Public address amplifier

[corbo]

Hello !!!
I try to make an public address amplifier .
The output of the amplifier is generally fed to a transformer that has a secondary winding arranged to produce 100 volts at full output.

Can be used an usual amplifier and an external step-up transformer  ?
How can be calculated this transformer (number of turns etc. ) .Can be used ferrite core ?

Or maybe somebody have an schematic of an transformerless  public address amplifier.

Which is the best choice  ??

Thank you !!!

[Walkura]

The transformer is from what i remember only there te reduce cable losses .
In this matter i would really wonder do you really need that .
I worked in a theater we had space for 500 people near the stage + 500 elsewhere .
We never used an 100 Volt system .
Unless you really have football stadium big places to provide with loudspeaker cables  i wouldnt mind the transformer .
Ferrite isn't usefull for this transformer .
You really need a iron core for this .
For as far my memory serves me audio transformers are just like voltage transformers but then they transform resistance (except some winding differences ).
R1>R2 = N1>N2 (sorry for not being able to provide the correct formula's ,school is 20+ years ago