The Magnus phase shifter

[Magnus Danielson]

From: Don Tillman <don at till.com>
Subject: The Magnus phase shifter
Date: Thu, 21 Sep 2000 01:16:05 -0700 (PDT)

Hi!

>    Date: Mon, 18 Sep 2000 02:31:00 +0200
>    From: Magnus Danielson <cfmd at swipnet.se>
> 
>    http://home.swipnet.se/cfmd/synths/schematics/
> 
> Wow, that's a very nice idea.  I like it. 

Oh, thanks!! Much apprechiated!

> A couple features I noticed: First, it can do thru-zero frequency PM.
> By that I mean if you shift the phase backwards quickly you can
> briefly take the frequency negative.

Certainly.

> Secondly, you can put a number of these in series to do more than
> 360-degrees of phase shift.

Oh yes, I have considered that. It's ultra-easy to do, and fairly cheap.

> (Ummm, I'm thinking a couple errors crept into the schematic.  Perhaps
> the comparator's input are swapped and the resistor values aren't
> quite right.  Also, since the circuit is really dependant on the power
> supply voltage it would be a good idea to specify that.  You want the
> comparator output transition to exactly compensate for the sawtooth
> reset, right?)

First note that the comparator's input order will set the polarity of the
comparator signal, second, note that the polarity you would like to have
depends on how you mix the sawtooth and the PWM pulse. If you switch from (+)
to (-) input on the pulse you also need to interchange the comparator inputs
in order to maintain the same function.

> This circuit is almost the same as the Chroma sawtooth mix.  
> 
> Quick description: The Chroma has a comparator, positive input
> grounded, negative input has an equal mix of sawtooth and the PWM
> control voltage, and the result is a resistor mix of the comparator
> output, the PWM control voltage and the sawtooth.  

I haven't seen the Chroma sawtooth mix.

> But the Chroma mixes in twice as much sawtooth because the goal isn't
> a phase shifter but a mix of the original sawtooth and the
> phase-shifted sawtooth for a thicker sound.

Ah.

Cheers,
Magnus