Two small audio transformers of very low power ratings had been pressed into service together in order to handle the required output power level of a particular audio amplifier. The arrangement worked well, but there was some 400 Hz interference getting into the intended signal.
The interference was found to be coming from a 400 Hz power transformer's stray magnetic field.
An approximately 10 dB reduction of that interference was obtained by reversing the phasing dots of both the primary and secondary windings of one of the two transformers, thereby achieving some measure of far-field cancellation without affecting performance with regard to the intended audio signals.
Nice reminder - opposing the fields is generally favourable for EMI.
Posted by: George Storm | February 01, 2011 at 03:49 PM
I used a similar technique with a magnetic amplifire I built.
Posted by: Frank Walker | February 01, 2011 at 07:03 PM
Very good tips and viewpoint. Usually the success of a business or a site comes from your own hands also. Think wisely and positive. Thanks for having it here.. :)
Posted by: Jacksonville Electrician | August 11, 2011 at 10:30 AM