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Ojd
Joined: Feb 22, 2008 Posts: 66 Location: Ua
Audio files: 1
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Posted: Tue Feb 08, 2011 12:06 am Post subject:
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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: 185 Location: Christchurch, New Zealand
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Posted: Tue Feb 08, 2011 3:42 am Post subject:
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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: 38 Location: USA
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Posted: Wed Feb 09, 2011 9:35 pm Post subject:
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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
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 Posts: 79 Location: austria
Audio files: 2
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Posted: Mon Sep 05, 2011 12:46 pm Post subject:
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he!
I build the VCLFO and the LFO from nicolas on one board. This circuit rules!!!
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 Posts: 9 Location: London
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Posted: Tue Jan 22, 2013 4:43 pm Post subject:
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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 _________________ http://www.warstware.der-warst.de |
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acidblue
Joined: Jun 26, 2009 Posts: 226 Location: The Darkside
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Posted: Mon Feb 11, 2013 8:48 pm Post subject:
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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 Posts: 594 Location: United Kingdom
Audio files: 64
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Posted: Tue Feb 12, 2013 4:20 am Post subject:
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Quote: | Sorry if this is a obvious question but where would one put a rate indicator led
on the LFO and the VCLFO??
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i would take a buffered output from the square/pulse out, a simple transistor driver would do it fine. _________________ _Richard_ |
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acidblue
Joined: Jun 26, 2009 Posts: 226 Location: The Darkside
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bubzy
Joined: Oct 27, 2010 Posts: 594 Location: United Kingdom
Audio files: 64
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acidblue
Joined: Jun 26, 2009 Posts: 226 Location: The Darkside
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Posted: Fri Feb 15, 2013 4:44 pm Post subject:
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Thanks..
You are awesome sir. |
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Taburn
Joined: Jul 18, 2013 Posts: 2 Location: Edmonton, Alberta
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Tim Servo
Joined: Jul 16, 2006 Posts: 924 Location: Silicon Valley
Audio files: 11
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Posted: Thu Jul 18, 2013 1:49 pm Post subject:
Can anyone suggest an LFO...? |
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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 Posts: 2 Location: Edmonton, Alberta
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Posted: Thu Jul 18, 2013 2:27 pm Post subject:
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Thanks Tim
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 |
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Starspawn
Joined: Jun 14, 2013 Posts: 85 Location: Oslo
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Posted: Fri Dec 20, 2013 7:04 am Post subject:
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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 Posts: 202 Location: uptown
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Posted: Sat Dec 21, 2013 2:40 pm Post subject:
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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
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OUT
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Starspawn
Joined: Jun 14, 2013 Posts: 85 Location: Oslo
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Posted: Sun Dec 22, 2013 7:19 pm Post subject:
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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 Posts: 878 Location: Lancashire, England
Audio files: 14
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Posted: Mon Dec 23, 2013 5:35 am Post subject:
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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? this thread is as good as it ever was and it was, as ever, pretty good!
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. _________________ As a mad scientist I am ruled by the dictum of science: "I could be wrong about this but lets find out"
Green Dungeon Alchemist Laboratories |
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blue hell
Site Admin
Joined: Apr 03, 2004 Posts: 24075 Location: The Netherlands, Enschede
Audio files: 277
G2 patch files: 320
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Posted: Mon Dec 23, 2013 9:11 am Post subject:
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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
And may you find your LFO back JJ _________________ Jan
also .. could someone please turn down the thermostat a bit.
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JingleJoe
Joined: Nov 10, 2011 Posts: 878 Location: Lancashire, England
Audio files: 14
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jukingeo
Joined: Oct 24, 2007 Posts: 166 Location: The dark side of the moon
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Posted: Sat Jan 25, 2014 12:13 pm Post subject:
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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 _________________ Lover...I won't take a back seat, tonight. Got some dancin' to do. |
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bubzy
Joined: Oct 27, 2010 Posts: 594 Location: United Kingdom
Audio files: 64
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Posted: Mon Jan 27, 2014 12:17 am Post subject:
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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" _________________ _Richard_ |
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kevtrout
Joined: Mar 07, 2016 Posts: 2 Location: Vermont
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Posted: Mon Mar 07, 2016 10:30 am Post subject:
Re: Can anyone suggest an LFO...? Subject description: Servo's 8K Waveshapers |
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I just prototyped this LFO and I'm very happy with it. I played with having two TSQ's with independent wave shaper pots - but the effect ended up being that the second pot also modifies the shape of the first wave adjust pot. I'm playing with making that a feature in my finished module. Hoping I can switch a second adjustment knob in and out.
The add-ons also seem to pollute the signal of the square and tri outs. Again - that adds to the uniqueness of this module. If you want perfect square and tri wave forms then there are plenty of other LFO's to build.
Point is, the circuit is functional and a good addition to my newbie rig.
- Kevin
Tim Servo wrote: | Here's a coupla add-ons for the 8K LFO. The first (TSW) uses the Tri and Square to make a Saw, or even a 2X Saw. The second (TSQ) takes a Tri and puts out a wave that is continuously variable from Tri to Square, with a "Trapezoid" shape in the middle. You can even take the output of the TSQ and put it into the TSW, and now you have a Tri to Square on one output and a Saw to Square on the other (both varied at the same time with the Waveshape control on the TSQ). By the way, a 1458 or other "low bandwidth" op amp works a little better for the TSW because it helps minimize the glitch in the reconstructed Saw output. I've got some more add ons that I'm still working on, but I thought I'd throw these out here because these variable outputs are so much fun.
Tim (also looks like a trapezoid in the middle) Servo |
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sharkattackeddie
Joined: May 24, 2016 Posts: 6 Location: UK
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Posted: Tue Jun 07, 2016 11:47 am Post subject:
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I've built the Nicolas LFO on solderless breadboard. I'm getting 0V where I should be getting -V and I can't figure out why. It's running on 9V battery. Pin 4 reads 7.35V. Virtual Ground is 0V. All the pot lugs seem to be 0V. One LED briefly flashes, once, when I first connect the power, then goes out.
Anyone have any suggestions? |
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madtextureenvy
Joined: Jul 27, 2015 Posts: 4 Location: California
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Posted: Thu Aug 25, 2016 12:36 pm Post subject:
Still dead? |
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I know this thread is likely still long dead.
I just thought I would chime in:
Just built it, Fantastic.
Thank you Nicolas!!!
Also, sort of new here. Hello all.
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acidblue
Joined: Jun 26, 2009 Posts: 226 Location: The Darkside
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Posted: Sat Jan 07, 2017 3:16 pm Post subject:
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Forgive my ignorance but why on magic smokes 8K LFO is there a 4.7k resistor to ground before the Square output, but on the Tri out it's 10K?? |
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