The more signal you can get out of the microphone the less gain you'll need on the PSR and then you'll get less hiss. A microphone pre-amp or any mixer with dedicated microphone inputs should improve the situation a lot. You'll get less total hiss because the pre-amp/mixer circuitry will generate lower noise than the circuitry in the PSR.

You could try a microphone transformer; however my experience with the (budget) unit in my possession was that the transformer was very susceptible to mains hum and so you got a hotter signal (so less gain and less hiss) but gained a hum which was even more noticeable.

The other possibilty would be a microphone with higher output than the SM58 (AKG?). But to get a microphone that is better than the '58 would cost more than a small mixer, so this doesn't seem like a very good idea to me!

[This message has been edited by MacAllcock (edited 11-10-2004).]