Doepfer

> hello,
>
> i'm sure this is achievable with existing modules, if it is could
> someone explain how (four phase shifters?), but the other day I
> decided that I could do with a module in which you can input a
> waveform audio or cv and have seperate outputs in 90 deg/180/270
> deg etc phases.like the quadrature modules which exist but from
> an input rather than internal occillators.
> a quad-phase shifter i suppose? using four seperate phase
> shifters-would you be able to set them accurately enough?
> diy'ers-would this be simple enough to knock up? i'm no engineer
> but i can solder things together ok. sounds simple to me....but
> then lots of things do that aren't. :(

A 90 degree phase shift over a wide frequency range is not easy to realize
because the phase shift of a normal phase shifter is not constant over the
frequency but depends upon the frequency! It's the function of the dome
filters in the (obsolete) A-126 frequency shifter. In the A-126 we used a
12-stage allpass filter to approximate a 90 degrees phase shift in the
frequency range 6 Hz ... 12 kHz with +/-2 degrees error. It's very difficult
to adjust a dome filter as the phase shift of each all pass affects the
others too. It took more than 30 minutes to adjust the dome filter of the
A-126.

180 and 270 degrees can be achieved by intverting the signal (180) or the 90
degree signal (270).

Best wishes
Dieter Doepfer