Gato Audio DIA-250S NPM Amplifier/Network DAC Lab Report

Lab Report

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


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 20.7A


Distortion versus 24-bit digital signal level over a 120dB range at 1kHz (black) and 20kHz (blue)

Continuous power (<1% THD, 8/4ohm) 240W / 480W
Dynamic power (<1% THD, 8/4/2/1ohm) 243W / 505W / 860W / 415W
Output impedance (20Hz–20kHz) 0.021–0.20ohm (72ohm, pre)
Freq. resp. (20Hz–20kHz/100kHz) –0.14 to –0.23dB/–5.5dB (8ohm)
Digital jitter (S/PDIF at 48kHz/96kHz) <10psec / <10psec
A-wtd S/N ratio (re. 0dBW/0dBFs) 83.2dB (Analogue) / 101.1dB (Dig)
Dist. (20Hz-20kHz; 0dBW/–20dBFs) 0.0028–0.110%/0.0015–0.003%
Power consumption (idle/rated o/p*) 24W / 526W (W standby)
Dimensions (WHD) / Weight 325x105x420mm / 10kg
Price £2995

Gato Audio
Supplied by: Elite Audio (Distribution) Ltd, London
0203 397 1119