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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Single supply VCA?
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tokyomatik



Joined: Jan 20, 2011
Posts: 170
Location: berlin
Audio files: 6

PostPosted: Mon Apr 20, 2015 1:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
commathe wrote:
I want to be passing tri/saw/sine signals without too much distortion and definitely not clipping so the diode/transistor method is out.

I failed to mention that omitting the 2nd diode from the 2-diode VCA the circuit handles analog as well digital inputs. Replacing the transistor in the "1-transistor" VCA with a single supply opamp makes it even better, as it allows bigger input swings.



looks like richardc64 already answered about this matter.....
so now refering to the pcb from hexagon5un
is D2 the 2nd diode mentioned by richardc64??
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hexagon5un



Joined: Apr 10, 2009
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Location: Munich, Germany
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PostPosted: Fri Apr 24, 2015 1:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

Heya! Sorry to come so late to the party here.

I actually had my old Lunetta modular in pieces in a box in the basement, and I found/pulled out the VCA circuit just now to see how it works with non-square waves. It's freaky!

Input is a (slightly overdriven) sine wave at 73ish Hz.

I've attached scope shots at two resolutions: one is the overall envelope and the other is a zoom into the top of the wave.

The waveform is actually pretty clean during the sustain portion, but you can see the strange way it's clipped during the attack and release. Pretty neat.

I also recorded this just for fun. I'm not 100% sure that I'm not distorting it further in my laptop, but you get the idea. It's got this woooomp kind of noise at the beginning for slow attacks. (I play around with attack and release a bit.)

Anyway, that's the deal with the active version of the circuit and non-square waves. Works great, but idiosyncratically.

edit: Oh yeah. I built the circuit without the output capacitor because I was using it for control voltages as well as audio, which make the super-long envelopes that it can produce even more reasonable. If you etch/build my version of the board, look out for that and add one if you're only doing audio processing.

Who knows which version I posted? Shocked


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single_sided_vca_demo.mp3
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tokyomatik



Joined: Jan 20, 2011
Posts: 170
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PostPosted: Fri Apr 24, 2015 2:19 pm    Post subject: Reply with quote  Mark this post and the followings unread

oh well
actually i posted here the version i etched (just a couple of msgs before) that is the same that u posted (9msgs before mine)
on the board i have in, out & cv
but in wich way u trigger the envelope??, than i thought that maybe you meant Gate...??
since this board looks a bit inspired by the schematics of richard64....
referring to the 2nd diode, is that D2 on your board?
thanks for jumping in and for sharing your pcb, saving us a lot of stress...
at least after that maybe i will have it more clear
Very Happy
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hexagon5un



Joined: Apr 10, 2009
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Location: Munich, Germany
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PostPosted: Fri Apr 24, 2015 2:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

And then to answer a curiosity of mine about the two-diode VCA circuit.

I built it exactly as indicated (with a 10uF cap on the output) and then pulled out the last / output diode.

Somewhere in between, I switched to 5V supply, so the input is a 5V sine wave at ~75Hz.

I did two experiements. First, I used a 5V square wave as the control voltage, and ran it with and without the output diode so you could see the effect at a constant level.

The only thing different is that the full swing of the control voltage (that shows up as negative through the cap) is supressed by the output diode. But I'd say that both work "fine" with analog signals, though the sinewave is visibly flattened at the top. (My guess, by the diode drop of the "input" diode.)

I guess you want the output diode in there, though, because there'll be a thump at the turn-on with a square wave control voltage, and it's going to be louder in the single diode version.

Then I tossed a 47uF cap on the control voltage to smooth it out, and hooked up the scope (in green) to the CV input. Not entirely surprisingly, the performance is a lot like the op-amp buffered version of the same thing in my last post.

So there you go. The buffers in the op-amp probably help a bunch to make the attack/release part perform more consistently, but otherwise don't seem to do much. OTOH, it's nice to have those long swooping envelopes.

The sine wave came through a bit less distorted in the op-amp version because it's being amplified before the diode, but it's really not that big of a deal.


vca_env_211_cropped.gif
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RichardC64's two-diode VCA, but this time fed with sine-wave input.
The circled diode is the one removed in the square-wave-CV experiments.
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scope_10.png
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Two-diode VCA as per Richardc64's circuit. 10uF cap on output.
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scope_11.png
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Same, but omitting output diode.
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scope_14.png
 Description:
Two diode VCA, both diodes, driven by a more analog control voltage (in green). Both diodes.
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scope_15.png
 Description:
Two-diode VCA, analog CV, analog input. Detail of envelope ramp and (slightly distorted) sine wave input.
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Last edited by hexagon5un on Fri Apr 24, 2015 2:38 pm; edited 2 times in total
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hexagon5un



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PostPosted: Fri Apr 24, 2015 2:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

tokyomatik wrote:
oh well
actually i posted here the version i etched (just a couple of msgs before) that is the same that u posted (9msgs before mine)
on the board i have in, out & cv
but in wich way u trigger the envelope??, than i thought that maybe you meant Gate...??


