HD668B

Tonal Profile

Semi-open, 56 Ohms, and the one Superlux with a detachable cable at both supplied lengths — which is why it outlives its own price class. The 56-Ohm load is the useful detail: it is nearly double the 32 Ohms of the HD681, so a source with a high output impedance loses less grip here, while a 250 mW-into-32-Ohm phone output has 2.6 dB less headroom in voltage terms.