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Review: Four desktop amplifiers/DACs

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To test these amplifiers, I used a few different devices as sources: an Airport Express (using both its analog and optical outputs), a MacBook (using USB, optical, and Bluetooth connections), an iPad (using Bluetooth and USB) and an Apple TV 2 (using its optical connection). I used a range of bookshelf speakers, including the $104-per-pair Dayton Audio B652 and the $199-per-pair Energy CB-5 (each of which can be found for substantially lower street prices), as well as the $460-per-pair NHT Absolute Zero and an NHT SuperZero XU/SW1P satellite/subwoofer system (discontinued—an approximate current equivalent, the Super Stereo, costs $499). Finally, I used the Etymotic mc3 ( ) and AKG K 701 headphones to evaluate each amplifier’s headphone output, comparing performance to a $149 HeadRoom Total BitHead headphone Amplifier.

Listening tests

I began my listening with each amplifier’s digital inputs. The Topping TP30’s amplifier had no problem playing loudly enough with any of the four speakers to fill my small office or bedroom. I do feel the TP30’s audio quality is lacking in absolute terms, as it sounds somewhat “hard” and obscures some instrumental detail. The effect is more noticeable with better speakers, like the Energy and NHT models. In relative terms, though, given the size and price, the performance is impressive.

NHT's Absolute Zero

Next I tested the NuForce Icon-2. The Dayton speakers minimized the differences between the two amplifiers, but when using the Energy and NHT Absolute Zero speakers, the Icon-2 lacked the TP30’s harshness, brought out some musical detail, gave a better sense of silence between notes, and tightened up the bass output. Overall, it’s a better match for the more-expensive NHT speakers, although whether that improvement is worth almost double the price is debatable.

I then switched to the NuForce Dia. With the Dia’s improved DAC, I noticed tighter, stronger bass; crisper, more-distinct highs; quieter space between notes; and improved detail, top to bottom. In fact, the Dia coaxed better bass performance from the Energy speakers than I thought possible. I initially attributed this solely to the Dia’s better DAC, but a NuForce representative suggested that the removal of analog circuitry (including the analog pre-amplifier stage) was the primary source of improvement.

When I first fired up the Neuhaus T-1 and played music from its optical input, the T-1’s “tube sound” was subtle but apparent. Instruments and voices were smoother and sounded more—for lack of better words—round, rich, and pretty. This portrayal of music seems to smooth over some instrumental detail and thus sacrifices some accuracy, but there was much to like about the T-1’s romantic presentation. Indeed, it does improve the sound of low-bit-rate MP3 files (although it won’t work miracles). In direct comparisons to the Icon-2, I preferred the T-1’s performance, although I’m not sure whether that’s because of the tubes or in spite of them. (My money’s actually on the T-1’s DAC.) Although the T-1 and Icon-2 offer comparable resolution of detail, The T-1 has noticeably stronger bass output and a warmer sound. Strictly speaking, the T-1’s sound probably isn’t neutral, but it sounds great with small bookshelf speakers, such as the Energy model, that generally lack bass impact.

When I compared the T-1 to the Dia, I found the two units offered similar levels of performance. The Dia was more crisp, clear, and detailed, and thus probably more accurate overall, but I can see some listeners preferring the T-1’s presentation, which was at times more engrossing. The biggest difference was in bass output: the Dia offered tighter, better-controlled bass, while the T-1 had more overall bass volume. (When I used either the Dia or the T-1 with the Apple TV and the NHT subwoofer/satellite system, neither amplifier had trouble providing a dramatic home theater experience.)

DAC or no DAC?

I did my initial listening tests using a digital signal to test each amplifier’s built-in DAC. However, I was curious how much of each amplifier’s sound quality was due to its DAC, so I also tested each with an analog source. When I switched from the TP30’s USB input to its analog input, connected to an Airport Express, I noticed decreased bass volume and depth, and a decrease in resolution—unless you have a good source, the Topping definitely sounds better via its USB input. Using the Icon-2’s RCA inputs, again connected to the Airport Express, I noticed a similar decrease in performance between the digital and analog inputs, with the Icon-2’s performance dropping closer to that of the Topping (although the Icon-2’s analog inputs still sound better than USB audio through the TP30). The Dia, of course, does not have any analog inputs.

