I’ve seen people state both that they so not influence the tuning as long as they deliver the same power and others stating that they can make headphones “sound warmer” or “brighter”. I don’t see how that would happen though and a lot of audiophiles just hear things that I feel aren’t there, like some noise difference between the Apple DAC Dongle and a 500 EUR DAC using an off the rack chip.
Take this comment from ASR:
Amps are more likely to make an audible difference than most DACs, but that certainly doesn’t mean there are audible differences between most amps
I’m talking purely about AMPs here, not a DAC combination.
I do not know how people could come to the conclusion that amps sound the same after doing some basic listening tests. With speakers, the differences are much more pronounced and I went to a handful of stores, listening to 4-5 amplifiers each and picking my favorite, but with headphonesamps the same thing applies: Violectric amps sound dark and pleasant, Ferrum have a dip in the mids, etc.
It might be that many brands try to be a wire with gain and not sound like anything, but a lot of brands have a „house sound“ that makes them work well with certain gear and not so well with others, depending on your taste.
AMPs can make certain frequencies go up (I see it mostly on bass).
Amp can make a difference in sound due to the nature of output impedance and damping factors.
But this is perceptually noticeable only in certain special circumstances.