n the primordial audio times before the iPod, the concept of high-end audio being portable seemed pretty far-fetched. If you wanted to walk about with your music, you were pretty much limited to plugging a pair of ear buds into a Sony Walkman or (beginning in 1984) Sony Discman. That level of portability seemed fairly remarkable at the time. However, no audio enthusiast was fooled into thinking that the quality of sound obtained from such gear was anything more than ordinary.

That situation began to change around the turn of the century. Even before the iPod was introduced in October 2001, a few portable headphone amplifiers started popping up. But the iPod spawned an entirely new industry, with portable headphone amplifiers, DACs, tiny interconnects, and even shoulder bags and other containers to cart all of those bits around. Most portable amplifiers and DACs were the size of a pack of cigarettes, and once banded together with an iPod, they looked more like an incendiary device than a gateway to audio nirvana. More often than not, the cable between the DAC and iPod had to be positioned just right in order for it to successfully "talk" to the other devices. In some cases, after software update to the DAC, the connecting cable stopped working and had to be exchanged for new cables cleared by Apple. Portable? Yes, but 15 years on, audiophiles expect an entire package of these goods to fit in a purse or pants pocket rather than a backpack. And let’s not forget about sound quality, which has advanced light years in a decade and a half.

While diehard adherents of high-definition recording technology may sniff at listening to CD-quality music from an iPhone, there is no escaping the convenience of carrying your music inside the same device you already lug around. Setting file-format ideology aside, lossless recorded music on a portable phone can deliver quite excellent sound -- with a little help from its friends. For some, the jury is still out on whether high-definition portable music (meaning music you have to pay for, even if you already own it in another format) is worth the added expense over the quality and convenience of re-storing your existing music collection on a portable device. New products from AudioQuest, CEntrance and Arcam make that experience lightweight and enjoyable. All units bypass the iPhone’s Cirrus Logic DAC to provide improved sound, and none of them breaks the bank, unless your bank looks like a piggy and is filled with pennies. The units have the added capacity to deliver high bit and sampling rates for streaming or use with computer-based applications.

The lightest of the new personal amplifier/DACs is AudioQuest’s DragonFly, the newest generation of which comes in two versions, Black and Red, priced respectively at $99 and $199. AudioQuest revolutionized the market for what are called micro DACs with its original DragonFly. The new generation of DragonFlys draws considerably less current than the original and incorporates a Microchip PIC32MX microcontroller, making them truly compatible with Apple and Android smartphones. The more expensive Red uses a 32-bit ESS Sabre 9016 DAC that incorporates a high-quality headphone amp and digital volume control. It generates a 2.1-volt output. Measuring 2 1/2" by 11/16" by 3/8", the DragonFly Red resembles a USB memory stick. Use of any DragonFly with an iPhone requires an Apple Lightning-to-USB Camera adapter that is available from Apple for $29 (Apple’s $39 Lightning-to-USB 3 adapter offers improved performance with the added ability of charging the iPhone while playing music). The DragonFly Red connects to the Camera adapter that in turn plugs into the iPhone’s Lightning input. Like all the devices mentioned here, the DragonFly Red has a 3.5mm headphone jack, but unlike some of them it is compatible with all iOS devices, including iPad. It weighs in at eight-tenths of an ounce. The adapter adds two-tenths of an ounce, so all told the kit weighs in at one solid ounce -- equivalent in weight to a dollar's worth of pocket change.

The Arcam Music Boost uses a different approach to connecting a DAC and amplifier to the iPhone. The electronic chips are molded into a phone case, and the iPhone slides into a Lightning jack built into the case. Headphones plug into a 3.5mm headphone jack built into the edge of the Boost. Weighing 3.5 ounces and measuring 6" x 2 3/4" x 9/16", the Boost is hardly larger than most phone shells that do nothing more than protect the phone from damage caused by misadventure. Arcam publishes no technical specs, but I would guess the Boost's voltage output to be very similar to the DragonFly Red's. The retail price is $199, but the Boost can be found online discounted to $189. Unlike the DragonFly Red, the Boost has a rechargeable battery, so rather than drawing power from your phone, it recharges the phone while it amplifies your music. The Boost uses a Texas Instruments DAC with integrated headphone amplifier. Arcam’s supplied materials and website provide a frustrating lack of specifications for the unit.

The heavyweight contender comes from CEntrance, and it comes in two versions. The HiFi-Skÿn, a two-piece phone case with built-in DAC and amplifier, shares the look and design of the Arcam Music Boost, but a Boost on steroids. The phone slides into the main unit and a second piece of the Skÿn slides over and locks in the phone. It can be obtained in sizes to match iPhones 5, 5S, 6, 6S, 6 Plus, 6S Plus and the fifth and sixth generations of the iPod Touch. It can be ordered in white, gray or black. The iPhone 6 version weighs in at 5.5 ounces, measures 7 3/8" x 2 7/8" x 3/4" and costs $399. It generates a 3.75V output.

