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 Forum index » DIY Hardware and Software » Thomas Henry designs
VCF-1 OTA problem
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earo



Joined: Apr 19, 2011
Posts: 12
Location: haifa

PostPosted: Fri Jan 18, 2019 9:43 pm    Post subject: VCF-1 OTA problem Reply with quote  Mark this post and the followings unread

Hi! Smile

I am building the VCF-1, and after having done this successfully many times (I love this filter) - this time somethings' wrong!

As soon as I turn on the power, the IABC inputs get locked at nearly -15V and the filter does not function!

I have tried numerous different ICs (including changing from the original CA3080 to a single LM13700 - making the necessary adjustments, and tinkered with the exponential convertor as well - to no avail. Any ideas?

Thanks!
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wackelpeter



Joined: May 05, 2013
Posts: 443
Location: germany
Audio files: 10

PostPosted: Fri Feb 01, 2019 3:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Do you used an Selfmade PCB or an available kit?
Also a link to the schematics and maybe Pictures of your build are always helpful.

Have you already tried to stick a pot wired between power rails and it's wiper with a bigger resistor (27k to 33K) to the bias Control Input?

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earo



Joined: Apr 19, 2011
Posts: 12
Location: haifa

PostPosted: Sun Feb 03, 2019 8:57 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey there. Thanks for taking the time! Smile

This weekend I finally had a chance to dig in.
I do all my circuits on proto boards so there's always chance for errors..
I guess it's time for better glasses because these molex pins were inserted the wrong order.. dah.. I should have tested before posting (and frying a few ICs in the process..)

Apologies and happy eyesight to y'all!

Very Happy
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wackelpeter



Joined: May 05, 2013
Posts: 443
Location: germany
Audio files: 10

PostPosted: Mon Feb 04, 2019 8:41 am    Post subject: Reply with quote  Mark this post and the followings unread

Nice to hear you got that solved… and don't worry i made all my boards on stripboard and i know how often i do some mistakes which cause me several headaches and Hours of Debugging before i spot them...
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