# Class D amplifier output filter calculation

I want to build a simple amplifier with TI's TPA3116D2, which is "filterless" Class-D amplifier. This device can be run with a traditional LC filter at the output, or, if the speaker wires are short, simply a ferrite bead with a 1nF capacitor.

I'd like to test with a traditional LC filter. The example values in the datasheet are 10uH and 680nF.

I don't happen to have any 10uH coils, but I have plenty of 22uH ones. What happens if I use a larger inductance and smaller capacitance?

According to my calculations, the suggested filter has a 61KHz cutoff frequency and 3.8 ohms impedance. A filter made with 22uH and 330nF will have a 59KHz frequency but the impedance will be 8.16 ohms

What does this mean in this case? Will it affect the performance of the device?

• @hjf - depending on output current into speaker you are significantly further from saturation because the current is halved into each (although there will be about 1.5 more turns on a 22$\mu H$ coil than the 10$\mu H$ coil). Do you have a spec for the inductor? – Andy aka Sep 1 '14 at 13:51