Integrated Amplifiers

While the DIA-250S NPM did not quite meet its rated 250W/500W 8/4ohm power output, the figures of 2x240W and 2x480W into 8/4ohm, respectively, still demonstrate the perfect 'stiffness' of its regulated PSU. As expected, there is very little extra headroom under dynamic conditions, but the 243W, 505W and 860W into 8, 4 and 2ohm loads is still a lot of bang for this elegant form factor. The maximum (protected) 20.7A current yields 415W/1ohm [see Graph 1]. Distortion climbs gently with power output from 0.001%/1W to 0.005%/10W, 0.017%/100W and 0.06%/200W through bass and midrange, and more steeply at higher frequencies up 0.08%/20kHz/10W. This is not atypical of Class D architectures as the amplifier's output impedance rises from 0.02ohm through bass and midrange to 0.2ohm/20kHz and 2.5ohm/100kHz as a function of the output filter's reactance. Noise is much lower than measured with the more powerful DIA-400S amp [HFN Oct '16], and the A-wtd S/N wider at 83dB (re. 0dBW), despite it sharing the same +29.6dB gain.

Gato's digital board features TI's PCM1794 DAC with its linear phase/fast roll-off filter offering a full 99dB stopband rejection [the circuit refined from Gato's PRD-3 preamp/DAC – HFN Oct '14 – and mirroring almost exactly the performance measured for the DIA-400S]. Tested via its balanced preamp (2.06V at 0dBFs, Vol = 66), distortion is uniformly low at 0.002-0.006% (20Hz-20kHz), reaching a minimum of 0.0005% at –20dBFs [see Graph 2, below], while the A-wtd S/N ratio is a ~17-bit 101dB. Jitter is fabulously low at <10psec while the DAC/preamp response is flatter than the amp's Class D output at –0.7dB/45kHz and –2dB/90kHz (96kHz and 192kHz media). PM