Magnus freq doubler.Oscillator beating!

[Magnus Danielson]

From: "Bjorn Julin" <bnillson at hotmail.com>
Subject: Re: Magnus freq doubler.Oscillator beating!
Date: Mon, 18 Sep 2000 23:52:44 GMT

> Hi.

Hi there...

> >Well, my sawtooth phase shifter is a 360 degree phase shifter, or at >least 
> >very close to 360 degree... just vary the comparator voltage >over the full 
> >sawtooth voltage and the comparator drops out the PWM >wave and the summing 
> >network will do the rest. Maybe it is time for
> >me to make a schematic of that and put up along the others?
> 
> Ahhhrg,sorry again, what i ment was that, it actually does 360 degrees, My 
> design is a 0 to 5 volt cirquit,i have just been sitting to long and looking 
> at the upp half of the waves on my scope, i
> forgot the down phase, Forget my hassle text!

Björn, those digital curcuits isn't good for you! ;D

> What i allso ment was the phase modulating "end result" by using frequency
> doubling, the viIibBbRrRrAaAtoo effect!

Ooohh...

> >Ah, but the thing is that the whole thing is balanced!
> >I get a DC error which I adjust by the resistor to negative feed. >Also, 
> >this is an ugly thing since I assume the saw to go from -5 V to >+5 V as 
> >well as assuming the powerlines to be at +/- 15V. That is the >ugly side of 
> >it. Removing the diode so that I get a (fairly) balanced >output from the 
> >comparator also removes the DC error from that signal, so then I can remove 
> >the DC correction. I actually spent part >of my efforts just to ensure that 
> >I still had
> >DC offset at 0V!
> 
> For a single know device it should be so, but i was more reffering
> to offset voltages and how close the op amp device can swing the output to 
> its both rails.

Yeah, offset and amplitude errors needs to be adjusted for. Jörgens design has
compensation trimmers for it.

> The chroma uses a different aproach, they just sums up the saw
> the square and the cv thuru weighted resistors (as currents tru a  4052) to 
> do the phase shifts, so the second OP acts as a mixer who then passes the 
> signal to a VCA.

In a way it is doing the same thing, the same trick... just a diffrent
representation.

> >When Jörgen took the doubler schematic and turned it into a phase >shifter 
> >based on my hints he realized this and things became even >simpler.
> 
> Actually, the whole idea with the phase shifter is that if the cv
> is sweept by a LFO it simulates the beating between TWO sawtoth
> oscillators.Anything from controlled slow beating into chorus/detune
> sound is produced, exactly one of the nice things with the Chroma.

Hmm... I haven't fooled around with a Chroma...

> > > Why not using a three way switch?
> >
> >Uhm, I am not sure that I know how it would help... ah well..
> 
> Just to switch between uni and bi polarities, nothing else.

To tired to get it right now, will ponder over it later.

Cheers,
Magnus