Tone Bender

COMPONENT LIST

PCB
PCB              TONE BENDER PCB

Capacitors
C1    10n       10NF 100V 5% POLYESTER FILM BOX TYPE CAPACITOR
C2    4.7u       4.7UF 50V ELECTROLYTIC CAPACITOR 5X11MM
C3    100n     100NF 100V 5% POLYESTER FILM BOX TYPE CAPACITOR
C4    10n       10NF 100V 5% POLYESTER FILM BOX TYPE CAPACITOR
C5    4.7u       4.7UF 50V ELECTROLYTIC CAPACITOR 5X11MM
C6    47u        47UF 50V ELECTROLYTIC CAPACITOR 6X11MM

Transistors (NPN version)
Q1    2N3904     2N3904 NPN GENERAL PURPOSE TRANSISTOR
Q2    2N3904     2N3904 NPN GENERAL PURPOSE TRANSISTOR
Q3    2N3904     2N3904 NPN GENERAL PURPOSE TRANSISTOR

Resistors
R1     100k     100K OHM 1/4W 1% METAL FILM RESISTOR
R2     10k       10K OHM 1/4W 1% METAL FILM RESISTOR
R3     100k     100K OHM 1/4W 1% METAL FILM RESISTOR
R4     470       470 OHM 1/4W 1% METAL FILM RESISTOR
R5     1M        1M OHM 1/4W 1% METAL FILM RESISTOR
BIASQ2    100k        100K OHM TRIMMER POTENTIOMETER
BIASQ3    10k          10K OHM TRIMMER POTENTIOMETER

Potentiometers
VOL          100k-A    100K OHM LOGARITHMIC TAPER POTENTIOMETER
FUZZ        1k-B        1K OHM LINEAR TAPER POTENTIOMETER
 

PCB

PCB SCHEMATIC

TRANSISTORS

The original Tonebender uses germanium transistors (AC128). Select the gain for each transistor within the following ranges:

Q1: β = 70-90
Q2: β = 50-70
Q3: β = 110-130

For the PNP silicon version, use 2N3906.

For NPN silicon version, use 2N3904, BC108 or BC109. To use the negative ground version (NPN transistors), flip the polarity of the electrolytic capacitors (C2, C5, and C6) and connect the +9V power supply to the pad marked as -9V.

Capacitors for PNP version                 Capacitors for NPN version

Refer to the images below for the correct transistor orientation.

TRANSISTOR SOCKETS

For easy swapping and experimentation, use either 3-PIN HEADERS or dedicated transistor sockets.

BIASING THE CIRCUIT

Use the trimmers to bias the circuit by measuring the voltage at the Bias pads with a voltmeter. First, adjust the Bias2 trimmer until the voltage is between –0.5 V and –1.75 V. Then, adjust Bias3 until the voltage is between –7.5 V and –8.5 V. Keep in mind that if you are using germanium transistors, the voltage will be affected by temperature.

POWER SUPPLY CHAIN WITH POSITIVE GROUND PEDAL

A positive ground pedal cannot be directly connected to the power supply in chain with your other negative ground pedals. Use the Charge Pump PCB to build a voltage inverter and power your positive ground pedal in chain with the rest of your pedals.