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
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.
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.
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.