A word to the wise about your transformer-
You know that the RMS secondary voltage multiplied by 1.414 is going to equal your rectified DC voltage (that is why you chose a 28Vrms secondary tranny)..... Only problem is it doesn't really work that way. In an ideal world you would get your 39.xxxx volts DC, but you will actually see more like 43-45V with no load and damage your chip, and here is why.
Most transformers spec out a 115V primary, most places you can live in the country are well above this. In Spokane I would see anything from 118-122Volts, depending on the time of day. So, that is going to add a volt or so to your secondary RMS voltage, even worse if the transformer has 110V primaries.
Second, the output voltage is figured under a prescibed load, it will be higher under low or no load (where an audio amplifier is about 90% of the time) It is going to be signifigantly higher with smaller transformers (like 500 watts or less) because they do not have the regulation charactoristics of the bigger ones. So figure a volt or so higher again under low or no load conditions.
Why are transformers rated like this? So they meet specification under worst case conditions, simple as that. Problem is, when you are running an Unregulated, Linear DC power supply, this means your DC voltage will always be higher than caluculated using the manufacturers specs. In fact, you would probably end up somewhere around 43-45 volts when you are all said and done, and damage the chip....
Linear power supplies are tricky, and you really have to be carefull about selecting a transformer that is right if you aren't regulating or are planning on running the upper limits of whatever circuit your are powering.
If you buy the P/E Avel Lindberg torroid
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=122-625 that has 25+25VRMS secondaries, your power supply will sit a few volts below 40vdc and everything will work happily ever after, and it's 250VA also, should be perfect... I have used many Avel Lindbergs in the past and have been real happy.
