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LPF (6th order) with TL072C

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JimWest:
Hi Guys,

I have a tricky job today. I hope you can help me.
At the moment I'm recreating an old sound module from 1992.
Unfortunately, I only have pictures of the board. But I was able to trace the circuit.
However, I miss the values ​​for the capacitors. These are SMD capacitors (0805) except C3/C4 these are 1206.
I think the circuit should be something like a LPF (6th order). At least according to the data sheet of the following surround sound ICs.

Does anyone have an idea whether the circuit makes sense so far and which values ​​are suitable for the capacitors?

Thank you for your help!

iMo:
Download the LTspice and put it there..

JimWest:
Oh cool. I did not know that there is something like that. I will try it. Thanks for the tip.  :)

Yansi:
U2.2 is a textbook sallen-key third order lowpass. Canbe readily calculated by using filter tables, or just find almost any online web application for that. (

preceding amplifier is just a textbook inverting amplififer, with a small compensation/bandwidth limiting cap. Input coupling cap sets the low frequency cutoff (C1, R1).

Not sure how you came up with sixth order. No way would that be needed.

PS: Okawa-Denshi has a very good set of tools for filters: http://sim.okawa-denshi.jp/en/Fkeisan.htm

//EDIT: C3, C4 = 100nF.  Decoupling.


iMo:
Below attached the .asc for LTspice. Doubleclick and it opens in LTspice. Click the runner to simulate the AC sweep.
You may select the opamps and R,C values and simulate.

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