HungryFuzz HEY GUYS, new module!

NEW MODULE TIME! Well, prototype time. The design is done, and there's some germanium transistors that will be going in there, and they need testing. So here's the rundown of the module and circuit, and if you're looking for build tips, those are after the break!

I like distorted kicks. It's part of my identity. Both modules in my Hungry- series work so well with kicks, the HungryRat (Proco Rat clone) is HARSH SHARP, and my HungryThumb is a compressor and does amazing things to kick drums, including soft clipping, compressing, saturation, lots of fun. Well, I don't know how many germanium transistor distortion pedals have been ported to Eurorack, but the number is probably low (germanium transistors aren't common) so here we go!

The original Fuzz Face pedal "remains an enigma". It was released in 1966, consists of a battery, four resistors, three capacitors, two germanium transistors, and two potentiometers. Ludicrously simple!  The page I just linked to talks about how some of the unique sound may have been a happy accident. There's asymmetrical clipping which starts out soft and goes harder with increased signal voltage. I think that's probably the main accident?

The design has been developed exhaustively over the years, with different designers experimenting with different transistors and transistor types (NPN silicon transistors, for instance), and tweaking resistor values, and (my favorite) hurling potentiometers in there wherever they might make a difference in the sound.

For pedals, where the knobs are in the stompbox which is usually on the floor, two knobs may be fine. But we synthesizer guys love to have all the knobs at our fingertips, and the Zvex Fuzz Factory seems to be the most complex design out there, with five whole knobs to play with. So I cribbed from that circuit, added my starve circuit which also allows the distortion core to work with bipolar voltages (so there's no DC swing when adjusting the starve, right?) (although I left the DC blocking capacitors in the signal patch) (which are MLCC in the prototype because I don't believe that most capacitors "sound" like anything). There's a stupidly wonderful tone control in there, and of course a proper output buffer with adjustable gain to get the output to be a nice safe 1K impedance at 10V peak to peak.

And that's the circut! I have zero zero zero hands-on experience with a Fuzz Face of any variety, so I'm.... excited to see how the prototype sounds?

But I'm neglecting to talk about germanium transistors! They're nifty! And very obsolete. So check after the break for what to do with these weird parts!

A very good synth friend sent me a box of old transistors and didoes. Turns out they're all germanium parts. Germanium is an element named after germs, I think that's probably correct, and before clever nerds figured out how to dope silicone semiconductors, germanium was in common use.

My box of new old stock parts has dozens of 2n2614s, 2n508a, and 1n270 parts. The first to are PNP transistors, the last are diodes. Germanium parts have softer clipping profiles than silicone parts, making a "warmer" sounding distortion. But back when germanium was infecting every circuit, they hadn't figured out how to get consistent specifications out of their parts. There's an easy way to test a batch of germanium transistor to make sure you choose ones that will sound good in your distortion module.

This circuit was designed with this specific transistor in mind, but any germanium transistor should be compatible, but the pinouts may be different. Be sure to check your part so your project works.

1. Connect your mostly-completed HungryFace to a Eurorack power supply
2. Insert the top and bottom legs of your transistor into the footprint.  Don't solder it in place, and don't put the base (middle leg) in yet.
3. Attach the negative probe of your digital multimeter to the "neg probe" hole or pin if you installed a pin for some reason. Set the multimeter to DC volts
4. Attach the positive probe to the "volt probe" and carefully adjust the "Starve" knob of your module until the voltage read between those two pins is 9.00 volts. Don't be too annoyed if it's not exact, the as long as it's fairly close
5. Attach the positive probe of your multimeter to the "gain probe" pin or hole. Write down the voltage you're seeing between gain probe and neg probe. Write it down and label it "leakage". If this value is more than 2.472 volts, set that transistor aside, it probably won't be useful for this circuit
6. Next, put the base of the transistor in the middle pin of the footprint. Wait a few seconds for the transistor to cool (the gain and leakage of these little guys is very dependent on temperature) and take a reading. Write this value above the "leakage" value, and label it "gain + leakage". Do the subtraction problem you've got there, and you've arrived at your gain number (except multiply it by 100)

Transistors with a gain value of 70 to 110 seem to be in the sweet spot for a Fuzz Face distortion. The second transistor (Q3 in this module) can be higher gain than the first, and some builders have experimented with much higher gains in the second transistor.

 huge warning flashing notice

Germanium parts can be damaged by heat. Leave a healthy amount of lead when soldering your transistor in place, work quickly, and use lead-bearing solder if possible. When finishing up your project, lay the transistors down and arrange the legs so they won't short out on each other or on parts on the PCB.

 Enjoy your full-featured Eurorack fuzz distortion! 

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