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Rohde&Schwarz UPV audio analyser – used for all measurements.
The Plato’s power amplifier produced 66 Watts into an 8 Ohm load and 110 Watts into 4 Ohms, enough to drive most loudspeakers to very high volume in the average sized room. Distortion levels were very low in the midband and at high frequencies; there is little sign of crossover products in our distortion analysis, the sound will be clean and lacking any sign of harshness. The amplifier’s output impedance was low too, resulting in a high damping factor figure of 40, so the amplifier will have relatively tight bass. Frequency response was very wide, stretching from below 2Hz up to 71kHz (-1dB).
Phono stage equalisation was accurate, resulting in flat frequency response, the warp filter acting sharply below 20Hz (see analysis below). Input sensitivity was 5mV and 0.7mV max for MM/MC respectively – low values – and overload levels fairly limited at 2.6mV and 20mV respectively too; an Ortofon 2M red produces up to 35mV. The change from MM to MC sometimes didn’t happen immediately either, so there are niggles here. Noise was very low.
The S/PDIF digital inputs were inconsistent, with the electrical connection via phono socket working to 96kHz sample rate maximum, whilst the optical input managed 176.4kHz maximum, neither working with a 192kHz sample rate signal. With 24/96 PCM digital, distortion measured a low 0.03% and EIAJ Dynamic Range (see analysis below) was commensurately high at 117dB – a good value up with market norms, if not the 120+dB nowadays possible from the best chips (ESS 9018, Texas Instruments PCM1795). With CD (16/44.1) however, EIAJ Dynamic Range was a high 103dB, so the Plato matches the best here.
Frequency response at 176.4kHz sample rate extended to 42kHz before rolling away slowly, about as expected using slow, but well damped filtering.
The Plato is a complex and ambitious product that worked well all round. Its phono stage in particular, with Gracenote ability to identify music and bring up artwork etc was especially comprehensive, if in need of a little buffing up of sensitivity and overload levels. NK
Frequency response 2Hz-71kHz
Frequency response 5Hz-20kHz
Noise (e.i.n.) 0.08/0.22µV
Sensitivity (MM/MC) 5/0.7mV
Overload (MM/MC) 2.6/20mV
FREQUENCY RESPONSE – LP
DYNAMIC RANGE (56.730dB+60dB=117dB)
24 bit digital