RATINGS (relative to comparably priced integrated amps)
• Treble: 9
• Midrange: 8.5
• Bass: 8
• Soundstaging: 9.5
• Dynamics: 8
• Value: 8.5
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).