The first time I ever saw a Negistor was at Christian’s (aka hemmo p) old, original web site (now gone). Then, I heard tell that Zachary Vex had brought up this Negistor idea on Aron’s DIY Stompbox Forum some time ago. Now, apparently ZV is using them in his micro-amp, little head, thing. To be honest, the theory is a bit over my head, but if you are curious and yearning for more than I can give you, you might give KeelyNet a try?
All I did with this is put three Negistors in series and tweak some of the component values a little. Initially, I had some simple switching to select between several different coupling capacitors. I found that switching the coupling capacitors between the second and third oscillators sounded a lot more interesting than between the first and second oscilators. I also found that doing things like jumping a cap in the first coupling stage to one in the second coupling stage, and connecting some of these coupling caps to ground (among other things) also made for new interesting noises.
NOTE: Others who have experimented with the following have had mixed results. The only advise I can offer to those who choose to experiment with it and wind up having difficulty getting the thing to make any noise is to maybe try using a higher supply voltage like 18VDC instead of 9VDC.
Every part of this circuit can be tweaked or changed in some way for different effects. If you decide to build one, I’d recommend trying some different component values and wiring/switching schemes on a breadboard until you get something that you like. On mine, I have a frequency knob for each of the three oscillators, some momentary push-buttons, and some 3-position (on-off-on) toggle switches. Ended up with a number of ‘do nothing’ settings, but that’s cool. It’ll make a whole lot of wild freaky noises, too. Try some different stuff and make it your own.
I did not include an input for external audio in this build, although it is possible to feed audio into the base of the first transistor (or maybe somewhere else, like the second or third one, through a 10pF cap, or something). Anyway, so all the audio clips, above, are just my Tri-Negistor spazzing out on it’s own with copious knob twiddling, button pushing and switch flipping on my part.