Tri-Vibe Triangle Wave Generator Question

[knutolai]

Hi all
Was looking for a LFO for a modulation circuit and stumbled across the Tri-Vibe and its triangle wave generator. It has an extra resistor and capacitor which sets it apart from a standard Triangle/Square Wave Generator. Does anyone know the benefit of these extra parts? I' talking about the 100k resistor and 10n capacitor connected to U3a pin 1 & 2.





Many thanks!

[blackieNYC]

The 100K resistor is coming from Vref.  It isolates this circuit from others in your build that might also use Vref.  If the 100k was just a wire, all those various points would be shorted together.
The 10n is probably getting rid of unwanted very high frequencies.
The other drawing is a simplified representation of an oscillator for learnin'.  You should stick with the first circuit, especially if you found it in the schematic.  Don't let that stuff throw you.  The only significant difference is that the op-amp is referenced to ground or to the Vref voltage.  either can be made to work I believe.

[PRR]

10nFd against 100K is 166Hz. It will slow the "square" transitions. This also round-tips the triangle wave.

The comparator (U3a) nominally "snaps" down or up. With 10nFd+100K, it will "slide", not "snap".

166Hz is far above usual LFO rates, so it is still near-square, just less abrupt.

http://oi59.tinypic.com/etgu3q.jpg

[amz-fx]

10nFd against 100K is 166Hz. It will slow the "square" transitions. This also round-tips the triangle wave.

The comparator (U3a) nominally "snaps" down or up. With 10nFd+100K, it will "slide", not "snap".

166Hz is far above usual LFO rates, so it is still near-square, just less abrupt.

By slowing down the "snap" it helps reduce the clicking that is often heard in the audio output.

That is its purpose here. 

Best regards, Jack

[knutolai]

Brilliant! Thank you for your help.