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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Simple LFO schematic, opinions?
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stolenfat



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PostPosted: Sun Dec 28, 2008 7:37 pm    Post subject: Simple LFO schematic, opinions?
Subject description: pulse, tri & sine out
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I found this schematic in an old book and I copied it down because it looked great while also looking very simple. I posted it in this forum because it runs on 5 volts.

I havent built it yet but i thought i'd toss it towards you guys to get some opinions on it. Is this feasible? To get this kinda of functionality from just some 741s?

Also, theres one input missing from an opamp in the schemy, i dont think thats a mistake i made copying it down, i really think it's left empty, is that bogus?


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Rykhaard



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PostPosted: Sun Dec 28, 2008 9:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Shocked The Negative input for the pulse waveform's output, show be going to Ground. Smile

The circuit works wonderfully and IIRC is the same circuit that I used for my 2 very first modules in my modular synth, in July 2005. Smile I'd gone from the version of it that was published in Barry Klein's book.

( Laughing Edit #3 ) I'd originally run the 1st test module off of 2 x 9V batteries, hooked together to provide me with positive and negative 9 volt supplies, on bread board.

When I made the PCB for the pair of them, they ran perfectly fine unmodified, from my +/- 15VDC Power One power supply. (I'd used an LF347 for each of the LFOs.)
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stolenfat



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PostPosted: Sun Dec 28, 2008 9:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

wait +-15 volts?

darrgg i could have sworn it ran off 5 volts!
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slacker



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PostPosted: Mon Dec 29, 2008 5:33 am    Post subject: Reply with quote  Mark this post and the followings unread

That circuit will work fine on a single supply.
You just need to make a 1/2 supply "virtual ground" using a voltage divider like shown in figure 4 on this page http://www.geocities.com/thetonegod/opamp/opamp.html.
Then connect the opamp supply pins to V+, and ground (zero volts) and connect all the ground points in the schematic to 1/2V+.
You'll probably need a rail to rail opamp or one that's designed to run off low voltages to run it off 5 volts though, I don't think it will work with a 741.
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badstatic



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PostPosted: Wed Jan 21, 2009 12:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

couldn't get this one to work for me...

I was using an lm324 and an electrolytic cap, is it possible that I need another IC or non polarized cap?

It's a shame, 'cus this LFO would be ideal for my VL-1..
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Adam-V



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PostPosted: Wed Jan 21, 2009 2:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

The LM324 should be OK, but I'm sure you will need a non-polarised capacitor in order to get it to oscillate.

Cheers,
Adam-V

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JovianPyx



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PostPosted: Tue Jan 27, 2009 9:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

http://home1.gte.net/res0658s/fatman/4069_lfo.html

This is a "triangle" LFO. As you can see, it's very simple and uses only one IC. The triangle output is available at the pot wiper on the right. There is also a square output at pin 4 of the IC. I put triangle in quotes because it has kind of bent ramps. It works from a single or dual supply, but for a dual supply, you really should not go larger than +/- 7.5 volts.

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Gonecat



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PostPosted: Sat Aug 22, 2009 4:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hello Gents,

I tried breadboarding this circuit at the top but am not getting it to work. It looks awesome, so i'm not giving up yet!

I have all the exact parts including 3 LM741s.

My first question is this:

How do i power this thang?

Right now i have V+ going to pin 7 on all 3 ICs, and V- going to pin 4 on all 3 chips. (I have two 9volts wired up as a 'dual' supply, and nothing is going to 0v). There's no connection from ground to power, though i did try a few combinations out of frustration!

I also gave it a shot as a single supply with one 9v - got nuthin.
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JovianPyx



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PostPosted: Sat Aug 22, 2009 5:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

The schematic for that has been tailored for the FatMan power supply system.

The FatMan has +8 and -12 volts.

I know, it's weird.

So it should probably work with +9 and -9. However, all signal grounds must go to the 0 volt connection between the two batteries. Anything in the schematic that shows going to the ground symbol or GND etc, should also go to the 0 volt point of the power supply.

The FatMan regulators are 1 ampere each and it doesn't take much to overtax them. Keep that in mind, your batteries may not last very long. An unfortunate thing about CMOS circuits running in linear mode is their power consumption. I like the way they sound, so I put up with that and expect to use more 3 terminal regulators.

EDIT ADD: I don't show power connections to ICs, but power is mentioned in text appearing in the schematic graphic. Usually, I give pin numbers and the voltage it requires in the context of intended use.

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Gonecat



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PostPosted: Sat Aug 22, 2009 5:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, thank you for that.

question is, where would V+ go if not just to the LM741 V+ pins?

i see in most circuits with the 741 that power is coming off of a cap'd line or other and usually not just direct to the chip.

i'll connect the grounds up to 0V (i did try this already, got some buzzing, will try again)
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JovianPyx



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PostPosted: Sat Aug 22, 2009 5:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry, my bad. This LFO can't run from +9/-9 because that would be more than 15 volts. You can run it from one 9 volt battery, say the plus side. However, it will then give you only positive voltages. In that case, Vss (pin 7) should connect to ground or zero volts and Vdd (pin 14) should connect to the positive supply (+9). Output comes from the output pot tap and the 0 volt side of the suppy (also known as ground).

EDIT ADD: If I were doing this - I'd use +6 / -6. It's easy to find powerful batteries and you could run circuits like this LFO in dual supply mode so that you can get a true AC voltage from it. It's also easy to make a +6 / -6 plug-in supply. Sure, it's nonstandard, but so is Lunetta. Rolling Eyes

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Gonecat



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PostPosted: Mon Aug 24, 2009 4:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

hey Scott,

were you ref'ing to the LFO schematic that you posted or the one at the top of the post?

if i can get the one on the top rolling, i'd be thrilled since it has these 3 different waveforms. (that's the one i was asking about). I really need a sine wave.

