![]() ![]() If it's that complicated, I probably won't understand the math. I can show you how I worked out the transfer function, how we solve the equations and just how complicated this can be I I were you I would use an RC filter, very easy to design, very easy to work with, no resonance but it will still filter good enough for you, we can even do the same thing to get the equations for that and its a nice learning curve I can show you how I worked out the transfer function, how we solve the equations and just how complicated this can be the advice Mike gave was actually really bad advice and the filter would not last very long I used matlab to do a bode plot of the system you propose, then I changed the components to 3mH and 10uF Have no idea what I should set the impedance to,īut you design a filter to pass certain frequencies and block others, you are filtering square waves, square waves contain infinite harmonics so its not just one frequency you have presentĭesigning resonant filters to filter these waveforms is not trivial, you have to make sure the resonant frequency is not excited which means doing a FFT to see what frequencies are present and designing around that not easy to doĪ 330mH inductor is a very big inductor, a 153nF cap is very small Its first order differential equations and second order differential equations, the number of energy storage devices determines what order differential equations you end up with Yes, one energy storage component, an LC filter is a second order systems as it contains two energy storage devices Is a first order filter one with just a capacitor or just an inductor Imaginary numbers is just trigonometry and quartic equations are raised to the power of 4 I don't know how to deal with imaginary numbers, and until today I'd never even heard of a quartic equation. You can throw all the deep theory at it if you like, at the end of the day its nothing more than the potential divider equation I didn't fully explain, however I did post the transfer function, do you know how to derive the transfer function I posted? I appreciate the help, but I don't understand a thing you just said Then they behave like the 3W amp where noise is minimal. unless they are powered from a wall adapter instead of the same battery (D cells or LiPo - should be plenty of juice). By which I mean, on the 3W amplifier, the noise is much quieter than the audio, while on the 20W amplifiers, the noise ends up being much louder than the audio. If I recall correctly, this does affect the 3W amplifier on the board, but again, the effect is lessened. If I connect a servo to the board, or dim an automotive LED driven by a 12V boost converter using PWM I also get varying amounts of static. The issue with the external amps is an extremely loud high pitched buzzing noise that increases in volume as more LEDs light up. Well, it may, but it's so quiet that it doesn't matter. The issue does not seem to affect the 3W amplifier I have integrated into the board itself. It happens with both the Lepai2020A+ and the DTA-2, both available on Parts Express. I assume the amplifier has sufficient filtering on its input. I don't know, nor do I know how to determine this. One is to filter the power supply better where it feeds the audio amp. Or are the audio input lines picking up emissions from the LED switching?Ģ different solutions. Is the noise coming in on the power supply lines? (You know, I'm still not clear on why this affects my amplifier when it is powered from the same battery, but not when the power source is separate.) PWM noise from some LED drivers is getting into my audio system. Oh, and yes, this is for filtering power. I have no idea if the values I am getting are sane, and I don't know whose advice to trust. That's way off from what DC42 suggested here: I have no idea what I should set the impedance to, but setting it to 1466 ohms gives me 330mH for the inductor, and 153.5nF for the two capacitors. That only calculates PI filters, not LC, and I find the fact that it accepts frequencies only in the MHz or GHz range suspicious, but it does seem to allow me to enter. I have tried adding all sorts of capacitors to remove the noise, and had only moderate success by adding several caps of different values (up to 4700uF), and I've read using inductors alone is no more effective at reducing noise. Is a first order filter one with just a capacitor or just an inductor? Wikipedia wasn't clear on that. (I had to check to make sure you didn't mean to write quadratic.) I appreciate the help, but I don't understand a thing you just said.
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