Evaluating the T-1’s other inputs was more complex, due to both their number and some odd issues I encountered. First, I switched to using the Airport Express as an analog source, and I noticed similar effects to those I observed with the TP30 and Icon-2: a loss of detail, looser bass, and less of a sense of momentum to the music. The T-1’s DAC paired with the AirPort Express’s optical output offered a definite improvement over analog.

Desktop amp/DACs compared

Price Rating Power (watts/channel @8 ohms) Digital Inputs Analog Inputs
Neuhaus T-1 $495 18 USB, optical, Bluetooth RCA (2)
Nuforce Dia $299 18 optical (2), coax none
Nuforce Icon-2 $349 18 USB RCA, 3.5mm
Topping TP30 $180 10 USB RCA

When I switched to the T-1’s USB input, though, I noticed a slight decrease in quality, with sustained musical notes taking on an odd vibrato, and a slight echo to the sound. (This was most noticeable with headphones, but it occurred with speakers, as well.) The effect was apparent only with “louder” recordings, such as rock mastered with compressed dynamic range, and it occurred regardless of the actual playback volume; quieter recordings such as classical music displayed this issue only in their loudest passages. Overall, this issue was subtle through speakers, but much more pronounced with headphones, giving the impression that the left and right channels were slightly out of sync. A Neuhaus representative claimed that this was not normal behavior, and sent me a second review unit, which displayed the same behavior. The representative also provided a third unit from the latest production run, which again had the same odd, slightly distorted sound through the USB input. Sound through the USB input wasn’t awful in most cases, but I preferred even the T-1’s analog inputs to its USB input.

I also tested the T-1’s Bluetooth connection. With my Mac streaming music over bluetooth, I noticed a significant reduction in dynamic range and musical detail compared to the optical input, and even compared to the Airport Express’s analog output. Bass sounded muddy, and high frequencies lacked energy. I could also clearly hear some intermittent buzzing (similar to interference caused by older GSM cellular phones) when no music was playing. This was annoying when the system was otherwise silent, but as long as music was playing at moderate volume, the music obscured this sound. Overall, the Bluetooth input may be fine for background music, and its wireless nature makes it a nice convenience, but for serious listening, the optical or even analog inputs yield far better results.

I noticed one other problem with the T-1’s DAC: On the first two units I tested, the optical and Bluetooth inputs swapped the left and right channels when listening to speakers, though the USB and analog inputs worked as expected. Through headphones, this was reversed: The left and right channels were correct when using the optical and Bluetooth inputs, but backwards through the USB and analog inputs. I requested a third review unit, and on that unit, the result was slightly different, though similar: Both analog inputs had correct left and right channels when listening through speakers, but the channels were swapped when using headphones; the digital inputs had correct channels when listening through headphones, but the channels were reversed when using the speaker outputs. In discussions with Neuhaus, a representative told me that they had investigated the issue, identified the problem, and would fix it future production runs. (The company did not provide us with a unit from those production runs.) We asked Neuhaus whether customers who are experiencing the swapped-channel issue could get their T-1 replaced with a new model; the company had not responded by the time of publication.

Headphone jack of all trades

Each of these units features a discrete headphone amplifier, letting you take advantage of the built-in DAC when listening to quality headphones—a feature that should be particularly handy in a desktop audio system. I tested this component by comparing it to my Total BitHead, a relatively inexpensive, but solid, standalone headphone amp with a USB DAC. First I compared the BitHead to the Topping TP30 using AKG’s K 701, which I found readily reveals differences between headphone amplifiers. The BitHead provided stronger low-bass performance, better detail, and a better sense of momentum—usually an indicator of better resolution of transient response. However, the TP30’s headphone output was entirely listenable, and it sounded less harsh and offered better resolution than my MacBook’s built-in headphone port.

