Gotta say I'm not totally familiar with the McIntosh Power Guard trade mark but my chicken shite guess is its some form or another of a input/output comparator circuit.
Back in the early '70's Crown's DC-300A and DC-150A amplifiers called such a circuit IOC ... Input Output Comparator. Because of inherent and often destructive, threshold rail voltages in higher powered A/B amp designs .... don't most quality amps have such a IOC or "power Guard" implemented? Marketed as such or not?

Originally Posted by legend94 View Post
pioneer lacks power guard which to me is the main reason to won mcintosh other than build quality.