They are usually quite small. Use a relay to switch on the primary of the big transfo. There is much less current on that side.Practically all comercial amplifiers use what pinkmouse suggests, a small transformer to run a soft-start or even a simple relay switch for the main amp transformer(s) and other standby curcuits. Unless you're using a complex smps supply to get the voltages you need for the microprocessor and the amp supplies, it would be best to run only what is needed to switch the amp on and off from another smaller transformer, as pinkmouse said.
The relay contact rating may become irrelevant should you connect the relays between the caps and supply. Larger power supply capacitors effectively represent a short circuit to the power supply before they begin to charge; connecting a discharged capacitor to a supply could instantly destroy relay contacts, but (I would guess) this all depends on how much peak current the supply could source and the value (size) of the capacitors (and of course the relay contacts).
Someone else will probably be able to give you a definitive answer with more details on your project, though.
The relay contact rating may become irrelevant should you connect the relays between the caps and supply. Larger power supply capacitors effectively represent a short circuit to the power supply before they begin to charge; connecting a discharged capacitor to a supply could instantly destroy relay contacts, but (I would guess) this all depends on how much peak current the supply could source and the value (size) of the capacitors (and of course the relay contacts).
Someone else will probably be able to give you a definitive answer with more details on your project, though.
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