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Low Pass Filter Design

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AltAudio

New Member
Hello,

I am trying to design an audio low pass filter that lets kick drum and percussion through but not much else, perhaps something like 40Hz. I am using a 1/8" output from portable CD player. With multimeter, the 1/8" output shows an impedance of 474Ω when + lead is on tip(of tip-ring-sleeve configuration) and - lead on sleeve, and 170Ω when + lead is on ring and - lead on sleeve.

Reading through post from Russlk - https://www.electro-tech-online.com/threads/low-pass-audio-filter.13192/, I wonder if this configuration will work with impedance I have on my circuit board. The load impedance is quite low though, as I am using an op amp(LM 386N 440mW) to boost the audio signal and output as electical impulse through electrode. So fidelity is not an issue, I just need the low end to pass through.

Many thanks for your consideration.........Mickey
 
That circuit will likely work for you. Its rolloff is at about 100Hz, but that may be acceptable since there is not a lot of signal below 40Hz from a kick drum. It has a 10k ohm output impedance which should be ok
 
Active Low Pass with LT Spice

Hello,

Trying to get the low pass schematic to graph but receive attached error. Was not able to find exact op amp model - LM324. Thought perhaps universal op amp would work, but all seem to throw errors.
 

Attachments

  • LowPass.JPG
    LowPass.JPG
    39.5 KB · Views: 215
If you're looking for a very steep cutoff, check the MF4 or MF6 series from National Semiconductor. I've had good results with them. <<<)))
 
OK I actually have National Semi's LME49720 which I will ultimately use in finished product, but for testing purposes I am using the lousy old LM324. How then do I replicate the graphing output as seen in attachment? If I replicate specs it will not graph, just throws one error after another.
 

Attachments

  • DF133.png
    DF133.png
    55.1 KB · Views: 188
Here you go.
 

Attachments

  • DF133.png
    DF133.png
    46.7 KB · Views: 153
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