JEN Fuzz PCB layout with Mods
FuzzPCB_FT
 
All resistors are 1/4 watt
Components


C1        0.1uF metallised polyester film
C2        0.1uF metallised polyester film
C3        10uF radial electrolytic NP 50v (non polarised)
Q1        BC548B or 2N3904
Q2        BC548B or 2N3904
R1        18k
R2        270R
R3        10k approx (adjust for half battery voltage on Q2 collector) (see below)
R3b      jumper wire (see below)
R4        68k
R5        2.7k
R6        100R
R7        18k
VR1     100k linear pot controls fuzz level, unity to full fuzz range, or soft to hard fuzz
 
Misc
1x Stereo 1/4" Jack Socket for input
1x Mono 1/4" Jack Socket for output
1x 9v Battery Clip
1x 25k linear pot for biasing transistor (see below)
 
NOTE: You only have to do this once for a pair of transistors.
To get a fuzz that cleans up nicely when you turn down the volume, you have to wire a pot (25k linear, middle and 1 outside lug) to where R3 goes and adjust it until the voltage read on the collector of the Q2 transistor is half the voltage of the battery.  Make sure the fuzz is powered on when doing this and the jumper wire is soldered in place at R3b.  It also helps to wait a while (30 mins+) after you finish soldering with the fuzz plugged in/turned on, so everything is at normal operating temperature before and during taking any measurements.
 
1.        Make sure the effect is on/input plugged in, fuzz control on max gain.
2.        Measure the voltage of the battery.
3.        Measure pin C of Q2 transistor by placing 1 probe on ground connection (-9v) and 1 probe on pin C of Q2 transistor.
4.        Now turn the pot until you read half the voltage of the battery.
5.        Then disconnect the pot from the circuit and measure its resistance.
6.        Now place a resistor of this value into R3.
 
If you want/need to be more precise, you can add the value of 2 resistors in series by placing them in R3 and R3b positions (dont forget to remove the jumper wire first in R3b!).
 
Doing this will virtually guarantee a good sounding pick responsive fuzz with most transistors.
 
Mods: For more bass/lows, raise the value of C1 (input) and/or C2 (output) capacitors.  E.g. 0.22uF or 0.47uF.
 
Fuzz Schematic