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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Schmitt VCO w/Up-Down sweep
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richardc64



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PostPosted: Sun Aug 31, 2008 8:14 am    Post subject: Schmitt VCO w/Up-Down sweep Reply with quote  Mark this post and the followings unread

The circuit I suggested and posted here http://electro-music.com/forum/post-203237.html#203237 gave me some trouble. Not only was upward sweep much greater than downward, but no matter how I tinkered with the values, with the Sweep potentiometer centered (zero sweep, equal amounts of "up" and "down",) I couldn't get the frequency to stay the same with maximum CV and zero CV.

To deal with down sweep depth being not as great as up, I thought instead of having the bottom transistor affect a single capacitor, why not have it add a varying amount of a second cap? It turned out that the second, "down" cap had to be about 4 times the "up" cap. This sort of worked, but "down" still didn't go as low as I wanted. I eliminated the lower transistor and instead used a diode. Surprisingly, this worked much better than the transistor. How it works is, as the voltage rises and the diode conducts more heavily, its "dynamic impedance" decreases, connecting "more" capacitance to ground. (Or something like that. Think of it as similar to the variable resistor of a cheesey 1960s phonograph's "Tone" control.)

All that remained was to get the centered position of SWEEP to give the same frequency with or without a CV applied. A resistor to ground at the "up" end of the pot, forming a voltage divider, took care of that. (A trimpot here to get zero sweep precisely in the center of the pot's rotation might be a good idea.) Values shown are for a 9V supply. It's highly probable that values will need adjusting for a lower or higher supply voltage.

If the modulating signal is an LFO's triangle or square wave, there isn't much difference between up sweep and down. But if the modulation is a ramp (sawtooth) or, better yet, an envelope, then adding the extra few components becomes worthwhile.


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synthmonger



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PostPosted: Tue Sep 02, 2008 10:03 am    Post subject: Reply with quote  Mark this post and the followings unread

My 40106 vco has expo control (could be modded for linear) and produces a ramp and super narrow pulse waveform.

I thought the lunetta didn't use transistors though?


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richardc64



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PostPosted: Tue Sep 02, 2008 10:26 am    Post subject: Reply with quote  Mark this post and the followings unread

synthmonger wrote:
My 40106 vco has expo control (could be modded for linear) and produces a ramp and super narrow pulse waveform.


Care to provide more details?

Quote:
I thought the lunetta didn't use transistors though?


Perhaps it's time Mosc restated the Way of Lunetta Razz

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synthmonger



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PostPosted: Tue Sep 02, 2008 3:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

Pin 1 = ramp pin 2 = super narrow pulse, similar to the bugcrusher vco.

I used a ghetto NPN/PNP expo arrangement and it worked well. I didn't test tracking or anything, but the range is huge. Obviously some sort of buffers will be needed.

You can get a linear response and other goodies by using any typical cv source found on cgs, mfos, google, etc.

I added a sloppy sync using a transistor as a switch between pins 1 and two but it cuts out at times and is just too sloppy. I need to fix that.

My lunetta type vco is a bit whacky. I really wanted a phat square wave and was only able to get it by using a frequency divider. I ran the narrow pulse into a 4024 and it's first two sub octaves each through a pair of 40106 gates to get the old fashion PWM trick. To get use out of the other 5 sub-octaves I mixed them together seperately and XOR'd them with a 4030 for staircasing and neat harmonic effects.
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loss1234



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PostPosted: Tue Sep 02, 2008 8:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

richard 64


there was a BIG thread on using inverters with expo converters...based off of ideas inspired by bissells article in EDN. i dont know the thread off hand but i will get back to you.

i was doing it a little differently than synthmonger but we both got interesting results.

