[sdiy] Filter problems

Jay Schwichtenberg jschwich53 at comcast.net
Sat Jan 27 22:33:57 CET 2018


Tim,

Look at the Shruti state variable filter schematic. It's pretty much the
same circuit.

1) 3.6V zeners are used in Shruti verses 3.9V, not a problem.
2) Your R11 is 33K, Shurti it's 15K.
3) The BP out in the Shruti filter is feed back into the input (your U2B)
with a 330K resistor.

Have you put a meter/scope on FC to see what it is doing?

Jay S.

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tim
Ressel
Sent: Saturday, January 27, 2018 8:28 AM
To: SYNTH DIY
Subject: [sdiy] Filter problems

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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