Headphone Heights

Disagree, for the most part...

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This Post Has Been Edited by the Author

In Reply to: RE: Sure, headphone output jacks can be used as a "preamp out"... posted by Caucasian Blackplate on December 21, 2013 at 21:37:12

What manufacturers "should" do and what they actually do are often two different things, in part because industry standards have a way of changing more slowly than marketplace innovations do. I know it sounds strange, but many (or even most) headphone amps have output impedance ratings much higher than 2 ohms, even at their lowest impedance setting. There are exceptions, of course, but headphone amps still tend to have higher output impedance ratings than dedicated preamps do. I think it has something to do with the fact that very low-impedance headphones were once more rare in the "high-end" and/or professional fields than they are today.
High impedance headphones tend to sound best when amplified with high output impedance (120 ohms was once stipulated as the IEC "standard"), while low impedance headphones tend to like a low(er) impedance output. But even today, it can be hard to find full-sized headphone amps with output impedance ratings of much less than 30 ohms. My DNA Sonett has switchable "hi/low" output impedance (28 ohms/120 ohms) but (especially with tube headphone amps) lower output impedance ratings than that still seem to be relatively rare. This is ironic, because very low impedance headphones definitely seem to perform better (especially in the bass) when driven by a suitable amplifier with an ultra low output impedance.
I believe that, with the rise in popularity of of micro-sized portable players and the portable low impedance "easy-to-drive" headphones designed for them, manufacturers started to adopt low(er) impedance standards. But dedicated preamps still tend to have lower output impedance ratings than many headphone amps do, and this is one possible reason why they might not perform as well as real preamps for the task of pre-amplification.
The TRS output jacks used on most headphone amps might also create some sonic degradation when the amp is used as a "preamp". Dedicated RCA or XLR output jacks, asd used on real preamps, are superior connection devices.
I once owned a solid-state Meier Corda headphone amp that was rated at "0 ohms output impedance", but such seems to be the exception rather than the rule as of yet.
It has been claimed that, for maximum EFI/RMI rejection the higher the aforementioned input/output impedance ratio, the better. Others claim that this entire impedance matching issue matters but little. I, of course, tend to think that a higher ratio is best.

Edits: 12/22/13 12/22/13 12/22/13

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