Hi to all the terminally puzzled,
THE *problem* with the Crown DC300A is simple, but virtually unknown in the industry.
Any amplifier that has response to DC is similarly questionable as being su itable or safe to use driving loudspeakers or transformers.
Such amplifiers produce a large DC component when driven into clipping with an unsymmetrical wave (eg speech or singing). Peaks of one polarity passin g undistorted while peaks of the other become clipped off = DC offset cre ated.
With a high powered audio amp, the DC component can reach *25 volts* or mor e with speech or music. Enough to bottom a woofer cone in its frame and pu sh the voice coil almost completely out of the magnetic gap. Bad news for t he speaker and sound quality - results in severe compression.
Most amplifiers avoid the issue simply by having a low frequency pole in th e feedback network, usually an 100uF or so electro cap to ground - so the a mp exhibits only unity gain at DC. Asymmetrical clipping then only causes a small sub sonic signal to appear that tracks the clipping. See this page by my colleague Rod Elliot, who carefully simulated the situa tion after I explained the problem to him 16 years ago.
FYI: the above plays havoc with speaker muting systems whose drive circuits detect the DC component and open the relay.