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Opamp bandpass filter too noisy

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dusan:
I have band pass filter made from opamp (picture in attachment), the peak is around 650Hz, the problem is that it is too noisy. I hear a lot of white noise in headphones (maybe it's not pure white noise, it has some hollowness to it, like a wind). To reduce the possibility the noise is in the input I replaced U1 with 1k resistor and the noise is still there. I also try different opamps (741, lm258, jrc4558, ne5532p, op27g) and also tried polyester caps instead of ceramics. I also tried 2 different headphone amps. It's still there so I think the noise is by design, not bad part. How can I make bandpass filter less noisy?

Kleinstein:
The filter has quite some gain (~500), at least if you count from after the initial divider. I assume the divider (R1,R6) part is just there for tests. If not, this should be the main point for the noise, making tghe circuit high noise by design.

For the lower frequencies the OPs input also sees an increasing impedance. So current noise from the OP can contribute at low frequencies. This could be bad for the NE5532 and OP27. The TL071, 741 and LM258 are rather high noise to start with.
With so much gain the LM258 is also a bit on the slow side.

Holowness / wind like soud may indicate a possible EMI problem,  like picking up some RF signal. This should however depend on the OP used.

I don't know the MFB filter in detail. The high gain may be needed to get a high Q. Instead of a 2nd order high Q fitler one may consider a 4th order lower Q fitler.

iMo:
Where your filter's R and C values come from?

PS: try with this tool:
http://sim.okawa-denshi.jp/en/OPtazyuBakeisan.htm

Your values show large gain (28dB) and possible ringing (I do assume it is a CW filter)..

dusan:
Ok, so which opamp should I use to get least amount of noise?

jmelson:

--- Quote from: dusan on December 09, 2021, 10:34:10 am ---Ok, so which opamp should I use to get least amount of noise?

--- End quote ---
My favorite, all around op amp is the OP275.  For really low noise, I use the AD706, which should have enough bandwidth for your 650 Hz filter.
Jon

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