Need understanding on amperage

agree, Dhl93449 calculations showed the delta-V (or droop) across the power supply cap to be 24V meaning that the final voltage after 10mS would be 80V-24V=56V but at this point in time the fuse would have blown (per the Littlefuse data sheet) as the current draw from the wall would have peaked at 8A in a valliant effort to re-charge the drooping power supply caps. Thus, the output protection ckt should have kicked in ASAP to cut off the output signal from reaching the speaker binding posts & there should be pin-drop silence from the speakers! ;-) And, as Dhl93449 noted, the output stage is hopefully intact & there is no smoke curling out of the amp......

Right! Now this is just my feeling about the matter, but I don't think the 60 amp rating is realistic if it means that the amplifier could be damaged or the like in the process. At that point we are clearly operating outside of the linear region of the amp- and such an amp is intended for music not square waves.

Bombaywalla, its not a given that the caps would be charging if the window is 10mS. A lot would have to do with where the AC waveform was at the time of the 'event' :)

BTW thanks to all that have contributed here.

You know, Murphy's Law says that a $20 transistor will blow to protect a $0.05 fuse. I wonder how Murphy's Law applies in the world of HiFi where fuses cost $80.

Yes, I have often wondered whether this claim for 60 amps by Parasound was an actual measured performance spec or strictly hypothetical "potential" capability. I guess only John Curl can answer this question.

If the current limiters kick in long before the 60 amps, then its hypothetical. Something I did not consider in my analysis.

Tony,

It is possible that the entire output stage could fail if the safe operating area of those transistors is not broad enough to allow the fuse to burn before the transistors fail. This is the potential weakness of having a plurality of power transistors in parallel in the output stage. The weakest one fails first, then the others have to carry the remaining current and they start failing in a cascade phenomena.

Atmasphere:
You are correct re the re-charge. 1/2 sine at 60 Hz is about 8 milliseconds, so it would depend on where in time the transient occured. Nevertheless, I doubt of the power transformer could supply anything near 60 amps. Bombay also seems to assume the 8 amp fuse is in the AC input side but it is actually on the DC power busses supplying the output stages.

So Murphy's Law in the World of HiFi: 24, $20 transistors will blow to protect a $0.05 fuse.