Tremolo Effect Generator

Stand-alone, 9V battery powered unit

High overload margin, low distortion circuit

Circuit diagram:

Tremolo Circuit Diagram


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.

Circuit description:

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.


Technical data:

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: