Yamaha YMC-700 neoHD Media Controller Page 4
Yamaha's unique media controller produced some unique test-bench behavior. First, sine waveforms below about 1-watt output displayed a pagoda-like shape - perhaps the result of a digital amplifier power-supply voltage switch lagging the input waveform at very low levels? The YMC-700's very modest power capability wasn't affected at all by speaker load or channel number: Around 12 watts (or 24, at 4 ohms) is what you get from its currentsource-like amps, no matter how many channels you drive. That is, until the Yamaha's thermal/ current watchdogs shut it down, which they did whenever I tried to clip 2 or more channels into 4 ohms for more than a second or two on sine waves. (I clipped the units extensively into loudspeakers without interruption.)
Finally, the Yamaha appears to mute its outputs whenever digital signals fall much below -60 dB. This made acquisition of any of our signal-to-noise, linearity, or other noise-related tests impossible, since the unit showed better than 130 dBW in every case, which is clearly impossible and roughly the same result I'd expect from measuring a chunk of glass (a perfect insulator).
The YMC-700 didn't appear especially noise-prone in my listening tests.
Clearly, there's some specialized engineering going on in the YMC-700. (Yamaha employs the YMC architecture in several complete home-theater-in-a-box systems as well.) The fact that the neoHD sounded as good as it did (and leaving audiophile standards aside for the moment, it sounded quite impressive - especially after I'd measured it!) suggests that its designers knew what they were doing and that, as usual, numbers tell only part of the story.