Guitar Tone Control

Stand-alone, 9V battery powered unit

Three-level input selector, three-band tone control

Device purpose:

This preamplifier was designed as a stand-alone portable unit, useful to control the signals generated by guitar pick-ups, particularly the contact "bug" types applied to acoustic instruments. Obviously it can be used with any type of instrument and pick-up.
It features a -10dB, 0dB and +10dB pre-set input selector to adjust input sensitivity, in order to cope with almost any pick-up type and model.
A very long battery life is ensured by the incredibly low current consumption of this circuit, i.e. less than 800µA.

Parts:

P1,P2_________100K   Linear Potentiometers
P3____________470K   Linear Potentiometer
P4_____________10K   Log. Potentiometer

R1____________150K   1/4W Resistor
R2____________220K   1/4W Resistor
R3_____________56K   1/4W Resistor
R4____________470K   1/4W Resistor
R5,R6,R7_______12K   1/4W Resistors
R8,R9___________3K9  1/4W Resistors
R10,R11_________1K8  1/4W Resistors
R12,R13________22K   1/4W Resistors

C1____________220nF   63V Polyester Capacitor
C2,C8___________4µ7   63V Electrolytic Capacitors
C3_____________47nF   63V Polyester Capacitor
C4,C6___________4n7   63V Polyester Capacitors
C5_____________22nF   63V Polyester Capacitor
C7,C9_________100µF   25V Electrolytic Capacitors

IC1___________TL062   Low current BIFET Dual Op-Amp

J1,J2__________6.3mm. Mono Jack sockets

SW1______________1 pole 3 ways rotary or slider switch
SW2______________SPST Switch

B1_______________9V PP3 Battery

Clip for PP3 Battery

Circuit operation:
IC1A op-amp is wired as an inverting amplifier, having its gain set by a three ways switch inserting different value resistors in parallel to R4. This input stage is followed by an active three-band tone control stage having unity gain when controls are set in their center position and built around IC1B.

Technical data:

Frequency response:20Hz to 20KHz -0.5dB, controls flat.
Tone control frequency range: ±15dB @ 30Hz; ±19dB @ 1KHz; ±16dB @ 10KHz.
Maximum input voltage (controls flat): 900mV RMS @ +10dB input gain; 7.5V RMS @ -10dB input gain.
Maximum undistorted output voltage: 2.5V RMS.
Total Harmonic Distortion measured @ 2V RMS output: <0.012% @ 1KHz; <0.03% @ 10KHz.
THD @ 1V RMS output: <0.01%
Total current drawing: <800µA.