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A tube headphone amplifier is a specialized audio component that amplifies an audio signal for use with headphones. Most personal electronic devices that support headphones have their own internal electronic amplifiers. Headphone amplifiers are designed to take a line level signal and amplify it, specifically for headphones, instead of standard speakers. A tube headphone amplifier uses vacuum tubes instead of transistors to amplify the signal and is favored by many audiophiles who insist that they deliver superior sound quality and fidelity over solid state amplifiers.
Speakers, whether they are standard speakers or headphone speakers, require a coded audio signal to produce sound. The strength of the signal is the primary factor which affects output volume. An amplifier increases the strength of an audio signal in order to enable increased volume. While many personal and home audio components have internal amplifiers, stand alone amplifiers are very common, although stand alone headphone amplifiers are much less common than amplifiers for standard speakers.
Stand alone amplifiers for standard speakers can produce signals with thousands of watts of power. Headphone amplifiers produce signals with much smaller power ratings, typically less than ten watts, and most produce signals that are significantly weaker, some measured in milliwatts (mW). The goal is to provide an extremely efficient and high quality audio signal, free from distortion and background noise. Headphone amplifiers are designed specifically to be used with high quality headphones as lower quality headphones lack the frequency response to take full advantage of the high fidelity signal.
Modern amplifiers are generally built using solid state construction, which means that they rely on entirely solid electronic components to amplify the audio signal. Tube amplifiers use vacuum tubes, which are glass enclosures, internally evacuated to create a vacuum, that are designed to carry electric current. A tube headphone amplifier is simply a small, low power, very low distortion tube amplifier.
Amplifiers and speakers both have impedance ratings, and amplifiers work best when matched with speakers that have the an identical impedance rating. Impedance is rated in ohms, and the volume and sound quality can be affected by a difference in impedance ratings. For a tube headphone amplifier, this is typically rated in the range of 20 to 50 ohms, although one industry standard suggests an output impedance of 120 ohms for such components. Headphones can have a wide range of impedance ratings. Many audiophiles prefer lower output impedance ratings as they tend to produce less signal distortion when paired with headphones with a higher impedance.