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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
john loffink mod for steiner vcf
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numbertalk



Joined: May 05, 2008
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PostPosted: Fri Jan 15, 2010 8:17 pm    Post subject: john loffink mod for steiner vcf Reply with quote  Mark this post and the followings unread

On Ken's site, John suggests changing the divider resistor for the CV inputs from 1K to 680R. Then because of this change he also suggests changing the input resistor for the FM input from 220K to 120K. My question is, then should the input resistor for the Freq control stay at 220K or does that need to change as well? Since the whole point of changing the divider resistor was to adjust the response of the Freq control, I'm guessing he'd mention needing to change that resistor as well if it were necessary, and that changing that resistor would throw off the effect of changing the 1K resistor, but just wanted to make sure. I asked Ken and he seemed to think this made sense but had never built it with these mods so wasn't totally certain.
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slacker



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PostPosted: Sat Jan 16, 2010 4:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah you leave the resistor from the wiper of the Freq pot as 220k.
Like you said, if you change that to 120k as well you'll just cancel out the effect caused by changing the 1k to 680.
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numbertalk



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PostPosted: Sat Jan 16, 2010 7:46 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks!
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The Bad Producer



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PostPosted: Sun Jan 17, 2010 6:20 am    Post subject: Reply with quote  Mark this post and the followings unread

This is interesting, but I haven't tried it myself yet...

http://synthnoise.com/synthacon.html

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numbertalk



Joined: May 05, 2008
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PostPosted: Sun Jan 17, 2010 6:28 am    Post subject: Reply with quote  Mark this post and the followings unread

The Bad Producer wrote:
This is interesting, but I haven't tried it myself yet...

http://synthnoise.com/synthacon.html


I forgot about this. I followed John Loffink's suggestion and used a 220K resistor. Ken had suggested I put it between +VE and the CW lug, but I got weird results with that, so I moved it to the wiper and worked much better - this is the way I saw that Richard Brewster had done it so assumed it was correct, but maybe it would sound better with a 22K in this different location. If I play around with it more and am not happy with the response of the freq control maybe I'll try this.
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numbertalk



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PostPosted: Sun Jan 17, 2010 4:25 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just tried that adjustment to the Loffink mod, changing that resistor to 22K and putting it directly in line with the +VE lug and it worked great. The frequency control now works better than when I had a 220K in series with the wiper lug.
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