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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
CGS49 Dual CMOS filter - Odd problem with both filters
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Flareless



Joined: Jan 16, 2016
Posts: 27
Location: Ontario, Canada

PostPosted: Mon Jan 23, 2017 11:08 am    Post subject: CGS49 Dual CMOS filter - Odd problem with both filters Reply with quote  Mark this post and the followings unread

I've built a few of these modules but this one seems to be giving me an interesting problem;

When I run an oscillator into Filter 1 it's sound comes out the High Pass and Notch filters loud and clear but when I switch to Low Pass or Band Pass the volume decreases sharply. Further, the Frequency pot has no effect on the sound no matter which selection I make. The CV inputs don't either. The Resonance and Distortion % pots seem to work fine.

The exact same thing happens on Filter 2.

I've wired this module with the -15V going to the Frequency knob rather than 0V and with the spread coming from both CVSN on Filter 1 and pin 3 of the TL072 (where it meets the 2K2 resistor).

This has worked for me on other CGS49 modules I've built but this is a strange problem that I can't seem to figure out

Does anyone have suggestions as to what I might do to test / fix this problem? Any help would be greatly appreciated.

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Rich
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Flareless



Joined: Jan 16, 2016
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Location: Ontario, Canada

PostPosted: Mon Jan 23, 2017 11:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Here is a copy of the wiring diagram I used...

Posted Image, might have been reduced in size. Click Image to view fullscreen.

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Rich
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Flareless



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Location: Ontario, Canada

PostPosted: Wed Jan 25, 2017 2:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

This turned out to be due to bad CA3080 chips that I purchased from China.

Thanks for the tip Ken!

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wackelpeter



Joined: May 05, 2013
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Location: germany
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PostPosted: Thu Jan 26, 2017 7:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Think i have some similar issue... can't recall it exactly right now, but i think it was BP and ??? which were very quiet compared to 2 of the other Outputs...
Good idea to swap the CA3080... but i think i didn't got mine from China/eBay... don't know... i will try it out as the rest seems to be correct from what i remember...

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