seems to treat your signal for goodness. I decided to start posting projects on here in the spirit of DIY. I have made my own alterations to the pedal, in a attempt to make it easier to build, with some of the more hard to find parts being replaced with modern, easy to find alternatives. I have also included my own PCB layout and schematic. I'm not a pro electronics designer, so if you find anything that is plain wrong, I would appreciate some redirection. Enjoy.
Steve Albini Talks Harmonic Percolators
The only part in the Harmonic Percolator that can be difficult to find is the 2N404 germanium transistor. Although you can find these on eBay, and various parts stores, I have found that a number of germanium options will do the trick. I used a Russian MP16B which is similar in gain to the 2N404. The one I used has a gain of around 110hfe. It seems to work well, but I have heard of lower gain transistors doing the job just as well. I also tried the germanium diode option and diddnt like it (1N34A) they sounded too compressed to my ear. So I switched to standard 1N4148 silicon diodes instead, and found it gave a little more gain and "better" clipping characteristics. Also the 2N3565 found on the og schematic is hard to find to say the least. Steve at Small Bear has some in stock I think. but I found a standard 2N5088 NPN fills the space very well. I tried a 2N3904 to begin with, but found it hissed like hell on my amp, the higher gain 5088 for that matter sounds perfect with no alteration to the gain level..... go figure.
The schematic
My version of the circuit
The Layout
The layout is single sided and well spaced for easy etching. It is my own design, produced on the freeware version of Eagle. This image is not to scale.
The PCB
below is the self etch file for the PCB. Im not sure if it scales properly, but it was exported at the correct print resolution. It is pre-inverted, so its ready to print and transfer.
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