please help me build a 12volts rectifying circuit

[Basics]

I really need a help on how to build a 12volts rectifying circuit, that will be stable when it is supplied to a power amplifier.With the ones that i built, when i check for the output it gave me 12.09volts but when i connect it to a power amplifier it reads as 9volts which is not able to drive the power amplifier. Also it makes my amplifier produce a lot of noise.So please help me out. Thanks.

 

[Harald Kapp]

Here are the basics of rectifying and smoothing circuits.
Do you use smoothing capacitors?
What is the current you draw by the amplifier?
What is the rating of the transformer you use?