Astro Amps Astrotone

I consider this 1966 "fuzz" pedal to really be the proto overdrive/distortion pedal. It is an overdriven linear amplifier that squares up with diode clippers, and an output buffer in the form of an emitter follower drives a simple high pass filter stage.

The schematic I had from one floating around online, but when I took a look at one in hand, in the photos above, I noticed there are 2 3.3M resistors in parallel instead of a single 3.3M. So there may be some variation out there.

Q1's collector will actually bias up to around 1/2 V+, unlike many '60s "fuzz" designs which tend to set the operating points where clipping comes early. Q2's emitter is biased surprisingly low due to the high value 1.2M base resistor, but the diode clipping ensures that the output is small enough that the follower probably doesn't add any noticeable distortion.

The high pass filter does a good job of mimicking the Maestro Fuzz Tone's thin and sharp fuzz sound. This pedal is versatile in that it can do both the "early fuzz" sound (to a limited degree), and have a nice overdrive that cleans up if desired. It lacks much "boost" capability, and doesn't provide a sustaining lead tone. The only voltage gain is from the first transistor stage. The second transistor stage provides output drive for the tone control. Eliminating the clipping diodes would allow more boost but would change the character of the pedal. Adding or changing the diodes to other types (with different forward bias voltages) is another option.