Variable "Through Zero" Crossover Distortion

[ashcat_lt]

Most of the time when we talk about crossover distortion, we talk about a "gap" between when the two "sides" of the waveform hit zero.  Like when we put two back to back diodes in series with the signal.  The output sits at 0 until the input swings far enough in one direction or another to overcome the diode drop, and then jumps, so there's a gap at the zero crossing.

It seems to me that there's another type of crossover distortion which I'm calling "overlap".  This would be where each "side" of the waveform overshoots 0 by some amount, and the two sides reinforce one another for a little while.

I had the idea to build a little thing that had a pot which would allow me to dial it in from some amount of "gap" type distortion, through no distortion, to "overlap" distortion.  I breadboarded it up, and it didn't work.  I don't know enough about this stuff to tell why.  So, I'm coming here to ask if anybody can point out where I've gone wrong, or maybe just point me to a circuit that is known to do what I'm trying to accomplish.

Here's a schematic version of what I (thought I) had on the breadboard:

Is there any good reason this won't work?

[phector2004]

I put this in Falstad's sim real quick:

with the pot at Vref, it was showing a regular sine wave
with the pot at 100k, it changed the waveform to something that looked more triangular. The slope was different, but it didn't resemble the clipped sides you get from putting diodes in series with the signal.

I can't really follow your schematic to well, as I'm still in the process of understanding opamp circuits. It would seem to me, though, that there's a simpler solution to your desired outcome:

Class AB amp's have a push-pull pair of tubes. By changing the bias, it changes when one tube "turns on" for one half of the signal and the other "turns off". I'm pretty sure you can cause the waveforms to overlap or for there to be a "gap" at the zero point. And all it takes is an NPN and a PNP and some experimenting.

Good luck!

[The Tone God]

Here is a circuit that gives alot of control into that aspect (with scope pics):

http://www.thetonegod.com/tech/blade/blade.html

Here is another way that has a low part count:

http://www.thetonegod.com/tech/finish_line/finish_line.html

Andrew

[phector2004]

Nice circuits

How does the "Finish Line" multiply the frequency?

Oh and to ashcat_lt, on the sim I did, the waveform looked like The Tone God's "Blade" with depth at zero

[ashcat_lt]

I, OTOH, (think I) understand opamp circuits better than transistors.  I had looked at both of these circuits previously but can't quite tell what's going on.  The Blade doesn't look like it's giving that "overlap" distortion I was talking about, unless that's the triangle looking thing with depth at 0.  Shouldn't that really just be like taking the diode bridge out altogether?  At half it's got that "gap".  So doesn't look like it goes "through zero.". It does allow a whole lot of waveshaping flexibility, though.  Might be worth playing with...

The Finish line looks a bit like Push-me-Pull-You, wneither of them make sense to me with those transistors, and there's no scope shots to tell me what's happening.  Do these go "through zero"?