Amp Slew Ratings

[Markd102]

Hi Guys

I was told that when it comes to monitors amps, you need something with a high SLEW rating.

Here is my version of how it was explained to me.

"You want an amp with a high SLEW rating (80-100+) which is basically the response time (I think). From what I understand, the higher the SLEW rating, the quicker the speaker cone gets back into position and can the produce the next tone cleanly. Speakers sound muddy on cheap amps because they are trying to suck and blow at the same time."

Please let me know if this is how it works, sort of how it works or is a load of crap.

Thanks
Mark

[EZP]

Mark,

I don't exactly follow your story here, but this is what I know about slew rates:
The Slew Rate determens how fast the output can change its voltage. This is measured is Volts per second. Slew rates are especially inportant for high frequenties at high volumes. High frequenties changes voltage quickest, so when the amp doesn't cut it, the High Frequenties will be distorted.

Is this an answer? If not, I'll make a bigger story!!

Good luck!

EZP

[TexRoadkill]

So what slew rating would be needed for perfect reproduction at 20Khz? Or is it different for every speaker?

[Markd102]

Thanks Guys.

It was explained to me by a guy from around here who "thinks he's a pro" and needless to say his explanation was vauge. So I though I'd ask where I new I'd get some real answers.

Basically I spose I'm asking that "Is it true that the higher the slew rate, the better my speakers will sound." and "What should the slew rate be in a good monitor amp?"

Also, is there a way to test an amp to see what the slew rate is?


EZP. Feel free to elaborate as much as you like.

Mark

[zadar]

hi mark

of course you can measure the slew rate of an amp.
one way could be to put an sqare pulse generator in the input of the amp and look what is coming out (with an oscilloscope). you will see the output signal will be a little bit different from the input. (rise of the signal will be less steep).
in principle you can say if the bandwith of the amp is higher it has a higher slew rate.
but in reality and with speakers connected it is not that simple.

the diaphragm of a speaker has a mass and it is mounted in the speaker like a weight on a spring. so if you want the diaphragm follow the signal of your amp precisely (e.g. sqare signal with theoretically 90 degree ramp ) you will need a high (theoretically unfinite) force to move the mass.
as you can only get a defined maximum force (depending on the watts of the amp, the strength of the magnet of the speaker, the inner resistance of the amp, the resistance of the cables . . . ) you will usually have a much better slew rate reached by an amp than the speaker can follow.

the reason why some amps are sounding better with the same speaker usually is because the the power suppy of the amps often is not as strong as it should be. so when the input has strong transients (and you need some power for a bass signal at the same time) the supply voltage (not the mains voltage from the power plant) of the amp sinks an you will have some distortion of the input signal. (-simply spoken)

hope this was not too technical and my technical english not too bad.

regards
zadar