AKG's K 701

The Icon-2 got closer to the Total BitHead’s performance, with better control of the K 701’s bass and a more-detailed, less-crowded sound than the TP30. However, the Icon-2’s headphone output emphasized high frequencies and gave them a slightly harsh edge, which doesn’t make for a great pairing with the K 701, a headphone that can sound harsh at times. Given that the Dia’s headphone jack features the same circuitry as the Icon-2’s headphone amplifier, the Dia’s sound through headphones was very similar to the Icon-2, except that the Dia’s better DAC offered improvements similar to those I heard through speakers. Still, as with the Icon-2, I found the Dia a little harsh with headphones. Finally, turning to the T-1, I noticed only marginal differences compared to the BitHead: The T-1 had weaker low bass and a comparative lack of detail and space between notes. But these were marginal differences, and the T-1’s tubes gave the sound a beautiful sweetness. The BitHead’s presentation was better overall, but as with speakers, the T-1’s reproduction of music via headphones was charming and lovely, and some people might prefer it.

My observations were similar when using the Etymotic mc3, but far less dramatic. With easy-to-drive headphones such as most inexpensive canalphones and canalbuds, any of the models here do a great job as headphone amplifiers. There is one notable exception to this, which is that sensitive headphones such as the mc3 will make more noticeable any electronic noise. With the TP30 and Icon-2, these noises were low enough in level to be easily covered by music, but when using the T-1’s Bluetooth input, the interference I noted earlier made the mc3 unlistenable, and it was loud enough to be annoying even with the K 701.

Macworld’s buying advice

Any one of these products, paired with a set of quality bookshelf speakers, makes a solid computer-based audio system. Given the range of prices, features, and sound quality, choosing between these amplifiers comes down to your budget and exactly how you’re planning to use them. If you want to bring sound to a small room as inexpensively as possible, and you have a set of unused speakers gathering dust (or plan to buy something inexpensive like the Dayton or Energy speakers), the Topping TP30 will allow you to do so for a great price. In fact, the Topping’s street price is considerably lower than its suggested retail price—at the time of publication, it was only $109.

The NuForce Icon-2 offers solid performance, versatile features, an attractive design, and the perfect size for a computer-based desktop audio system. But at about twice the price of the TP30, you’ll want to be sure your speakers are good enough to take advantage of the Icon-2’s superior sound quality. And if you have the space, $349 can get you a full-size stereo component that might provide better performance, although built-in DACs can be difficult to find in full-size amps at this price.

At $50 less than the Icon-2, and with a better DAC, more-compatible speaker connections, and a remote, the Dia is a real winner, although the lack of USB and analog inputs could kill the deal for some people. Sonically, the Dia was my favorite of the bunch, demonstrating the impact of the design changes introduced since the Icon-2. And as with the Icon-2, there are some great full-size integrated amplifiers in this price range, but few (if any) will have a built-in DAC, and none will have such a tiny footprint on your desk. I recommend the Icon-2 over the Dia only if you need USB or analog inputs.

At $495, and with a remote control and a full array of audio inputs, the T-1 is less a budget desktop amplifier and more a solution for a moderately priced compact stereo system. A full-size component might give you better amplifier performance, but, again, you’ll likely be sacrificing the T-1’s built-in DAC, Bluetooth functionality, good looks, (relatively) small footprint, and luscious tube sound. However, I don’t recommend the T-1 if you plan to connect to a source via USB (and you should consider Bluetooth connectivity as a convenience rather than a quality audio connection). Also, while I’m glad that the swapped-channel is being addressed, it’s disconcerting that the flaw wasn’t caught until I tested the T-1. These issues aside, the T-1 is a beautiful-sounding amp and DAC in an attractive package.

R. Matthew Ward lives in St. Louis and looks forward to reclaiming the closet space occupied by a stack of empty amplifier boxes. He writes about audio, Apple, and other cool stuff on his personal blog.

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At a Glance
  • NuForce Icon-2 Integrated Desktop Amplifier

  • Topping TP30 Class T Digital Mini Amplifier with USB-DAC

  • NuForce Dia Digital Input Amplifier

  • Neuhaus Laboratories T-1 Amplifier

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