Matthew98 , you should open the datasheet of the amplifier and look at the pretty graphs first.
Link :
http://www.st.com/content/ccc/resource/technical/document/datasheet/4f/18/a6/c8/21/33/41/8d/CD00001887.pdf/files/CD00001887.pdf/jcr:content/translations/en.CD00001887.pdfFirst... page 5... the amplifier chips need MINIMUM +/-12 , meaning a -12v rail and a +12v rail. With your 24v AC transformer, you'd need much more than 5000uF to keep the voltages as close to -12v and +12v as possible all the time, but even then it would be tricky. The amplifier chips may stop and restart randomly.
Then, look on page 16 at figure 19, bottom right corner. You can see the curve for 0.5% thd , at +/-12v (24v in total) the output will be less than 10w, in reality closer to 5w. On figure 18 you can see that the amplifier may actually dissipate more than it outputs as heat... at +/- 20v more than 10w will be produced and if image where the curve will be at +/- 12v then you're looking at more than 5w wasted as heat.
So you're making this amplifier and you're only going to get 2 x 5w ... you don't really need to heatsink the transformer at those power levels, just the amplifier chips.
If you just want to make an audio amplifier, you should start with something small and simple, like TPA3125 chips :
http://www.ti.com/lit/ds/symlink/tpa3125d2.pdfThey don't need split power supply, they can run directly from 12v or 19v from a computer power supply or a laptop adapter for example, and they can output up to 4w per channel at less than 0.1% THD using a 18v power supply (see figures 5-7 in the datasheet).
You could use your 24v AC transformer, rectify the voltage to DC and you'll get a voltage with a peak DC voltage of 24 x 1.414 - ~1.5v, or about 32v. Add capacitors to keep the minimum voltage above a desired level, for example 30v , and then use a linear regulator (something cheap and simple like LM317 for example) to make sure the voltage doesn't go over 26v at any point (because that's the maximum these chips can handle)
Then you can use one of the two schematics from the datasheet, figure 19 or figure 20 .. either one chip for both channels, or one chip for each channel (in btl mode)