Current limit onset definition?

The 60 amp figure is the maximum amount of current the amplifier can supply into a very low impedance (probably a short circuit, i.e. zero ohms) for a very short period of time (probably a few milliseconds). It is not representative of anything the amplifier would be able to do under realistic operating conditions, as 60 amps into 2 ohms is 7200 watts; 60 amps into 4 ohms is 14400 watts; 60 amps into 8 ohms is 28800 watts.

The 40 amp figure is the point at which one of the self-protection mechanisms in the amplifier starts to kick in. I suspect that the reason that figure is less than the 60 amp figure is that the response time of the protection mechanism is a bit slower than the amount of time the 60 amp figure is based on. In other words, the amplifier could provide more than 40 amps into a short circuit for a few milliseconds, but a few milliseconds later the protection mechanism would kick in and either limit that current or shut down the output altogether.

I have no specific knowledge of the design of Spectral amplifiers, but that would be my interpretation of those specs.

Regards,
-- Al

Almarg... since the Spectral DMA 180 is 200 Wpc amp into 8 ohms and can deliver 683 Wpc into 2-ohms, wouldn't it look like a melted puddle of sludge at any of the wattage figures you presented? I'm assuming this is wattage pulled out of the wall (not delivered to the speakers) we're speaking of... but really!!!)???

Hi Plato,

I'm not sure that you read my comment accurately.

The point to my mentioning those ridiculous wattage numbers was to illustrate that, as I said, "the 60 amp figure ... is **NOT** [emphasis added] representative of anything the amplifier would be able to do under realistic operating conditions."

As I indicated, the 60 amp figure most likely represents how much current the amplifier would be able to output into a dead short across its output terminals, for a few thousandths of a second. Since 60 amps into a realistic load impedance (2 ohms, 4 ohms, 8 ohms, etc.) would correspond to an absurd amount of power, the amplifier is obviously not capable of putting an amount of current remotely close to 60 amps into those impedances.

Some further comments:

A peak current spec such as that is therefore essentially meaningless. In saying so, btw, I'm not singling out Spectral, as a lot of other amp manufacturers provide similar specs. And adding to the meaninglessness of that kind of spec is the fact that the amount of time the specified peak current can be sustained for never seems to be indicated.

A more meaningful indication of the current capability and general robustness of a solid state amplifier would be whether or not its maximum rated continuous power capability doubles into 4 ohms, relative to 8 ohms (or if not, how closely the 4 ohm rating approaches being double the 8 ohm rating), and doubles again into 2 ohms, relative to 4 ohms (or if not, and if the amp is rated for 2 ohms, how closely the 2 ohm rating approaches being double the 4 ohm rating or four times the 8 ohm rating).

Regards,
-- Al

Peak current is akin to saying a circuit breaker may let through 150A of *instantaneous* current before it trips (in fact, in a short circuit that many instantaneous amps aren't unusual before the breaker trips or wires start to melt); and continuous current is akin to saying the breaker may trip when you reach that many continuous amps flowing through.

Instantaneous current will only be available in low impedances, and as a "spec" it's mostly meaningless, other that to probably somehow try to infer high slew rates (though they are spec'd in Volts, so there, this is why it's really meaningless to me)...