Tracing the origin of successful and great sounding recordings of all time one can find more than one signal transformer in the signal path from record producer's brain to listener's brain. An obvious example is for example the transformer inside a Neumann U47. The input, output transformer of the following preamplifier,..., the output transformer of the class A 300B power amplifier of the listener.
Some reasons why.
1. Restricted bandwidth helps make the sound correct to the listener's brain. If gentle roll offs do not exist then the sound is bass heavy and treble heavy to brain perception due to voice effort curves, Fletcher-Munson equal loudness curves, proximity effect for low frequencies, pressure doubling effect for high frequencies, low frequency reasonant modes of 99.9% of environments not treated with low frequency absorbing membranes for example.
2. Possible peak limiting saturation characteristics due to B-H curves. This may result in an increased average value of signal. And also a subjective increase of loudness due to lifelike overtones produced. In fact an audio transformer is close to a simulation of an analog tape recorder instanteniously reproducing.
3. Canceling of RF and other noises, from balanced operation. If in phase moving electrons enter both input terminals they electrically collide so those fields are extinguished. In fact it is the electromagnetic fields that collide, one field entering one terminal, a similar filed entering the other terminal.
4. Damping of the electron carrying (moving to sound) element in moving coil or ribbon microphones. By Lenz's law or conservation of energy. The same way electromagnetic brakes operate on metro trains or other electrical vehicles. So reduced pops.
5. Stepping up the signal voltage reduces hiss produced by the following active preamp stage.
6. They do impedance matching. Therefore no reflection of signal energy back or less reflected back. Impedance matching is one of the most important principles used by human civilization. An obvious example is how the Pyramids, or Parthenon in Acropolis were built, by using mechanical passive impedance matching amplifiers.
7. Stepping up the voltage and therefore impedance makes a moving coil's signal high and high Z like a condenser capsule. Then an electron tube or JFET is used as an active device to further increase voltage and increase current so it can drive long cables just like condenser internal prepreampifiers.
Disadvantages:
What are the disadvantages of transformers?!
They may not be easily mass produced?
Why should one eat a mass produced cake, bread, snack which has in the tiny letter ingredlists list of the packaging, (cheap) vegetable oil, palm oil or palm fat which have a reputation of clogging blood arteries? That makes the mass produced snack cost less than a euro and thousands of euros to be spent for the long run health damage.
In the well known fairytale series, Canelina the Cat needs her friend the Patient Tortoise to hand wind the transformers and inductors.
References:
The Feynman Lectures in Physics - Feynman, Leigton, Sands
Flat frequency responce not from mic to loudspeaker but from singer's vocal chords to listener's brain, Sound Picture Recording and Reproducing Characteristics - Loye, Morgan - Journal of the Motion Pictures Sound Engineers
Sound and Hearing - Stevens, Warshofsky - Time Life
Tubes vs Transistors, is there an audible difference? - Russel O. Hamm - Journal of the Audio Engineering Society
Fringe Knowledge for Beginers - Montalk
Enchiridion - Epictetous
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