Enclosure not stated · 2 knobs
Hornby Skewes Zonk Machine IVerified
Based on the Hornby Skewes Zonk Machine Mk I· 3 other boards clone it
From the post
Well got time for another study break, so it's that time for another layout. Just like the last layout I posted, here's another uber rare fuzz, a gift from the fuzz gods that no worshiper of fuzz should be without IMHO.
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
Layout 2: Original NPN
Some suggested gains and tips I found over at DIYSB:
Q1=53hfe
Q2=126hfe
Q3=98hfe
Q1=70hfe,
Q2=116hfe
Q3=97hfe
One suggestion with the leakage:
Q1=180hfe/.142ma
Q2=176hfe/.177ma
Q3=195hfe/.124ma
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.
Schematic
This is a board layout, a drawing of where each part goes, and the post may link the schematic it was drawn from. Open the layout at Tagboard Effects. No KiCad fragment has been drawn for this circuit yet.
Parts list 19 rows
Report a wrong parseGot parts in a drawer? See what you can build with them.
Check before you build · 2 values the reader of this layout was not sure of
- 47nF at columns 15, rows E-H: the text is partly covered by the Q3 transistor outline, read as 47nF
- Q1 part number printed 'A02650' in the legend: the second character could be a letter O (AO2650); printed clearly, unusual part number
| Ref | Value | Normalized | Type | Notes |
|---|---|---|---|---|
| Resistors 10 | ||||
| ×1 | 4.7k | 4.7k | read from the layout by eye | |
| ×1 | 1M | 1M | read from the layout by eye | |
| ×1 | 33k | 33k | read from the layout by eye | |
| ×1 | 470k | 470k | read from the layout by eye | |
| ×1 | 10k | 10k | read from the layout by eye | |
| ×1 | 2.2k | 2.2k | read from the layout by eye | |
| ×1 | 3.3k | 3.3k | read from the layout by eye | |
| ×1 | 15k | 15k | read from the layout by eye | |
| ×1 | 56k | 56k | read from the layout by eye | |
| ×1 | 2.2M | 2.2M | read from the layout by eye | |
| Capacitors 4 | ||||
| ×1 | 1nF | 1n | read from the layout by eye | |
| ×1 | 100nF | 100n | read from the layout by eye | |
| ×1 | 47nF | 47n | read from the layout by eye | |
| ×1 | 25uF | 25u | electrolytic; read from the layout by eye | |
| Transistors 3 | ||||
| Q1 | A02650 | A02650 | PNP Ge; read from the layout by eye | |
| Q2 | OC75 | OC75 | PNP Ge; read from the layout by eye | |
| Q3 | OC44 | OC44 | PNP Ge; read from the layout by eye | |
| Potentiometers 2 | ||||
| Fuzz | A50K | A50k | Potentiometer | read from the layout by eye |
| Swell | A500K | A500k | Potentiometer | read from the layout by eye |
Other boards based on the Hornby Skewes Zonk Machine Mk I
- Hornby Skewes Zonk Machine Mk I Dirtbox Layouts
- Hornby Skewes Zonk Machine Mk. I Si/Ge Hybrid Dirtbox Layouts
- Zonky Five Cats Pedals · 1590B · £4.50