AC Power Cord Wire Gauge

The national electrical code requires minimum AWG 12 for 15A circuits.

If you're going to put in new ded. cts, for your audio, and the receptacles will be more than 20 feet from the panel, i recommend going up to AWG 10 to make up for slight voltage drop as the runs get longer.

Tvad, you're not imagining things. The age-old question, "Why make PC's any bigger gauge than what's in the wall?" has a very simple answer: 'energy transfer' I'll explain:
When you plug your whatever into a wall receptacle, you are basically hooking it up (in parallel with other devices plugged into that same 'branch' circuit) across two buss wires (hot and neutral) coming from the panel. Think of this buss (usually a long length of Rom-ex in the wall) as a reservoir of water that under most conditions can never be emptied. Think of the power cord as a pair of tubes (hot conductor and neutral conductor) that you stick into this reservoir. Now water can flow (current) into one conductor, through the whatever, and back out the other conductor (and this process reverses 60 times a second because the current alternates.)

If the water is flowing through an amplifier, it's doing quite a bit of work, but in just a sixtieth of a second, it has to get back to the reservoir and then reverse direction! Sounds like an electron traffic jam waiting to turn into gridlock! To insure this doesn't occur, you provide many many lanes (or in this case, large conductors) and you lay them out so drivers aren't blinded by oncoming headlights (inductance and capacitance) slowing things down unnecessarily ;-) Simply put, the energy transfer requirements, back and forth between the device and the reservoir, are quite different in nature than what it takes to keep the reservoir full.

Devices requiring less power (preamps, tuners) can transfer current back and forth through smaller conductors without "impediments" arising -- with one bizarre exception: DACs! (or any device with a D/A or A/D chip in it.) Don't ask me why, I don't know, but they benefit from big AC conductors also (but probably for different reasons than amps.)

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Al -- your explanation represents sound engineering, and I know it well; in fact some embrace those principals to the point of hardwiring their amps' power supply right back to the panel, convinced that strategy will provide the very best energy transfer. Good for them;-)

A real scientist would not be so sure. The facts are a little different than you imply:

As I said earlier, there may be subtle reasons why subtle sonic differences may result when 10 gauge power cords are hooked into 12 gauge house wiring, but the differences are not due to the gauge per se.

First, the difference is NOT subtle (you should try it ;-)
Second, the effect of using larger (and larger!) gauge conductors is the same, regardless of the brand or topology of the cord -- the sonics of the amp will "open up" dramatically! In my own experiments, this improvement continued incrementally up to 8 AWG which is as far as I went, but PS Audio (I think) makes 6AWG PC's, which might make sense to some ;-)

So, counterintuitive or not, it IS the gauge. Why? Well maybe Quantum physics will explain it one day ;-) I'm certainly willing to accept my own explanation as flawed (from an ENGINEERING standpoint) but it's the best I can conjure until science discovers the REAL reason. It's just a matter of time, I'm sure.
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And my basic point, I guess, is that having no explanation is far preferable to having an incorrect one. Because the incorrect perspective that can result from an incorrect explanation can negate the value that good science and engineering CAN bring to the table.

Al, I'm down with that! And I'm a big fan of the physicist Richard Feynman, who has said many times that he's comfortable knowing there are things he can't know ;-) Punch him up on You Tube. But some people just HAVE to have an answer, even if it's a bit of a fairy tale. (I think they call it religion or something ;-)

In any case, so far, I've not found anyone who couldn't hear a consistent improvement (in their amplifiers that is) using larger conductors. Other components, maybe not so much (except DACs as I mentioned.)

But I do share your basic position, even though unlike Dr. Feynman, most folks won't be able to live with it.

Neil