The THX Ultra2 certification insures that no matter the configuration that the amplifier is used in, there is sufficient power to handle the job. The amplifier is rated at 150 Watts per channel into eight Ohms with two channels driven. While this may seem like a modest amount, the amplifier never seemed to be straining at reasonable listening levels in my five-channel system.
The PA-MC5500 features Onkyo's WRAT (Wide Range Amplifier Technology) topology, push-pull amplification design with three-stage inverted Darlington circuitry, auto-power down function to reduce energy waste, a twelve volt trigger as well as balanced and single-ended inputs. Behind the sculpted aluminum front panel of this 51-pound amplifier is a large toroidal transformer then a large heatsink that runs the width of the amplifier. The backside of the heatsink has a pair of 22,000 µF capacitors, which are flanked by nine-circuit boards, which contain the above-described Darlington circuits and "audio-tuned reference capacitors" and "custom-designed large power transistors to drive high currents". The circuit boards feature µm thick copper traces to handle the high current demands without impedance problems.
I connected the amplifier to my system using balanced interconnects even though the Onkyo is not a true balanced design. I used a variety of speakers including some from MartinLogan, Dynaudio and Acoustic Zen. The MartinLogan and Acoustic Zen speakers proved to be the most challenging for the Onkyo amplifier. Driving the six-Ohm Acoustic Zen Adagio's (Adagio front left and right, Adagio Juniors at center and rear) at the louder end of reasonable for a few hours resulted in a very warm amplifier. Comparing the Onkyo to other multi-channel amplifiers I have had in my system I found that the revealing tweeter of the Adagio's showed that the Onkyo was not quite as open and airy as the Marantz MM-8003 amplifier but the Onkyo had more impact on the low end. The MartinLogan Summits revealed that the several times as expensive Halcro MC-50 were more revealing and less likely to get congested in the midrange area.
Overall the Onkyo was well balanced with the high end being only slightly forward. This was most noticeable at high volumes through the Adagio speakers where the treble tilted towards hardness. Any other sonic shortcomings were those of omission. Quite simply, the Onkyo performed very well as far as it went but it did not reach absolute reference levels is dynamics, resolution and transparency, nor did I expect it to. The amplifier performed as well as, if not better than one could expect a $1,699 amplifier to do.Read about the high points and the low points of the Onkyo PA-MC500 on Page 2.