Yamaha CS80

The signal to the VCO FM is attenuated significantly, as the main
purpose of the CS-80's 
FM feature was subtle vibrato. This is not the case with the VCF FM
and VCA mod so you 
can get quite dramatic filter mod and AM effects using the EXT input.

I don't know if it's possible to modify the circuit to produce more
dramatic FM effects. It's 
probably not practical if it involves a change to every voice board.

The main out feedback to external input trick can be cool on some
synths. It was a wild 
trick on the MS-20.

--- In yamahacs80@yahoogroups.com, "David Rogoff" <david@t...> wrote:
> The EXT input is one of the selectable "waveforms" for the Sub
> OSC/LFO.  If you stick an audio signal in there, select EXT for the
> Sub OSC and send the Sub OSC to the VCO (all the time, or via
> aftertouch), you'll have some FM.  I guess you could loop the
> general/mono audio out back into EXT and get some weird
modulations. 
> I'll have to try this later.  I don't know if the voltage levels are
> high enough.
> 
> Anyone else try this?
> 
>  David