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Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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The answer is "it depends"

Posted by jj on May 18, 2001 at 14:22:09:
You can count on "way too slow" to matter, and "way too fast" to perhaps indicate that the amp *could* be unstable (BUT that doens't have to be, it's just possible).
To give you an idea, a 20kHz sine wave at maximum amplitude 'X' in volts (1.4 * RMS value) has a slew rate of
2*pi*20000*X. in volts/second. Divide by 1,000,000 for volts/microsecond.
If your amp delivers 'Y' watts into 8 ohms, that means that the RMS voltage is sqrt( 8 * Y) volts. An easier way to calculate 'X' above is to figure out, then, sqrt(16*y) (that accounts for the 1.4 factor), and put that into the 2*pi*20000*X equation above.
ANY amp with power output Y should ALWAYS have a higher number than what you get out of that equation. Another spec to look for is "full power bandwidth", it will usually tell you the maximum frequency you can get through the amp without slope (slew-rate) limiting.
btw, sqrt() means "square root".
What IS slew rate? It's the rate at which the amp can change its output voltage, in calculus terms, it's the minmax of the absolute value of the derivitive of the output voltage. (I.e. the minimum value that the maximum absolute value of the derivitive can take)
JJ