An LM556 dual oscillator/timer, U1, configured as a two-tone oscillator drives U2, a dual4-watt amplifier. One of the oscillators, pins 1 to 6, contained in U1 produces the upper frequency signal of about 200 Hz, while the second oscillator, pins 8 to 13, provides the lower frequency signal of about 140Hz. Increase or decrease the frequencies by changing the values of C2 and C3. U1`s outputs, pins 9 and 5, are connected to separate potentiometers to provide control over volume and balance.
Each half of U2 produces 4 W of audio that is delivered to two 8-0 loudspeakers via capacitors C7 and C8.