Author Topic: Purpose of Ge diode in OC-2  (Read 3179 times)


Purpose of Ge diode in OC-2
« on: February 05, 2011, 04:24:20 PM »
   Hey gang!

IM trying to get my diy ampeg octaver to work a little better and am comparing it to the chopped oc-2.

The ampeg doesnt have the Ge diode like the OC-2 and was wonder what its purpose is.

Does anybody know what it does?

Thanks! :)

Rob Strand

Re: Purpose of Ge diode in OC-2
« Reply #1 on: February 06, 2011, 08:19:06 AM »
It does change the sound, in fact the diode characteristics change the sound quite a bit.
The octave sound is smoother and stronger.
The diodes change the reference point that the inverter flips around.

Without diodes
- Draw a three cycles of a sine wave.
- Redraw the waveform with the phase of the second cycle inverted.
  The waveform will have two -ve humps in the middle, followed by
  two +ve humps.  You can see this waveform will have an f/2 component.

With diodes:
- Draw three cycles but this time shift the sine wave up so the -ve peaks are now at zero.
- Now invert the second cycle about the DC =0 line.  You should see that the level of the peaks are twice as high,
  and the waveshape is more like a sinewave at f/2.  There's no sharp notch which
  makes the sound more buzzy.

In reality everything sits Vcc/2 higher DC wise but it's easier to see the way I've explained it.

Anyway that's the general idea.  It's a neat trick.

« Last Edit: February 06, 2011, 08:22:03 AM by Rob Strand »
Plopping around the pot since an early age.


Re: Purpose of Ge diode in OC-2
« Reply #2 on: February 07, 2011, 01:17:25 AM »
Cool! That actually makes sense. I have a couple other octave schematics with the diode in their and wondered what it did.

Now I can do my layout.

ty. :)


Re: Purpose of Ge diode in OC-2
« Reply #3 on: February 07, 2011, 02:42:45 AM »
Anyone else that've trouble visualizing this?

Rob (or someone else who "sees it"), could you be bothered to do an illustration?
My stompbox wiki ->

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