Quote:
Originally Posted by pedxing
In m opinion, headphone amps are over rated. Usually they provide better performance at a subtle level. They usually provide the most benefit while used with a portable audio device which has limited output power.
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This is a great view of it.
To put it technically, you need a headphone amplifier when your source's output is either too low voltage or too low current (or both). Most portable players output less than 20mw per channel at a voltage swing of sometimes under 1 volt! That's not enough to drive most headphones to an acceptable volume; high impedance headphones need more voltage to reach excursion but will sound okay, just very quiet, while low impedance headphones will likely drain the current output capacitors (if it doesn't use a push/pull system) resulting in extremely poor bass reproduction.
A headphone amplifier brings a line-level signal (or, in this case, any weak signal) up to appropriate voltage and current figures.
So, you need it with portable players and weak sources. It will help you less with, say, an M-Audio Revolution 5.1's op-amp powered headphone out (as I recall, roughly 50mw/channel at ~3.3v) than it will with an iPod (which manages a voltage swing of under 1.7v from its lithium battery). Very dynamic music (and very loud music) on high impedance headphones requires high voltage; I'd recommend a headphone amplifier of at least 9V for 250ohm+ impedance headphones. All music on low impedance headphones requires high output current in order to accurately reproduce bass frequencies, which most capable amplifiers are able to provide (but not all). The PA2V2 is one of the few high current/low voltage designs, and is well matched to low impedance (120ohm or less) cans. Your receiver may or may not adequately power the headphones; some receivers have very nice headphone amplification circuitry, while some are total afterthoughts with high output impedance, poor SNR, poor THD figures, and generally inferior characteristics. If it offends your ears, you ought to get a headphone amp; if not, save money.
This is somewhat simplified, of course; if you need more depth, I'll try to further explain, but this answers your question.