what is Slew Rate ?

Slew-rate refers to a rate-of-change limit. This limit is set by bandwidth and/or output impedance. For example, if an amp uses feedback and has a narrow open-loop bandwidth (i.e., before feedback is applied) then this amp will probably have a poor slew-rate. Also, if the amp contains stages that cannot supply current at high frequencies (due to high output impedance) then that stage will slew-rate limit. Slewing means distortion on high-slope signals (i.e., signals that are both high in level AND high in frequency). If you want a faster sound, I would look for an amp that is dead flat to 20kHz (i.e., not more than 0.1dB-0.2dB down at 20kHz). After that, I would look for a higher slew rate, which is less critical at normal listening levels and with typical program material. Rather than ultra-high slew-rate, I would look for a direct-coupled amp, which will sound faster (as a rule) than cap-coupled amps. Finally, I would look for an amp with a regulated power supply, as these are most often the fastest in terms of pumping current around the audio circuit.

-Herman

Shayner, excellent textbook definitions! As far as electronics that have the highest slew rate, I believe it's Spectral, at like 1000 volts/microsecond. HOWEVER, Herman, I have the feeling what you are craving would be best served by seeking a high damping factor in an amp (say over 500), as opposed to a high slew rate. Just my opinion, but try anyway. If you can afford to buy new and expensive amplifiers, you can afford to buy several used ones, and sell what you don't like. Or, you could seek out friendships with other dealers outside your area, who will sell to you, or allow you to demo their amps. The whole territorial thing with dealers is so stupid, and the internet is finally showing them who's their daddy now!! It's fun to watch, and helps to hurt the bad dealers who've had a "captive clientele", IMHO.

Does this help? Slew rate: The term used to define the maximum rate of change of an amplifier's output voltage with respect to its input voltage. In essence, slew rate is a measure of an amplifier's ability to follow its input signal. It is measured by applying a large amplitude step function (a signal starting at 0 volts and "instantaneously" jumping to some large level [without overshoot or ringing], creating a step-like look on an oscilloscope) to the amplifier under test and measuring the slope of the output waveform. For a "perfect" step input (i.e., one with a rise time at least 100 times faster than the amplifier under test), the output will not be vertical; it will exhibit a pronounced slope. The slope is caused by the amplifier having a finite amount of current available to charge and discharge its internal compensation capacitor. 2. Mathematics. Slew rate is defined to be the maximum derivative of the output voltage with respect to time. That is, it is a measure of the worst case delta change of voltage over a delta change in time, or the rate-of-change of the voltage vs. time. For sinusoidal signals (audio), this equals 2 pi times the maximum frequency, times the maximum peak output voltage. You must also consider the Damping Factor of the amp, which deals with how well it handles back emf from the speakers.

Slew rate, I believe, is how fast your amp can recharge it's main power capacitors. If a humongous crecendo sucks all of the reserve power out of your caps, you want to replace it pronto (sorry, I watched M*A*S*H today). Compare Krell's slew rate (at least their older amps) to a typical Audio Research product. If memory serves, its like one hundred times more (i.e. quicker). As far as a snappier sound from your gear, try: Nordost cable; more efficient speakers (or speakers with a more stable impedence curve e.g. KEF); a more powerful amp; less sound absorbing material in your listening room; etc. Good Luck!