Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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Not all of it.

Posted by Al Sekela (A) on February 21, 2009 at 16:12:12

In Reply to: RE: Speaker RFI filter test posted by fmak on February 21, 2009 at 03:22:45:

RF noise goes wherever parasitic capacitances and feedback networks allow it to go. RF noise picked up by the speaker circuit gets into the amplifier through the output terminals. Some of it then goes directly to the input if the amp has any global feedback. If the amp does not, then the noise can still get to the active stages through parasitic capacitances inside the amp.

Damping the speaker cables with the kind of filters described here affects noise over 1 MHz, and will have negligible effect on the audio band gain and phase response of the amp.

The other ports to the amp (or any other active device) are also susceptible to RF noise. The input is obvious, but the power entry port may also admit enough noise to degrade the signal. The main filters in the power supply have very low resonant frequencies, and are ineffective in stopping RF noise. Ayre, for one, recognizes this and builds RF noise filters into their power supplies.

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