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 Forum index » DIY Hardware and Software » Developers' Corner
Moog VCF - Resonance, Voltage Control of ?
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unshaven



Joined: Feb 18, 2012
Posts: 8
Location: Germany

PostPosted: Sat Jan 26, 2013 11:28 am    Post subject: Moog VCF - Resonance, Voltage Control of ? Reply with quote  Mark this post and the followings unread

UPDATE:
I might go with that nice high voltage digi pot here somebody elsewhere just suggested to me, although costs 5..6 EUR - it is hassle free for my application & needs no extra parts (compared to what I#d need to do if I have a VCA chip like was suggested by somebody posts down below):
http://www.analog.com/en/digital-to-analog-converters/digital-potentiometers/ad7376/products/product.html


-----------------
Hey there!

Looking at the Minimoog VCF circuit (e.g. the Yusynth or other variants), how would you go about adding voltage control for the resonance, or in moog terms, "emphasis" ?

I thought about using digi pots - but it seems they usually are for current in one way only.
I just built such a VCF on prototype board & saw on the scope that, if there is an input signal (vs. self oscillation), the voltage in the resonance path swing positive and negative, so digi pots are out, I guess. (or could one use two in opposing polarities? I know electronic basics only, excuse stupid questions Very Happy )

I have a few LDRs & bright LEDs laying around for experimenting, but I'd prefer not to use this poisonous and hardly obtainable stuff.
I wouldn't care about them being slow, though, so if there are other slow solutions, keep 'em coming Wink

I have thought about putting a VCA in the feedback path, but my limited knowledge failed me there. Current vs. voltage, differential amplifier - amplifying what difference there? etc... I'm lost. I was drawing an OTA based minimum parts count VCA in there the other day and just realized that, hehe.

Has anyone done this, successfully, knows what he's doing, and could give me advice? Wink

Last edited by unshaven on Sun Jan 27, 2013 1:40 pm; edited 2 times in total
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elmegil



Joined: Mar 20, 2012
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PostPosted: Sat Jan 26, 2013 8:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

I can't say a lot, I'm still in the start of my learning curve, but I'm willing to bet that if you wanted to do a VCA solution you would do well to use the CoolAudio 2164 (SSM2164 clone), it's two VCAs on a chip, and ought to save you the trouble of the OTA.
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unshaven



Joined: Feb 18, 2012
Posts: 8
Location: Germany

PostPosted: Sun Jan 27, 2013 3:30 am    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
CoolAudio 2164 (SSM2164 clone), it's two VCAs on a chip, and ought to save you the trouble of the OTA.


A tad pricey those things. And don't those things not aly have current output?
Well, I don't really know what's important to replace the feedback potentiometer anyway, so can't make decisions.
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elmegil



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PostPosted: Sun Jan 27, 2013 8:14 am    Post subject: Reply with quote  Mark this post and the followings unread

The original SSM2164's are definitely pricey, $8 a chip and up. However, the Cool Audio V2164 is available for less than half that (even though the list price is nearly the same). Folks frequently cite Small Bear Electronics as a source, but I can't find it on his site. However, Magic Smoke has them for $3.50 in small quantities. http://magsmoke.com/pricelist.asp

And I was wrong, it's not dual, it's quad.

Cool Audio does make a V2162 with two VCAs per chip, but their list prices are basically the same as the V2164.
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unshaven



Joined: Feb 18, 2012
Posts: 8
Location: Germany

PostPosted: Sun Jan 27, 2013 1:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

elmegil wrote:
The original SSM2164's are definitely pricey, $8 a chip and up. However, the Cool Audio V2164 is available for less than half that (even though the list price is nearly the same). Folks frequently cite Small Bear Electronics as a source, but I can't find it on his site. However, Magic Smoke has them for $3.50 in small quantities. http://magsmoke.com/pricelist.asp

And I was wrong, it's not dual, it's quad.

Cool Audio does make a V2162 with two VCAs per chip, but their list prices are basically the same as the V2164.


Nice to know this exists, may be good for other stuff, thanks!
But I might go with another component - see updated first post.
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