One of the more famous Tone Bender MKI influenced fuzz boxes and now almost as legendary as its golden cousin was the John Hornby Skewes Zonk Machine. A little more wacky in the graphics department, but not as heavy duty or robust as the MKI, the Zonk Machine was almost identical in its circuitry. Made between 1965 and 1966 in Leeds, England, the Zonk Machine like the MKI was only made in small numbers before the pedal was updated with a more modern and easier to produce unit.
Layout 1: Original PNP
One suggestion with the leakage:
Values taken from an Original Unit
Q1=TI AO2 650 Hfe= 180, leakage= 0.12mA.
Q2=Mullard OC75 Hfe= 78, leakage= 0.29mA
Q3=OC44 Hfe= 58, leakage= 0
Tips for other builders interested in the Zonk Machine:
1. Socket all transistors because you’re likely to go through a bunch of them before you find some that work well.
2. The Zonk is very bright. Play around with the input cap and try values between .001uF and .01uF. Maybe even set up a three way switch to toggle between different values.
3. Definitely use a log/audio taper “Fuzz” pot. I used linear at first but it greatly limits the useful range of the pot. The name “Fuzz” is a bit of a misnomer as it doesn’t really fulfill most people’s definition of a fuzz control. It essentially adjusts the bias of Q2. The Sola Sound Tonebender Mk1, which is a topographically identical circuit (sans the 33K resistor), called this pot “Attack” which is a bit more appropriate IMO.
4. Set up an SPST switch to bypass the 2.2M resistor for nasty, all-out craziness!
5. Some came with 25k Log Fuzz pot, and 220k resistor instead of 470k.