There's a renowned former Japanese design engineer for Matshu**** (Panasonic) who spent years listening to many many parts of amps/preamps and other electronic goodies. And learned through his experience that even an IEC connector, power cord, chassis and even the selection of footers can influence an amp's sound.
R.I.P. Ken Shindo
Founder; Design Engineer - Shindo Laboratory
There's no doubt he was quite the stereo guy but for many folks, there's also no doubt that suggestibility or expectation can greatly influence what we hear.