MEASUREMENTS
Iexamined the EMM Labs MTRS’s measured behavior with my Audio Precision SYS2722 system.1 After connecting the amplifier to the wall supply with the supplied Kimber Ascent cable, I preconditioned the MTRS, following the CEA’s recommendation of running it at one-eighth the maximum power into 8 ohms for 30 minutes. At the end of that time, the temperature of the top panel was 80.6°F (27.0°C) and that of the heatsinks 94.4°F (34.7°C). Given the relatively low heatsink temperatures and the amplifier’s massive size, I subsequently ran it for an hour at one-third the maximum power into 8 ohms. (With a class-AB amplifier, one-third power results in the maximum heat dissipation in the output devices.) At the end of that time, the heatsinks were somewhat warmer, at 104.2°F (40.1°C). The MTRS has more-than-sufficient heatsink capacity for its high output power.
I performed all the testing using the EMM’s balanced inputs, then repeated some tests with the single-ended inputs. (Although this wasn’t mentioned in the manual at the time, I needed to short the XLR jacks’ pins 1 and 3 for these tests, as otherwise the amplifier’s gain changed unpredictably.) Both input types preserved absolute polarity, ie, were noninverting. The MTRS’s input impedance is specified as 100k ohms for both input types. I measured 114k ohms at 20Hz, 100k ohms at 1kHz, and 90k ohms at 20kHz for the balanced inputs. The single-ended input impedance was 47k ohms at 20Hz and 1kHz, 40k ohms at 20kHz. The voltage gain is specified as 30dB for both balanced and single-ended inputs. I measured 29.6dB at 1kHz into 8 ohms for both types.
The EMM amplifier’s output impedance, including the series impedance of 6' of spaced-pair cable, was relatively low at 0.22 ohm at low and middle frequen