audio transformers

[monkeytree]

i may be missing something
but what is the point of audio transformers?
plz help

 

[audioguru]

In the olden days, an output transformer matched the high output impedance of tubes, oops you're English---valves to a low impedance speaker. :lol:

 

[audioguru]

Oh yeah,
Today audio transformers are still used to isolate and balance microphones. :lol:

 

[Laplink]

It is an impedance matching and isolation transformer.

Maximum power transfer is obtained when the impedance of the output is the same as the input it is connected to.

I guess you want to connect a 100 Ohm amplifier output to an 8 Ohm input of a speaker.

It also isolates the amplifier circuit from the speaker circuit, they are not joined in any way. Magnetism generated by the amplifier circuit is is what couples the speaker circuit to follow what is happening in the amplifier circuit. It can keep the hundreds of volts from the amplifier away from unsuspecting fingers at the speaker terminals.

It's main job is impedance matching, but consider what would happen if a microphone was at, say 100 Volts and somebody touched it with their tongue or lips?

 

[audioguru]

I don't think an amplifier's mic input would be 100V. A microphone's transformer isolation prevents hum caused by a ground loop. :lol:

 

[monkeytree]

thanks now i know one more thing actualy has a perpose in life

 

[Nigel Goodwin]

There are also other audio transformer uses, converting amplifier outputs to 100V line for PA systems is a common one (and of course the opposite, converting 100V line back to low impedance for the speaker).

In the past driver transformers were quite commonplace as well, which gave the advantage of seperating the output devices from the rest of the circuit - meaning less damage when the amplifier failed.

But mostly, since the advent of transistors, audio transformers have become fairly rare things - even microphone transformers are pretty uncommon, due to their high cost and fairly low performance. Apart from the isolation aspect (DI boxes etc.), a semiconductor input stage provides better quality for a balanced input.