The waveform generator is a helpful instrument if you want to test frequency responses and audio amplifiers. Also you can check your filters with it. For the FMAS a waveform generator was constructed around the XR2206CP chip. This is a really old monolithic function generator. That means you do not need external semiconductors for it to work. And this chip has some serious stuff in it.
The circuit for the function generator (sorry, but I’ll use the terms ‘function generator’ and ‘waveform generator’ as the same thing…) is a bit hard to read because there are a lot of rotary switches for all the different frequency domains.
As the datasheet tells us, this chip can generate from 10mHz up to 1MHz and more, but mine sadly only goes up to 200kHz and then the output stage is cutting it off.
For the frequency domains I used rotary switches with multiple commen pins, so one rotary switch is switching three signals simultaneously, which is important.
In order for the generator to deliver some current I built an output amplifier stage. This stage controls the amplitude of the signal, as well as DC-offset. Frequency is controlled by the 2206.
Next to the DC output I decoupled the signal with two capacitors and now I have an AC output as well.
If the sine wave looks more like a triangle, you have two trimmers for the harmonic distortion. With these you can make your sine wave perfect. But take your time with this.
The output is powered with symmetrical 15V, but because I built the stage this way you can achieve only 22Vpp max. This is intended though so the transistors won’t short out the power.
Schematic and a few pictures as usual.