On the one hand, any loudspeaker amplifier with feedback is going to have very low output impedance (minimum acceptable damping factor of 20 with an 8 ohm load

On the one hand, any loudspeaker amplifier with feedback is going to have very low output impedance (minimum acceptable damping factor of 20 with an 8 ohm load or .4 ohms max). So for at home, AC powered use just hook your headphones to the speaker outputs. On the other, things do get interesting with low power / battery powered amplifiers, for example where they use a low power OP-amp for headphone drivers. For this case, the article is very relevant. Heh, or get headphones with nearly flat impedance, for example Sony MDR-v600: http://www.cliftonlaboratories.com/headphone_impedance.htm http://www.cliftonlaboratories.com/headphone_impedance.htm