[Phil Allison[_4_]]

Don Pearce wrote:



Transformers were an unfortunate necessity back in the days of valves,
both for hum rejection and impedance matching. Now, though, when an
op-amp and a couple of discrete transistors at the front can give an
ideal noise match to about 160 ohms (ideal for most mics), and CMRR of
in excess of 100dB is not a problem, there is really no point in using
a transformer, unless it is as an effect (more distortion and more
noise). Although why anyone would really want that is beyond me.




** A few words in defence of audio transformers.

1. When used for coupling a mic to a pre-amp, the audio signal is truly floating - so incidental DC voltages have no effect and it is very easy ( using a CT on the tranny) to provide full 48V phantom power for those mics that need and or benefit from it.

2. The use of a step up transformer inside a ribbon mic is virtually essential to match the sub 1 ohm impedance of a ribbon to typical mic input stages.

3. Conventional dynamic mics can benefit from an internal step-up tranny - as found in many older mics and still fitted to Shure SM57s and 58s. This allows the voice coil be of much lower impedance using fewer turns of heavier gauge wire improving both ruggedness and longevity of the mic.

NB:

I am well aware of the various issues with transformers which require some real "audio engineering" to render negligible in practice.


..... Phil