Need understanding on amperage

Atmasphere/Tonywise

Yes, the remaining voltage would be 56 volts, and the average power delivered would be between 3600 and 3136 Wts. And it may be somewhat less because we are not accounting for the voltage drop across the output stage transistors (it won't be zero, and will be dependant whether the transistors are being driven into saturation or not).

Guys, it was just a ballpark analysis. It also did not include the re-charge of the capacitor by the transformer or that perhaps both the V+ and V- capacitors might be discharged partially.

My point being is that the delivery of 60 amps to the load will be limited by the fuse characterisitcs primarily. Whether it is 10 milliseconds or 15 milliseconds is not that important.

BTW, I would hope that the fuse was sized to prevent the bipolar output transistors from going into secondary breakdown. If this happens, the power transistors fail and the entire output stage is toast before the fuse can protect them.

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......

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.