[sdiy] LFO with two outputs (one being variably phase shifted)

[DSL FODA01]

Actually, while I was at work this evening I had time to brainstorm a
solution using a total of four op-amps.

The first two op-amps form a simple integrator/comparator oscillator, where
you have the output of a comparator feeding into the input of an integrator.
This gives nice triangle and square wave outputs.  You can vary the rate of
this LFO by varying the resistor in the integrator.

The triangle output also feeds into a second comparator, having a variable
hysteresis resistor.  This creates a square wave output that can be offset
in time relative to the first square wave output coming from the main
comparator by varying the hysteresis and thus the point in the triangle at
which the comparator switches.  You then feed this "delayed" square wave
into a second integrator, making sure the C/R of this second integrator
match the C/R of the one in the oscillator proper (IE use a dual pot, one
side to alter the LFO freq and the other to alter the timing of the second
integrator), and you get a second, phase-shifted triangle out from this.
Also make sure to add a large resistor across the cap of this second
integrator.  It's a little hard to explain verbally, but I cobbled one
together and it surprised me by working.

Dave









----- Original Message -----
From: "David Brown" <davebr at earthlink.net>
To: "DSL FODA01" <foda01 at epix.net>; <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, March 30, 2006 10:41 PM
Subject: Re: [sdiy] LFO with two outputs (one being variably phase shifted)


> I did one of these in code with my PSIM.  Could only get it the max
> frequency to 5 Hz at 256 point resolution.  The variable phase shift
> is 0 - 359 degrees.  Easy to do digitally ...
>
> Dave
>
> At 11:34 AM 3/30/2006, DSL FODA01 wrote:
> >Hello all,
> >
> >I am looking for an LFO circuit that puts out two triangle waves (or
> >approximations therof) in which one wave can be variably offset from the
> >other one in terms of phase.  It would have two knobs - one to control
the
> >frequency (say from 0.1 Hz to 10 Hz) and another to adjust the phase
offset
> >of the second output with respect to the first one, say from 0 to 180
> >degrees.  Also hopefully there would be little or no interaction between
the
> >two knob settings.  If anyone has an idea for such a circuit, please pass
> >along...
> >
> >thanks!
> >
> >Dave
>
>