Re: The Audiophoolery Thread.
A few numbers might illustrate what is needed. Suppose we need an amplifier to deliver 100W into an 8 ohm driver. That is 28.3V rms or 40V peak. Add a Vce(sat) of a volt or so, 1V of capacitor ripple, and a volt of diode drop and get to power supply rails of +/-45V, or a +/-35V transformer. That will deliver a bit more than 100W (130W).
So let's respecify this amp at 130W into 8 ohms. The peak current requirement will be the peak output voltage divided by the loudspeaker resistance, or 5.7A. Of course this amp will have to work into 4 ohms too, and need to supply 11.4A peak.
In practice a nominal 4 ohm driver might be closer to 3 ohms so the peak current becomes 15.2A.
The output stage would need to be specified as 130W into 8 ohms (and not quite twice that into 4 - say 200W, because of Tx losses and capacitor ripple), and a peak current of 15A.
Heatsinks would have to cope with that, because although most listening is at an average power of ~1W, (a) reviewers tend to test continuous output into a dummy load and (b) modern massively compressed rock music played loud might get close to full power sine wave tests.
Craig
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