Slew Rate

My understanding is that slew rate needs to be faster as the amount of negative feedback goes up. Even Nelson Pass has said that anything over 50v/microsecond is not describing anything happening in audio or even low RF on a low feedback design. And this is for a power amplifier; a preamp needs even less.

That being said, what is even more important than Slew rate, but seldom if ever mentioned, is "settling time" the time it takes the amp to settle down to its quiescent conditon. Lots of 70's amps had fast "attacks" but took forever to settle down; in a crude way one can say the amp described the leading edge of the waveform well but not the back side (or decay side).

That being said companies like Spectral have 700 to 1000 volt/microsecond slew and nano-second settling times. It sounds good, but does that make it the best preamp? No, not really (it is my favorite, but that is not the point). There are just too many other important qualities that matter to the sound. Sure, it is nice that an amp or preamp can describe a color TV signal perfectly, but that has nothing to do with audio.

Sean, I once heard that Sunfire amps have very low slew rates, (part of what gives them a "tubey" sound). I can't find any specs though. I know that you're a fan of these amps (and in fact, I just ordered one). Do you think that your comment above regarding low slew rates,

"...can sound quite "musical" but typically tend to be far less resolving, not nearly as transparent and tend to get "hard, nasty and gritty" with a less cohesive presentation as they are pushed harder."

applies to their amps? I always thought sunfire was known for standing up well under tough loads. Just curious. Thanks for the great explanation above.

rp1@surfnetusa.com...Trailing edge transient response is of little interest for music reproduction, because music does not have sharp trailing edges. This characteristic is used in the restoration of antique records, to disciminate between musical transients, and media damage (scratches). The record is played backwards, and any transient seen under this condition is identified as noise, and edited out.

sean...I think that the "textbook" value of acceptable slewrate is correct, but what has not been talked about is slew "acceleration". Maybe two amps achieve the same slew rate, but one gets up to that rate quicker, and this might permit greater fidelity in following transient waveforms.

Do you know how slew rate is measured? (The procedure). In the case of digital pulse rise time measurement, we measured time between 10percent and 90 percent of the pulse amplitude. The circuit may take less time to go this 80 percent of the amplitude than to go the other 20 percent.