It's no big deal to just solder on an output capacitor if you want one. Just put one leg in the circuit board's hole, and solder the other to your output wire.

And yeah, I guess I meant "gate". There's an audio input and then there's the control voltage / gate input.

If you send too short a CV pulse in, and have the attack set very long, nothing happens. So in that sense, you surely want a "gate" rather than a "trigger".
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tokyomatik



Joined: Jan 20, 2011
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PostPosted: Tue Jun 02, 2015 7:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

hexagon5un wrote:
tokyomatik wrote:
oh well
actually i posted here the version i etched (just a couple of msgs before) that is the same that u posted (9msgs before mine)
on the board i have in, out & cv
but in wich way u trigger the envelope??, than i thought that maybe you meant Gate...??


It's no big deal to just solder on an output capacitor if you want one. Just put one leg in the circuit board's hole, and solder the other to your output wire.

And yeah, I guess I meant "gate". There's an audio input and then there's the control voltage / gate input.

If you send too short a CV pulse in, and have the attack set very long, nothing happens. So in that sense, you surely want a "gate" rather than a "trigger".
....So I actually build the pcb using your layout and all the parts/values suggested..... it works
sine waves are a bit distorted and there is a bit of volume drop
my idea was to use this circuit to make a small percussive envelope/vca
so honestly i dont need the attack pot, at least on the amplitude, or maybe i could reduce from 1M to 500k or less, to have a shorter attack
the circuit anyway it's so small that i could use 2 together with common gate input so that one is taking care of the vca and the other for a kind of "sweep" frequency
in case I wanna have more volume without adding distorsion(eventually less distorsion would be even better)...do u have any more suggestion?

and if I wanna remove the attack pot?
i'm powering everything with 12v wallwart.... surprise
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Steveg



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PostPosted: Wed Jun 03, 2015 1:02 am    Post subject: Reply with quote  Mark this post and the followings unread

I haven't seen any mention of the simple one transistor VCA synaesthesia used in his gong drone http://electro-music.com/forum/topic-62791.html. I guess it is the same as the ones PHOBoS posted without the op-amp buffer.

Also the "diode vca and ar.jpg" circuit should be able to be used with any control voltage driving the lower LM358 you don't have to use the depicted AR generator.
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Steveg



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PostPosted: Wed Jun 03, 2015 3:08 am    Post subject: Reply with quote  Mark this post and the followings unread

This site has a bunch of different designs, some of which look quite buildable.
http://sound.westhost.com/articles/vca-techniques.html
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okelk



Joined: May 08, 2014
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PostPosted: Wed Jun 03, 2015 3:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Steveg wrote:
This site has a bunch of different designs, some of which look quite buildable.
http://sound.westhost.com/articles/vca-techniques.html


thanks but...the link doesn't work..
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Steveg



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PostPosted: Wed Jun 03, 2015 3:28 am    Post subject: Reply with quote  Mark this post and the followings unread

I think the site must have just gone down ... it worked ok 15 minutes ago and my bookmark is having the same problem.

[edit] It is working again.
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richardc64



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PostPosted: Wed Jun 03, 2015 8:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

Let's not forget that the original inquiry was for a single-supply VCA. Many of the circuits that have been suggested will need modification to operate single-supply -- the more complex circuits needing more that just a pseudo ground of 1/2V+.

Let's also not forget where we are: The Lunetta sub-forum.
mosc wrote:
Lunettas are very simple, digital, noisy, quirky, and lots of fun.

Low distortion need not be a major concern.

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Blue Hell
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PostPosted: Thu Jun 04, 2015 6:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey ... you quit smoking, great :-)

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Steveg



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PostPosted: Thu Jun 04, 2015 7:05 am    Post subject: Reply with quote  Mark this post and the followings unread

This also ought to work as a Lunetta VCA. Signal is a square wave. I have shown a simple drum type AR envelope but any CV envelope ought to work. The envelope may need to be buffered.

[Edit] Then I found that Richard had posted almost this exact circuit over here http://electro-music.com/forum/post-315593.html


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richardc64



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PostPosted: Thu Jun 04, 2015 9:27 am    Post subject: Reply with quote  Mark this post and the followings unread

Steveg wrote:
Then I found that Richard had posted almost this exact circuit over here http://electro-music.com/forum/post-315593.html

Original idea of Tom Servo.

Blue Hell wrote:
Hey ... you quit smoking, great Smile

Actually, I haven't. I just thought that since his passing Mr. Nimoy should be depicted without a cigarette.

