ASTRO AMP: Astrotone Fuzz, with Analog Man Mods

Perhaps best known as the Analog Man Astrotone Fuzz now, this started life as the Sam Ash Fuzzz Boxx and the same circuit also appears in the Astro Amps Astrotone Fuzz - which is a supremely cooler name, which is maybe why it has stuck.

The original has 47n caps on this input and output, and a larger resistor on on the tone control causing it to be kind of thin and awful (which explains why I threw out my first attempt when I first started building).

The Analog Man version basically fixes a couple of minor deficiencies in what is otherwise a pretty cool circuit.

The fuzz pot acts as a volume control in front of the circuit, and the tone is a high-pass filter at the output of the circuit.   The fuzz section is roughly an Electra distortion - single transistor hitting some hard clippers with a lot of already distorted level.  This is followed by a buffer and the tone and volume pots.

ASTRO AMP ASTRONTONE FUZZ - WITH ANALOG MAN MODS - 0.15" VERO LAYOUT

The layout above was created for looks as well as functionality, hence the links under the board.  It's not the most practical in some respects.

Transistors are Fairchild mushroom tops, roughly ~200hfe.   I also used some interesting looking UK Military spec diodes.  

Before building this I did have it on the breadboard and tested vintage parts against modern ones.  I could hear a difference in sound between vintage and modern, but it was minimal.  It's certainly not worth spending money on vintage parts unless you want it to look more vintage.  Same with the capacitors I used, strictly just for looks.

A lot of the rock here is done by the diodes, so all the usual mods are fun to play with - asymmetric clipping, silicon and germanium paired together etc.  

LTSPICE

As you can see, the differences in frequency response between the modded circuit and original are fairly dramatic.  You can still get a thin sound from the Analog Man version if you want the original - but it's not nice.   It is however nice to be able to take a bit of bottom end off the fuzz, to help tighten things up before you hit your amp with it.

And here's some fun squiggly lines to look at - this at the base of the second transistor, after diode clipping.  Fuzz pot swept.

Some schematics also show the biasing resistors as 3m3 - as this is such a simple circuit, the value of the biasing resistor does affect the sound.  Especially the first one (R2).

ASTROTONE VIDEO DEMO

I feel like this is a pretty reasonable demo - listen for how clean (or not) the amps are running.   I feel that this effect sounds best running at a decent level pushing an amp.