Headphone amplifier

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Headphone amplifiers as referred to here are commercially available separate devices, sold to a niche audiophile market. These devices allow for higher possible volumes and greater audio clarity than the smaller, cheaper amplifiers that are used in most audio players. (In the case of the extremely-high-end electrostatic headphones, such as the Stax SR-007, a specialized electrostatic headphone amplifier or transformer step-up box and power amplifier is required to use the headphones, as only a dedicated electrostatic headphone amplifier or transformer can provide the voltage levels necessary to drive the headphones.) Most headphone amplifiers provide power between 10 mW and 2 W depending on the specific headphone being used and the design of the amplifier.

1 How they work
2 The DIY approach
3 Crossfeed and other audio processing
4 Cautionary note
5 External links

[edit] How they work

Effectively, a headphone amplifier is a small power amplifier which can be connected to a standard headphone jack or (usually) the line output of an audio source. The headphone amplifier improves the sound quality by increasing the amount of power available to move the transducer, increasing the control that the source has over just where the transducer is in space. This is often expressed as damping factor. For example, a 32 Ω headphone (such as the Grado line) driven by a popular DIY headphone amp with a <1 Ω output impedance (the Gilmore Dynamic) would have a damping factor of >32, whereas the same headphone driven with an iPod (5 Ω output impedance) would have a damping factor of just 6.4. Of course, damping factor is not the only specification relevant to choosing a headphone amplifier — just as with speakers, harmonic distortion, frequency response, IMD, and a myriad of other measurements make choosing a headphone amplifier based on specifications rather difficult.

The logical solution would encompass all of these measurements into a concise summary of the subjective "sound" of the amplifier, and is found in the form of subjective reviews of various amplifiers. The online forum Head-Fi has a sub-forum of magazine-length reviews of various commercially available amplifiers.

[edit] The DIY approach

For those who are more electronically inclined, the low-power and fairly simple nature of the headphone amplifier has made it a very popular DIY project. There are a great many designs for headphone amplifiers posted on the Internet varying considerably in complexity and cost. The cardinal example is the simple opamp-based Cmoy design, arguably one of the most popular headphone amplifier designs available. The simplicity of the Cmoy makes it an easy build, while it can be made small enough to fit inside a tin of breath mints (including batteries!).

The more complex, higher-fidelity headphone amplifier designs are exemplified by those of Phillip LaRocco and Kevin Gilmore. Mr. LaRocco is notable for the introduction of the buffered-opamp topology to the DIY headphone amplifier community. Dr. Gilmore's designs are notable for their resemblance to high-end high-power amplifiers and their adherence to purist ideas. Both Mr. LaRocco and Dr. Gilmore's designs are commercially available for those unable or unwilling to build them.

[edit] Crossfeed and other audio processing

The first popular commercial designs were manufactured by HeadRoom of Bozeman, MT., and included a feature called crossfeed. In essence, crossfeed blends the left and right stereo channels slightly, reducing the extreme channel separation characteristic of headphone listening that is known to cause headaches in a small fraction of listeners (and compensating for extreme separation in older stereo releases). While some swear by crossfeed, many prefer amplifiers without it. (In addition to HeadRoom, Meier Audio is also noted for their crossfeed technology.) The introduction of DSP technology led a number of manufacturers to introduce amplifiers with 'headphone virtualization' features. In principle, the DSP chips allow the two-speaker headphone to simulate a full Dolby 5.1 (or more) surround system. This feature has not caught on in high-end audio circles.

[edit] Cautionary note

Using headphones at high volume can lead to considerable ear damage. In noisy surroundings, it is tempting to turn up the volume while wearing headphones — this is very harmful to the ears. It is therefore advisable to use headphones at low to moderate levels and in quiet surroundings.

It should be mentioned also that around 100 dB SPL sound level is perceived as not particularly loud so playing real loud is approx. 105-120 dB which is not good for the hearing in the long run. Let the ears rest often from high level listening.

When it comes to noisy environment less than 85 dB is considered as safe so consider what is said above.

[edit] External links

[edit] Online Headphone-related Forums

Head-fi: A Forum Site for Headphone Fans.
The iPod & Portable Audio Studio
Headwize: A Resource Site for Headphones and Headphone Listening
Head-Case: Ad and Commercial Free, just-the-facts Forum Site for Headphone Fans.

[edit] Examples of commercial manufacturers

These manufacturers are listed as examples only based on the author's experience in the field, and such listing should not be considered Wikipedia's endorsement or recommendation. Please do your own research.

HeadAmp manufactures both in-house and Gilmore-design amplifiers for electrostatic and dynamic headphones. One of the few manufacturers to offer discrete-transistor based amplifiers.
HeadRoom is the oldest and largest commercial headphone amplifier manufacturer, known for their crossfeed ^{[citation needed]}. .
Meier Audio is a German manufacturer of opamp-based designs with their own crossfeed.
Grace Design is an American company offering a combined headphone amp/pre amp/DAC.
Earmax is a UK based firm offering single-ended triode headphone amp.
Creek Audio offers headphone amps as well.
Ampli-Fi is a Turkish local Headphone Amp. manufacturer.
Dark Audio Labs is a manufacturer of innovative amplifiers using only one transistor per channel.
CI Audio manufacture an amp which uses as a main part a current feedback amplifer, TPA6120.
mSEED LABS offers a high power portable headphone amplifier