On 6/19/2014 5:52 PM, Ellis Burman wrote:
> I think there is a common misconception that balanced audio circuits help
> eliminate RF interference. Common mode rejection of typical balanced audio
> input circuits quickly falls apart above a few hundred kHz. At typical
> radio frequencies, the circuit looks more like a bunch of diodes, detecting
> any RF that enters, whether common mode or not.
> If there is any improvement, I think it is due to better design and RF
> shielding of professional balanced devices, not common mode rejection at
> MHz frequencies.
But *transformer* balanced inputs reject common-mode crap way, way up.
And in transformerless balanced circuits, common-mode inductors help a lot.