If you decide to step up from mass-market headphones to serious audiophile cans, one thing’s for sure: You’ll be hit with online ads promoting headphone amps. Most jazz fans, who for years have simply plugged their headphones straight into a smartphone, will wonder why they suddenly “need” a headphone amp—or if someone’s just trying to sell them another unnecessary accessory.
Unfortunately, the answer isn’t simple. A headphone amp probably won’t make a big difference when used with most mass-market headphones, because those are designed to deliver good sound from smartphones. But for listeners who’ve stepped up to audiophile headphones, the right amp can give your sound quality a kick—especially if you’re a big fan of Ron Carter and Christian McBride.
Yes or No
There are two reasons why some headphones and earphones benefit from the use of a headphone amp.
The simple one is that many audiophile headphones need more power than the chip-based headphone amps built into smartphones, tablets, and laptops can deliver. These headphones tend to have low sensitivity, which means they deliver less volume with a given amount of power. The engineers who design them assume you’ll use a dedicated amp, so they can avoid sonic compromises that would allow the headphones to play loud when plugged into a smartphone.
Fortunately, most companies publish the sensitivity ratings of their headphones, and the ratings are usually accurate. Any set of headphones with rated sensitivity of about 98 dB or lower may not play loud enough when plugged straight into a phone. You’ll probably notice the biggest difference in the bass; skimp on power and these headphones will start to sound shrill because they don’t have the power they need to pump out a double bass’ lowest notes.
The technical reason has to do with the fact that people tend to disconnect and reconnect headphones while the music’s playing, which can create a momentary short circuit. The amps built into phones and laptops often use a resistor or capacitor to protect themselves from these shorts. But that extra component will interact electrically with the tiny speaker drivers built into headphones, sometimes to the point where it boosts or cuts the bass or treble. This is especially an issue with large headphones using dynamic drivers and earphones using balanced-armature drivers. (Note: There’s no way to tell at a glance what kind of drivers you have in your headphones or earphones. Check the manufacturer’s website; if the driver type isn’t specified, it’s dynamic.)
Most high-quality headphone amps have what engineers refer to as a low output impedance, which indicates that they use more sophisticated means to protect themselves from shorts without affecting the sound you hear. I always look for headphone amps with an output impedance rating of 5 ohms or less, although many manufacturers don’t publish this spec.
Surprisingly for a niche item, headphone amps come in a wide variety of forms, with all sorts of features. Even the smallest ones generally have enough power to drive all but extremely insensitive headphones such as HiFiMan’s Susvara (rated sensitivity 83 dB); those demand the use of a large, powerful amp.
Many headphone amps incorporate a digital-to-analog converter (or DAC), which converts the digital audio signals from a computer or smartphone into analog audio that can then be amplified. The DAC built into the headphone amp may sound better than the one built into your phone or computer, and may accommodate higher-resolution audio formats, although it probably won’t sound noticeably better if you’re mostly listening to Spotify and YouTube.
Headphone amp-DACs can be as simple and inexpensive as AudioQuest’s $99 DragonFly Black, a thumb-sized device that plugs directly into a computer’s USB output—or, through an adapter, into an Android phone’s USB jack or an iPhone’s Lightning connector. An amp-DAC might also be a large component priced in the high three or even four figures, such as iFi’s $2,499 Pro iDSD.
Many higher-end headphone amps, like Questyle’s $798 CMA400i, include balanced output, with fully separate connections for the left and right stereo channels. Some headphone enthusiasts believe this connection delivers better sound, and most audiophile headphones are compatible with balanced connections.
Some headphone amps are designed for portable use, primarily to fortify the sound of a smartphone. These include the $279 Monoprice Monolith 24460, which is sized like a smartphone so the two can be strapped together. It has a built-in rechargeable battery, along with THX amplifier technology that provides about 10 times the power of the headphone amps typically built into smartphones.
A lot of headphone amps use vacuum tube technology, which most audiophiles find delivers a warmer and more natural sound than solid-state amplifiers. While some, like the iFi Pro iDSD cited above, use one or two tubes to add a little extra warmth, others, such as the $1,700 Amps & Sound Kenzie, are tube through-and-through—and have the added benefit of looking like something Charlie Parker might have seen in the studio when he made his first recordings.
So when you’re ready to step up to audiophile-grade headphones or earphones, consider getting at least a small headphone amp or amp-DAC to go with them. It might give you a subtle improvement—or it might make all the difference in the world.