IEEE Consultants' Network of Long Island

Filter Pins - John Dunn, Consultant, Ambertec, P.E., P.C.

The physical structure of a single pin of a filter pin connector is represented as follows as a ferrite bead over the center pin with shunt capacitors to the shell on each end:    

 

Transformer Primary Winding Capacitor - John Dunn, Consultant, Ambertec, P.E., P.C.

When a transformer winding is driven from an amplifier whose DC voltage level must be blocked from the driven winding and high isolation requirements are an issue, it is better from a cross-coupling suppression standpoint to put that capacitor in the low side of the transformer winding instead of in the high side. 

Audio Transformer Far-Field Cancellation - John Dunn, Consultant, Ambertec, P.E., P.C.

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.