Follow up to the question here: Generated sound
I now understand better the oscillator circuit, but what's the purpose of the diode here?
I want to learn more on the topic, but I don't know where to start and if there is a name associated with this forward feedback? Is it there to bias positively the resulting wave-form, and why would you do that in an audio circuit?
The 339 would not oscillate without the diode. It toggles the reference voltage at IN+ to produce new target voltages for IN-. The circuit has properties of a VCO.
As @Jens said in his answer, the circuit has the properties of a VCO, but it is a "weird" VCO. EE&O. Somebody to confirm?
For those interested, here is the link of the file. Just zoom also the "double pulse".
Made with microcap v12, just click (in the simulator) on the switches to change the configuration.
Here is what I get when simulating this circuit (driven by a Voltage supply, test).
And a "zoom" in the picture ... for some voltage, it is a "double" pulse.