The Skÿn design also comes in a $349 skin-less version called the DACportable, which eschews the case and is configured much like the DragonFly. The DACportable shares the same circuits as the Skÿn. It weighs 4.3 ounces and measures 3 7/8" x 1 5/8" x 7/8". Like the DragonFly Red, it connects to an iPhone through an Apple Camera adapter. Unlike all of the other units discussed, it bypasses the Apple volume control and has its own built in. Like the Skÿn, the DACportable includes a rechargeable battery -- a 3000mAH Li-Po battery that lets you listen for over eight hours without draining the phone's own battery. It also includes two EQ switches that allow you to subtly boost bass and treble.

How well does each perform? Although the iPhone's DAC has improved over the years, most discerning music lovers will still find its performance unacceptable. I tested these units with a variety of headphones, including Ultimate Ears UE18 Pro custom in-ear monitors (claiming an efficiency of 115dB at 1kHz); Audeze LCD-3 headphones (102dB efficiency), with Crystal Cable portable cable; and PSB M4U 2 headphones (102dB efficiency). Each of these headphones can be driven to listenable levels by the iPhone DAC at full volume. The quality of sound ranged from dull to barely adequate with the built-in DAC and amplification.

The good news is that each of these units makes a significant improvement to the sound of music played by phone. However, there is no free lunch: the more expensive units sounded better than those costing half as much. On the other hand, the larger and more costly the amp/DAC, the less portable it is. The DragonFly Red gets lost in your pocket, while most users will find the HiFi-Skÿn too large for anything shy of a handbag or briefcase. Like the DragonFly, the Arcam Boost is very portable, in that once the phone is inserted, the Boost is only slightly larger than most phone-protection cases, and will easily fit in a pocket.

All of the amplifier/DACs made a significant improvement to music reproduction compared to the built-in iPhone DAC and amplifier. The DragonFly Red and Arcam Boost added a level of refinement to the tonal palate missing in the iPhone’s internal electronics. Where piano recordings sounded like toy instruments through the iPhone, the DragonFly and Boost reminded me that the piano is a percussive instrument. Vocal recordings felt stripped of color through the iPhone DAC, compared to their sound with either the DragonFly or Arcam Boost, which added warmth and dimension to vocals. The added output of both the Boost and the DragonFly Red served more to facilitate the better dynamic range of the DACs than to increase the volume significantly.

Doubling your investment with either of the CEntrance models gives you all (and more) of the tonal refinement of the smaller units plus a significant boost of dynamic range, a sense that amplifier power has been doubled. As a result, the CEntrance opened up a bigger stage, with the musical image extending further out from my head, with more air or space between the instruments. While the DragonFly Red and Boost added a lightweight improvement to the sound of an iPhone, the CEntrance units competed with, and beat some of, the best of the much heavier portable separates on the market.

The longer I used each of these units and compared them to each other, the more I became convinced that they really serve two markets. While each of the four choices is portable, some are more portable than others, and sacrifice the last ounce of sound quality for a light and extremely small package.

At the light and unobtrusive end of the scale, the DragonFly Red and Boost seem like very different products, but once you slip your phone into the Boost, the combination takes up no more space in your pocket than a phone, phone case, DragonFly Red and Apple adapter. The DragonFly Red has a slight weight advantage; when combined with a very light case and adapter, the combination can tilt the scales at under two ounces, compared to the 3.5 ounces of a Boost setup. That derives from the lack of a rechargeable battery in the DragonFly Red. The Boost and DragonFly Red sounded remarkably similar and their prices are almost identical, so the choice between them boils down to ergonomics and aesthetics. The Boost is essentially invisible to the casual observer, while the DragonFly Red’s lacquer finish has a hipness factor that cannot be ignored. The DragonFly Red also does double or triple duty outside the cell-phone application, as it can be used as a high-resolution DAC or headphone amplifier in a computer-based audio system.

For those willing to part with a couple hundred dollars more and lug around a somewhat heavier device, CEntrance’s two units offer a significant step up in sound quality and enough added output power to never run out of steam. The Skÿn is the ultimate travel kit -- an all-in-one unit with no extra connectors to get lost in transit. The DACportable forgoes the integrated approach in exchange for the same versatility as the DragonFly Red. For others, the CEntrance devices may be just a bit too heavy or clunky to lug around for everyday use -- jogging on the beach would call for the lightweight approach.

Regardless of what your needs are, all of these devices are very well constructed and raise the bar for music lovers who need to get their music fix on the go.