0

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?

enter image description here

Null
  • 7,448
  • 17
  • 36
  • 48
Paperino
  • 205
  • 1
  • 7
  • One more question. My ultimate goal is to contribute to MAME by supporting this circuitry. Feel free to PM me. https://electronics.stackexchange.com/questions/624087/lm139-equivalent-circuit?noredirect=1&lq=1 – Paperino Jun 18 '22 at 18:00

2 Answers2

4

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.

Jens
  • 5,598
  • 2
  • 7
  • 28
1

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".

enter image description here 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).

enter image description here

And a "zoom" in the picture ... for some voltage, it is a "double" pulse.

enter image description here

Antonio51
  • 11,004
  • 1
  • 7
  • 20