phasers (was: Mutron)

[Haible Juergen]

Sorry for the delayed reply.
This was a great list of phasers you posted !

	> - Op-amp phase shift stages, with CD4069 (operating in linear
mode) used as
	> 6 voltage-controlled resistors (Don Tillman's clever design)

Never seen this one - has Don published it anywhere on the web ?

	>- Op-amp phase shift stages, with ultrasonic PWM switchable
resistor
	>thingies controlling phase shift amount (ADA Final Phase)

	> - LM3900 configured as phase shifter (per Serge Tcherepnin's
patent - anyone
	> tried it yet?  Looks like the easiest method of all)

Do you have the patent # at hand ? 

	>Any other phaser methods I left out?  I left out some of the
ones I really
	>don't understand, like the Hammond vibrato. 

That's what I think how it works (but I may be wrong):
The "Line Box" is a fixed frequency high order low pass filter built
from
passive (RLC) components. The cutoff frequency is above the audio range
(well, probably not the theoretical audio range, but the one used by the
Hammond organ). Below the cutoff frequency, you have a rather flat
amplitude response (with some ripple), and you also have a certain phase
shift,
and group delay. As the filter is built from many similar stages, the
delay time
increases linearly as you scan along the line. Scanning is done by a
motor-controlled set of capacitors; there are several fixed plate
packets (stator)
around one moving plate package, so you get a capacitive coupling to
different
positions along the lpf depending on the motor position. Not all the
taps
along the lpf are used. There is some weighting that approximates a sine
wave modulation function.

JH