Small appliances have microcomputer that requires 5V power supply. Why it can use only 1.5V battery? The 1.5V to 5V boost converter circuit inside them.
Your amplifier may sound better than before. Just change the appropriate power supply circuit. Multiple levels of output voltage. For example 15V Dual regulator for pre amplifier. And 38V Dual for main amplifier etc.
This is dual 15v power supply schematic, using LM7815,LM7915,and power transistor and zener diode for voltage stable voltage 15 volts positive and negative. [...]
If you need a dual power supply. But you only have a single supply source. So should build this power supply splitter circuit.