[sdiy] analogue DX-7-style Phase Modulation using quadrature signals ?

[Don Tillman]

   > From: "jhaible" <jhaible at debitel.net>
   > Date: Sun, 26 Oct 2003 01:51:04 +0200
   > 
   > This is just an idea at the moment, and I wonder if this
   > would work. It's about making DX-7-like Phase Modulation
   > (often misnamed as Frequency Modulation) with analogue
   > oscillators. From earlier discussions on synth-diy I know that
   > FM of a VCO is easy, thru-zero FM is difficult but possible,
   > but PM - easy in digital - would be most demanding on an
   > analogue VCO.

Hi JH!

Yes, this is absolutely right.

   > But what about using a quadrature signal? 

It's possible to perform voltage controlled phase shift with my
Quadrature Trapezoid VCO.  That was, in fact, one of the goals of the
project, and I hint about it in the article.

I have a circuit to do this worked out, but it hasn't been tested yet.
It's intended to perform graceful Quadrature Trapezoid phase shifting
over 16 cycles.  The circuit is somewhat complex and took a long time
to design.  I'll publish it as soon as I know it works.

  -- Don

-- 
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com