Multipath Filters

[Haible Juergen]

Hi Grant,

	>I tried different sets of capacitor values. The more mis-match
between
	>capacitors, the more feed thru of the commutating frequency.
	>Try using 0.1 uF capacitors and set the state variable to
	>maximum frequency. The action is not actually that of
	>a state variable and the larger the capacitors, the more
	>pronounced the effect is. Excite the unit with a LFO and "ring"
	>the filter with slow pulses. With Q set to maximum, this
	>should produce metallic decay sounds (apparently all the
	>comb points will "ring").


thanks a lot for this - I should give it one more try !
(I see that changing the circuit I have made any possible error (;->) )

	>In my research, I managed to uncover a design from an early
	>organ manufacturer. The organ included a mechanical "vibrato"
	>circuit (read "get around Lesley patent"). This was a string
	>of about 25 passive LC circuits with a motor driven commutator.
	>Effectively the unit rotated through a series of taps in a passive
	>delay line. Apparently the manufacturer felt they could get away
	>with this trick even using mechanical contacts

This description sounds a lot like the Hammond Scanner Vibrato.
Scanning was done continously (rotating set of capacitor plates
will face a set of circular mounted fixed capacitor plates one by one),
and at sub-audio frequencies. Emulating a variable delay line by
tapping different stages of a fixed delay line.
But I suppose you're speaking of a different circuit ?

JH.