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

[Ian Fritz]

Great idea, Roman.  I just patched this up and as far as I can see it works 
fine.  I used my version of the Electronotes MPWA, which is actually two 
modules --  a bank of LFOs and a bank of sawtooth phase shifters with 
saw-to-tri converters.  I used a sine modulating signal into one of the 
shifters and the the tri output (no tri-to-saw conversion, 
yet).  Unfortunately, all the shifters are mixed into one output, so I 
can't try cascading at this point.

The only issue I see for accurate sin-sin phase modulation is accurate 
waveforms, not only for the converters (as you mentioned) but for the saw 
phase shifter itself, which has some semi-critical level adjustments and 
some switching transients.

But just as it stands the setup makes a great waveshaper.  I have been 
playing with using two VCOs (either synced or not) to drive the two 
inputs.  Very interesting.  This could be a great dynamic waveshaper module 
as well as a path towards phase modulation synthesis.  One nice feature as 
a waveshaper is that it is "filter-like", i.e., at zero modulation level 
the output automatically has low harmonic content (tri or sine).

   Ian



At 02:11 AM 10/26/2003, Roman Sowa wrote:
>I have a strong feeling that PM would be eassy in analog, maybe easier
>than thru-0-FM. Simply use wave multiplier from Ken Stone, or any
>similar circuit. It's straight phase modulation of saw wave.
>Then saw-2-tri, tr-2-sin and we have PM sines. And they are locked
>in phase thru entire CV range. It has linear phase/V relation and
>not limited to 360 deg, as it simply wraps.
>Am I missing something (beside waveform purity after saw-2-sin
>conversion)?
>
>Roman