Momentary, random tempo tremolo

[crab.teeth]

Okay bear with me, this will be my first circuit design so I wanted to keep it fairly straightforward but interesting. Drawing inspiration from the MASF- Raptio a glitch, stutter/ hold that is absolutely insane, really amazing pedal from Japan. Anyway I figured a tremolo with a momentary switch that sets a random rate for the trem every time you step on it. The best way I can think to do that would be to have a lfo modulated 555 clock setting the rate for a tremolo. Seems pretty straightforward enough, I hope haha, it very well might not be so easy, so I would very much appreciate any suggestions or info/ help anyone can offer (-:

[iainpunk]

do you want it to be a consistent rate, but a randomly selected frequency, or do you want a random time interval high and low movement?

randomness is kinda hard to replicate. you can sample/hold a noise source to get a random DC voltage to feed into a voltage controlled oscillator. this gives that random frequency effect.

on the other side, you can filter noise, to a really low frequency bandwidth, to get low frequency random wobbling. if you throw that through a schmidt trigger you can get random squarewaves. this latter technique is something i actually use on a pedal im building, that simulates random popcorn noise. theres a thread out there if youre interested in my whacky project, haha

there are numerous other ways to get these results tho.

cheers

[bartimaeus]

it seems you want the tremolo to hold its current rate, changing only when the footswitch is tapped. in that case, you want the footswitch to control a sample and hold circuit, as iainpunk suggests. the only problem is you need the tremolo rate to be voltage-controlled. but a lot of tremolo pedals use a resistance to control the tremolo rate.

that said, this is very easy to do digitally, including with a spin chip. you could grab one of the pedalpcb boards, then edit the code for a tremolo: https://www.pedalpcb.com/product-category/fv-1/

if you want to stay analog, you can buy sample and hold chips. LF398N should be suitable.

[PRR]

> you can buy sample and hold chips. LF398N should be suitable.

Yes, but low/no stock in the global crisis.

You can roll your own S/H; nobody I knew actually used the LF398. For the very low accuracy implied by random source, a "good" S/N is perhaps a waste of time, though low droop is good.