Someone earlier mentioned mains feed heat buildup. So I measure it.

My system is 715 wpc fed from a single 20A /12ga cct. Three bottle rocket amps account for 25% of the power, so average draw is larger than if all SS. Class A would be worse, but Class A power transformers negate the issue as we shall see.

After three hours of robust pop program, temperature rise on the 12ga cct was 2.9°C measured inside the yellow sheath with a T thermcouple. The really bad news is that over the 20 foot run, the resistance increase is a whopping 51mΩ or 0.051Ω for the non-technical types. This is added to the 20°C value of 32mΩ. The good news is the power transformer internal resistance also rises 1 - 2% or much more than the line feeding it. Calculated improvement in self-heating for 10ga is about 30mΩ, less than the PT and less than the connections from the power line to the transformer winding!

For those posting fancy graphs of diode current, those are steady state loads. Music current draw bears no relation to those graphs.

Spend all the money you want on overkill wiring. It will do no more for the sonics than a fancy faceplate or blue LEDs.

Sonic improvements can be achieved by ensuring that all connections from the utility input to amplifiers are pristine. Inspect and cycle all power plugs every six months.

FWIW, the 10 gauge dedicated orange romex line purchased at Home Depot and run from a 20 amp breaker to a 20 amp medical grade outlet sounds better with my gear plugged into it than the 12 gauge non-dedicated line right next to it on the wall with a "deluxe" but non-medical grade outlet.  The difference is not subtle.  I plug my amp directly into the green dot outlet, all other gear goes through the same outlet via a power conditioner.  If I had not installed the 10 gauge line while I had the wall open, I would have always wondered if I had made a mistake.  Now, in practice I have absolutely no regrets, although in theory some of you apparently believe I should be sad I spent the extra money and wrestled the stiffer wire.  YMMV.

kn

Good intentions and bad information about having 2 20amp 120v dedicated circuits & outlets will create a massive ground loop and hum.  A 15amp 120v outlet will generally suffice for 2 channel home audio. 

If you must add a dedicated 20 amp 120v circuit/outlet in your room....use the following: 1) compatible 20amp 120v breaker for your service panel 2) 12 ga Romex 2 conductor w/ ground 3) 20 amp 120v outlet. Do not increase the wire size beyond 12 ga. as this is a code violation and will not give you better ac quality or quantity.

You should use a large quality 15amp or 20 amp multi-outlet strip with enough outlets to plug everything you require into it.  If that is impractical then use identical smaller outlet strips piggy-backed into one another. I have great success using 2 identical Furman  6 outlet 15 amp rated outlet strips.

You can pm me for more advanced instructions to make your system as quiet as possible.

Do not increase the wire size beyond 12 ga. as this is a code violation

Not true...

FWIW:

National Electrical Code 90.1 Purpose:

(A) Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This Code is not intended as a design specification or an instruction manual for untrained persons.

(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance result in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.

NEC could care less how your audio system sounds. It could care less if you have ground loop hum. No where in the code is it mandated voltage drop shall be a consideration . NEC is bare minimum electrical safety standards.

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12 gauge non-dedicated line

A non-dedicated line is [almost] always a bad idea. Refrigerators, hair-dryers, SMPS, light dimmers, etc. add nasty stuff that some products cannot tolerate.

When we built recording studios, the gear and the garbage were often on separate services to the street! One well-heeled owner installed 100% system isolation via battery. IIRC, Sony NYC had its own gen set in the basement.