Constant Slew Rate LFO

[Steve Ridley]

> This might be what you want - assuming constant slew rate = constant
> slope for a triangle waveform. Start with  the simple two op amp
> (Schmitt trigger + integrator) triangle generator. Replace the resistor
> that connects the integrator output to the Schmitt (+) input with a
> variable resistor (pot) - this becomes the DEPTH control. The variable
> resistor (pot) that connects the Schmitt output to the integrator op amp
> (-) input gets labelled as SLOPE (was RATE in the original constant
> amplitude triangle configuration). This should give (untested...) a
> constant slew rate variable amplitude triangle - as the amplitude
> increases, the frequency decreases. The triangle is centered about zero
> volts. OTA's could be used to make this voltage-controlled. A version
> that has the bottom of the triangle fixed at zero volts could be useful

I've seen an LFO like this in an early 1980s Dod flanger.  I can't remember
the exact model, but I remember thinking how much better it was than
the usual "level and rate" LFOs on other pedals.

It's currently number 26 on my list of things to build when I've bought a
house...


Steve Ridley