[sdiy] Filter problems

David G Dixon dixon at mail.ubc.ca
Sun Jan 28 03:26:33 CET 2018


Yes, you simply cannot use 5532 in filters.  We learned that the hard way.
Their input currents are just too large -- so large, in fact, that the opamp
"golden rules" really don't apply to them.


  _____  

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Guy
McCusker
Sent: Saturday, January 27, 2018 9:02 AM
To: Tim Ressel
Cc: SYNTH DIY
Subject: Re: [sdiy] Filter problems


Are you really using 5532s there? Does it behave the same way with a FET op
amp (e.g. TL07x or similar) instead? I would have thought the input bias
current of a 5532 made it unsuitable for use as an integrator at all, and
especially with a device like a 2164 which I understand is fussy about its
current output. 

Guessing really...

On Sat, 27 Jan 2018 at 16:30, Tim Ressel <timr at circuitabbey.com> wrote:


Hi,

Filters can be a pain. I've got one that is misbehaving. Here is a link
to the schematic:

https://www.dropbox.com/s/acjvwb17nmuok1n/PrismFilter.pdf?dl=0

At low CVs it filters fine, but as the freq cv hits around 2 volts the
behavior gets odd. I start seeing a rising DC bias on all the outputs.
At about 3 volts all the outputs rail positive.

Any help is appreciated. Thanks for playing!

--
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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