One of the adjustable linear regulator IC's is your best bet IMO. 317,337 etc
Nearly all of their datasheets have a simple PSU circuit.
Easy to implement, reliable, inbuilt thermal and short circuit protection as well as fold-back current limiting.
Their main drawback is dissapation, but if you limit your design to say 15 V that will reduce it lots.
Spend good money on a Bournes 10 turn pot, you won't regret it.
Good output terminals also make a PSU a pleasure to use, see if you can find some with 4mm cross drilled holes as well as suitable for 4mm banana leads.
Speaker cabinet types usually are good grunty types.
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