What contributes most to a change in how an amplifier sounds?

@thecarpathian 

😂😂😂👍🤦‍♂️ CLASSIC 

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I would agree with @helomech on distortion signature. When people describe sound attributes of a power amp, it's likely the sonic signature the manufacturer was designing for. 

Audio Research’s WZ Johnson believed that the transformers were the make of break component in the quest for audio excellence.  

Without a doubt the power supply is critical. There is also the input stage, which if not done well will result in the output stage amplifying distortion and artifacts.