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what is Slew Rate ?

I am not a audio specialist so I would like your suport: I have a Jeff rowland model 1 amplifier and i'd like to know what it's specifications mean: most things I understand, but what is the "slew rate"? It's specified in the manual: 70 volts per microsecond. is this what technically determines how quickly the amplifier amplifies a siganl from the pre-amp? In that case, is a smaller value better? How can this be described from an empirical viewpoint? Is this what audiophiles describe by "speed", as in a "fast" amplifier; my stereo sounds good to me, but in real life music sounds better. ...Of course it does! Actually, vinil sounds much more realistic than CD's, but still I notice a lack fullness and "fastness" of music coming out of my speakers. I would like to somehow improve this sound area of my stereo. Does the slew rate relate to these sound qualities or do I need to look elsewhere? I wish I could just audition different equipment and choose the one I like best, but living in Chicago, I have access to only those brands that my local shop provides. I need some criteria to narrow down my search. Great site! yours, Herman
gerzhanda3b
carl_eber
1,425 posts
 
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.
gerzhanda3b OP
3 posts
 
-Herman
scottfrankland
4 posts
 
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.
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