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loss1234



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PostPosted: Tue Sep 02, 2008 8:12 pm    Post subject: 3 phase inverters...to expo 40106 Reply with quote  Mark this post and the followings unread

HERE IT IS

make sure to check out all the cool ideas presented in the article AND in the thread....

http://electro-music.com/forum/topic-27712.html&highlight=

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synthmonger



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PostPosted: Wed Sep 03, 2008 11:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

p.s. your up/down sweep vco also has a triangle output

http://www.elecfree.com/circuit/Oscillator-Generator/triangle-and-squarewave-generator-by-ic-40106/
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richardc64



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PostPosted: Thu Sep 04, 2008 4:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks, loss. I wasn't too interested in expo-control for my purposes, but that circuit certainly looks simple enough to try. But it's bipolar. Can it be made single-supply?

As for having up/down sweep, I wanted to keep an already simple circuit simple, and not resort to an op amp attenuverter, which I didn't know how to do in single-supply anyway -- until recently.

Yes 'monger, I knew there's a triangle at the gate input, but I thought it had to be buffered by a high-impedance op amp. I assumed a garden-variety transistor wouldn't be good enough. I'll have to try that, too.

Thanks.

(This is all straying far from Lunetta principles, I think.)

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loss1234



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PostPosted: Mon Sep 08, 2008 5:25 am    Post subject: Reply with quote  Mark this post and the followings unread

i dont think its straying too much...because in the end many of us are adding these creations or mods to our lunetta systems.

i think as long as its inspiring us to think about new ways of approaching Logic chips and weird noises, all the better.

you ever noticed how many amazing ideas have come up on the lunetta forum?

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mike page



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PostPosted: Wed Aug 01, 2018 5:35 am    Post subject: Reply with quote  Mark this post and the followings unread

A little modification I need to test but I think it should work
Posted Image, might have been reduced in size. Click Image to view fullscreen.

looking at it now tho, the CV in bit looks a bit weird
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Richarius



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PostPosted: Sat Aug 18, 2018 4:37 am    Post subject: Reply with quote  Mark this post and the followings unread

mike page wrote:
A little modification I need to test but I think it should work
Posted Image, might have been reduced in size. Click Image to view fullscreen.

looking at it now tho, the CV in bit looks a bit weird


Just read this one, now.

The CV input, has 2 separate inputs. 1 is from external to the VCO. The other, is a voltage divider between + voltage and Ground. It's the VCO's 'Frequency' / 'Pitch' control. Smile

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PostPosted: Sun Aug 19, 2018 5:10 am    Post subject: Reply with quote  Mark this post and the followings unread

[quote="Richarius"]
mike page wrote:


The CV input, has 2 separate inputs. 1 is from external to the VCO. The other, is a voltage divider between + voltage and Ground. It's the VCO's 'Frequency' / 'Pitch' control. Smile


yeah its my drawing ha ha Very Happy
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richardc64



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PostPosted: Sun Sep 16, 2018 11:25 am    Post subject: Reply with quote  Mark this post and the followings unread

(Late to the party... again)

The resistors' values were painstakenly selected so that with the Sweep pot centered a CV will not send the freq up nor down. Move the voltage divider pot out to the 100k and the changes might work.

YMMV

[quote="mike page"]
Richarius wrote:
mike page wrote:


The CV input, has 2 separate inputs. 1 is from external to the VCO. The other, is a voltage divider between + voltage and Ground. It's the VCO's 'Frequency' / 'Pitch' control. Smile


yeah its my drawing ha ha Very Happy



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PostPosted: Mon Sep 17, 2018 4:08 am    Post subject: Reply with quote  Mark this post and the followings unread

synthmonger wrote:
My 40106 vco has expo control (could be modded for linear) and produces a ramp and super narrow pulse waveform.

I thought the lunetta didn't use transistors though?


In my view, Lunetta can be whatever you want it to be using whatever parts you have or like. The most important part of the Lunetta paradigm, in my opinion, is FUN. If you're getting that, you're doing it right.

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PostPosted: Wed Oct 24, 2018 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
In my view, Lunetta can be whatever you want it to be using whatever parts you have or like. The most important part of the Lunetta paradigm, in my opinion, is FUN. If you're getting that, you're doing it right.


+1

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