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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS04 - bleed thru
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oozitron



Joined: Apr 02, 2007
Posts: 35
Location: USA

PostPosted: Sun Nov 20, 2011 6:39 pm    Post subject: CGS04 - bleed thru Reply with quote  Mark this post and the followings unread

I've built a CGS04 mixer in the +/- format for use with a VCO. (so I can mix the normal saw with an inverted pulse, etc)

When the pots are all at center (zero), there is a small amount of audio bleeding thru. Is there any easy way to stop this?

Would putting a larger resistor between the input and the pot's wiper help?
EDIT: tried adding a second 100k resistor on the input, but as expected it just makes the signal quieter (and cuts back the output as well)... not what I want to do!

thanks for any ideas!
Drew
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andrewF



Joined: Dec 29, 2006
Posts: 1174
Location: australia
Audio files: 4

PostPosted: Sun Nov 20, 2011 8:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

no easy way except very very careful fine tuning of your pot.

the regular inputs are simply voltage dividers and can be turned down to zero.
The processor inputs range from gain of -1 to gain of +1, there is a 0 point but hard to find.
One solution would be to add a pot wired as a voltage divider (like the regular input pots) between the input and the processor pot
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Mongo1



Joined: Aug 11, 2011
Posts: 411
Location: Raleigh NC

PostPosted: Mon Nov 21, 2011 4:30 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi,

I think if you look at the page for the CGS81 you'll get the help you need. On that page, Ken describes how you change the response of the attenuverter pots, so that you can get more precision around the 0 part of the pot.

I'm going to have to do the same thing on the DUSG modules I'm building. It's pretty hard to null out the CV input on that module, so I'm going to try doing some of the stuff Ken says. Hopefully that will improve it.

Gary
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fluxmonkey



Joined: Jun 24, 2005
Posts: 696
Location: cleve

PostPosted: Mon Nov 21, 2011 8:28 pm    Post subject: Reply with quote  Mark this post and the followings unread

i did a build using center detent pots. since the detent point is never exactly 50% resistance, i measured each pot and added a 20turn trimmer in series to the side that was lower, then i trimmed each channel to get 0 bleedthru at the detent point. downside is that full scale on that side is slightly lower than the other, but hasn't been a problem for me w/ audio.
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Mongo1



Joined: Aug 11, 2011
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PostPosted: Wed Nov 23, 2011 12:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
i did a build using center detent pots. since the detent point is never exactly 50% resistance, i measured each pot and added a 20turn trimmer in series to the side that was lower, then i trimmed each channel to get 0 bleedthru at the detent point. downside is that full scale on that side is slightly lower than the other, but hasn't been a problem for me w/ audio.


That's a very cool idea! Thanks for sharing that.
Gary
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sonicwarrior



Joined: Dec 22, 2005
Posts: 229
Location: Cologne, Germany

PostPosted: Mon Jun 18, 2012 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

fluxmonkey wrote:
i did a build using center detent pots.


May be simpler to use center detent pots with a center tap and then connecting the tap to ground. Idea
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fluxmonkey



Joined: Jun 24, 2005
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PostPosted: Mon Jun 18, 2012 8:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

sonicwarrior wrote:
fluxmonkey wrote:
i did a build using center detent pots.


May be simpler to use center detent pots with a center tap and then connecting the tap to ground. Idea


where do you get center tapped pots?

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sonicwarrior



Joined: Dec 22, 2005
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PostPosted: Tue Jun 19, 2012 1:32 am    Post subject: Reply with quote  Mark this post and the followings unread

I got them through a groupbuy some years ago. Unfortunately I lost my data in an HD crash and the manufacturer is not printed on the pots, only an encircled a + 6L2.
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elmegil



Joined: Mar 20, 2012
Posts: 1486
Location: Chicago
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PostPosted: Tue Jun 19, 2012 8:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Mouser appears to have some listed, but not stocked...

http://www.mouser.com/ProductDetail/ALPS/RK11K114F30C0B104-WITH-CENTER-TAP/?qs=aFAO38vVFuvRCPF%252bQmjOTIPYUa03ol1h
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