A headphone amplifier does exactly what its name says it does: it amplifies analog music signals so that they are loud enough to be heard.
Amplifiers are actually found in any device with a headphone jack like your smartphone or notebook - but they are usually very basic. So if you have invested in a high-end headphone, you should also invest in a proper headphone amplifier. Here’sa quick primer on the three main types of headphone amplifiers you’d likely come across.
1. SOLID STATE
The most common. It refers to any amplifier that uses transistors in its circuitry. Your phone and notebook’s built-in amplifier is a type of solid state amplifier. They are so widespread because they can be made inexpensively and effectively. There are some really small desktop solutions that can generate enough power to drive just about any headphone you can buy. Obviously, at the other end of the spectrum there are also high-end ones that are the size of large gaming systems, use exotic topologies, have class A designs, and generate enough power to even drive small speakers.
2. TUBE
While solid state amplifiers rely on transistors, tube amplifiers use vacuum tubes to amplify music signal. They are easy to identify; you will usually see tubes sprouting out of the chassis. The tubes can get really hot during operation, so the open design helps cool them and prevents heat building up inside the amplifier. There are different types of tube amplifiers, but the most common one you will find are output transformer-less (OTL) amplifiers. These amps are arguably the purest of tube amplifiers because they don’t have an output transformer, which can be a source of distortion. The downside is that they have high output impedances, which means they only pair well with high impedance headphones typically 300 ohms and above. Output transformers get around this problem by transforming the high output impedance of the tube amplifier to match the lower impedance of headphones. Unfortunately, really good output transformers with little distortion are pricey and big, which partly explains why some tube amplifiers can cost as much as a car.
Tube amplifiers are preferred by some listeners for their so-called ‘tube sound,’ which is generally referred to as a warm and rich tone. They are also said to sound less compressed with a more natural timbre. Swapping tubes in the amplifier can also gently alter the sound, which some enthusiasts find fun and addictive.
3. HYBRID
Hybrid amplifiers are amplifiers that have components of tube and solid state amplifiers. The philosophy behind hybrid amplifiers is to create an amplifier that combines the strengths of tube and solid state amplifiers, i.e., the warmth and organic sound of tube amplifiers and the power offered by solid state amplifiers. Typically, hybrid amplifiers have a tube gain stage and a solid state output stage. Like pure tube amplifiers, you can swap the tubes in hybrid amplifiers to subtly alter its audio characteristics.
Hybrid amplifiers are attractive to music lovers who crave the tube sound but also need the high power to get the best out of their headphones. Planar magnetic headphones are a good example as they typically have relatively low impedances and they sound their best when fed with lots of power. So if you want to pair them with a tube amplifier, it should be with a transformer-coupled one. But like I mentioned earlier, a good transformer-coupled tube amplifier can easily cost thousands. This makes hybrid amplifier attractive propositions since they are often less expensive than good transformer coupled tube amplifiers and can deliver a tube-like sound with high power output.
That said, many purists regard them as a compromise as they believe hybrid amplifiers don’t sound as euphonic as true tube amplifiers nor do they measure as well or sound as clean and transparent as pure solid state amplifiers.
