well, a no-input mixer setup involves analogue circuitry, since that's your noise source to feed the whole thing.
Some simple noise and a ton of filters, delay and spades of feedback would be a great place to start.
The main thing to look at is separating the emulation of the sound, and the emulation of the mixer interface - remember that they *are* a work-around, and dedicated systems to reproduce those sounds might have a more useful interface.
To get specific, most no-input things start out as just sinewaves, tuned and then faded in and out - at that point we're close to Berna, really:
Thanks, Wetterberg. I hear what you are saying about the mixer interface not being the best way of manipulating the sound. I will keep in this in mind. Now, by "spades of feedback" are you referring to....using envelopes to attenuate the feedback amount? Or? That Berna thing looks great, by the way. I have been working on some feedback using some delays and a sine wave. I'll clean it up and post it. I would be curious to see what you would suggest.