A headphone amplifier is an alternative to a standard home hi-fi amplifier or multimedia speaker setup for those that use headphones a lot, the main advantage of a headphone amp versus a full variant is that since the power requirements of a headphone are quite small, the designer can usually spend quite a bit more on the amplification components than he can when designing a normal amplifier, usually resulting in a pure Class A output stage which is something that is impossible to attain with a more powerful amplifiers except at exorbitant prices. In other words for something like 100 to 300 € you can get a sound quality that really approaches high end ideals.
Equally, a well designed headphone amplifier should also drive headphones that cheaper amps and systems have problems with and have a reasonable damping factor which is often more important for headphones than it is for loudspeakers, potentially resulting in a vastly improved sound. And please note that a headphone amplifier is not to be called a Head Amplifier and while Headphone distribution amplifiers perform the same basic function as a normal headphone amp their design is quite different.
1388 Technology Makes an interesting and unusual devise called the Bit 88, it's a headphone amplifier and signal enhancer, the signal enhancement side has both a valve based "enhancer" and more conventional SRS based IC's.
Boostaroo Makes a product that they call a headphone amp but is actually a signal booster and splitter, useful nevertheless but not for purists.
CEC Has a lovely little full class A amp called HD-51 that is unusual in that it has 2 output channels each with it's own volume control and has balanced input in addition the usual RCA's, also unusually since the circuit used was a fairly powerful or 8w the designers added loudspeaker outputs, very odd for a headphone amp, but it means that if you have very efficient or small easily driven speakers it can utilise them. This model is designed for the Japanese market in mind and I have not seen it for sale in the US or UK but a few shops are starting to carry it on mainland Europe since this unusual feature set is just what some people are looking for and it also has an unusual and reportedly good sounding amplifier topology.
Fostex Makes the PH-50 a 5 channel amp that sports balanced inputs.
Heed Audio Makes the keenly priced CanAmp, it's actually quite flexible, not only can it work with almost any headphone, have a pure class A topology (with an output power of a whopping 1w > 8ohms) but it also has a line output meaning that it can be used as a preamp or as a tape output in an amplifierless setup.
??!! SH4DRY Er....Namewise we are not sure but there is a gentleman selling headphone amplifiers on the Norwegian QXL auction site, these look terribly DIY but have interesting specifications and a keen price (600 NKR which should be 50 - 60 € depending on exchange rate). Interestingly it's designer claims that it can work both as a home hifi amplifier (it comes with a PSU) and as a battery driven portable amp (it has a belt clip), although judging by the specifications this is more a unusually high quality booster than a pure headphone amplifier per se.
Borbely Audio The company had 2 very well regarded kits available, so well regarded in fact that even though expensive at the time they sold fairly well but are almost impossible to get hold of on the second hand market. The best known is the EB804/421 that was introduced in 1998 or 9 and has a Dual Mono hybrid MOS-Fet/Valve output stage that is fully Class A, the model had a few minor refinements through its lifetime with the later models being the more desirable ones.
The other model was a refinement of the 804/421 known as EB602/210, it shared the same topology and basic design but instead of a hybrid it used an all FET output stage, people usually agreed on it having considerably more resolution than the 804/421 even though some preferred the sound of the 804 valve hybrid, Borbely amplifier designs tended to be highly damped which could be a minus in power amplifiers but it suited these headphone amps to a T. Both models cost the same, they retailed for 428 euros excluding VAT and case in 2010, or 478 euros if a Teflon based PCB was chosen, or 510/569 including VAT, a case vas available for 155 euros ex-VAT. Both models were discontinued in 2010 when the company closed down. It should also be noted that some of the Borbely pre-amp kits had unusually good headphone outs.
A headphone distribution amp is an utility product intended to drive a number of headphones, usually in a some sort of a professional situation such as a recording studio or a language teaching lab etc., the emphasis in the design of a distribution amp is usually more on cost per channel than on sound quality although there are some excellent quality distribution amps out there designed for use in recording studios.
Discontinued headphone distribution amps & systems
A portable, battery driven distribution amplifier with 3 electrically isolated outputs intended to be used in film and TV location work, was commonly referred to by the company simply as the HDA. Housed in a ruggedized brushed aluminium case, driven by a standard 9v PP3 battery, the battery lifetime is only quoted as 6 hours but that should be enough for its intended application. Introduced around 1990 and was taken off the market in ca. 2005.
The PSC Headphone Distribution Amplifier technical specifications are: Inputs: 6.35mm stereo male jack on a 45 cm long cable. Outputs: 3x stereo female 6.35mm jacks. Input impedance: 600 Ohms. Output inmpedance: 25 ~ 600 Ohms. Optimal otputs impedance: 50 Ohms. Frequency response: 20Hz ~ 20kHz. Size: 16.5 x 4 x 6 cm (Width x Height x Depth). Weight: 0.25 kg. Power requirements: 9v PP3 battery kg. Battery life: 6 hours.