The nice folks at Parts Express sent over an amazing-sounding little amplifier, the $129 Topping TP30. It's a tiny desktop Class T amp design, with one analog RCA stereo input and one USB connection (the TP30 has a built-in digital-to-analog converter). The amp delivers 15 watts per channel to 4 ohm-rated speakers (10 watts into 8 ohms), and has a 3.5 mm headphone jack on the front panel.
With its extruded aluminum chassis, 8mm thick, CNC-machined front panel, and solid-metal volume control knob the TP30 wouldn't look out of place in a high-end system. It even feels expensive, but I have just one nitpick: the illuminated blue LED ring surrounding the volume control knob is too bright. I wish there was a way to dim it or turn it off. The amp measures a tidy 4.13 inches by 1.77 inches by 8.07 inches.
The USB interface utilizes standard Windows audio class 1 drivers (it worked fine with my Mac mini). Internal parts quality is superb; the TP30 boasts Elna capacitors, Dale resistors, and an ALPS volume control. The Burr-Brown USB digital-to analog converter chip accepts up to 48 kHz sampling rates with 16-bit resolution.
I compared the sound of the TP30 with my Audioengine N22 amp ($199), and they're both pretty good. The N22 has a fuller, warmer tonal balance, but the TP30 has a more immediate, detailed sound with more tightly controlled bass. I used my Audioengine P4 speakers for all of my speaker-based listening tests. It's interesting, the TP30 is a digital amp and takes digital signals "straight-in" via its USB port; the N22 is analog-only and is a more traditional Class A/B amplifier design. It sounded softer, and a wee bit less defined than the TP30.
The TP30's sounded best with its USB digital inputs, the bass firmed up even more, and overall clarity went up a notch or two (compared with its analog connection). Still, it's nice to have the analog option to hook up a FM radio or maybe an old cassette deck.
Comparing the sound of the amps with headphones, the tonal balance issues were the same. The N22 was decidedly richer and had more oomph, but the TP30 better resolved details and dynamic subtleties on drummer Max Roach's all-percussion M'Boom "Collage" CD. The tactile shadings of the hand drums and full-on impact when the percussionists really whacked their instruments hard were more evident with the TP30, but I also liked the N22's fatter sound on the drums with my full-size Sennheiser HD 580 headphones.
Again, the two amps sounded different from each other; the N22 was fuller, the TP30 more transparent. The sound with the ER-4PT was exceptional, so much better than what I'm used to from my iPod Classic. Headphone amps and high-quality DACs can really make a difference in the sound you get from your 'phones.
The TP30 is a charmer, that's for sure! If you don't need the USB input, check out the Topping TP21 amp, it has more power, 25 watts a channel, and goes for $110.