Info requested on EMS Phase Frequency Shifter

[Magnus Danielson]

>>>>> "SC" == Sean Costello <costello at costello.seanet.com> writes:

 SC> Hi everybody:
 SC> Does anyone out there have any details whatsoever on the EMS Phase Frequency
 SC> Shifter?  I know that it was also included in the Vocoder 5000.  I have only
 SC> heard a little bit of tantalizing info - that the same circuitry is used
 SC> both for phasing and for frequency shifting.  Anyone ever use one?  Better
 SC> yet, anyone have schematics?  It would be cool to see if the circuitry is as
 SC> weird as the other EMS gear I have seen or have heard about.

Doesn't Hilton still sell service manuals?

 SC> Thanks,

 SC> Sean Costello

 SC> P.S.  Anyone have Synthi Hi-Fli schematics out there?  I'd like to see how
 SC> diodes are used for voltage-controlled phasing.

The phaser core is built up of 2 banks of 6 1-pole allpass filters.
The allpass filters is a modification of the standard RC+2R+opamp
cursuit. The resistor in the RC-bridge is built out of a stack of
standard diodes. The CV is being applied diffrentially at the ends of
the stack and the capacitor and op-amp is connected at half-stack.
Each stack-half is 10 diodes in series operating in their forward
direction.

What makes the Hi-Fli phaser interesting is all the signal and CV
processing around the core. I also find the vibrato/transient
generator interesting...

 SC> P.P.S.  Anyone out there know of any good digital frequency shifter
 SC> techniques? I'd like to work on making Csound do this, but apparently the
 SC> Hibert transform is difficult to implement in a successful manner digitally
 SC> for this effect.

The Hilbert transform is as easy or complex as it ever was in the
analog domain. It is still the same math. However, using the propper
designtools will a good approximation be much more stable than the
analog counterpart.

Cheers,
Magnus