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iPod and iTunes Hacks by Hadley Stern

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Hack #27. Buy or Build a Headphone Amplifier

If the tunes from your iPod seem to lack punch or drama, the solution might be to add a headphone amplifier. You can buy one or build your own.

A question often raised in audio forums is whether the iPod benefits from boosting its output with an external headphone amplifier. When Apple redesigned the iPod back in 2002, among the upgrades was a new 30-mW-per-channel headphone amplifier circuit that is still the standard today. 30 mW is a hefty figure compared to that of other energy-conscious portable audio players (a paltry 5–10 mW per channel), and many iPod owners have appreciated the extra power for driving their favorite power-hungry headphones.

Tip

High-end audio guru John Atkinson (reviewing the iPod with Sony MDR-7506 headphones) gushed about the iPod's sound quality, calling it "excellent, cost-effective audio engineering from an unexpected source" (Stereophile, October 2003).

However, the 30-mW-per-channel specification does not tell the whole story. iPods sold in Europe, for example, have output limiters that can prevent headphones from reaching maximum volume. Even on iPods without limiters, many headphones will never see 30 mW. The 30 mW spec is applicable only to 32-ohm loads, the nominal impedance of the stock iPod earbuds. When driving 100-ohm headphones (such as the in-ear Etymotic ER4S or Shure E5c), the maximum output is ...

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