MEASUREMENTS

I measured the Exposure XM5 integrated amplifier and D/A processor with my Audio Precision SYS2722 system (see the January 2008 “As We See It”¹). Usually before performing any testing, I run an amplifier for an hour at one-third power into 8 ohms, which is thermally the most stressful condition for a design with a class-AB output stage. With the Exposure XM5, however, I cut short this preconditioning after 15 minutes. The temperature of the amplifier’s bottom panel, to which the output devices are fastened, had already reached 163.6°F (73.1°C), and I was concerned that the XM5 would go into thermal runaway. The top panel was also hot, at 105.1°F (40.6°C). Clearly, this little amplifier doesn’t have enough heatsink capacity for sustained operation at highish powers. The owner should ensure that it’s well ventilated.

Looking first at the line-level analog inputs: With the volume control at its maximum setting, the voltage, were non-inverting) from both outputs. The input impedance was 14.7k ohms at low and middle frequencies, dropping slightly to 12.4k ohms at 20kHz. The preamplifier output had an appropriately low output impedance of 68 ohms at 1kHz and 20kHz, but this rose to 430 ohms at the bottom of the audioband.