Question about this 'clickless' LFO schematic I found

Started by BluffChill, September 16, 2018, 12:17:21 PM

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BluffChill

I recently came across this schematic for a 'clickless' LFO which uses an extra resistor and capacitor to decrease the time it takes for the pulse to rise, so you don't get a spike at the start of every ON. Under the scope I saw very little difference between the 'vanilla' version and the version with the extra components, and when I hooked it up to part of a bigger audio circuit (not even connected to any signal path) I heard a definite clicking. Without the r/c, it's a faint tick, and with the r/c it was a deep thuddy tapping, and if anything was more noticeable. Does anyone know what I might be doing wrong? I'm running it off a basic 9v battery with a voltage divider to provide VRef.



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Danich_ivanov

#1
You could try capacitor from out to ground, 470nf or so. Are you using square or triange output? Square output will definitely be more clicky.

I read it one more time, and as far as i understand clicks happen without lfo hooked up, meaning around the power supply?

Sorrey, i had a few pints already  :D

merlinb

Quote from: BluffChill on September 16, 2018, 12:17:21 PM
I saw very little difference between the 'vanilla' version and the version with the extra components
Also you:
QuoteWithout the r/c, it's a faint tick, and with the r/c it was a deep thuddy tapping,
Sounds like it's working fine.

Mark Hammer

Boscorelli notes that the "clickless" circuit is one implemented by Boss, so I assume that, since we don't hear endless complaints "ticking" Boss modulation pedals and how to fix them, that the circuit works.  What may vary from circuit to circuit is not the form of the tick-reduction circuit, but rather the specific value of biasing resistor needed for the specific op-amp LFO circuit, and perhaps the value of the added cap.  Keep in mind that the tick is audible because of the sudden large current draw from that initial square wave.

Note as well, that the circuit, as implemented by Boss, also assumes use of a lower-current dual op-amp, like an LM358 or TL022.  Decoupling the LFO chip from the rest of the circuit, by use of a small-value resistor going to the V+ chip (10-100R), in tandem with a medium-value (e.g., 10uf) cap to ground, also means that whatever current the LFO needs to generate that initial trapezoidal wave will come mostly from that added cap on the power line, that serves as a micro-battery.