This tremolo effect circuit uses the XR2206 and the TCA730 IC which is designed as an electronic balance and volume regulator with frequency correction. The circuit is usefull for stereo channels and it also has the ability to simulate the Lesley effect aka rotating loudspeaker effect.
How does the tremolo effect circuit works
Balance and volume settings are done with a linear potentiometer for both channels. If this potentiometer is replaced with an AC voltage source, a periodic modulation of the input signal can be achieved. This AC voltage source comes from the function generator IC XR2206. This IC generates square, triangle and sinewave signals but for this project we use only the sinewave.
The modulation voltage can be varied with P1 from 1 Hz up to 25 Hz. Resistor R3 sets the operation level of the sinewave generator. R5 and R6 set the DC voltage and the sinewave amplitude at the output. C2 is a ripple filter. The squarewave output of the XR2206 drives T2 and a LED to optically display the frequency.
The modulating voltage reaches pin 13 of TCA730 via P3 and R10. This input functions as the volume control or in this case the volume modulation. The degree of the balance modulation (Lesley effect) can be varied with P2. A regulated power supply using 7815 IC is recommended. Do not use a non-stabilized power supply since the current variations would influence the modulation negatively.
Attach the 7815 IC to a good heatsink (about 10 cm2).