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 Forum index » DIY Hardware and Software » Thomas Henry designs
VCA for the 21st Century
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numbernone



Joined: Aug 16, 2006
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PostPosted: Tue Oct 16, 2007 12:31 pm    Post subject:  VCA for the 21st Century Reply with quote  Mark this post and the followings unread

In hunting down a nice simple VCA I found that the example from the book had a nice low parts count, and could be laid out in a small footprint. However it was pointed out to me that it is a combo VCF/VCA.

From what I can see they are only sharing the SSM2164, with no real interdependence from each circuit. Am I on the right track?? I plan to breadboard it over the weekend, but if I am barking up the wrong tree I could much better spend the time on the 8038 VCOs.

Thanks!
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Tim Servo



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PostPosted: Wed Oct 17, 2007 7:38 pm    Post subject: Re: VCA for the 21st Century Reply with quote  Mark this post and the followings unread

numbernone wrote:
In hunting down a nice simple VCA I found that the example from the book had a nice low parts count, and could be laid out in a small footprint. However it was pointed out to me that it is a combo VCF/VCA.

From what I can see they are only sharing the SSM2164, with no real interdependence from each circuit. Am I on the right track?? I plan to breadboard it over the weekend, but if I am barking up the wrong tree I could much better spend the time on the 8038 VCOs.

Thanks!


Hey Number,

Yes you're right. You can easily wire up just the VCA (sheet 2 of the schematic / page 17 in AS21C). Only half of the 2164 is used in the VCA (so you could build a dual VCA without too much effort), and IC3 only uses sections b, c and d. Still, very easy to build only the VCA. On the unused op-amp section, I'd probably ground the + input, and connect the - input to the output.

Tim (no unused sections) Servo
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numbernone



Joined: Aug 16, 2006
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PostPosted: Thu Oct 18, 2007 7:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Tim,

I am aiming to make 4x VCA boards, I need lots and lots of them. And this is a very low parts count circuit, which I love. And Thomas' assertion in the intro that these are among his best circuits, is a very reassuring statement.

Matthew
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philpeery



Joined: Nov 08, 2006
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PostPosted: Fri Oct 19, 2007 9:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

I breadboarded the 2164 as a dual VCA about a month ago or so. It worked very well, and sounded great even on the breadboard. It was rather trivial to "map" a second VCA to the other side of the chip. For the opamps, I used a tl074 and a tl072.

As I said, it worked great, so now all I need to do is layout a pcb. Yup, in my spare time!

Phil
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fonik



Joined: Jun 07, 2006
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PostPosted: Wed Jan 02, 2008 4:44 am    Post subject: Reply with quote  Mark this post and the followings unread

i am now starting to build a dual VCA from this schematic.

i wonder if there is any limitation to the amplitude of the input signal? i was not able to extract this information from the SSM2164 datasheet.

if not i would omit the input attenuation to spare some frontpanel space. in fact i only wanted 5 frontpanel elements for each VCA (input, initial, cv in, cv att., output).

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Tim Servo



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PostPosted: Wed Jan 02, 2008 9:38 am    Post subject: VCA for the 21st Century Reply with quote  Mark this post and the followings unread

Hey Fonik,

It looks like the input resistors to the 2164 (30k in series, 510r and cap to ground) attenuate the input signal properly. I haven't looked at the 2164 data sheet, but is it possible that it's a current in rather than a voltage in (therefore the max input level will be listed in mA)? I'm assuming that it would still be possible to overdrive the 2164 with this setup, so you may want to include a PCB mounted trimmer to attenuate the signal if you find you're consistently getting distortion.


Tim (a little distorted) Servo
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philpeery



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PostPosted: Wed Jan 02, 2008 2:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi everyone,

I breadboarded this when the AS21C book was released. It's a great sounding VCA. I did not use attenuating pots on the audio input, and had no distortion issues when running a 10 volt peak to peak (+/- 5v) VCO square and triangle signal through it. These signals were not mixed, they were separate tests. I didn't get the chance to try to push it or run CV's though, which I wanted to do, before I needed my breadboard for another test however. But everyone should have at least one of these in their modular!

And I STILL have to get back to the PCB (single sided) design! There's never enough time in the day for all the modular stuff I want to do!

Fonik - if you come up with a press 'n' peel layout, will you share it? I do think you need Tim Servo's okee-dokee first as he's got the rights. As I said, everyone should build one of these! It's a great sounding VCA!

Happy New Year, E-M!

Phil
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fonik



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PostPosted: Thu Jan 03, 2008 8:02 am    Post subject: Reply with quote  Mark this post and the followings unread

thank you boys. i am currently working on a single sided press'n'peel layout for a dual version (sharing the SSM2164).

i will leave off some components, though: the attenuated CV in and the AC/DC switch. that would be no big issue, i guess, since these parts are frontpanel mountable...

will be finished next week. i will have to ask thomas first and if he said yes i would create a building documentation. it won't come without any schematics, these are already available from magic smoke Wink

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Coriolis



Joined: Apr 11, 2005
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PostPosted: Thu Jan 10, 2008 12:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

fonik, that would be great!
And you're right about the cv-attenuators and the ac/dc switch - beter suited for panelmounting imo.
Looking forward to a layout!

