thanks a lot guys.
i want to add up that i know nothing about electronics, i study computers. i started a few months ago as a hobby that i always liked, some things (of the very little i know) are still confusing. thats why i ask these things that are, maybe, a bit dumb.

about the size of the trafo, im planning to do a big box with 2x 12'' speakers, so it wouldnt be a problem. i will give some real power to this )

thanks!

im curious on how to calculate the VA i need for such things...

i guess not as they work with a max of 1A

hey, thanks a lot for the replies. just another little thing, if i wanted to build a diode bridge, would some 1N4007 diodes work?
thanks! :duh

Hello, this is my first post...
Ive been searching posts about this topic, but after reading, I dont really get my question answered. So Ill make it concicious:

Ive done a 20W amp with a tda2040 IC, just as its posted in general guitar gadgets (bah, with some modifications, i just added a pot for the volume and a jack for input). We tested the amp at university, with an ocilloscope and a big variable power supply, and it works fine.
My questions are: what transformer do I need for supplying enough power to this amp? It says i need 18v bipolar power. I plan on putting a 50w, 4ohm speaker as output.
I read that these bipolar power supplies in general guitar gadgets wouldnt work fine to supply the amp. So should i get a transformer and solder the secondary directly to the circuit?
What secondary should I buy? And how much Ampere should i look for?
Any other recommendations? (on the speaker / transformer).
Thanks!