Audio Signal Generator

A couple of cheap CMOS ICs are used to digitally generate audio sinewaves across a wide range in this compact battery-powered test instrument. The oscillator features both unbalanced and balanced outputs. I use signal generators of one sort or another all the time as I design and build circuits. They include a pair of simple oscillators; a transis
Audio Signal Generator - schematic

tor oscillator for testing crystals, and a CMOS square wave clock source, built on a scrap of PCB. I also have a homebrewed RF signal generator which covers up to about 50 MHz in a dozen ranges, and an audio signal generator. For many years, I used a kit-built audio oscillator, a design from the now defunct Electronics Australia (EA) magazine. It used a couple of op-amps, and was stabilized with a thermistor. It worked, but it had some serious limitations. The output level would vary with frequency, and it was annoyingly microphonic. Knock it by accident, and it would make a "boinnngggg" sound over top of the wanted tone. The oscillator`s frequency also had a habit of drifting a little over time. The most critical limitation however was its power consumption. It seemed to gobble batteries! Whenever I went to use it again, the bothersome thing would require a (yet another!) new battery before I could begin to use it. Along with the one or two seconds it took to start up, a product of its thermistor stabilization scheme, I became sufficiently annoyed with it one day that I designed and built this simple CMOS-based version. The oscillator described here is now more than a dozen years old. After all that time, and some fairly heavy use, I finally replaced the original 9V battery I put in when I built it about six months ago. It draws a miserly 3mA at 9V, but it is possible to power it with any voltage from 3V to as much as 15V,...

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