Slew rate question

[Ramcres]

CD goes up to 20kHz. That is not very fast.

The claim that an amp needs to be very fast needs explanation.

You're right , we should say "precise in time" . Obviously both expressions are related , because it takes speed to be precise.



For example .



In this simple circuit -with ideal sources-, the signal time is modulate with VBE , no precise in time .


An sinus wave doesn't show the timming errors ,which could occur in a complex signal , where the amplittude could moves in anywhere in the VBE .


Conclusion with this cicuit is impossble to get a free error timming , wherever it is placed.



This is fast? , yes , but not precise .


I hope I have explained .


BR

 

[nigelwright7557]

Given all this, I did not understand slew rate as well as I thought I did. But, you all have been very helpful. I still wonder if a higher slew rate amp has any real advantages over a lower rate amp?

The better the slew rate the better it does high frequencies at larger AC voltages.
I designed a USB scope and had problems at high frequencies despite having a fast op-amp. I changed to a higher slew rate op-amp and the problems went away.

 

[DF96]

Audio amplifier must be fast , but ...... for every tone and overtone - at every frequency simultaneously , at every amplitude , at every load ..etc



SR says nothing about this .



Can be useful for designing puposers , but not for audio qualities .

No, audio is fairly slow. Slew rate limit tells you how fast a voltage can change; it does not know, does not care and does not need to know what this voltage represents. Amplifiers do not see music; they just see a varying voltage. They simply have to ensure that the output voltage is as similar to the input voltage as reasonably possible. That is engineering; all else is alchemy.

Speed in audio amplifiers is like acceleration and speed in cars.

Only in the sense that in both cases people with more money than wisdom can be persuaded by marketing and fashion to buy something whose performance far exceeds what they need or can use. Such people then fool themselves into thinking that others envy them. We don't.

I hope I have explained .

No.

 

[nigelwright7557]

CD goes up to 20kHz. That is not very fast.

The claim that an amp needs to be very fast needs explanation.

Am amplifier can drive a tweeter upto about 40KHz.
It can also need to output up to +/- 75 volts for a large power amp.
So that would need to be about 75v/6uS slew rate or 12v/uS.

 

[29285]

Am amplifier can drive a tweeter upto about 40KHz.
It can also need to output up to +/- 75 volts for a large power amp.
So that would need to be about 75v/6uS slew rate or 12v/uS.

This is a very secure method to kill any tweeter within a fracture of a second

 

[nigelwright7557]

This is a very secure method to kill any tweeter within a fracture of a second

On a large system you wouldn't have one tweeter across the output !
They would be in arrays with crossovers.
You can get full range drivers that go up to 20KHZ so even then that's 6v/uS. And that isn't hanging around.

 

[Ramcres]

In a car engine there are pieces that need to move fast , very fast , a piston , its lineal speed and acceleration is huge , even when the car is traveling slow.


Anyway I first tried to do a musical amplifier , without books and others things , and I discovered that it was fast , very fast .
IMHO this is the correct way , the other way could not work .


BR

 

[cbdb]

An amp is not an engine, your analogies dont make sense. And frankly either does your last sentence.

 

[Ramcres]

I thought this is a discussion forum, not to judge evaluations that are personal
in any case.