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 Forum index » DIY Hardware and Software » Arduino
Simple VCA design
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synthjakk



Joined: Feb 12, 2018
Posts: 20
Location: UK

PostPosted: Tue Mar 27, 2018 7:44 am    Post subject: Simple VCA design Reply with quote  Mark this post and the followings unread

I have built a simple VCO, which outputs a sawtooth and a gate signal (0 Low, 5v High). No ADSR, or anything fancy. I want to add a simple VCA for these two signals, as well as a volume control. Can anybody recommend a design direction or topology? most online examples seem to be rather complicated. Thanks


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Last edited by synthjakk on Tue Mar 27, 2018 8:59 am; edited 1 time in total
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icnagy



Joined: Jan 29, 2017
Posts: 3
Location: Glasgow, UK

PostPosted: Tue Mar 27, 2018 8:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Have you looked at the farmVCA from Motohiko Takeda?

http://www.aleph.co.jp/~takeda/radio/farmVCA.html
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synthjakk



Joined: Feb 12, 2018
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PostPosted: Tue Mar 27, 2018 8:55 am    Post subject: Reply with quote  Mark this post and the followings unread

I guess it is not is English? I only get a bunch of ? when I open it
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icnagy



Joined: Jan 29, 2017
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PostPosted: Tue Mar 27, 2018 8:59 am    Post subject: Reply with quote  Mark this post and the followings unread

Use Chrome's translate feature, it does a pretty good job.
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synthjakk



Joined: Feb 12, 2018
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PostPosted: Tue Mar 27, 2018 9:49 am    Post subject: Reply with quote  Mark this post and the followings unread

Apologies, maybe it is my chrome, But it doesn't seem to work for me. Could you post the schematic that is on the site? I cant seem to see anything Smile
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Blue Hell
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PostPosted: Tue Mar 27, 2018 10:33 am    Post subject: Reply with quote  Mark this post and the followings unread

http://www.aleph.co.jp/~takeda/radio/img/farmVCA-scheme.gif ... probably ... anyway .. 2nd unreadable link on that page .. the 3rd one has a PCB layout.
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LFLab



Joined: Dec 17, 2009
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Location: Rosmalen, Netherlands

PostPosted: Wed Mar 28, 2018 7:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Slightly more complicated than the Takeda circuit:
http://kassu2000.blogspot.co.uk/2015/10/vca.html
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cslammy



Joined: Apr 27, 2018
Posts: 22
Location: USA

PostPosted: Sat May 19, 2018 1:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for sharing these designs.

I couldn't see why farm VCA wouldn't work....

I made up a PCB layout of the farm VCA schem using eagle, got it fab'd up in china, and tested it working. Good VCA.....It's clean, not prone to distortion, and quiet.

So as far as I can tell, FarmVCA is simple and works great.

I am working on incorporating 3 VCA's into a 3900 based waveshaper, and will try using the farm-VCA vs. 2164 based etc. once I do I will post this on my website.

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cslammy



Joined: Apr 27, 2018
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PostPosted: Thu May 24, 2018 8:01 am    Post subject: Reply with quote  Mark this post and the followings unread

Update, I fab'd the farm VCA and it works.


http://www.charlielamm.com/gear/gain/forums.html#farmvca

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Last edited by cslammy on Fri Jun 15, 2018 8:25 am; edited 1 time in total
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JovianPyx



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PostPosted: Thu May 24, 2018 9:34 am    Post subject: Reply with quote  Mark this post and the followings unread

cslammy wrote:
Update, I fab'd the farm VCA and it works.
http://www.charlielamm.com/gear/gain/forums.html#farmvca


I get a 404 error on the URL.

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Blue Hell
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PostPosted: Thu May 24, 2018 10:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm .. link works here :-)
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JovianPyx



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PostPosted: Thu May 24, 2018 10:51 am    Post subject: Reply with quote  Mark this post and the followings unread

I didn't when I first tried it. It works now. Prolly some server goofup.
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Hashtag Octothorpe



Joined: Jun 11, 2017
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Location: Grand Rapids MI

PostPosted: Thu Jun 14, 2018 3:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

The simplest VCA of all is a diode.

I've used a ton of them and in my percussion circuits. They're quite common in Roland TR-808 voice circuits.

Roland calls it a "swing type VCA". The attachment is a schematic that'll work with a low-impedance trigger, but if you feed a signal into the 33K resistor where it meets the 10uF capacitor, and delete that capacitor and everything to the left of it, you should have a workable VCA.

You will need to high-pass the audio input and outputs to keep the DC out of the signal. And if the filter is low enough for full-range audio, you'll hear the CV. Maybe a 100nF capacitor in the signal path with a 10K resistor to ground just after the capacitor. That's about a 160Hz high-pass filter. That's great for snare, chime, cymbal, high toms... stuff like that.


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cslammy



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PostPosted: Fri Jun 15, 2018 8:32 am    Post subject: Reply with quote  Mark this post and the followings unread

JovianPyx wrote:
cslammy wrote:
Update, I fab'd the farm VCA and it works.
http://www.charlielamm.com/gear/gain/forums.html#farmvca


I get a 404 error on the URL.


CL: The URL tags on the forum made the link not always work, I have changed that to HTML. Thanks.

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