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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
A VCA of sorts
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richardc64



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PostPosted: Wed Feb 13, 2008 12:02 pm    Post subject: A VCA of sorts
Subject description: and simple EGs
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At some point you'll want to hear the results of interconnecting all these digital circuits, and you'll probably want some dynamic control of the amplitude. The first circuit provides amplitutude control of digital waveforms without resorting to OpAmps, OTAs, or (ugh) cmos in linear mode.

Basically, as CV rises, the rectangular wave from the digital output to be heard "stands up" at the junction of the two diodes and passes through the 100K resistor and the coupling capacitor. This method was used in paia's Stringz-n-Thingz and a similiar technique was used in their Cosmic EGG.

Two simple EGs are shown, which don't really need much explanation. Select pot and cap values for the desired durations. The Gate Inputs should probably be buffered by an AND gate with both inputs tied together. If the output is to be routed many places, it can be buffered by a single-supply OpAmp such as the LM324.


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widdly



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PostPosted: Wed Feb 13, 2008 6:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Rather than an opamp buffer, would it be possible to use a 4050 cmos buffer?

I think this could be implemented in a general sort of a fashion so it could be used whenever you want to route one thing to a lot a places.
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Tim Servo



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PostPosted: Wed Feb 13, 2008 9:19 pm    Post subject: A VCA of sorts Reply with quote  Mark this post and the followings unread

I've thought of a slightly different approach to a "Logic VCA" (LVCA ©)...
Wink

You apply the digital signal to the control pin of an analog switch, and apply the CV to the INPUT of the switch. Now, at the output of the switch you're getting whatever level the CV is at, but turned on an off by the digital signal. The effect is that you get a signal with the frequency of the digital signal, but the level of the CV. The nice thing here is that you can use a bipolar CV and get a bipolar output signal (just don't apply a bipolar signal to other logic; use a diode to chop the negative portion off). I've designed something like this into my version of Ian Fritz's double pulser, but I haven't breadboarded it yet. Might also be fun with a multiplier and/or divider ciruit to get CV control of output aplitudes (and polarity). Like I say, I haven't tried this yet, but I'm pretty sure it would work.

Tim (might be fun) Servo
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richardc64



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PostPosted: Thu Feb 14, 2008 6:26 am    Post subject: Re: A VCA of sorts Reply with quote  Mark this post and the followings unread

Pretty cool.

Tim Servo wrote:
I've thought of a slightly different approach to a "Logic VCA" (LVCA ©)...
Wink

You apply the digital signal to the control pin of an analog switch, and apply the CV to the INPUT of the switch. Now, at the output of the switch you're getting whatever level the CV is at, but turned on an off by the digital signal. Tim (might be fun) Servo


That's essentially what the 2-diode version does: "chops" the CV at the digital (audio) rate. I hesitate to use the word "elegant" but your way is more efficient, in number of parts and number of holes. And you get four of them from one IC.

I'm not sure about the bipolar aspects, though. Analog switches like the 4016/66 don't have level translation. If you want to switch a bipolar signal, the control signal has to be bipolar too, as does the switch's power.

The 74HC4316 is a quad switch with level translation. It can switch bipolar signals with a unipolar control. Power has to be +/-5v.

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Pehr



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PostPosted: Thu Feb 14, 2008 7:55 am    Post subject: Re: A VCA of sorts Reply with quote  Mark this post and the followings unread

richardc64 wrote:
I'm not sure about the bipolar aspects, though. Analog switches like the 4016/66 don't have level translation.


Why not use the TL604? Wink

Oh, that's P-MOS... right Rolling Eyes

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Tim Servo



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PostPosted: Thu Feb 14, 2008 12:24 pm    Post subject: A VCA of sorts Reply with quote  Mark this post and the followings unread

Ah, I'd forgotten about the switching level requirements for CMOS analog switches. You're right: on a 4016 / 4066, the "logic" for turning the switch on and off has to swing between the supply rails (or close to it). So if you're powering an analog switch with ±7.5V so that you can switch a ±5V analog signal, the switching input has to flop back and forth between +7.5V and -7.5V. Still, might be worth looking for a simple level shifter for the switching input.

The 74HC4316 looks like an ideal solution. This part is still in production, and can be had for under a buck. Also looks like it would be happiest running on ±6V supplies (still allows switching a ±5V analog signal with 'standard' 0 to 5V logic). I think this would be something worth looking into, as I think I'd want my Lunettas to be able to play nice with my other modular stuff.

The TL60x series is interesting, but they only have one or two switches per package (with only a single control pin), AND it doesn't look like they're cheap. Might not be in production anymore.


