Review: Three amps for building your own desktop audio system

At a Glance
  • Orb Audio Mini-T Amplifier V2

  • Dayton Audio DTA-100a Class-T Digital Mini Amplifier

  • Audioengine N22 Premium Desktop Audio Amplifier

I suspect a substantial number of people have an old pair of speakers sitting in storage: hand-me-downs from a family member, perhaps, or the remnants of a stereo of their youth. Such speakers can be repurposed to build your own iPod stereo or AirPlay audio system, but they can also be used to put together a quality desktop stereo. (If you don’t have an old set of speakers, there’s a huge variety of unpowered speakers available that offer impressive performance, beauty, or value—or some combination of the three.) All that’s required to get your old (or new) speakers making music is an audio source (an iPod, iOS device, Apple TV, Airport Express, Bluetooth audio receiver, old CD or DVD player, or computer) and an integrated amplifier or stereo receiver.

Unlike powered speakers (such as computer speakers, powered monitors, and speaker docks), which have built-in amplification, passive speakers require pre-amplification to adjust the signal’s volume to desired levels, and power amplification to further boost the signal so that it’s strong enough to make the speakers move and produce sound. An integrated amplifier combines a pre-amp with an amp.

But while many people think of an amplifier as a big, bulky piece of hardware, these days it’s easy to find integrated amplifiers that provide good sound while being small enough to fit on a desk or nightstand. I previously reviewed several compact models with built-in digital-to-analog converters (DACs)—these accept a digital signal rather than an analog one, processing that signal with higher-quality circuitry. But if your source’s audio quality is “good enough” without an external DAC, or if the source offers only analog outputs, a traditional analog amplifier will suffice. This time around, I look at three small, integrated amplifiers—just what you need to make an affordable desktop audio system.

Orb Audio Mini-T

Orb Audio's Mini-T

The most basic—and least expensive—model here is Orb Audio’s $118 Mini-T Amplifier V2. (Despite the official price of $118, Orb Audio seems to perpetually offer the Mini-T for $69). Orb Audio’s focus is on the company’s spherical Orb passive loudspeakers; the Mini-T is offered primarily as an easy way to turn a couple Orbs into a simple stereo-audio system. But the Mini-T works with passive speakers from any vendor, as long as they don’t demand more power than the Mini-T can provide.

The Mini-T is a surprisingly light, glossy-black rectangular box—about the size of a small paperback book—with rounded ends. Its front panel features a volume knob that also acts as a power on/off switch, with a blue power LED that rings the volume knob. (The LED shines through the case, producing a subtle but cool effect.) The amp’s back panel features spring-clip speaker terminals that accept bare wire or speaker cable terminated with pins; a jack for connecting the Mini-T to the supplied power adapter (a brick that weighs more than the Mini-T itself); a 3.5mm stereo-audio input, and a mono RCA output for use with the company’s subwoofers. The Mini-T’s compact size and light weight are nice, but they do have one drawback: If your cables are on the stiff side, they can make it difficult to keep the Mini-T stationary.

Like the $180 Topping TP30 (3 of 5 rating) I previously reviewed, the Mini-T is built around a Tripath Class T amplification chip, similar to high-efficiency switching Class D designs. Orb says the amp produces 10 watts per channel when connected to typical 8-ohm speakers.

Dayton Audio DTA–100a

Dayton's DT-100a

Like the Mini-T, Dayton Audio’s $130 DTA–100a Class-T Digital Mini Amplifier is a Class T design. Also like the Mini-T, the DTA–100a seems to be perpetually discounted: It’s available from Parts Express, Dayton’s official distributor, for just $89.

Though the DTA–100a is also a small black box, it’s narrower and taller than the Mini-T, and noticeably heavier, due in part to its black, extruded-aluminum body and brushed-aluminum front and back plates. The look and feel of the case make it a substantial improvement on the Mini-T’s plastic case.

