Why cant step up transformers be used as audio amplifiers? Or can they? why have i never seen this. Am i missing something?
They can, and are.
There are microphone input transformers that use step up for this to get past noise limitations.
The limitations are that
1. Transformers can multiply voltage or current, but not both at the same time - that is, they cannot be a POWER amplifier. You get out slightly less power than you put in.
2. It is generally quite difficult to get good frequency response in a wideband amplifier. The cost of the amplifier often means that it 's cheaper to make a separate amplifier than to make an equally good transformer.
i figured it would be something like that. I didnt realize that the transformers in microphones were step up i thought they were for isolation or something. Is that why some microphones are so expensive, because they use good transformers?