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.

[ElectricDruid]

This sounds like a job for the StompLFO!!

https://electricdruid.net/datasheets/STOMPLFODatasheet.pdf

This chip produces two random waveforms. One is the classic "Sample+Hold" random levels waveform, and the other is the same thing but instead of holding the level it glides from one to the next, producing a "Random Slopes" waveform. It's like a triangle waveform, but random.  You could use either of these on its own or to control some other element to inject some randomness. Here's the full set of waves:



Since the parameters on the StompLFO are controlled by 0-5V voltages and the output is also a 0-5V signal, you can do really crazy stuff with two of them, since you can feed a random signal from one to one of the inputs of the other and have a random frequency waveform (any of the above waveforms) or a random depth waveform amongst other possibilities.

Using the 555 is not a great idea in a tremolo because it's notorious for dumping big switching spikes onto the power supply wires, which nearly always finishes up as clicking or ticking in the output. The CMOS version 7555 is much better but not totally immune.

[iainpunk]

haha, the 555 is kind of a b1tch to work with in general, not just for LFO purposes.

for the sample/hold, you can just pluck something basic from the web, your putting noise into the circuit anyway. and to drive an LFO, you can use a transistor in some circumstances to act as a variable resistor in an oscillator, making it a bit janky, but its a random rate, so it doesn't need to be volt/octave or nearly as precise as those circuits.

cheers