Problem with OC-2 chopped

Started by isildur100, November 28, 2009, 12:17:08 PM

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liquids

Thanks John! looks like I have something to print and read at work tomorrow.   :)   Very interesting that it's a different function than the typical 4013...sorry for the misleading and incorrect assumptions.  :(

Anyhow, I'd love to see your schematic and what you did with it...all the talk on this thread has me itching to try it out on the breadboard myself!
Breadboard it!

isildur100

This is what I did with the OC-2 chopped. Basically, I added the original OC-2 jfet input buffer and added a mid boost pot for the octave'd signal. This gives more mid-bass tones to the octave down. I know, it adds to the part count but personally, I didn't mind adding it while it was on the breadboard :)


liquids

Isildur - do you have a layout for your build, or does anyone have a layout for the OC-2 chopped?
Breadboard it!

chicago_mike

I know this is an old thread...but could someone tell me the purpose of the GE diode in the circuit?

Stabilization or anything like that?

Processaurus

Quote from: chicago_mike on August 22, 2010, 02:54:44 AM
I know this is an old thread...but could someone tell me the purpose of the GE diode in the circuit?

Stabilization or anything like that?

Good question, I'd like to hear someone's explanation too. 

That stompboxology article (page 3 especially)  linked to earlier in this thread is a fantastic explanation of octave circuits.  It explains there are two variations on this type of octave divider that switch the phase  (with the FET) every full cycle on the input signal to synthesize an octave down, one with the diode and one without the diode.  Far from a satisfactory explanation, but I remember trying it without the diode, and the diode added an interesting DC component to the phase switching that, when the signal's cycle peaked and the FET either opened or closed to switch the opamp stages phase, the diode added a DC offset so that the bottom of the now inverted waveform lined up with the  peak, so that there wasn't a jagged transition.  That ends up sounding like a stronger sub octave fundamental / a more vaguely triangle wave-like sub octave, than the easier to understand diode-less circuit, which just switches the phase every other time the input signal crosses zero, making a kind of v^^vv^^vv^^vv^ looking wave, which is more vaguely square wave shaped. 

Here's a geofex article on the phase switching, minus the diode:
http://www.geofex.com/article_folders/polarity_reverser/polarity_reverser.htm