Tri-Tone Generator

This little circuit is a 3 tone generator. Back in the late 1970's and 1980's EDCOR used this generator on the a number of input modules that were used in their modular power and mixer amplifier. This module would supply a tri-tone to the amplifier when a set of connection was complete. It was use security and notification across the background sound system. A simple usage, would be to have the tone sound out of the background music system when a door was open. There was a lot of different applications it was used in. It is a simple circuit, but then simple is good when designing. It could be used on any line level input. It was used to signal an alarm or buzzer when pin 2 and pin 3 of T1 were connected together.

The generator needs a bipolar power supply of 15 volts DC. When a switch connects pin 2 and 3 of T1 a tone is generated out pin 1 of P1.

You can change the sound by changing R3, R4 and R5.

Note on connector P1:

  1. Pin 1 is tone out
  2. Pin 2 is +15 VDC
  3. Pin 3 is ground
  4. Pin 4 is -15 VDC
  5. Pin 5 not used
  6. Pin 6 not used

Tri-tone Generator

1 comment



Interesting – I might re-create it with a little modification: using an non-inverting unity gain opamp output stage with single supply. NB there’s a little bug on the schematic – the negative DC rail goes nowhere. If I’m correct, it should go to the C9-C10-R10-R11 node.

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