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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Tue Dec 02, 2014 9:35 pm Post subject:
Single supply VCA? |
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Has anyone got any good ideas for something along these lines? I've tried making ones using a Vref/virtual ground but it never quite works out. I need something that will not just pass digital signals and won't clip things. I need a "true" vca.
I'm totally lost. It seems the only options left are some sort of OTA as a voltage controlled resistor design or to use a vactrol (not so great).
Log & linear response would be nice, but not essential. |
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Cynosure
Site Admin
Joined: Dec 11, 2010 Posts: 966 Location: Toronto, Ontario - Canada
Audio files: 82
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Posted: Thu Dec 04, 2014 10:57 am Post subject:
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I would recommend an OTA. You can get two VCA's with one LM13700. I have done it by replicating the configuration used in the JH Wasp filter schematic.
You will need to make sure you attenuate the voltage on the input. OTA's distort easily and the distortion does not sound nice. Also, add a 15k resistor to +V from the diode bias input. |
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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Thu Dec 04, 2014 11:25 pm Post subject:
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Thanks! OTAs definitely appear to be the way to go. I'm worried about how close they will get to the rails though. I'm considering trying them in the feedback loop of an op-amp... |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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LFLab
Joined: Dec 17, 2009 Posts: 497 Location: Rosmalen, Netherlands
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Posted: Fri Dec 05, 2014 6:10 am Post subject:
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THAT4315? No experience whatsoever, but seems appropriate. |
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synaesthesia
Joined: May 27, 2014 Posts: 291 Location: Germany
Audio files: 85
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richardc64
Joined: Jun 01, 2006 Posts: 679 Location: NYC
Audio files: 26
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Posted: Fri Dec 05, 2014 4:28 pm Post subject:
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It started out that way, but without the 2nd diode of the 2-diode design, it more resembles the "1-transistor VCA" used in the TR-808, TR-606 and DR-110: The output is taken from the point where the CV controls the amplitude.
Using an opamp instead of a transistor as the active element allows for a larger input amplitude. In the 1-transistor circuit the input must be limited to less than the transistor's base-emitter saturation voltage -- about 850mV for a 2N3904.
(In that circuit Gate In needs a resistor of 2K or so to Gnd, otherwise Release will be longer than it should be.) _________________ Revenge is a dish best served with a fork... to the eye |
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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Sun Dec 07, 2014 12:03 am Post subject:
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I want to be passing tri/saw/sine signals without too much distortion and definitely not clipping so the diode/transistor method is out. Looks like I'm going to have no choice but to go OTA. Bummer because I also wanted rail-to-rail output (was hoping to do some CV processing) but to be honest it serves me right being so fussy.
Hopefully I'll come back with my own solution some time soon.
I've got my eye on this guitar compressor schematic at the moment. I think using the OTA as a voltage controlled resistor in an op-amp feedback loop would hopefully work well.
[/url] |
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LFLab
Joined: Dec 17, 2009 Posts: 497 Location: Rosmalen, Netherlands
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Posted: Sun Dec 07, 2014 8:18 am Post subject:
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Seems like quite a lot of parts. Have you checked out that4315? 3,60euro at mouser. |
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richardc64
Joined: Jun 01, 2006 Posts: 679 Location: NYC
Audio files: 26
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Posted: Sun Dec 07, 2014 11:56 am Post subject:
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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.
Quote: | I've got my eye on this guitar compressor schematic at the moment. I think using the OTA as a voltage controlled resistor in an op-amp feedback loop would hopefully work well. |
I agree with LFLab that looks like too many parts for a single-supply VCA, unless you have your heart set on the compression capability.
Here's a couple more core circuits:
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what's missing is the V/I converter. |
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This image has been reduced to fit the page. Click on it to enlarge. |
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Same operation as what PHOBoS posted. The 909 circuit is dual supply, but that's just for the opamp. Substitute a '324 or '358 for single-supply. |
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This image has been reduced to fit the page. Click on it to enlarge. |
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_________________ Revenge is a dish best served with a fork... to the eye |
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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Vanwonky
Joined: Jul 24, 2013 Posts: 22 Location: Perth, Australia
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Posted: Sun Dec 07, 2014 9:58 pm Post subject:
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Hi - I built this and it worked brilliantly for my needs. Output is a little quiter than I would like but I am sure that could be fixed easily by anybody on this forum but me!
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elektrouwe
Joined: May 27, 2012 Posts: 143 Location: Germany
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hexagon5un
Joined: Apr 10, 2009 Posts: 38 Location: Munich, Germany
Audio files: 1
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Posted: Wed Mar 25, 2015 12:17 pm Post subject:
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Man, that brings back memories. I've used that and loved it. It's super-minimalistic but gets the job done. I have a lunetta-esque synth with 4 of them in it.
I've attached are my eagle design files, and a mirror-imaged layout that you can use to toner-transfer to the bottom of a board, if anyone wants to make these at home or get them fabbed.
