Best way to add LFO or Envelope to Gargletron?

[Top Top]

I haven't seen many mentions of people modding this circuit for envelope or LFO control of the "gargle," but it seems to be one of the best ways to use this effect.

I built one a while ago and added an LFO which interfaces to the gargletron via a LED/LDR combo - the LFO is made from 1/6 of a 40106, the same LFO used as the optional LFO in the PWM circuit.

The way I have mine integrated into the gargletron is via the two legs of the LDR jumpered to pins 1 & 3 on the "gargle" pot. It sounds cool, but I can't help but think I could be getting a little more out of it. It sort of sounds like the LFO is varying the frequency of only one of the filters, while the other sits static.

If I understand the gargle pot, the pot should be controlling the frequency of both filters inversely at the same time, right? That is what it sounds like to me when I just turn the gargle pot with no LFO effect.

Would there be a better way to integrate the LDR into this circuit?

[space_ryerson]

At first glance, it looks like jumpering a LDR to pins 1 and 3 of the gargle pot won't do what you want it to. On the standard circuit, it looks pins 1 and 3 are always separated by 10k, and that doesn't vary. What varies is how much signal is being sent to the ground before making it to the two filters. I think what you need is to modulate the resistance between pins 1 and the ground of the gargle pot; while simultaneously, but inverted, modulate the resistance between pin 3 and the ground. I don't know LFO's well enough to do that, but I suspect looking at LFO's in stereo panners or stereo tremolos maybe provide some clues.

[~arph]

You need two LDR's, both jumpered with 10k,  so max res is 10k. You can feed the LFO to a NPN and a PNP that both drive a LED, this way when one LED will lights up, the other will dim.

I now see that the Easy LFO you refer to allready has a NPN 2N3904 in there, so I'd suggest putting a 2N3906 parallel with it.

[Top Top]

Very good info. The two LDR thing is what I suspected it needed. I didn't know you could use a PNP that way to simultaneously drive a second inverted phase LED.

Thanks!

[~arph]

That's the difference between them, the NPN needs a positive voltage to start conducting. The PNP needs a positive voltage to stop conducting.

[~arph]

I  believe the tone god has a circuit for this actually.

http://www.thetonegod.com/tech/rockncontrol/rock.html

The 3-pole is precisely what you need.