The DTA–100a’s front panel has a central volume knob that doubles as a power switch. To the left is a 1/4-inch jack for connecting headphones; doing so mutes output to the speaker outputs. To the right is a 3.5mm stereo-input jack for connecting an audio source. Unfortunately, the DTA–100a, like many other inexpensive electronic devices, sports an annoyingly bright blue power LED—bright enough to serve as a flashlight, or, unfortunately, a distraction.

The DTA–100a’s back panel has a set of stereo RCA inputs for connecting an additional source. This input is intended for a permanently-connected source, while the front input is intended for temporarily connections—plugging a source into the front panel’s input overrides the rear input. There’s also a jack for connecting the included large power brick, and, of course, speaker connections. The speaker terminals accept only banana-plug connectors, but these are included and relatively easy to install on standard speaker wire. The package also includes other useful extras such as a 3.5mm-to–3.5mm interconnect and a 3.5mm-to-stereo-RCA adapter for connecting audio sources, and a miniplug-to–1/4-inch adapter for connecting headphones. Dayton rates the DTA–100a at 50 watts per channel into an 8-ohm load.

Audioengine N22

Audioengine's N22

At $199, Audioengine’s Audioengine N22 Premium Desktop Audio Amplifier is the most expensive unit here. It’s also the biggest, offers the most features, and has the sturdiest construction. Audioengine markets the N22 for use with the company’s $249 passive P4 Premium Passive Bookshelf Speakers, but, like all models here, it can be used with any set of passive speakers.

The N22 is about twice the size of the DTA–100a and has an attached stand to position the unit vertically, which aids the N22’s convection-cooling system (warm air rises out of the top of the unit, replaced by cooler area coming in from beneath). Although the N22 is larger and heavier than the other amplifiers—attributable at least in part to the quality of its components—this heft makes the amp substantial enough to stay in place, and its vertical orientation keeps its footprint small. The front of the N22 is relatively sparse, featuring a blue power LED (of reasonable brightness, thankfully) above a centrally located, solid-feeling volume knob that also serves as a power switch. Below the knob is a 3.5mm headphone jack, which will probably be more convenient for most users than the 1/4-inch jack on the DTA–100a. Connecting headphones mutes the N22’s speaker outputs.

The back panel hosts a set of stereo-RCA inputs, a 3.5mm stereo input (which takes priority over the RCA inputs if you connect a source to each), a mono RCA output (with its output level tied to the N22’s volume level, useful for adding a subwoofer), a connection for the substantial power brick, and a power-only USB port (for charging a smartphone or media player, or powering the company’s W3 Premium Wireless Audio Adapter, but not for audio input). Below the USB port is a set of binding posts for connecting speakers. The N22’s speaker connectors are the sturdiest and most-versatile in this roundup: They can accept bare wire, pins, banana plugs, or spades.

Audioengine rates the N22’s power output at 22 watts per channel into an 8-ohm speaker load. This may make the N22 seem less powerful than the DTA–100a, but based on weight, build quality, and manufacturer, I wouldn’t be surprised to find that this difference is due to variations in measurement techniques. I suspect the N22 can actually produce more power than the DTA–100a. Notably, the N22 is based on a Class A/B amplifier design, which is less power-efficient than the Class T circuitry used in the other two amplifiers—hence the emphasis on airflow in the N22’s case design. Proponents claim that Class A/B designs offer better sound quality than Class D or T amps. Are they right? Read on.

Testing, testing

I tested the three amplifiers as part of a desktop-audio setup. Specifically, for most of my testing I used my MacBook with a quality USB DAC (Audioquest’s $249 DragonFly, slated for future review) to ensure that I heard the limitations of the amplifiers rather than the limitations of my MacBook’s audio output. The DragonFly’s output was connected to the inputs of each amplifier as I tested it, while that amplifier drove a pair of Pioneer’s shockingly good (but unfortunately named) SP-BS22-LR bookshelf speakers ($130). The speakers were set up for desktop use on Audioengine’s $34 DS2 Desktop Stands, which do a great job of improving the sound of bookshelf-style speakers on a desk.

