Fuzz/Distortion (new design)

[earthtonesaudio]

This is a 3-knob, opamp based, diode clipping fuzz.  As far as I know, it's totally original.  I owe some credit for the tone stack concept to Mr. Mark Hammer, for inspiring me to investigate scoop-shift and panning tone controls further than what I had previously.

Input Z is about 10k, output Z is about 100 ohms, so it plays well with other effects (at least ones I tried) as well as does a decent amount of "volume knob cleanup" when you plug straight in with a passive guitar.  The tone control (R16) is my favorite part.  It goes from heavy treble cut, up through an apparent mid boost, on to a mid cut.  Sort of similar to a BMP tone control, but more about the mids/highs than the bass/highs.

The gain control (R14) is also kinda interesting.  It works in 3 ways simultaneously.  Most obviously, it forms part of an attenuator (in conjunction with the 1k resistors) for the output from the first opamp stage, so as you turn it up, the tone stack and second opamp stage receive a larger voltage signal.  The gain control is also connected to the second opamp stage's feedback loop, so turning up the gain control increases the gain of the second stage too.  Finally, it forms a "resistor multiplier" for the first stage's feedback loop.  Basically it divides the output voltage down on its way to the inverting input pin, causing the feedback resistor to appear larger than it really is.  Because the stage inverts, the fractional division is inverted so the gain of the first stage is also variable.  There are some caps in there to make the gain somewhat frequency dependent, especially on the second stage.  The result is less bass and a "tighter" sound at low gain, with more bass and a "thicker" sound at high gain.


I used a generic TL022 salvaged from my Boss GE-7.  I liked this low-power (and consequently lower bandwidth) opamp better than the faster RC4558 or much faster TLE2072, mainly because the lower bandwidth cuts a tiny bit of fizz in the highest treble frequencies.  The minuscule power consumption is a nice bonus (about 100 microamps for the audio portion... the LED uses 10x that much current!).





[reposted from here]

[TELEFUNKON]

No picture appearing there!

[earthtonesaudio]

Thanks for pointing that out!  Fixed.

[glops]

Thanks for posting the schematic.  Looks great.  Will put it on my list....

[earthtonesaudio]

By the way, R6 is totally unnecessary, I just needed a jumper and a 10 ohm resistor was close enough.

[Mark Hammer]

That gain control is smart.  I love reciprocal gain controls.

Incidentally, people too often think that pots used in this manner have to be unadulterated ans symmetrical.  But sometimes you want/need a greater range of adjustment in one direction than in the other.  So it is not unreasonable to choose a larger value pot and stick a fixed resistor in parallel with one leg so that there is more resistance change on one side of the wiper than the other.