Phaser LFO idea

[jh.]

> Forgive me if this has been done but I've always wondered if it would be
> possible to build a phaser with an LFO that, rather than the usual GAIN
and
> DEPTH controls or sometimes just DEPTH, had 2 pots marked TOP OF SWEEP and
> BOTTOM OF SWEEP. The advantage being that instruments in different
registers
> need a different sweep to get a nice even swirl and avoid the part where
> nothing much happens.
> Put in another way can you make an LFO where you specify the exact height
of
> output swing, top and bottom using analogue stuff? I'm sure it can be done
> but can't picture it. Another thing that springs to mind (that could be
> used) is the idea of a slider pot with 2 wipers (homemade?) to avoid
> problems of crossing over ranges.

This is a nice idea ! Reminds me of the Yamaha CS-80 VCF envelopes, which
look
quite strange at first, but are so very useful once you learned towork with
them.

I see two possiblilities for realisation:
(1) use the two pots to set the two trigger thresholds in the oscillator
core, and
      re-adjust the integrator current with the difference of the two
voltages
(2) use an ordinary LFO and map the two voltages to an ordinary Amount +
Offset
      scheme.

The Yamaha envelopes use option (1), but here we have exponential rather
than
linear slopes, so the time constants don't change (not much, at least) with
the voltage
span. For a LFO, I think option (2) would be easier to implement.

The slider pots could be mechanically locked like the Korg Traveler sliders,
or
one could simply define overlap as "zero amount" and the maximum of both
sliders
for the offset.

Very nice idea Lincoln, really !

JH.