***i am going to be building yours, too for the 4069 VCO i built!

Smile
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JovianPyx



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PostPosted: Mon Aug 24, 2009 4:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hmm. "the one on top"... ??? URL?? I have no idea to what you are referring.

Cool Cool

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Gonecat



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PostPosted: Mon Aug 24, 2009 4:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

My bad - i meant the 741 LFO at the top of this post:

http://electro-music.com/forum/phpbb-files/741lfo_169.jpg
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JovianPyx



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PostPosted: Mon Aug 24, 2009 4:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, I hope I am now answering the question you really want an answer to:

The power V+ and V- do indeed connect to the 741 IC (get a datasheet to see which pins are for which).

The 0 volt connection between the + and - supplies, whether they be batteries or wallwart regulators, that connection goes to everything shown in the schematic with a ground symbol AND the input and output connection grounds.

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Gonecat



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PostPosted: Mon Aug 24, 2009 4:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

you rock, i'll give it another shot...
thanks Scott
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ErichBreakfast



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PostPosted: Mon Aug 24, 2009 5:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

I built two of these for my modular using Tl084's instead of 741's. I also built one without the shaping for triangle and sine to use as a clock for my Baby 10 (I used a TL082 for that one) and it's a really a wonderful little LFO. I'm considering adding a larger capacitor to one of my standalone LFO's, when using the .1uF as the schematic shows it doesn't always slow down quite as low as I'd like it to. I run it off of the +/- 15 volt supply that's in my rack.
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aerogramma



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PostPosted: Tue Aug 25, 2009 4:43 am    Post subject: Reply with quote  Mark this post and the followings unread

ScottG wrote:
http://home1.gte.net/res0658s/fatman/4069_lfo.html

This is a "triangle" LFO. As you can see, it's very simple and uses only one IC. The triangle output is available at the pot wiper on the right.


Hey Scott with 'pot on the right' you mean the 100k, the one that is also connected to ground?

it's a very interesting LFO, will definetely try it out, thanks!

aero
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JovianPyx



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PostPosted: Tue Aug 25, 2009 7:10 am    Post subject: Reply with quote  Mark this post and the followings unread

That is correct.
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acidblue



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PostPosted: Fri Sep 11, 2009 3:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

ScottG wrote:
http://home1.gte.net/res0658s/fatman/4069_lfo.html

This is a "triangle" LFO. As you can see, it's very simple and uses only one IC. The triangle output is available at the pot wiper on the right. There is also a square output at pin 4 of the IC. I put triangle in quotes because it has kind of bent ramps. It works from a single or dual supply, but for a dual supply, you really should not go larger than +/- 7.5 volts.


Could you use a 741 chip on that schematic?
I don't see where V+ would go, Would it simply go to the V+ pin
I plan on using a single power supply.
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JovianPyx



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PostPosted: Fri Sep 11, 2009 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

This is a very common configuration for a triangle waveshape oscillator.

It is an integrator driven by a switch with hysterisis.

You could probably do this with a 741 (or 2, you would need 3 OpAmps total), but I think there would be more components. I've not done this with an opamp.

You should be able to find schematics for opamp based triange oscillators.

I designed this because I had a fetish for making a synth out of mostly 4069UB and 4007 ICs. I was able to make a lot ciruits using those ICs, but things that accurately control current based on an input voltage (like a current sink or current source) are more difficult. I like these because the waveforms are _not_ accurate. Close, but no cigar.

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acidblue



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PostPosted: Fri Sep 11, 2009 11:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok I abandoned the 741 LFO and decided to try 4069 one since it seems easier.
How ever I don't have a 1.33uF cap but i do have a 1uF one.
BTW in the schematic it looks like a polarized cap, is this right?
Any Way I tried breadboarding it with the 1uf cap, i tried both polar and non-polar
but I can't seem to get it to work .

I'm using a single 9v battery, I got pin 7 to GRND and pin 14 to +.
I'm pretty sure I got something wired wrong.
Here's a couple of pics of my breadboard.
The 2 pots were kinda in the way so I took pics with and with out them.


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JovianPyx



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PostPosted: Sat Sep 12, 2009 8:39 am    Post subject: Reply with quote  Mark this post and the followings unread

The cap can be polar or nonpolar. 1.33 uF would give a lower frequency range. It should still work with the 1uF cap.

A 9volt battery should work.

All I can say is to really go over the wiring well, it's a simple circuit, nothing tricky at all.

Your output should come from the wiper of the rightmost pot and ground (or the negative side of the 9v battery).

What are you using to test it - to determine if it's working? If the frequency pot is set to high resistance, the output will change slowly, so you may want to turn it to a lower resistance.

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acidblue



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PostPosted: Sat Sep 12, 2009 6:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks scottG.
It ended up being my amp, one cap was loose on the breadboard.
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stolenfat



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PostPosted: Wed Oct 07, 2009 11:51 am    Post subject: Reply with quote  Mark this post and the followings unread

I just got this email regarding this circuit:

I read there were some troubles with the circuit above, which makes sense- there always is, but this chap seemed to get it to work fine.

His email:

Hello,

I just found your post to the electro-music forum about a 5V 741 lfo (http://electro-music.com/forum/viewtopic.php?highlight=battery&t=31166). I built it in a simulator and it works beautifully! I put the simulation online at ollieglass.com/circuits if you'd like to see it. Hope you're okay with me posting it on my site.

Best wishes,

Ollie



-------

Nice Site Too!

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