C
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fonik



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PostPosted: Fri Jan 11, 2008 12:33 am    Post subject: Reply with quote  Mark this post and the followings unread

it's actually finished, even i had not the time to etch it yet. i will have to do some documentation next week and then i will post it...
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Luka



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PostPosted: Sat Jan 12, 2008 8:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

great, i have a 2164 spare! and i'm in need of some more vcas!
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fonik



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PostPosted: Mon Jan 14, 2008 2:36 am    Post subject:
Subject description: PCB layout for a dual VCA
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so here we go. i triple checked my work as usual but i have not had the time to etch a board and test it.
anyway you will find the layout here:
TH_dual_VCA.pdf

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creatorlars



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PostPosted: Thu Jan 31, 2008 11:08 am    Post subject: Reply with quote  Mark this post and the followings unread

I may build this with your layout -- any results yet? It's either this or the VCA-1. Know anywhere to get those SSM2164s? I know I can order them directly from ADI, but just wondering if there was a better price elsewhere...
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fonik



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PostPosted: Thu Jan 31, 2008 12:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

the PCB is etched and drilled. have not had the time to populate it though.
i ordered the ICs from bridechamber

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Tim Servo



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PostPosted: Thu Jan 31, 2008 2:26 pm    Post subject: VCA for the 21st Century Reply with quote  Mark this post and the followings unread

Magic Smoke also carries the 2164 Quad VCA chip for $3.50 (or less if you buy more than two).

Thomas' AS21C book is also available through our print-on-demand service at
http://www.lulu.com/content/1065518



Tim (now if I could just print the chips) Servo
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philpeery



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PostPosted: Mon Feb 11, 2008 9:34 am    Post subject: Reply with quote  Mark this post and the followings unread

I just finished etching Fonik's design for this board, and will be loading it with parts in the next few days. I'll report back, hopefully with pic's, on my build. Also, I had to hack in, using photoshop, an MTA156 connector for the power, which is what I use. Turns out it wasn't as tough as I thought it was going to be.

As I always say, the more VCA's you have, the better!

Phil
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frijitz



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PostPosted: Mon Feb 11, 2008 11:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Does this have linear or expo control?

Very Happy

Ian
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Tim Servo



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PostPosted: Mon Feb 11, 2008 12:28 pm    Post subject: VCA for the 21st Century Reply with quote  Mark this post and the followings unread

Linear. The VCA uses the four sections of a 2164 Quad VCA chip (each section with expo control) to create two linear response VCAs. The 2164 chip is very quiet and has a VERY wide dynamic range.


Tim (not very quiet) Servo
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frijitz



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PostPosted: Mon Feb 11, 2008 2:35 pm    Post subject: Re: VCA for the 21st Century Reply with quote  Mark this post and the followings unread

Tim Servo wrote:
Linear. The VCA uses the four sections of a 2164 Quad VCA chip (each section with expo control) to create two linear response VCAs. The 2164 chip is very quiet and has a VERY wide dynamic range.

OK, so it's the old Mike Irwin trick?

I always thought it would be fun to try antilogging the input CV to get a linear response, rather than dedicating a VCA stage to be a servo.

Very Happy

Ian
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State Machine
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PostPosted: Fri Feb 15, 2008 4:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
OK, so it's the old Mike Irwin trick?


Ian, I have used the basic Mike Irwin circuit for my VCA design and it works very nicely. When I saw the TH VCA circuit, I knew exactly where it came from. Not that it was a bad thing, the Irwin circuit is very clever. I just changed a few things in my front end for my circuit. I really like this chip because it runs very quiet, as has been mentioned, and it has fantastic dynamic range. The CV response time is very good also.

Quote:
I always thought it would be fun to try antilogging the input CV to get a linear response, rather than dedicating a VCA stage to be a servo.


Boy, I thought the same thing myself Ian. A cool approach. Wink This way I could get 4 linear VCA sections from one IC. Or use one SSM2164 for two LIN/LOG VCA's and one VC "Stereo Panner" using the other two sections. Very Happy

Bill
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Sound



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PostPosted: Tue Mar 18, 2008 6:50 am    Post subject: Reply with quote  Mark this post and the followings unread

locking at the schematics, I have a question.

For what is used a negative voltage initial?
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fonik



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PostPosted: Tue Mar 18, 2008 8:11 am    Post subject: Reply with quote  Mark this post and the followings unread

i'd thought you may want to compensate an offset of another cv source.
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Sound



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PostPosted: Tue Mar 18, 2008 8:24 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:
i'd thought you may want to compensate an offset of another cv source.


Thanks fonik... but the most useful is the positive voltage, so positive to ground? is it?

When we will use the negative initial? Any example?
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Coriolis



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PostPosted: Tue Mar 18, 2008 11:03 am    Post subject: Reply with quote  Mark this post and the followings unread

fonik: did you have success with this layout?

C
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Scott Stites
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PostPosted: Tue Mar 18, 2008 8:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
When we will use the negative initial? Any example?


One reason would be that if your control voltage, say an ADSR EG, for whatever reason, has a positive offset on it, the only way you could close the VCA while the CV is connected would be to mix a bit of negative voltage with it.

Cheerio,
Scott

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