I have a outboard dac which also doubles as a headphone amp. Build quality is very good with large toroidal psu a discrete output stage capable outputting up to 4.5v...
However the designer has informed me that the output impedance of the headphone out is 50ohm... This seems very high as most seem to aim for as low as possible?
My headphones are 32 ohms (fidelio x1s). Since reading about the 1/8 impedanance matching rule there is a big mismatch here... Ideally I want to keep the amp so am I better off using higher impedance cans which prefer voltage over current (e.g hd650, dt990 pros)?
Many headphone amplifiers are even designed to work with a 120 ohms output impedance to suit headphones designed for the old IEC61938 standard, which is used irrespective of the actual impedance of the headphones, which may even be 32 ohms or less. I would see how they go with this amplifier. If the output level is more than adequate, but the sound is a little too detailed, you could even try series resistors at the amplifier's outputs, of up to an additional 68 ohms to see if that improves tonal balance. Alex.
They sound fine to my ear and playback undistorted at comfortable levels, so no obvious audible issues. I don't believe the x1s are particularly neutral anyway, but they make for an enjoyable listen. I didn't know anything about impedance matching until yesterday (I just assumed the lower the rating the easier to drive), but following the 1/8th rule would mean ideally I should be using >400ohm cans which rules the majority out.
Interesting to hear about the 120 ohm IEC61938 standard, are many headphones designed to accommodate this anymore?
Hi I think that this standard may have fallen into disuse in recent years, however the AKG K701 and some others in the series do, as well as my own Audio Technica W1000. I have heard that the HD800 also sounds best when driven from a 120 ohm source. Obviously you can't have headphones used with portable amplifiers having low voltage supplies that meet this standard.