Modulating Audio Tone Generator

Thread Starter


Joined Apr 5, 2006
I'm trying to make a device that will (through a speaker) produce a tone modulating between 20kHz and 30 kHz. I know that this is out of the hearing range of most people, but thats ok.

My plan was to have a ramp generator that would power a VCO. At the lowest voltage the VCO would produce 20kHz and at the highest is would produce 20 kHz. I would then run the ouput of the VCO through an amplifier circuit.

The problem is that I can't find a VCO that will opperate in the coorect range. All that I find opperate in the 1MHz+ range.

I've thought about just using a two crystals and running them through a summing amplifier, but I dont think it will produce simlar results (I know there would be no modulation).

Any I ideas or timps on parts would be helpful. Are there any PLLs out there that opperate this low?


Joined Apr 20, 2004

Get the datasheet for an ICL8038. It's out of production, but several places have the spec's. Then go to Mouser Electronics and get an NTE864, which is an identical device. It runs under $10.00.

The NTE864 will run in that range and has an input for FM modulation. You also get sine, triangle and square wave outputs. The sine out is pretty weenie for drive, so use an op amp buffer.