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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
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diablojoy
Joined: Sep 07, 2008 Posts: 809 Location: melbourne australia
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Posted: Sat Dec 03, 2011 12:10 am Post subject:
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hmm very interesting and good to know it works
but with the 2 sides in parallel as drawn i see no advantages
over just using one half of the chip though.
if the circuitry could be duplicated but kept seperate for the signal in / out
but still a single bias for both halves would this allow one cv control over 2 signal paths ?
in this instance perhaps a very limited dual VCA
perhaps more interesting is if more change can be made to each side
will need to play around with this a bit i think _________________ In an infinite universe one might very well
ask where the hell am I
oh yeah thats right the land of OZ
as good an answer as any |
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andrewF
Joined: Dec 29, 2006 Posts: 1176 Location: australia
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Posted: Sat Dec 03, 2011 3:59 am Post subject:
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Thanks Ian
that puts quite a few EN circuits back on the menu. |
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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Posted: Sat Dec 03, 2011 5:10 am Post subject:
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diablojoy wrote: | hmm very interesting and good to know it works
but with the 2 sides in parallel as drawn i see no advantages
over just using one half of the chip though. |
Improved S/N? The pins are opposite each other so it's simple to do. I'd be interested to see a circuit diagram what other ideas you have.
Ian |
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EdisonRex
Site Admin
Joined: Mar 07, 2007 Posts: 4579 Location: London, UK
Audio files: 172
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Posted: Sat Dec 03, 2011 11:17 am Post subject:
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Very timely of you to share this, Ian. Thanks. _________________ Garret: It's so retro.
EGM: What does retro mean to you?
Parker: Like, old and outdated.
Home,My Studio,and another view |
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Dan Lavin
Joined: Nov 09, 2006 Posts: 649 Location: Spring Lake, Mi, USA
Audio files: 21
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Posted: Sat Dec 03, 2011 10:26 pm Post subject:
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Thanks Ian! I like to keep a stock of LM13700's since they are versatile for easy VCA's and VCF's. I'll have to try these out! _________________ Synth DIY since 1977! |
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Boogdish
Joined: Sep 21, 2009 Posts: 122 Location: Bloomington, IN
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Posted: Sat Dec 03, 2011 11:22 pm Post subject:
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I hadn't heard of this trick before, is there an article somewhere that explains the benefit of drawing bias current from V-? I feel like there's something obvious that I'm missing. |
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diablojoy
Joined: Sep 07, 2008 Posts: 809 Location: melbourne australia
Audio files: 11
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Posted: Sun Dec 04, 2011 12:52 am Post subject:
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Quote: | Improved S/N? The pins are opposite each other so it's simple to do. I'd be interested to see a circuit diagram what other ideas you have.
Ian |
improved signal to noise - valid point i didnt think of that possibility.
as far as other cct idea's i havent actually thought of anything specific yet
just considering i dont like to leave such a chip only half used if i can help it.
I suppose as this was brought up most recently in the simple x-fader topic
and i stated there that i would look into drawing up a board for a dual module from the elegant schematics by richardc64
i could see if a linked cross fading quad VCA could be accomplished
using 2 x lm13700. mind you this is a very unthought out proposal
just the very vaguest concept of this moment .
but it may hold some merit
2 CV's controlling 4 VCA's in pairs crossing each other
I am sure its been done before but perhaps not exactly this way _________________ In an infinite universe one might very well
ask where the hell am I
oh yeah thats right the land of OZ
as good an answer as any |
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richardc64
Joined: Jun 01, 2006 Posts: 679 Location: NYC
Audio files: 26
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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Posted: Sun Dec 04, 2011 10:16 am Post subject:
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diablojoy wrote: | improved signal to noise - valid point i didnt think of that possibility. as far as other cct idea's i havent actually thought of anything specific yet just considering i dont like to leave such a chip only half used if i can help it. |
It could be used as a stereo VCA, I guess, if you ever needed that.
Ian |
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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Posted: Sun Dec 04, 2011 10:21 am Post subject:
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Boogdish wrote: | I hadn't heard of this trick before, is there an article somewhere that explains the benefit of drawing bias current from V-? I feel like there's something obvious that I'm missing. |
It's just a simple (low part count) method. Myself, I prefer the 1 opamp / 1 transistor method, but if someone wants to follow one of the old designs exactly, this will work. It's disadvantage is that the 100k input resistor produces a pretty low bias current range, so the S/N isn't as good as it could be.
Ian |
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oldcrow
Joined: Sep 24, 2008 Posts: 25 Location: Chicago, IL USA
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Posted: Wed Dec 21, 2011 10:43 pm Post subject:
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Ian, have you tested a paralleled-cell version for SNR? Interested in seeing what improvements, if any, can be made there.
Crow
/**/ _________________ http://www.last.fm/music/Scott+Rider |
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frijitz
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
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Posted: Thu Dec 22, 2011 8:18 am Post subject:
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oldcrow wrote: | Ian, have you tested a paralleled-cell version for SNR? Interested in seeing what improvements, if any, can be made there. |
I believe Serge in his old EN article mentioned paralleling devices for the expected sqrt2 improvement.
Ian |
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oldcrow
Joined: Sep 24, 2008 Posts: 25 Location: Chicago, IL USA
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Posted: Thu Dec 22, 2011 10:46 pm Post subject:
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frijitz wrote: | I believe Serge in his old EN article mentioned paralleling devices for the expected sqrt2 improvement.
Ian |
Oh yeah, I'd forgotten all about that one. Thanks!
Crow
/**/ _________________ http://www.last.fm/music/Scott+Rider |
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