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 Forum index » DIY Hardware and Software » Developers' Corner
LM13700 VCA and other circuits
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alkopop79



Joined: Aug 21, 2008
Posts: 44
Location: London

PostPosted: Sun May 12, 2013 9:46 am    Post subject: LM13700 VCA and other circuits Reply with quote  Mark this post and the followings unread

I wonder how should I modify the VCA circuit in the datasheet to work with 9V instead of +-15V. Needless to say, the OTA would get +-4.5V respectively. How do I change the reistor values? Any help would be appreciated!


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richardc64



Joined: Jun 01, 2006
Posts: 614
Location: NYC
Audio files: 25

PostPosted: Mon May 13, 2013 7:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Forget that. Below is the VCA from "SynTom", a single-supply Percussion synth. The original supply was 12V. For 9V the resistors most likely to need adjusting are R32 and R33.

The signal input is reference to ground, and the low end of the output pot could connect to ground instead of 1/2V+.


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alkopop79



Joined: Aug 21, 2008
Posts: 44
Location: London

PostPosted: Mon May 27, 2013 12:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Eventually I've found a simple VCA that works fine at the Rockit Synth's blog:

http://hackmeopen.com/wp-content/uploads/2011/04/My-VCA.png

Thanks for the help!
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alkopop79



Joined: Aug 21, 2008
Posts: 44
Location: London

PostPosted: Mon May 27, 2013 12:50 am    Post subject: Reply with quote  Mark this post and the followings unread

Also, I've built a VCO circuit I've found in Ray Marston's article at Nuts&Volts:

http://www.nutsvolts.com/uploads/magazine_downloads/11/May%202003%20Ray%20Marston%20-%20Understanding%20And%20Using%20OTA%20OP-Amps.pdf

Page 10, Figure 19. square wave and triangle VCO[/url]

Instead of 30V (+-15) I used 9V (+-4.5V) and works just fine.
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alkopop79



Joined: Aug 21, 2008
Posts: 44
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PostPosted: Mon May 27, 2013 5:27 am    Post subject: Reply with quote  Mark this post and the followings unread

The VCO circuit.


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beep



Joined: May 05, 2013
Posts: 84
Location: Germany

PostPosted: Mon Jun 17, 2013 1:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

http://folkurban.com/Site/9VpoweredMS20SallenKeyLPVCF-690.html THIS IS REALLY COOOOL!

I built this today and finally got it working <3 I used 10k instead of 100k after cutoff cv, 100k limits the range too much




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analog_backlash



Joined: Sep 04, 2012
Posts: 391
Location: Aldershot, UK
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PostPosted: Mon Jun 17, 2013 4:00 pm    Post subject: Reply with quote  Mark this post and the followings unread

I've been playing "spot the difference" with your two schematics, but I've come to the conclusion that it's a double-post Very Happy . Anyway, it sounds really great. I've used this VCF in the past:

http://www.magicmess.co.uk/electronics/12dbfilter.php

I think that yours sounds better though. Also, I found that the BP signal was very weedy, so I added a single transistor amp on this output.

Gary
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beep



Joined: May 05, 2013
Posts: 84
Location: Germany

PostPosted: Wed Jun 19, 2013 3:27 am    Post subject: Reply with quote  Mark this post and the followings unread

"it distorts in a bit yukky way, perhaps clippers there could tame that a bit"

clippers where? at the output?

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L´Andratté



Joined: Sep 23, 2012
Posts: 57
Location: Hamburg, Germany
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PostPosted: Wed Sep 18, 2013 4:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Put one (or 2/serial/antiparallel/si/ge/experiment) diode to ground between the resonance pot and the 680 pf.
Probably with switch.
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