Every smartphone has a built-in amplifier and digital-to-analog converter (DAC). The amplifier cranks the audio signal to a level so that you can your headphones (or the smartphone's speakers) can actually play it. And the DAC is needed to turn the digital files from your music streaming service, be it from Spotify or Apple Music, Tidal or Deezer, into an analog file that the amplifier can actually crank.
The problem is that the amplifier and the DAC that are built into your smartphone, be it an Android or iPhone, could be a lot better. Both components are limited by the small constraints of a smartphone and the fact that most manufacturers don't want to spend extra on higher quality audio components that not everyone wants or needs.
The good news is that you can buy a separate device, a portable DAC/amplifier, that connects to your smartphone and a pair of wired headphones (or speakers). And it will greatly improve the sound quality. Your audio will sound bigger, crisper and more natural.
If you have a nice pair of wired headphones and want to listen to high-quality audio on-the-go, you should seriously consider buying one of the below portable DAC/amps for your smartphone.
AudioQuest DragonFly Black
AudioQuest is the biggest name in portable DAC/amps and the DragonFly Black is its most entry-level model. It's not as powerful as the company's higher-end portable DAC/amps, like the Red and Colbalt, and can't drive the most demanding audiophile headphones. However, the DragonFly Black is still a worthy update for anybody looking to improve the audio quality of their smartphone (or laptop). It pairs a Texas Instruments TPA6130 amp and ESS ES9010 DAC chip, and it can play high-resolution tracks up to 24-bit / 96kHz. Like the other DragonFly series, you'll need a USB-C or Lightning dongle to connect to your smartphone.
FiiO Q1 Mark II
The FiiO Q1 Mark II is an entry-level portable DAC/amplifier that's specifically designed for iPhones (it comes with a micro-USB to Lighting adapter in the box). It's not a terribly small device — in fact it's only slightly smaller than the latest iPhones — but it comes with a built-in battery, meaning it won't draw power from your smartphone like most portable USB DAC/amplifiers and you'll thus be able to listen to music longer. Inside, the FiiO Q1 Mark II packs a AK4452 DAC chip and it's capable of playing up to 32bit/384kHz audio files.
Astell&Kern USB-C Dual DAC Cable
Released in early 2020, this is Astell&Kern's first ever USB DAC/amplifier. It features two high-quality DACs (both Cirrus Logic CS43198 MasterHIFI) that support native DSD256 and 32bit/384kHz playback; according to the company, the dual DACs are paired with an independent analog amplifier to help the audio feel the live, warm and clear. The body of the USB DAC/amp is entirely metal, too, similar to the company's other portable hi-fi players. The best part? It can improve the audio of any smartphone with a USB-C jack — no extra dongle or headphone jack needed.
The iFi Hip-DAC is a great all-around portable DAC/amplifier. It's shaped like a small flash drive and, despite that fact, it still manages to be one of the prettiest portable DAC/amplifiers you'll find. It has a wonderfully tactile volume knob, support for 3.5mm and 4.4mm audio jacks, and it runs on 2,200mAh battery (delivering roughly six hours of playtime) so it won't drain your smartphone while you're using it. (It also charges via USB-C, which is nice.) The Hip-DAC supports audio files up to 32-bit/384kHz files and there's a gain-control button so you can adjust its internal amp's power depending on your headphones — basically, it will improve your smartphone's audio no matter what streaming service or headphones you're using.
AudioQuest DragonFly Red
The DragonFly Red has a lot in common with the company's higher-end (and significantly more expensive) DragonFly Cobalt. It outputs the same amount of power (2.1 volts), which enables it to drive a wide variety of headphones; has the same ESS Sabre 9601 headphone amplifier; and it supports up to 24-bit/96kHz audio files. The two big differences is that the DragonFly Red's DAC (ESS ES9016) isn't quite on par with the DragonFly Cobalt's DAC (ESS ES9038Q2M), and it isn't quite as power efficient. Like the DragonFly Black, you'll need to spend a little extra on a smartphone dongle.
AudioQuest Dragonfly Cobalt
The DragonFly Cobalt is the crown jewel in AudoQuest's famed Dragonfly series. It draws significantly less power than the company's DragonFly Red, meaning you'll be able to listen to better music for longer on your smartphone. It also does a an impeccable job of picking up and eliminating unwanted jitter and digital noise, so your music sounds best. It has a ESS ES9038Q2M DAC chip and supports 24-bit/96kHz playback, MQA, which should allow you to hear greater levels of detail in your music.
The Cobalt is the only USB DAC/amp in the Dragonfly series that ships with a USB-A to USB-C adapter, so you can connect it to your smartphone or USB-C laptop right out of the box.