Comment by hakfoo

Also 20% for a big heavy transformer.

Sometimes I see cheap "amplifier only" designs that are about the size of a small 2U rackmount, but then you usually give up a lot of inputs and controls; they seem to be used either as PA amplifiers or as "extra room" units in the weird whole-house audio systems that apparently thousands of people had at one point and all dumped in the Goodwill.