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Eagle design files and gerbers for LM358 EG/AR. |
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vca_eagle_and_gerbers.zip |
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PDF of traces for toner-transfer PCB production, if you're into that sort of thing. |
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vca.toner_bottom.pdf |
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Components and layout for the top of the PCB |
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vca.components.pdf |
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okelk
Joined: May 08, 2014 Posts: 71 Location: Vienna
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Posted: Thu Mar 26, 2015 8:20 am Post subject:
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I find the tda 7052 vca interesting! ...never heard of this chip.
the scott gravenhorst 4007-based VCA reminds me if this:
(it's a 4007 based VCA by Osamu Hoshuyama)
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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Fri Mar 27, 2015 10:38 pm Post subject:
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I've seen that one too, though I had actually forgotten about it. Definitely going to be trying both of them out! |
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okelk
Joined: May 08, 2014 Posts: 71 Location: Vienna
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Posted: Sat Apr 04, 2015 11:38 am Post subject:
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Also, I just remembered seeing another 4007 based VCA as part as rene schmitz' 4007 VCF. (Has anybody tried it? I'd love to hear it...)
...It probably also would be possible to replace the opamp with a cd4069...
http://www.schmitzbits.de/vcf4007.html
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commathe
Joined: Jul 26, 2013 Posts: 153 Location: Beijing
Audio files: 5
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Posted: Mon Apr 06, 2015 7:34 am Post subject:
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Nice find! Could be perfect for building a wasp clone without a CA3080 or such. Definitely going to experiment with this too.
I'm slightly confused though because pin 7 is also the body connection for the N-channel MOSFETS on the chip? Obviously, Rene is smarter than me |
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DGTom
Joined: Dec 08, 2008 Posts: 211 Location: Adelaide
Audio files: 3
G2 patch files: 1
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Posted: Mon Apr 06, 2015 5:07 pm Post subject:
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I assumed the 4007 is being used as a 'passive' device in that set-up, tho I've not tried it.
Did have a play around with the 4007 + 4069 combo the way Scott Gs drawing above suggested, using the 4069 in linear mode as a gain stage after the 4007.
seemed to work OK, tho the control voltage range was very small & careful trimming of the CV is needed as per the single transistor VCA - 4069 works well for that as well, lots of distortion, but that is kinda the point right?
Don't overlook the 2164 quad VCA chip for single supply applications. I'm using it with a +10V & +5V supply. 0V goes to what would usually be the negative supply pin & +5V goes to the ground pin. Works great with the 4069.
I'm a fan of 4069s for audio (in case that isn't obvious) It is noisy but I love the way it bends waveforms
I've been meaning to try it with an OTA as well... maybe tomorrow. |
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tokyomatik
Joined: Jan 20, 2011 Posts: 171 Location: berlin
Audio files: 6
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Posted: Mon Apr 20, 2015 2:28 am Post subject:
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hexagon5un wrote: |
Man, that brings back memories. I've used that and loved it. It's super-minimalistic but gets the job done. I have a lunetta-esque synth with 4 of them in it.
I've attached are my eagle design files, and a mirror-imaged layout that you can use to toner-transfer to the bottom of a board, if anyone wants to make these at home or get them fabbed. |
I'm checking this board and looks realy usefull
still trying to understand, we have here an AD envelope and a VCA
the trimmer are Attack & Decay pots right??
but the CV connector is an input or an output? |
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DUBmatze
Joined: Feb 18, 2013 Posts: 150 Location: south Germaica (schwabilon)
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tokyomatik
Joined: Jan 20, 2011 Posts: 171 Location: berlin
Audio files: 6
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Posted: Mon Apr 20, 2015 5:28 am Post subject:
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perfect! now i'm a bit more confused
i thought the pcb made by hexagon5un were refering to this schematics
posted by synaesthesia on december 5 2014.
so to be precise, would be a GATE and not CV INPUT
another question is: does it work only with square waves or i can feed also sines for example? |
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DUBmatze
Joined: Feb 18, 2013 Posts: 150 Location: south Germaica (schwabilon)
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Posted: Mon Apr 20, 2015 6:39 am Post subject:
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tokyomatik wrote: | another question is: does it work only with square waves or i can feed also sines for example? | iam not shure wich pcbs you have and what kind of vca is on them. but the simple diode vca works only with squarewaves whre the low lvl is = gnd. |
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tokyomatik
Joined: Jan 20, 2011 Posts: 171 Location: berlin
Audio files: 6
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Posted: Mon Apr 20, 2015 7:05 am Post subject:
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i mean the PCB posted here 9 posts before on this page by hexagon5un, referering to the schematic of 20 posts ago also on this page by synaesthesia.....better if u check both so we can understand each other
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vcacomponents_105.pdf |
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vcatoner_bottom_872.pdf |
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Last edited by tokyomatik on Mon Apr 20, 2015 1:14 pm; edited 2 times in total |
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tokyomatik
Joined: Jan 20, 2011 Posts: 171 Location: berlin
Audio files: 6
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Posted: Mon Apr 20, 2015 7:56 am Post subject:
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- Last edited by tokyomatik on Mon Apr 20, 2015 1:20 pm; edited 2 times in total |
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