I also spent some time testing the amps with the analog output of my MacBook as a source, and with the $39 HiFiMAN Express HM–101 Portable USB Sound Card—a solid-but-affordable DAC and headphone amp.

Pioneer's SP-BS22-LR

When listening to the Mini-T with the DragonFly DAC and Pioneer speakers, I immediately noticed some harshness in high frequencies; and compared to the best performance I’d heard from the speakers, I noticed a decrease in bass performance (both in volume and tightness), detail, and the perceived momentum of the music. Compared to more-expensive amps, the Mini-T’s performance made music sound slightly more distant and veiled. This is relative, though, and I still enjoyed listening to the Mini-T-based system: The Pioneers still produced good sound with plenty of bass. The Mini-T’s volume knob also has a smooth feel and linear response—meaning that the volume level changes smoothly as you turn the knob, and that the left and right speakers stay in balance.

Overall, the Mini-T’s performance is perfectly acceptable in light of its $69 street price, and its 10 watts were capable of more volume than I needed in my small office (although the music started to take on a harsh edge when the amp was pushed to higher volume levels). If you don’t listen too loudly, the Mini-T can also perform capably in a larger room, matching or exceeding the volume level of most inexpensive smartphone speaker docks.

After swapping cables to accommodate different speaker wire and input connectors, I fired up the DTA–100a, and I found a notable increase in performance. Bass tightened up and increased in volume, treble frequencies came into focus and lost some harshness, and midrange frequencies increased in detail and texture. The music’s pacing also seemed to improve, likely due to better resolution of transients. Like the Orb, the Dayton did strain at higher volumes, with the music becoming increasingly harsh, but with the DTA–100a, such volumes were excessively loud in my desktop setup.

I did encounter a couple of issues with the Dayton’s volume control. At lower levels, the volume didn’t change as smoothly as it did with the Orb, sometimes dropping off suddenly—achieving a quiet level of playback took some finesse. And at these low levels, the stereo balance shifted noticeably to the left side, suggesting that the right side’s output level was attenuated more quickly than the left side’s. I didn’t notice this at higher volumes, however, and this sort of issue is common in inexpensive amplifiers. But if you have particularly efficient/sensitive speakers (in other words, speakers that can produce your desired listening levels without much power), or if you like to listen at very low volumes, it could be annoying.

Finally, I hooked up the Audioengine N22, and I heard the Pioneer speakers sound their best. Through the N22, bass was strong and tight, and high frequencies natural, without artificial harshness. When I pushed the N22 to louder volumes, it continued to perform well. In fact, when testing the N22 at loud volumes, I encountered the limitations of my listening setup—audible resonance from my desk—before I heard problems with the amplifier itself. Unless you’re using substantially bigger speakers in a large room, or need extremely loud volumes, the N22 will likely provide plenty of power. One minor complaint is that the volume knob feels a little loose; it could benefit from more friction.

Further comparisons

The three models here are similar in size and capability to several of the DAC-endowed models I previously reviewed. To put the performance of these DAC-less models into perspective, I compared the DTA–100a to the $180 Topping TP30, and the N22 to the the $229 NuForce Dia (4 of 5 rating) and its discontinued $349 sibling, the Icon–2 (3.5 of 5 rating).

Listening to the headphone output of my MacBook connected to the DTA–100a and the TP30 (specifically, to the latter’s analog input), the DTA–100a is a clear upgrade over the TP30, producing tighter bass and a less-crowded sound that enables each instrument and voice to better stand on its own.

However, when I connected the TP30 to my MacBook via USB to take advantage of the TP30’s built-in DAC, the two amps were more evenly matched. The TP30 still sounded a little crowded, but its bass tightened up and it offered improved midrange detail. I give a slight edge to the TP30, taking into account its DAC and amplifier, but the DTA–100a is still the better amplifier, and the DTA–100a represents a better option if you already have a high-quality source, or if you’re using an analog-only source.

At a Glance
  • Orb Audio Mini-T Amplifier V2

  • Dayton Audio DTA-100a Class-T Digital Mini Amplifier

  • Audioengine N22 Premium Desktop Audio Amplifier

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