Tim (looks interesting, but definitely NOT cheap) Servo
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mosc
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PostPosted: Fri Feb 15, 2008 9:23 am    Post subject: Reply with quote  Mark this post and the followings unread

I think this discussion is great but I caution people who are just starting out. These kinds of circuits will require a lot of experimentation and depending on the electrical characteristics of the input signals will work differently.

For beginners, just try to work with the OSCs, counters, shift registers, gates and other digital circuits that don't require too many resistors, diodes, or capacitors to work.

I don't want to see people get the feeling that you have to be a circuit designer to get these Lunettas to work and to have fun.

That said, please continue.

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Scott Stites
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PostPosted: Tue Feb 19, 2008 7:26 am    Post subject: Reply with quote  Mark this post and the followings unread

All I can say is whhhooooaaaaaaaaaa.....how did I miss this entire forum popping up? I need to wake up....thanks for this, Mosc, what an excellent idea...

Anyway:

Quote:
Ah, I'd forgotten about the switching level requirements for CMOS analog switches. You're right: on a 4016 / 4066, the "logic" for turning the switch on and off has to swing between the supply rails (or close to it). So if you're powering an analog switch with ±7.5V so that you can switch a ±5V analog signal, the switching input has to flop back and forth between +7.5V and -7.5V. Still, might be worth looking for a simple level shifter for the switching input.


If I'm not mistaken, there is a method by which bipolar signals can be passed through the standard CMOS switches without resorting to bipolar supplies. Seems to me, a few years back, Rene Schmitz showed me how to convert the signal to current, pass the signal through the IC, then convert to voltage on the other side. Either that, or I dreamed it. Doesn't Ken Stone do the same thing on one of his modules?

I better check, I guess.......

Cheerios,
Scott

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Scott Stites
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PostPosted: Tue Feb 19, 2008 7:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Badda-Bim, Badda-Bam:

http://www.cgs.synth.net/modules/cgs28_seq_switch.html

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PostPosted: Tue Feb 19, 2008 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmmm....I guess he's still using -0.6V and 14.4V for the rails, but the supplies aren't too complicated.

I've configured bipolar CD4066s using a dual op amp for the supply. In that case, IIRC, I used two 10K resisors to divide the +15V rail to 7.5V, then fed that to the dual op amp - one section was a voltage follower and the other was an inverting buffer. The outputs drove the CD4066s just fine.

This arrangement of Ken's looks a bit better - you have a wider range to play with, so you don't have to worry quite so much about exceeding the input level.

Cheers,
Scott

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Pehr



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PostPosted: Tue Feb 19, 2008 7:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Scott Stites wrote:
If I'm not mistaken, there is a method by which bipolar signals can be passed through the standard CMOS switches without resorting to bipolar supplies.


There's also this method by biasing the signal so that it oscillates around a higher voltage.

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richardc64



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PostPosted: Tue Feb 19, 2008 8:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Scott Stites wrote:
This arrangement of Ken's looks a bit better - you have a wider range to play with...


That's the other part I don't get. It still looks like a total of 15 volts to me. And more positive than negative at that.

Confused

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PostPosted: Wed Feb 20, 2008 2:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
That's the other part I don't get. It still looks like a total of 15 volts to me. And more positive than negative at that.


No, actually you can get as close to the rails as the op amp gets, both positive and negative. Remember, with this setup you are feeding current to the op amp - the CD4051 isn't passing the voltage - it's passing the current. It's the op amp that's providing the voltage.

The CD4051 will only see voltage if a switch is opened - then there is no path to virtual ground for the input signal. In that case, voltages lower than -0.6V are shunted to ground. Positive voltages don't matter in this case. Well, as long as they don't go above Vcc, which is 14.4V.

Cheers,
Scott

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PostPosted: Thu Feb 21, 2008 1:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, you guys are getting too complicated, or at least this talk of full-range bipolar switches should not be in this forum.

Using the CMOS decoder/switches is great, just use them to switch digital sigs.

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fluxmonkey



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PostPosted: Thu Feb 21, 2008 2:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

mosc wrote:
Hey, you guys are getting too complicated, or at least this talk of full-range bipolar switches should not be in this forum.


well, that's one way to put a damper on things.

kind of an interesting dilemma... if the intent is to recreate historically accurate reproductions of these instruments, my sense is that most of what's been contributed so far is a bit more complicated than the originals. of course, i can't know, since i wasnt there, and most of us weren't... i'm sure you're busy, mosc, but the promised drawings would be a big help in framing what is or is not historically accurate.

on the other hand, if we're interested in continuing the original spirit of simple cmos building blocks plus "experiment, see what happens", seems to leave open a lot more doors. i'd argue that building on that tradition but being willing to advance the art (as others have done, including Nic Collins, Ray Wilson, our own mr bugs...) seems to be truest to the original spirit. no one here's trying to recreate a full-featured expo vco using 40xx chips (yet), but i for one would be gladder for keeping the forum open and sorting things out for myself, rather than stay too stuck on the way things were back in the day... with all due respect, mosc, i'd prefer to do my own gatekeeping as to what's appropriate.

bests
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PostPosted: Thu Feb 21, 2008 4:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Good point, Bbob. Historical accuracy is not important at all, IMHO.

