Amp and preamp on same outlet?

A well regarded equipment manufacturer told me having everything on the same line is optimum. I suspect this is related to the ground loop considerations Al posted.

This has nothing to do with ground loops which are an entirely separate matter (FWIW, if your equipment is properly designed, ground loops should never be a problem).

The concern with different lines is that one might be on one side of the incoming AC power into the house, the other might be on the other. Sometimes you can have leakage problems caused by the two lines being of slightly different phase (or a lot different phase if taken off of a 3-phase circuit). Sometimes this can result in hum. If the equipment is properly designed though this should be a minor concern.

IOW two different lines off of the same side of the incoming AC line (which is 240 Volts in the US and then gets split into 2 halves each 120Volts...) eliminates that concern. If your equipment is prone to ground loops that can still happen though...

50 amps is correct.

But we should keep in mind that the amp is likely never going to produce such power, as it would only be possible if the load were one ohm. I remember the Apogee Full-Range speaker approached that value, but the speaker cables used in such an installation would add to the load impedance and limit the possibility of such power.

On most 4 ohm loads the output power is about 1500 watts.

In addition if I recall correctly, its the power transformer in that amp that has that rating, not the amp itself. The transformer would current-limit the amp even if the output section was capable of delivering such power.

Line voltage sag can cause some amps to heat up as the bias point can shift somewhat depending on the design so I can see that reducing the sag with a higher current breaker might have an effect. But installing such a breaker without upgrading the associated wiring would be foolhardy and would not meet code in any state in the country.

^^ If you are going to operate a 30 amp breaker, make sure the line it controls is also rated for 30 amps.

Otherwise you risk a fire. I bet you will find though that the 20amp wiring is also 'limiting' the amp; at any rate you will do well for yourself to follow my advice in the above paragraph.