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.
I wanted to perform a similar experiment to compare the Audioengine N22 to the NuForce Dia, but that's not quite possible, as the Dia doesn't have analog inputs. However, NuForce's Icon--2 features essentially the same amplifier, so I brought it into the mix as well. As expected, the Icon--2 (through its analog inputs) sounded great, with tight bass and a sound that gave each instrument some space to breathe. The N22 was even better, though, with more clarity, space, and instrumental detail, along with tighter bass.
Switching to the Icon--2's USB input put it more or less on par with the N22. There were some subtle differences in sound, but overall performance was comparable. It wasn't until I switched to the NuForce Dia (connected to my MacBook's optical output), with its better DAC, that I heard something that bettered the N22, justifying the Dia's $30 price premium. However, pairing the N22 with a quality standalone DAC (the DragonFly) offered even better performance, suggesting that the N22 includes the best amplifier of the bunch.
Headphoning it in
Both the DTA--100a and N22 include headphone jacks; I tested each with my AKG K 701 headphones (which are picky about amplification) to see if either is of sufficient quality to replace a dedicated headphone amplifier such as the the modest HiFiMAN Express HM--101. I used the HM--101's DAC as a source to feed the two amplifiers, and I also used the HM--101's headphone output to provide a benchmark for evaluating the headphone outputs of the two amplifiers.
The contest between the HM--101 and the Dayton DTA--100a produced mixed results. The DTA--100a pulled better bass performance out of the headphones, but I found that the HM--101 sounded less harsh and more pleasant overall. (Both improved on my MacBook's built-in headphone jack, however.) In other words, the DTA--100a's headphone jack is on par with that of an inexpensive headphone amplifier. In contrast, I preferred the N22's headphone jack to that of the HM--101. The N22 offered more bass, better pacing, more detail, and an overall more-enjoyable listening experience. If you've already got a good headphone amplifier, you'll likely want to continue to use it, but the headphone jacks on both units are a nice bonus if you've been using a standard headphone jack.
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