Purpose of Ge diode in OC-2

[chicago_mike]

   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]

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.

[chicago_mike]

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.

[Perrow]

Anyone else that've trouble visualizing this?

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

[Taylor]

http://moosapotamus.net/IDEAS/stompboxology/Vol13No3/Page_03.gif

[Perrow]

http://moosapotamus.net/IDEAS/stompboxology/Vol13No3/Page_03.gif

Thanks.