[sdiy] Synthex Oscillator

[rsdio at audiobanshee.com]

I'm influenced by my own attempts to make a flexible sawtooth oscillator as well as studies of odd techniques like the Roland GR-300 chopper wave.

I think it was this list where I read about the idea of changing the slope of the sawtooth integrator in order to combat the issue with fixed slope integrators where high frequencies have low amplitudes and low frequencies have high amplitudes. When I read that, I always assumed a current source or current sink that was digitally controlled. As long as the current is constant, the slope would be linear. I hadn't thought of a passive circuit that is switched.

Seeing the Synthex oscillator, and reading Mario's comments about digital-controlled current, definitely colors my attempt to understand the circuit.

Brian


On Jul 9, 2017, at 12:51 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> Brian,
> 
> Your idea that the falling counter acts to linearise the RC curve of the capacitor discharging is very clever. However, I can't believe it's true. After all, why not just [ut the cap in the feedback loop of the op-amp (there is one there already, so it's no big deal) and linearise it like that. Alkternatively, why even bother with all that when you've *got* a highly linear ramp from the counter. It doesn't make enough sense to me just yet, but it's a very interesting notion, and it goes a long way to explain what Mario might mean.
> 
> Thanks,
> Tom
>