Circuit Snippet's PWM Question

[bobbletrox]

Long time no see!  I've been looking at the PWM circuit from Circuit Snippets because it looks like a simple, cheap build and it sounds unique in the sample mp3.   But I've got some questions about it...

Q1: Does the "pulse width" pot control the sweep rate, or is it more like a "manual" control to set a static position in the sweep?  I'm guessing it's the latter because you'd expect the optional LFO to provide the sweep rate.

Q2: Part substitutions...
40106 Schmitt Trigger: 74C14 Schmitt Trigger?
386D: LM386N-1?

Q3: What else could be used for external CV?  There might be some cool sounds to be made!  Something that provides a random control voltage would turn it into a weird random filter type effect.  I could just ditch the LFO and have a CV jack instead to make it a modular guitar pedal -and make dedicated modules for control voltage later down the track.

So...has anyone built the PWM before?  Thanks for any help.

[Tim Escobedo]

You're correct. The "pulse width" is more like a "manual" control to set a static position in the sweep.

I think the 74C14 is only spec'd to 5V supply voltage. I'm not sure if a LM386N-1 will work OK at 5V (it may). As a result, I specify the 40106, which will work to 15V or 18V.

I'm sure a external CV could be rigged up. It may be a bit fiddly, though, and scaling may be needed.

[Peter Snowberg]

As far as I know, the 74C series parts are all clear up to +15V supplies. I know the Fairchild 74C14 is +15 rated (just looked up the datasheet).

The LM386N-1 will work fine at +5, but it's getting pretty close to the limit. Once you get below 4V for Vcc it will start to sound really ugly and not a pretty kind of ugly if you ask me. I'm sure it's pretty to somebody.

take care,
-Peter

[bobbletrox]

Yeah, both the 74C14 and LM386N-1 look good up to 15v from what their datasheets say.

*MASSIVE EDIT* I didn't realise half of my questions have been answered before (hello search function)...

One thing I'm still in the air about:  could I use a 1/4" jack connected to pin 3 as an external LFO in?  At least then I could build a stand-alone EZ LFO or give something like RG's Pseudorandom LFO a go...

[bobbletrox]

Hey...I wonder if the EZ LFO could be turned into a random LFO by wiring up more inverters?  If there were 4 inverters with mix and rate pots instead of just one, you could fine tune the effect each LFO has on the final randomness of the waveform (like the pseudorandom lfo).  I'm guessing lowering the value of the 100uF cap in the EZ LFO would make the waveform more angular from what I'm getting outta RG's article.

Have I gone completely insane...or would that actually work?