I still endorse his quotation as my sig Wink

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jurekprzezdziecki



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PostPosted: Mon Sep 12, 2016 2:24 am    Post subject: Reply with quote  Mark this post and the followings unread

commathe wrote:
Thanks again guys! It is time to get bread boarding and see what gets closest. Simulations of the MFOS one are looking ok. More distortion than I'd like but beggars can't be choosers!

EDIT: I just discovered this 4007 based VCA that I would have just glanced over if it wasn't for the fact that I have a note that the schematic as it is drawn here is WRONG. The body connections of the internal MOSFETs are tied to Vss and Vdd, meaning that this may actually work!


so did you tested this 4007 circuit finally? is it well designed?
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kybernetika



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PostPosted: Mon Oct 31, 2016 11:01 am    Post subject: Reply with quote  Mark this post and the followings unread

this is another variation on the 4007 vca Idea


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Hammer



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PostPosted: Tue Mar 13, 2018 11:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Is it posible to make LPF with TDA7052A like this: http://electro-music.com/forum/topic-34891.html

It could be VCA + LPF just in one tiny chip.

Last edited by Hammer on Thu Mar 15, 2018 3:40 am; edited 1 time in total
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Steveg



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PostPosted: Wed Mar 14, 2018 12:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Hammer, I've just trawled through that thread but I can't see anything relating to a TDA7052. Mostly it is about sallen-key filters.

I have been trawling through a lot of posts recently and I'm sure I've seen something talking about using a low pass VCF as a VCA. The resting state of the filter is sub-sonic and you feed it an envelope that raises the cutoff frequency and as the signal moves higher on the attenuation slope more is passed. It would probably not work too well for mixed frequencies because the attenuation is frequency dependent.

Is that what you were thinking of?
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Hammer



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PostPosted: Wed Mar 14, 2018 1:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello, Steveg!

I'm talking about circuit from first page of this topic (elektrouwe):

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Steveg



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PostPosted: Wed Mar 14, 2018 3:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Without knowing much about the chip I thought at first it might be possible but the more I look at it the less certain I am. The differential outputs might be a problem. Electrouwe seems to only use one output so I guess it could be used as a voltage controlled attenuator. You would need two in a Sallen Key or State Variable filter.

The link you supplied is to a completely different thread which is why I was confused.
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Hammer



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PostPosted: Wed Mar 14, 2018 3:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Steveg, thank you for reply! Today I will get this TDA chips, will see...

Steveg wrote:
Electrouwe seems to only use one output so I guess it could be used as a voltage controlled attenuator.


And he doesn't use signal ground pin. But it's nessesary for me.
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Harry



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PostPosted: Wed Mar 14, 2018 10:15 am    Post subject: Reply with quote  Mark this post and the followings unread

Steveg wrote:
I have been trawling through a lot of posts recently and I'm sure I've seen something talking about using a low pass VCF as a VCA. The resting state of the filter is sub-sonic and you feed it an envelope that raises the cutoff frequency and as the signal moves higher on the attenuation slope more is passed. It would probably not work too well for mixed frequencies because the attenuation is frequency dependent.

Is that what you were thinking of?

Sounds like you're describing a (Buchla) Low Pass Gate. Can operate as a low-pass filter, vca or both simultaneously.
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Hammer



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PostPosted: Thu Mar 15, 2018 2:02 am    Post subject: Reply with quote  Mark this post and the followings unread

TDA 7052A sounds a lot better than all this single transistor and diode VCA!

But I can't eliminate distortions. And it works a little bit weird. I'm using Arduino with DDS output as source. TDA 7052 is not distort the signal if there are no any caps in input (even DDS cap), the same thing with simpliest 40106 oscillator. And I can't understand why.

In spite of this, it works very well with this 4069 LPF: http://aeeprojects.blogspot.ru/2011/09/filters-with-cd4069.html

What can I do with differential outputs? May be any audio transformer will be correct decision?

Last edited by Hammer on Thu Mar 15, 2018 2:34 am; edited 1 time in total
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elektrouwe



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PostPosted: Thu Mar 15, 2018 2:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Hammer wrote:
TDA 7052 sounds a lot better than all this single transistor and diode VCA!

that's why I suggested it Wink
PS: please write TDA7052A, because when people read your post and buy a TDA7052 it will not work because this one has no DC gain control pin !

Hammer wrote:

But I can't eliminate distortions.

TDA7052A has a gain of ~ 56x, which means Vin should be in the 100mV range, otherwise you need an input voltage divider. You MUST use an input coupling cap., because the chip generates an internal DC bias voltage.

Hammer wrote:

What can I do with differential outputs?

unless you don't need diff. outputs, just use 1 of them. Inverting or noninverting is only important if you use the chip in a filter loop
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Hammer



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PostPosted: Thu Mar 15, 2018 3:39 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, input cap. was too small, signal was too high! Thank you a lot, now it's working as it should.
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