> How about a small step sequencer that modifies an incoming vc
> signal So you bring in a pitch, and it adds/subtracts to the
> vc, so you get an arpeggiator affect that is relational to the
> note you play on the keyboard. (Or does this already exist )

If you use e.g. the A-185-2 precision adder that's already possible. You
simply add the external CV to the sequencer CV and use the sum to control
your VCOs.

Best wishes
Dieter Doepfer