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.
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
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.
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.