90-degree phase tri lfo revisited

[Tom May]

Paul Perry <pfperry at melbpc.org.au> writes:

>  You can get arbitrary phase shifts by
> >starting with a saw oscillator, going through an ElectroNotes sawtooth
> >phase shifter, and then a saw to tri converter.
> ..I dont know this ckt, I presume there is a comparator which says
> when to add or subtract the comparator input from the original
> sawtooth.. cant quite see how yet..

Pretty much.  The EN design (app note 73?) was for sawtooth and CV in
the range 0-5V, I built a similar circuit but for sawtooth and CV in
the range +/-5V.  Put the following through a summer with 100K in the
feedback loop using the specified input resistors to get things
weighted right.  Or use whatever resistor values you want but keep the
ratios.

1. Inverted sawtooth (100K).

2. Output from a comparator with + input connected to the non-inverted
   sawtooth and the - input connected to the CV (slightly less than 300K
   to compensate for the fact that the output is not rail-to-rail,
   I used a 270K + 50K single-turn trim which measured out to 296K
   with a TL082 for a comparator).

3. The CV (100K).

4. (Optional) some kind of additional offset voltage to adjust
   for the fact that the comparator probably doesn't have symmetric
   output levels.  This will keep things symmetric about zero volts.

fTom.