phasers

[Joachim Verghese]

Don wrote:

> The idea of using the FETs in a hex inverter wasn't entirely original,
> I saw it metioned in an old issue of Radio-Electronics magazine or
> something, but I had never seen it applied to a phase shifter before
> or since.

The Matiné organ, a constructional project that appeared in UK
mag Electronics & Music Maker in 1981, had a phaser section
which used 4069 inverters as VC resistors. This was a six-stage
design, I think.

BTW, I did some reverse engineering on an MXR Phase 100, and
found that part of the all-pass stages are indeed fixed, just
as R.G. Keen suggested a while back.

The Phase 100 is a 10-stage device but the first two, and last
two stages are fixed. The six intermediate stages are variable,
and use linear opto-couplers as VC resistors. The feedback path
is made around the variable stages only, if memory serves. No
wonder it sounds different from most other phasers.

I'll make some images of the Matiné and Phase 100 schemos available
next week.

-joachim