P1______________22K Log Potentiometer P2______________22K Linear Potentiometer R1,R6__________150K 1/4W Resistors R2_____________220K 1/4W Resistor R3______________56K 1/4W Resistor R4_____________470K 1/4W Resistor R5______________68K 1/4W Resistor R7______________39K 1/4W Resistor R8,R13___________3K9 1/4W Resistors R9______________15K 1/4W Resistor R10,R11,R15_____10K 1/4W Resistors R12______________6K8 1/4W Resistor R14,R17__________5K6 1/4W Resistors R16____________330R 1/4W Resistor R18_____________47K 1/4W Resistor R19______________1M 1/4W Resistor R20,R21_________22K 1/4W Resistors C1,C7,C8,C9____330nF 63V Polyester Capacitors C2______________10µF 25V Electrolytic Capacitor C3,C10,C11_____100µF 25V Electrolytic Capacitors C4______________47nF 63V Polyester Capacitor C5_______________2µ2 25V Electrolytic Capacitor C6_____________220µF 25V Electrolytic Capacitor Q1,Q2_________BC557B 45V 100mA PNP Transistors (or 2N3906) 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 Toggle, slider or Pedal Switch SW3______________SPST Toggle or slider Switch B1_________________9V PP3 Battery Clip for PP3 Battery
In the old days of tube guitar amps a tremolo circuit, i.e. an amplitude modulator of the input audio signal, was invariably present, even in the cheapest amplifiers. In practice, the signal level was increased and decreased at a rate typically ranging from about 5 to 10 times per second.
This effect is no longer available in most modern guitar amps, but since some players like to use it yet, a stand alone, 9V battery powered tremolo unit primarily intended for electric guitars was designed on request.
IC1A is wired as a linear input amplifier. The input sensitivity of the circuit can be varied from -10dB to +10dB in three fixed steps by means of SW1, in order to cope with almost any pick-up type and model. The audio signal is then routed to the modulator stage formed by a transistor long-tailed pair (Q1 and Q2) whose tail current is made variable by the output voltage of a sine wave generator. The amplitude modulator circuitry is rather complex if compared to usual tremolo circuits, but it allows superior distortion and overload margin performance. IC1B is wired as a sine wave phase-shift oscillator: its output frequency can be varied in the 5Hz - 10Hz range by means of P2 (Tremolo Speed Control).
P1 is the Tremolo Depth Control: a more or less heavy modulation of the tail current of Q1 and Q2 is obtained by a partial shunting, through the network formed by R12, R15, C5, C6 and P1, of the sine wave generated by IC1B. If a log potentiometer is used for P1, as recommended, a very fine Depth Control will be obtained, ranging from a fixed tone to a gently wavering sound and finally to a more in-deep modulated tremolo.
C4 and R11 form a 160Hz high-pass filter, necessary to reduce the presence of unwanted 5-10Hz frequencies at the output of the circuit.
- P1 pins connection: with the shaft of the pot pointing toward you and the three pins pointing down, connect C6 to the leftmost pin and the remaining two pins to negative ground.
- P2 pins connection: with the shaft of the pot pointing toward you and the three pins pointing down, connect R17 to the rightmost pin and the remaining two pins to negative ground.
- Input Gain:
- Three selectable positions: +10dB, 0dB and -10dB
- Maximum Input Voltage:
- 250mV RMS for undistorted output (SW1 set to 0dB)
- 750mV RMS for undistorted output (SW1 set to -10dB)
- 85mV RMS for undistorted output (SW1 set to +10dB)
- Adjustable from 5 to 10Hz
- Total current drawing: