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.
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.
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.
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