As for schematics, there really were no schematics. We just wired chips up direct to the banana plugs - for the most part.

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23isgood



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PostPosted: Thu Feb 21, 2008 6:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Really? Thats it? No resistors or diode protection? Im adding some protection circuitry to mine. I want to be absolutely sure that whatever I plug up to these circuits will not blow them up. I do plan on interfacing mine with my modular gear, for sequencing. So on a proto board you could have a few cmos chips on there. I guess the majority of the work is in the case.
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PostPosted: Sat Feb 23, 2008 12:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, CMOS chips these days are much better than in the past for ESD protection. Still, it's not bad to be careful.
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PostPosted: Tue May 13, 2008 6:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

im think slow vactrols are a nice match for the lunettas

this of course only gives you percussive envelopes but i think that is actually enough for the lunetta style
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otherunicorn



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PostPosted: Tue May 27, 2008 2:58 am    Post subject: Re: A VCA of sorts Reply with quote  Mark this post and the followings unread

Tim Servo wrote:
I've thought of a slightly different approach to a "Logic VCA" (LVCA ©)...
Wink

You apply the digital signal to the control pin of an analog switch, and apply the CV to the INPUT of the switch. Now, at the output of the switch you're getting whatever level the CV is at, but turned on an off by the digital signal. The effect is that you get a signal with the frequency of the digital signal, but the level of the CV. The nice thing here is that you can use a bipolar CV and get a bipolar output signal (just don't apply a bipolar signal to other logic; use a diode to chop the negative portion off). I've designed something like this into my version of Ian Fritz's double pulser, but I haven't breadboarded it yet. Might also be fun with a multiplier and/or divider ciruit to get CV control of output aplitudes (and polarity). Like I say, I haven't tried this yet, but I'm pretty sure it would work.

Tim (might be fun) Servo



It definitely works. It's an organ trick, using the square waves from the dividers to switch the 4066, and the key providing the envelope for the "CV" passing through the switch. You start to have even more fun when you pass a different envelope through the different switches from the same divider. Try slaving one of my analog switch matrixes to the master divider if you have them. I was playing with the idea of releasing an new sub-oscillator that did this, but concluded it was too easy to do with existing modules

Ken

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stolenfat



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PostPosted: Sun Dec 28, 2008 2:45 am    Post subject: Reply with quote  Mark this post and the followings unread

maybe i missed it while reading over this forum, but using the schematics at the top to send to a VCA... is there a simple way to do that? eg an easy circuit in the lunneta style that would take the digital audio signal and amplitude modulate it in accordance with the AR signal?
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richardc64



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PostPosted: Mon Dec 29, 2008 6:22 am    Post subject: Reply with quote  Mark this post and the followings unread

The circuit at the top IS a VCA. Can't get much simpler than a couple of diodes and resistors or, as Mr. Servo suggested, 1/4 of a 4066.
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stolenfat



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PostPosted: Mon Dec 29, 2008 2:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

oh i see! that is incredibly simple.. wow

one question, theres a cap in the top schematic, does it have to be a specific value (i'd gues 10uf) or can you tinker with it- it seems so simple yet so delicate.
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PostPosted: Mon Dec 29, 2008 2:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

stolenfat wrote:
theres a cap in the top schematic, does it have to be a specific value


It's just DC blocking, so feel free to experiment (until there is enough bass in the output signal).

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adammokan



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PostPosted: Sun Apr 19, 2009 11:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey everyone. I posted this question over at the Deathlehem forum, but wanted to throw it out here, as well...

I'm trying to run a simple 4093 output into the dual-diode VCA. Signal doesn't seem to be hot enough when I check the anode side on that first diode. So I'm running it through a 4049 to attempt boosting the signal. Still extremely faint, but I may have something wrong with my resistors on the feedback loop of the 4049. I forget the math there. Positive my oscillator is working because it sounds fine on the cathode side.

Either way, I need to take a break for a few hours and just wanted to make sure I'm heading in the correct direction and that my theory of simply running the output of the 4093 is not hot enough to be audible through this VCA without pre-amping... or should I just throw an amp on the output of the VCA? 741, etc?

Trying to keep it simple.

Thanks!!!
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