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Can anyone suggest an LFO...?
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Ojd



Joined: Feb 22, 2008
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PostPosted: Tue Feb 08, 2011 12:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Wrong diode polarity? Didn't cut traces on stripboard? Contact between tracks (frequent problem of mine)?
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nicolas3141



Joined: May 25, 2007
Posts: 139
Location: Christchurch, New Zealand

PostPosted: Tue Feb 08, 2011 3:42 am    Post subject: Reply with quote  Mark this post and the followings unread

If both LEDs are lit then either the LEDs are not opposed as they should be, or the circuit is oscillating at a high frequency (instead of a low one).

So first check the LEDs - are you sure one is facing this way and one that way?

Second, look at the op-amp with the 1uF cap in its feedback loop. It is the integrator. Find the - input of that op-amp. It should be getting fed via a network of resistors/diodes/pots from the output of another opamp. Measure the resistance of that network from the output of one op-amp to the - input of the integrator. Resistance should be approx 100K.

Third, check that all the pins that should be at 0V are actually at 0V. The + input of the integrator especially. And the pots that should have one side at 0V. Check all those points with the circuit running to make sure they are all really at 0V exactly.

Hope this helps.

Cheers,
Nicolas
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oozitron



Joined: Apr 02, 2007
Posts: 35
Location: USA

PostPosted: Wed Feb 09, 2011 9:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the replies & ideas... I think the problem was that I had it on the same board as my ADSR (which isn't working either; see that thread!) and that has electro caps on the +/- power. I built the LFO all by itself and it works perfectly Smile

I'm working on a "rack monosynth" and am now going to build three of these LFOs and have them normalled to the FM and PWM of my JH Living VCOs. Massive...

thanks Nicholas!
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synthesist



Joined: Feb 17, 2011
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PostPosted: Mon Sep 05, 2011 12:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

he!
I build the VCLFO and the LFO from nicolas on one board. This circuit rules!!! Cool
It's a nice patch if you plug the saw out of the "normal LFO" at a very slow rate to the CV input of the VCLFO. So the VCLFO output is getting faster and faster then slower and slower and faster adn fsater nda slower adn sowler...
that's exactly what I needed and it works!

The next module will be the ADSR Generator.
Biggest thanks for this one nicolas3141
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der Warst



Joined: Apr 09, 2010
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PostPosted: Tue Jan 22, 2013 4:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey,

I hope it's alright that I'm reviving this thread. Those LFO's just look very useful for what I'm planning to do. Especially since I have quite a few LM324's kicking around.
I just wanted to know if the first one can be adapted to a single 5V supply as easily as to 9V.
Also, for using it to control resistance, would you rather suggest to run its output into a Vactrol or a Transistor?

cheers,
Simon

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acidblue



Joined: Jun 26, 2009
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PostPosted: Mon Feb 11, 2013 8:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

Sorry if this is a obvious question but where would one put a rate indicator led
on the LFO and the VCLFO??
Or are the blue leds used for this?
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bubzy



Joined: Oct 27, 2010
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PostPosted: Tue Feb 12, 2013 4:20 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Sorry if this is a obvious question but where would one put a rate indicator led
on the LFO and the VCLFO??


i would take a buffered output from the square/pulse out, a simple transistor driver would do it fine.

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acidblue



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PostPosted: Thu Feb 14, 2013 12:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

something like this maybe?
http://www.pcbheaven.com/userpages/LED_driving_and_controlling_methods/?topic=worklog&p=1
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bubzy



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PostPosted: Fri Feb 15, 2013 12:50 am    Post subject: Reply with quote  Mark this post and the followings unread

well, check this link out, this is from tim servo, after ANOTHER LFO discussion Smile
http://www.electro-music.com/forum/topic-49449.html

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acidblue



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PostPosted: Fri Feb 15, 2013 4:44 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks..
You are awesome sir.
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Taburn



Joined: Jul 18, 2013
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Location: Edmonton, Alberta

PostPosted: Thu Jul 18, 2013 1:17 pm    Post subject: Purpose of R2? Reply with quote  Mark this post and the followings unread

Hi Tim. I'm reviving this 4 year old thread to ask you a question about your TSQ circuit.

I can't for the life of me figure out why you added that -V connection to the inverting input of the op amp. I've attached an analysis below that may interest people who are obsessive about rigour. I get a kick out of algebra Shocked

What is its purpose? I noticed that you kept R2 in the LFX schematic you posted, even though you revised the circuit in general. Something to do with op amp unidealities?


Circuit Analysis.pdf
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Tim Servo



Joined: Jul 16, 2006
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PostPosted: Thu Jul 18, 2013 1:49 pm    Post subject: Can anyone suggest an LFO...? Reply with quote  Mark this post and the followings unread

Hi Taburn,

Wow, that's a neat analysis. However, the circuit really is fairly simple. It is just a non-inverting buffer, and the ratio of R3 to R1 determines the gain. The circuit is set so that at the maximum setting of R1 (at the 'triangle' setting), the triangle wave comes through at its original amplitude and shape. As R1 is reduced, the negative feedback into the "-" pin is reduced (more of it is shunted to ground) and the gain increases, and as the output amplitude rises it starts to bump up against the output 'rails' which causes the peaks to flatten off. R4, R5 and R6 take what is a +/-12V wave and reduce it to a standard +/-5V. You could probably tweak the value of R5 a bit (reduce it) and actually get rid of R4. The purpose of R2 is simply to introduce a teeny DC bias to make the output centered around 0V. This was a value derived just from simple experimentation, and it's what worked with the op-amp I was using at the time. You may need a slightly different value.

