Changing square LFO wave to sine/triangle?

[Top Top]

I just made a Gargletron and I am attempting to put it under control of an LFO via a home made vactrol (LED feeding into LDR).

I built this LFO with a 40106: which is also really similar to Tim Escebedo's "ez LFO" that is included in the PWM schematic.

But the wave is completely ON/OFF square wave. It would be nice to be able to have more of a sweeping change rather than an on/off change. In the sound samples of the PWM, it sounds like the change is more gradual.

Is there a simple (simple like 5 parts or less) way to curve off the edges of the waveform? Is the only simple way to get an LDR that has slower response? This one can go up into audio frequencies and keep up with the swings.

By the way I made this thing with a little 1/2 sized 40160 that I ordered accidentally... that was some interesting soldering    Luckily it only uses 4 of the pins.

[R.G.]

Is there a simple (simple like 5 parts or less) way to curve off the edges of the waveform?

You can filter it down some, but this only curves off the leading edges, not the trailing edges.

There is no way that is both simple (as you've defined it) and good. But try a simple R-C filter to slow down the edges a bit.

[Top Top]

I put a stack of high pF electrolytics in parallel across the LED legs. It isn't exactly elegant or pretty, but it brings it from a DADADADADADA pedal to a YAYAYAYAYAYAYA pedal

[brett]

Hi

Is the only simple way to get an LDR that has slower response?

IIRC, LDR "off" response slows down with more light (ie a saturation effect).  So turn off time might be greater with a brighter LED and if it's right on top of the LDR.
cheers

[Top Top]

I experimented a little more and found that also having a 10K pot inbetween the LFO and the LED, in  combination with the caps, helps get a more rounded wave. I do have the LED right on top of the LDR, and what it seems is that the LED maxes out in brightness at a certain point, and in effect "clips." If I limit the power to the LED with the pot, I can get a little more roundness out of it and it seems to sit on the high point for a shorter time.

I still can't quite get slow deep sweeps, but I can get somewhat shallower sweeps that sound pretty smooth.

At certain settings, this effect sounds a lot like the "yayayayayaya" sound in the sonic youth song "diamond sea." Great sounding effect really.