Tim escobedo's "Octup!" in spice simulation

[Steben]

just tested the thing with and extra emitter follower in front.
The result was...
...a perfect sine wave at double frequency.

Man, that's a shock!

Tim is tha man...

[earthtonesaudio]

What was the input waveform?

[Steben]

a perfect sine wave at half the frequency of the output.



green = input
red = output

I must add that I inserted a 12k resistor at the drains of the FET's, which were 2N5457

[gigimarga]

Nice...what emitter follower did you used?

[Kultur Vultur]

The question is how does it preform when fed with more complex waveforms.

[earthtonesaudio]

There are a couple of things to consider when you import this circuit into the "real world"...
First, even in SPICE, the octave up waveform Steven shows in the graph isn't a perfect sine.  Notice that every other lower peak is of a different amplitude compared to its neighbor.
Second, the SPICE simulation probably used perfectly matched JFETs.  (Correct me if I'm wrong, of course!) That will give you the best cancellation possible, better than any real pair of JFETs could hope to achieve.
Third, the only way for the Octup! circuit to pass sound is if there is some distortion present in the JFET stage.  It's a cancellation stage, which means the original waveform is nulled out, leaving only the distortion products.  The distortion is summed at the drains of the JFETs, giving a prominent octave up (plus higher harmonics).  If it didn't distort at all, no sound would come out!

In spite of all that, it's still a VERY "clean sounding" method of getting an octave up.  Much more so than full-wave rectification, which doesn't give much of a sine output at all (more like hypertriangular than sine).  So the sound should be cleaner than other octave up boxes, just don't expect polyphonic 12-string textures, that's all I'm sayin'.

[mac]

I breadboarded it once using a couple of well matched 2s117. Nice almost-clean octave.

mac

[Steben]

There are a couple of things to consider when you import this circuit into the "real world"...
First, even in SPICE, the octave up waveform Steven shows in the graph isn't a perfect sine.  Notice that every other lower peak is of a different amplitude compared to its neighbor.

true, however, it is not the dry output of the Octup!
It is the outer position of a blend pot. Which means there is a percentage original wave in it. ;-)

[earthtonesaudio]

Touché! 

Nice work with the SPICE sim Steven.