Super Simple LFO?

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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I have been bouncing back and forth with this and I think I’ll use the David Haillant’s LFO and mash it together with @juggle 's clock divider. Somehow. I wonder if I could squeeze it on the board somewhere…

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I’ve heard that operation way below tolerance can shorten lifespan but I have yet to see it happen on any passive component.

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Dead bug the lfo and wire it on if you’re out of space

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Are the two diodes oriented correctly?


But I pulled it all apart for now. I’ll take another stab at it some other time.

I found the electronic site which spoke about it (a french one)


" Condensateur de 63V pour montage alimenté en 9V ?

A de rares exceptions près, vous pouvez utiliser un condensateur dont la tension de service est très supérieure à la tension qu’il se verra réellement appliquée, par exemple tension de service de 40 V dans un montage alimenté en 12 V. La tension de service indiquée par le fabricant est en effet une indication de valeur maximale. A noter toutefois que pour certains condensateurs, il n’est pas conseillé de choisir une marge trop grande (par exemple prendre un condensateur 100 V pour réguler une tension de 5 V), sous peine de les “sous-utiliser” et de les vieillir plus vite. "

Traduction :

63V capacitor for assembly supplied with 9V?

With rare exceptions, you can use a capacitor whose operating voltage is much greater than the voltage that it will actually be applied, for example 40 V operating voltage in an assembly supplied with 12 V. The operating voltage indicated by the manufacturer is indeed an indication of maximum value. Note however that for some capacitors, it is not advisable to choose too large a margin (for example take a 100 V capacitor to regulate a voltage of 5 V), under penalty of “under-using” and aging them. faster.


At the risk of leaving “super simple” territory - is there a simple sync option?


Interesting question!

I found:

Added: Here’s what that links to:


I am having a hard time with this circuit either and I really want to have it!


I tried first the triple LFO stripboard from @Dud since I blindly trust in his stuff, but this time had no luck. If I turn on the power rails, I get 0mA current and no oscillation whatsoever.

Then I rebuilt it on the breadboard and the situation is the same. I also simulated the circuit in CircuitJS but even there, I get no oscillation (however, that software is sometimes buggy).

@Dud what kind of caps have you used?

It’s quite a desperate move but maybe someone has an idea, here is my breadboard (some legs are long I know, but they are not touching). +12V and -12V are stable but I get only some DC values on the outputs.

I am sure that the circuit works since @Dud has three of them demonstrating in a video but I don’t understand it :laughing:

I also noticed that in the stripboard version the LEDs are backwards connected. I thought that the electrolytic caps might be wrong as well so I checked and reversed them. Then I see only a very slow raise or drop on Pin 7 (second output - TRI) which then saturates at the maximum level. If I adjust the shape or rate, the signal starts to move but again, stays after many seconds at some saturation voltage.

Any ideas? Has someone maybe successfully simulated that in CircuitJS or so? I am currently clueless… usually I do not give up that quickly and ask for help but this is now bugging me since yesterday evening :see_no_evil:

Here is my breadboard (notice that I replaced the trimpot with two 27k, so it’s basically in the middle position (the two tiny carbon resistors joining Pin 1 and 7).

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They’re seeing bipolar voltages, so I’d be wary of polarized electrolytics there. In the oscillator mentioned below I use 220 nF for fairly low frequencies, but if you need much lower (22 µF), bipolar electrolytics might be a good idea. Anyway, I would not think reversing these caps would do much, since the voltage isn’t polarized. Or at least, it isn’t if it’s oscillating, which it isn’t… Yeah, if it’s not oscillating, and there’s a large enough DC voltage on them, then polarized electrolytics definitely are at risk!

I’D SUGGEST IMMEDIATELY SWAPPING IN THE BIGGEST FILM OR CERAMIC CAP YOU’VE GOT FOR NOW, TO AVOID A LOUD AND POTENTIALLY DAMAGING INCIDENT. Once it’s working you can go back to the electrolytics, though, again, I’d use bipolar ones.

It’s fairly similar to this one

which has some description of how it works. (And I’ve built that one, it does work — simulated it too, in CircuitLab.)

There the feedback and input resistors on the comparator are 220k and 100k, so the comparator flips when the triangle wave reaches about ±6 V. In the schematic you’ve used there’s instead a pot which would allow changing that amplitude, but if it’s centered then the comparator would not flip until the waveform is at about ±10.4 V, i.e. the maximum output of the TL072, and if it’s slightly beyond centered so the feedback resistance is smaller than the input, it seems to me it would not oscillate at all. If so then half the range of the trim pot is useless. And in your build you’ve used two resistors to sit somewhere close to, maybe just the wrong side of, the centered value. Maybe try something like a 20k for the input and 30k for the feedback instead.

Disclaimer: I haven’t had breakfast yet. My ability to think is suspect. The above paragraph may be dead wrong.


many thanks! I will try later: the trim pot range is probably it, makes sense!

Yea you are right with the polarised caps, I made sure that I will not blow them before I reversed them :sweat_smile:

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Ok thanks, that was it!

This is now with 33k as feedback and 18k as input:

I’ll try to tune it to ±5V. Currently it does not even trigger the LED :stuck_out_tongue_winking_eye:


Thx @analogoutput for these explainations, so not really anything to add.

just i think that the trimpot was very important for ease of adjustment,
but now your on the good way :slight_smile:

with big value the electro polarized cap sometimes struggle to load in a very slow range, for tests maybe tried with smaller values, or better with bipolar

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The final tuning for my setup is 65k as feedback and 30.5k as input:

And here is a demo of the shape pot turned to min and max (saw and reversed saw):

really cool! I was struggling with the dead simple System 100M LFO since its amplitude was correlated to the rate. This LFO is stable as hell!

Thanks @Dud for the strip board, as always and thanks @analogoutput for troubleshooting and explanation!