Most headphone amps use an Op Amp or two somewhere in the chain to amplify the signal.
Op Amps use a lot of feedback to reduce distortion, reduce output impedance, increase input impedance, increase bandwidth, etc.
Op Amps are used throughout the recording and mastering chain.
But for some wierd reason Audiophiles think feedback is bad.
There may be no overall feedback in the amp, but if you look at the circuit long enough, you'll find some feedback in the circuit somewhere.