Note: This is a First Listen, so take these comments as preliminary. The review process inevitably involves some learning about component matching, set-up and response to different recordings.
The Wadia 151PowerDAC effectively combines a D/A converter and a pre/power amplifier in a single very small chassis (8” x 8” x 2”). That language may be misleading though, since the Wadia 151PowerDAC doesn’t work like traditional gear. In most audio equipment, the D/A conversion is one circuit and the power amplification is another (analog) circuit. In the Wadia PowerDAC, D/A conversion is, in effect, done by the power amp. Signals are digital right up to the output stage (where they must be analog so that speakers can use them).
While this sounds like a good thing—analog having been portrayed as old school and prone to noise, and digital being the progressive approach—it isn’t as obvious as one might think. After all, as one designer puts it “what circuit design rule says that doing the D/A conversion at the output stage is optimal, given its possibly competing need to swing big voltages and deliver massive current?” I’ll leave judgment on that to our listening sessions.
The 151PowerDAC is nominally a 25 watt per channel device. Into 4 ohms, Wadia claims 50 watts per channel, which suggests a good power supply design and ample heat dissipation (made easier because Class D amps are thermally efficient).
The 151PowerDAC does have some nifty features. There are four inputs: two Coaxial S/PDIF (RCA), one TOSLINK optical, and one USB. All inputs, excluding the USB (which is limited to 24-bit/96kHz), can accept digital audio data at up to 24-bit/192kHz input rates. This means that the highest resolution discs and downloads can be applied to the 151PowerDAC (if you have the right connection). Since many of our reviewers have noticed the superiority of these recordings, I would consider this an important feature.
Incoming data is always up-sampled to 24 bit/ 384kHz. This is necessary because the 151PowerDAC also has a digital volume control. A digital volume control has the advantage of avoiding the contact noise and distortion of an analog volume control (or a volume control and an entire preamp circuit). However digital volume controls typically operate by a form of bit shifting that throws away some bits and results in reduced resolution. With a digital volume control operating on a 16-bit signal, one has simply traded forms of distortion. But remember, Wadia starts with a 24-bit signal, which means they can perform 36 db of attenuation with no resolution loss. At maximum attenuation of 50db, the Wadia still offers 14-bit resolution.
The 151PowerDAC is controlled primarily by a remote. There are also basic controls on the front panel, along with a status display.
The size of the 151PowerDAC is impressive. Impressively small to be exact. It matches the Wadia 170 and 171 iTransports, which is nice if that’s the device you use as your server. But even if you use a PC/Mac as a server, the size of the 151PowerDAC strikes me as very desk-friendly.
The Wadia 151PowerDAC is priced at $1195. Our review sample was kindly loaned to us by Wadia for this test.
For this initial coverage of the 151, I used my Room 2, which is medium-sized (19 x 17 x 8). I hooked up the S/PDIF digital output of a Yamaha universal player to the 151 and connected the outputs of the 151 to a pair of Monitor Audio Silver RX 1 stand-mount speakers.
The basic character of the 151 doesn’t take long to discover. The first and most noticeable aspect of the 151 is its bass performance. Bass is very tight, with excellent definition and control. In this sense, the 151 is reminiscent of other Class D amps I’ve used (from NuForce, Audio Research, Kharma and others). As a group, these amps excel at bass definition.
The quality of bass from the 151 is impressive, but prospective purchasers should be aware that what one gains in bass definition one seems to lose in bass power. If you have a small room with difficult to tame bass resonances or a speaker that is a little loose down low, the 151 may create a heavenly match. But if you have a bigger room or mini-monitors that are on the shy side in the bass, the 151 may not be satisfactory.