Hope this helps!

Tim (I just plug stuff in and hope it doesn't go KaBlooey!) Servo
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Taburn



Joined: Jul 18, 2013
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PostPosted: Thu Jul 18, 2013 2:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Tim Very Happy
If I had to curse one thing, it would be that we don't live in a perfect world. Input offset voltage sucks.

In other news, I got R1 and R2 mixed up in the analysis I posted Embarassed
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Starspawn



Joined: Jun 14, 2013
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PostPosted: Fri Dec 20, 2013 7:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Nicolas, would adding a LFO amount knob be as simple as for instance a 100K pot at the waveform outputs?
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roglok



Joined: Aug 28, 2010
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PostPosted: Sat Dec 21, 2013 2:40 pm    Post subject: Reply with quote  Mark this post and the followings unread

Starspawn wrote:
Nicolas, would adding a LFO amount knob be as simple as for instance a 100K pot at the waveform outputs?


yep. make sure you wire the pot up as a voltage divider.

Code:


IN ---VVVV--- GND
        |
       OUT

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Starspawn



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PostPosted: Sun Dec 22, 2013 7:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

Bah, I was too ambitous and tried to build 2 into 1 pedal box with just one 9V battery, seems like thats not enough to drive them.
The virtual ground and such does work, but with 2 the voltages are off at the input, 1 of them seems to do all it should as well, blinking slightly on one led in time and giving off a small but correct waveform, but the other hangs, and both get -6.3V and +3.1
However even when disconnecting the other, the working one only gets +/- 5V. Waveforms go between +/- 1V.
I did what was suggested, replaced leds with green, changed resistor to 47K, and used 2 more 10uf electrolytic caps negative leg to negative V input, positive to positive V, and the others to virtual ground.

Now, they are cheap batteries, but Ive run a MFOS mini synth fine off two of them, so they should have more than enough juice really?
The potential of the battery is 9.5ish, so it looks more like it divides unequally or equally, but doesnt give out 9v on both?
Is that how the virtual ground works or something?

If not, what can lower the input voltages in the circuit?
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JingleJoe



Joined: Nov 10, 2011
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PostPosted: Mon Dec 23, 2013 5:35 am    Post subject: Reply with quote  Mark this post and the followings unread

der Warst wrote:
Hey,

I hope it's alright that I'm reviving this thread.


why do people allways think it's bad to revive old threads? Confused this thread is as good as it ever was and it was, as ever, pretty good! Smile

I was going to contribute my LFO circuit but I can't find it now and it's not as good anyway but it has a lower parts count.

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Blue Hell
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PostPosted: Mon Dec 23, 2013 9:11 am    Post subject: Reply with quote  Mark this post and the followings unread

reviving old threads means a sure death sentence by flaming on some forums I saw - soo .. I'd be careful with that too on a forum I don't know ... anyways, indeed perfectly OK to necro post here Wink

And may you find your LFO back JJ Laughing

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JingleJoe



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PostPosted: Mon Dec 23, 2013 3:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

I couldn't find the original schematic but I could pretty much remember everything, so I drew up another one.
There is another LFO of mine somewhere on this forum, but it's a simple 555 timer based thing, uses more parts than this one!

this one is, as it says, optimized for single supply operation.


GDAL LFO.png
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Forgot to add: +V is 12V
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GDAL LFO.png



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jukingeo



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PostPosted: Sat Jan 25, 2014 12:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

While this replay is mainly for Nicolas, others feel free to chime in.

For a long time I was considering a build of the Variable Skew LFO circuit that is on the MFOS website. However, since that circuit no longer has a PCB for it, I am a bit at a loss of how to layout something like that on a strip board.

Low and behold doing a bit of searching it seems that Nicolas has made his own variant of the Variable Skew LFO that uses few parts AND has a strip board diagram.

But further down I noticed that Nicolas also created a VC-LFO variant, and that had me doing one of these The trouble with that LFO is the mentioned issue with the Skew control. I am curious if this issue was straightened out? If not, is there a fix for it by adding a few more parts?

Overall, down the road, I would be looking into a tracking VCO that has similar features to this. I would like the ramp-tri-saw adjustability in addition to 1v/Octave tracking. Further, I would be interested if something like this could also do double duty as an VCO / VC-LFO.

Oh! As of now my planned power supply is a +12 0 -12 running from AC.

Thank You,

Geo

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bubzy



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PostPosted: Mon Jan 27, 2014 12:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Starspawn wrote:
Bah, I was too ambitous and tried to build 2 into 1 pedal box with just one 9V battery, seems like thats not enough to drive them.
The virtual ground and such does work, but with 2 the voltages are off at the input, 1 of them seems to do all it should as well, blinking slightly on one led in time and giving off a small but correct waveform, but the other hangs, and both get -6.3V and +3.1
However even when disconnecting the other, the working one only gets +/- 5V. Waveforms go between +/- 1V.
I did what was suggested, replaced leds with green, changed resistor to 47K, and used 2 more 10uf electrolytic caps negative leg to negative V input, positive to positive V, and the others to virtual ground.

Now, they are cheap batteries, but Ive run a MFOS mini synth fine off two of them, so they should have more than enough juice really?
The potential of the battery is 9.5ish, so it looks more like it divides unequally or equally, but doesnt give out 9v on both?
Is that how the virtual ground works or something?

If not, what can lower the input voltages in the circuit?



you might want to try a buffered virtual ground, its more stable

http://www.schematica.com/active_filter_resources/op_amp_virtual_ground_circuits.html

scroll down to "buffered resistor divider" the "output" on the far right of the schematic should connect to your "VGND"

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