The Wadia 151 has a distinctive approach to music that I think will work exceedingly well in some systems but not as well in others. Because amplifiers do not differ to the degree that speakers do, let me try to outline the 151’s sound in several different ways.
To start, the 151 has a very clear sound, which I think reveals the smidge of opaqueness we tend to view as “normal” in other amplifiers, especially in this price range. The 151’s clarity comes through where you might expect it, in the midrange. Instruments with strong midrange energy (i.e., most instruments) seem to have a light shining on them. That’s partially true because there is no boomy bass or bright treble to overpower the midrange frequencies. In the same way, the 151 maintains an excellent sense of instrumental separation, a capability that usually requires superior handling of micro-dynamics.
The 151’s sense of clarity extends up and down the frequency spectrum. Bass is very tight and many bass instruments (e.g., kick drums, string basses) are delivered with a sense of definition rarely heard except on very high-end rigs. Treble clarity is also exemplary, with cymbals in particular rendered with appropriate definition and decay rather than as a splash of energy. This suggests to me that the D/A circuitry is quite good.
I do think that some listeners will find the 151’s approach to frequency balance less than ideal. If you want big, punchy bass or a warm, relaxed sound you should probably look elsewhere. Mid-bass seems slightly too light and controlled on the 151 to be satisfying with those goals. Even judged against the absolute sound, I’d say the 151’s bass lacks some depth and air (just as many other amps lack some control when judged this way). And the midrange glow provided by the 151 tilts it to the dynamic and involving side of the flavor spectrum. In this latter sense, it is more like live music than some of the competition.
While we’re on the subject of dynamics, it seemed to me that the 151 had adequate power, but nothing more. Wadia only claims 25 watts per channel, of course. I did have to crank the 151 up pretty far to get satisfying levels with the admittedly low sensitivity Usher S520 speakers in our 1900 cubic foot lab. I also used the PSB Image B4 speaker to similar effect (note that small speakers tend to have low sensitivity). Happily enough, the 151 doesn’t sound strained when you push it. In a desktop setting or with more efficient speakers, you’ll probably be fine.
The 151’s soundstaging is also extremely good. Low-level detail, as mentioned above, is handled well rather than trampled into the dust. As a result you can hear the recording venue quite clearly. This isn’t a matter of audio geekery, but rather a characteristic that is required in order for an amp to deliver a sense of depth and air and instrumental color.
In a sense, the 151 reminds me of the choice stereotypically presented by electrostatic speakers. Bass is well defined, but not deep or powerful. Midrange is stunningly clear without being edgy. Treble is smooth and accurate without being bright or edgy. Ultimate volume capability is limited, though quite dynamic within it’s volume envelope. The only thing is, electrostatic speakers have traditionally been very expensive—whereas the Wadia 151 really isn’t, at least within the grand sweep of audio pricing.
The 151, like any product, raises questions of value. If you assume that a good DAC costs $400-$500, then the $1195 Wadia effectively sports a $700-$800 integrated amp. That’s not cheap, but it isn’t exactly a stratospherically priced single-ended triode product either. My point here is that some people are willing to pay a lot for sonic subtleties and the price premium that the Wadia extracts for such subtleties is pretty modest.
Another interesting comparison is with the excellent Peachtree iDecco, which Playback Editor Chris Martens reviewed a few issues ago. Compared to the iDecco, the Wadia seems a bit feature-reduced (and at a higher price). The Peachtree, for example, has a headphone amp built in, offers analog inputs, has a switchable tube stage, can be used as a standalone preamp or DAC, and even includes a built-in digital iPod dock (conceptually similar to Wadia’s iTransport). Of course, the Peachtree is quite a bit larger (not that it is large) and to my ears has a more conventional sound, with less absolute clarity than the PowerDAC mini, but a more balanced mix of bass/midrange/treble frequencies. You probably know which kind of buyer you are, so it really isn’t absolute value that we’re talking about, but which sonic value set fits your needs (and listening tastes) best.