Super Simple LFO?

Recently I’ve made my first soldering ever and it was ofcourse Super Simple Oscillator but I’ve built 3 of them and I’ve put them in a box in witch all the components were sent to me:

For my next project I want to build something very simillar to @Dud Pink Drone Box.
On/off switch, main pitch pot, 4 oscillators with separate volume controll, mixed signal will go to RC filter and from there to audio out.

I want to be able to control RC filter with pot, and also I would like to switch on/off some kind of lfo to control filter for me (just like @lookmumnocomputer in his vdeo about RC filter). So I need to build some kind of LFO and I just need it to have pot to control blinking LED.

Since we are all locked down maybe you can give me some ideas how can I make one? I have a lot of capacitors, resistors, some transistors and few 555 and 556 timers (but I’m will be feeding 19V into this machine and that’s a little to much for 555 :confused: ).


I dont have an LFO right now. I am making due with my 3340 OSC tuned waaaay low. Since it can reach the low frequencies needed, it can function as an LFO is i desire.

Im not sure, but i think the super simple osc cannot get that low frequency because of the nature of the reverse avalanche deal may have som hard limits that stop oscillation. I actually dont have a super simple osc to test :(.

Perhaps the 555 could produce a low enough frequency, but you would be limited to a pulse wave shape unless you did some fancy filtering. WORTH EXPERIMENTING!

The old MiniMoog didnt even have a dedicated LFO, you just used it’s 3rd OSC as one.


You can use a voltage regulator to get a lower voltage to feed your 555.

To be honest I’ve tried super simple oscillator with diffrent capacitors and the one with 100uF or 220uF value (I can’t remember now) could get that LED blinking pretty close to my desire but that was not it.

Maybe if I mess with big capacitors and with this littlle pot fix: I could get there. But it’s just big maybe :slight_smile: I’ll try it tomorrow.

It will be my second device so I think I don’t need diffrent wave shapes in lfo for now and I’ve found out that I can reduce voltage for 555 with resistors but I don’t exacly know if I will be able te get it right. Will see.

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I don’t have components for now but I’ll try with resistors.

maybe for LFO you can use a vactrol on the level or pitch of your osc with jack to control it with an external CV
like i do for add a little keyboard to control the generel pitch to have some differents chords

and for a simple LFO

or this one with shape and depth :

more for modular synth :

this one :

and a best one :

(there is an automatic translator at the top right on my site, but the diagrams speak for themselves :slight_smile: )


If the issue is getting a low enough frequency without using huge capacitors, perhaps a frequency divider would do that.

Another possibility to consider is using a microcontroller such as Arduino. You may even be able to get different wave forms by generating PWM and using that to drive a low pass filter.

@Dud thanks!
I have one question for you. Do you need some specific kind of pots to control volume? On your mixer schematics I’ve noticed A500k pots and I have B500k pots. Will they work fine?

yes it’s better for audio to have Log, but I think in this old construction I did not have one and I put Lin (the sound goes up more suddenly )
it was my beginnings in electronic hack
also an active mixer would work even better, but it works

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I have cheap Behringer mixer maybe i will disassemble it and put into my box - it has exactly 4 in channels

Or maybe this pot fix will work for now.

I will have to use this fix on pitch pots in super simple oscillator coz they have a lot of “silent parts” at the bttom.

If you have silent parts, tweaking the potentiometer curve won’t help you since you can still reach the same 0 and max values at the end positions. You need to add some resistance in series with the pot to prevent it from hitting zero (or you can add mechanical limits, but that’s trickier :slight_smile:).

(Also, the wiper to ground trick you linked to results in huge variations in impedance for the driving circuit since you’ve connected a small resistor in parallel with a portion of a big one, so there’s plenty of cases where it doesn’t work well, and about one case where it kind of works – between a low impedance output and a high impedance input.)

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I’ve been attempting to breadboard this one

By following the steps here. I swapped out the BC550c for a 2n3904 (which you have to rotate 180) without success. I dont suppose anyone can spot any obvious errors?


I made one (a double infact) in my second case and it’s a good LFO (test with different cap value), i think to make a triple version of it in the near future.

To see some error it’s difficulte but with the stripboard you can check it easily, just in your pic the 2 power cap seem very big, it’s really 10uf ?

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Yes, those are 10uf.

Making two of these while using a single TL074 was my hope! I still wonder if it is a transistor issue.

I built this one using the same power set up lower down on the breadboard and it seems to work perfectly. I would just have to have another entire TL074 to build a second one which seems crazy if I can get the first one to work.

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400-500 V? (or more – biggest 10uF kemet electrolytic I found on digikey is 12 mm, and those look bigger…)

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is it not a too big voltage for a 12V utilisation ? i know that not good to use a too big difference, which under exploits the capacitor and can damages it more quickly, but i don’t know where is the limit .

The transistor just drives the LED, leave it out and check if you have some output signals…


Perhaps overkill, but its the only 10u I have right now!

And as I understand it, the voltage value really does not matter.


I also have never heard that going overkill on the tolerance would be bad. Is that actually a thing?

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