Wadia 151 PowerDAC mini Combination Integrated Amp/DAC (Playback 33)

Glimpses of Sonic Greatness

The Wadia 151 PowerDAC mini combines a class D integrated amplifier with an advanced DAC in a small package. This combination of functions not only matches Wadia’s well-known 170 iTransport (one of the few iPod docks to actually extract digital data from the iPod), but it also presents a very attractive solution for desktop audio (or other small systems) where space is inevitably at a premium. By design, the iTransport and the PowerDAC mini share the same footprint so that the transport can be stacked on top of the amp.

The questions for products like this always represent a combination of “does it sound good?” and “is it a good value?” The answers are slightly complex, but let me summarize by saying that after many weeks with the 151, I want one. You, of course, aren’t me, so read on for a more objective view.

Consider this amplifier/DAC if: You want a refined, dynamic sound that majors in instrumental separation. Also check this out if desktop space is at a premium.

Look elsewhere if: You want flexible input/output capabilities, or you favor a robust, rich sound.

RATINGS (relative to comparably priced integrated amps)

• Treble: 9
• Midrange: 8.5
• Bass: 8
• Soundstaging: 9.5
• Dynamics: 8
• Value: 8.5

FEATURES

The 151 PowerDAC differs in circuit concept from typical integrated amplifiers (including those with a DAC connected), even if they are built around Class D switching amps. The short version of Wadia’s idea is that the 151 is a DAC that is powerful enough to drive loudspeakers. The volume control is done in the digital domain and the signal is only converted to analog by a very simple filter circuit at the output of the 151.

To be more specific, after accepting a digital input, the 151 upsamples it and performs a digital-to-digital conversion from PCM (pulse code modulation) audio signal to PWM (pulse width modulation). A PWM amplification stage (a type of switching amp circuit) creates the voltage swing and current needed for loudspeaker use. A simple passive low-pass filter transforms the pulses into an analog power signal.

Wadia claim this approach be less influenced by potential nonlinearities and noise. Wadia’s use of digital volume control is interesting, and is based on some careful thinking about how to address the standard problems with this idea (truncation of bits). Wadia uses a 32-bit digital attenuation system, which is carefully explained on the Wadia site (http://www.wadia.com/technology/technicalpapers).

The 151 also uses Wadia’s WadiaStream USB 2.0 technology. WadiaStream supports a maximum throughput rate of 12Mbs and the preferred isochronous output scheme, which Wadia says provides bit-accurate data transmission along with good jitter suppression.

The Wadia 151 comes in an attractively simple package. It is a purely digital device, designed to accept a few digital sources and connect to one pair of speakers. The rear panel has one set of five-way speaker connectors, two coaxial RCA S/PDIF digital inputs, one USB digital input, one TosLink digital input, and the standard IEC three-prong connector for an AC power cord.

To be clear, I should mention that the 151 has no analog inputs or outputs. You can, of course use an outboard A/D device, but the size and expense of this cuts against the grain of Wadia’s concept here.

As with many modern products, the 151 is really designed to be operated via remote. The 151’s remote has the normal controls for volume, muting and input, as well as phase and sampling rate (confusingly labeled “Enter”). The control also covers some items like track selection that are needed if you are also using the 170 iTransport. The remote has no LCD to confirm response to your commands.

On the front of the 151 box itself, you’ll find a monochrome LCD window and five buttons in a row. The buttons let you control input selection, phase, muting, and volume up and down. This makes the 151 perfectly usable without the remote, though I would have preferred a rotary control for volume.

The 151 box is 8”x 8” x 2” high—the same size as the 170 iTransport and quite similar to the old Mac Mini. While this makes for an attractively small chassis, as mentioned above, the 151 is not designed to be mounted on its side, which would further reduce its desktop footprint.