I start a new thread which came from here
So, mr. amp_man, how do you calculate the slew rate you will need?
Let's say, 500 watts out, 4 ohms, 50 kHz bandwidth at least. ( I know how to calculate slew rate)
SR= 2*pi*f*SQR(2*P*R) = 2*3.14*50000*SQR(2*4*500) = 19 V/us = absolute minimum. Some overhead is wanted, let's say 25-50 V/us is what you need.
Here is good link for this:
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/a741p3.html
amp_man says:
amp_man says:
My conclusion so far is the formula above is valid.
So, mr. amp_man, how do you calculate the slew rate you will need?
Let's say, 500 watts out, 4 ohms, 50 kHz bandwidth at least. ( I know how to calculate slew rate)
SR= 2*pi*f*SQR(2*P*R) = 2*3.14*50000*SQR(2*4*500) = 19 V/us = absolute minimum. Some overhead is wanted, let's say 25-50 V/us is what you need.
Here is good link for this:
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/a741p3.html
amp_man says:
Somewhere here I got lost. From a CD you can get out 20 kHz and in this bandwidth you have all attacks, transients etc. Absolutely zero above 22 kHz contains music. For a vinylplayer I'll gather that the limit is slighly above. Can a pickup really produce frequencys above 30 kHz?
amp_man says:
From what I know damping factor is output impedance in relation to the speaker impedance. What has slew rate got to do with output impedance?
My conclusion so far is the formula above is valid.
I believe your numbers are good.
In actual testing of audio, you do not get such high numbers.
The best I have ever seen is 5 V/uS with a vinyl copy of the
Sheffield Drum record just short of clipping a 100 watt amp.
This would translate to about 11-12 V/uS on your larger amp.
Keep in mind that this was the highest I could find at the time,
and .5 V/uS was a far more typical peak, even when you thought
there was a lot of top end. Peter Walker got similar results in
his measurements at Quad.
The question inevitably boils down to how much margin do you
want? Last time I looked John Curl advocated 10 times. For a
complex circuit with ordinary amounts of feedback, I would agree,
but for simple circuits with low feedback, I think the margin can
be less.
In actual testing of audio, you do not get such high numbers.
The best I have ever seen is 5 V/uS with a vinyl copy of the
Sheffield Drum record just short of clipping a 100 watt amp.
This would translate to about 11-12 V/uS on your larger amp.
Keep in mind that this was the highest I could find at the time,
and .5 V/uS was a far more typical peak, even when you thought
there was a lot of top end. Peter Walker got similar results in
his measurements at Quad.
The question inevitably boils down to how much margin do you
want? Last time I looked John Curl advocated 10 times. For a
complex circuit with ordinary amounts of feedback, I would agree,
but for simple circuits with low feedback, I think the margin can
be less.
I don't have taken into account how much additional speed you must have in order to get distortion figures low. I'll imagine that it's not good to be very near slew rate limiting when it comes to all sorts of distortions.
I'll have serious doubts though that a good PA amp must have SR far beyond 100 V/us. Isn't this asking for trouble in a professional enviroment?
I'll have serious doubts though that a good PA amp must have SR far beyond 100 V/us. Isn't this asking for trouble in a professional enviroment?
I gather, then, that it must always be greater than or equal to what can be directly measured at the output? Other than being an upper limit to what can be measured at the output does it have any additional significance? That is, is there any advantage if it is, for example, twice that achievable at the output versus 1-1/2 times?
Nelson Pass said:
High slew rates are not required soley for processing audio frequency signals, but to reduce the likelihood of slew overload in the amp. due to RF ingress.....
An amplifier driven to it's slew limit by such spureae is unlikely to simultaneously process audio frequency stimuli......
Specs to compare
Just throwing in some specs to cover the statement:
"The normal Signal transient require a slew rate of no more than 50V/us.
But to Produce fast transient Signal at high Accuracy at especially High Voltage and Current level that is I mean to say that For High Sound Pressure level the high slew rate requirement is evident to produce high voltage transients. Therefore a clear Factor is to increase the normal slew rate to about 3 to 4 times in order to create a signal transient of high speed at high Voltage thereby producing High SPL which is requirement of Large PA's and are catered by Professional equipment only."
Some specs:
#1 Labbgruppen fP6400 at 1200 W stereo in 8 Ohms with a slew rate of 20 V/us
#2 Peavey CS3000H at 700 W stereo in 8 Ohms with a slew rate of ">15 V/us"
#3 Crest Pro 9200 at 1300 W stereo in 8 Ohms with sleq rate ">10 V/us"
Crown, AFAICT, no numbers which speaks against the quote:
"Every high end Pro amp such as Peavey, Crown, Crest, etc Quote the slewrate of their amps so that the customer feels a better possession of technical specs."
With the numbers above I can only conclude that since these are high power amps and the slew rates are much lower than needed according to amp_man_1 then they will all fail to reproduce music with high quality and be unsuitable to Pro use. I never would've guessed given that they are by most people regarded as being pro amps...
Just throwing in some specs to cover the statement:
"The normal Signal transient require a slew rate of no more than 50V/us.
But to Produce fast transient Signal at high Accuracy at especially High Voltage and Current level that is I mean to say that For High Sound Pressure level the high slew rate requirement is evident to produce high voltage transients. Therefore a clear Factor is to increase the normal slew rate to about 3 to 4 times in order to create a signal transient of high speed at high Voltage thereby producing High SPL which is requirement of Large PA's and are catered by Professional equipment only."
Some specs:
#1 Labbgruppen fP6400 at 1200 W stereo in 8 Ohms with a slew rate of 20 V/us
#2 Peavey CS3000H at 700 W stereo in 8 Ohms with a slew rate of ">15 V/us"
#3 Crest Pro 9200 at 1300 W stereo in 8 Ohms with sleq rate ">10 V/us"
Crown, AFAICT, no numbers which speaks against the quote:
"Every high end Pro amp such as Peavey, Crown, Crest, etc Quote the slewrate of their amps so that the customer feels a better possession of technical specs."
With the numbers above I can only conclude that since these are high power amps and the slew rates are much lower than needed according to amp_man_1 then they will all fail to reproduce music with high quality and be unsuitable to Pro use. I never would've guessed given that they are by most people regarded as being pro amps...
Reply
Mr URSV,
Kindly Review ur Knowledge and Glance at the Manuals of Crest, Peavey, Crown as they have mentioned the slew rate .
Peavey 1200W has 45V/us
Crown 2200WRMS has 150V/us
Crest 10000B 4500WRMS has 80V/us
Secondly Would u plz Check WWW.MEYERSOUND.COM for their active transducers and ask them about the need of high slew rate as their amps are rated at 300V/us
regards and ThanX
Mr URSV,
Kindly Review ur Knowledge and Glance at the Manuals of Crest, Peavey, Crown as they have mentioned the slew rate .
Peavey 1200W has 45V/us
Crown 2200WRMS has 150V/us
Crest 10000B 4500WRMS has 80V/us
Secondly Would u plz Check WWW.MEYERSOUND.COM for their active transducers and ask them about the need of high slew rate as their amps are rated at 300V/us
regards and ThanX
Hi !
Shouldn't there be a harmonic compromise between speed of amp
and effective slewrate ?
In my amps i often reduce intentionaly the slewrate to avoid overshooting...
My experience/believing is, that all parameters must harmonize to
give a good sounding amp. Otherwise you get stuff like sounding
unprecise, false trebles, harsh sound and so on.
If an amp has given bandwidth, doesn't this result automatically
in high enough slewrate ?
If an amp has bandwidth of 50khz, then it automatically should be
able to reproduce a sinewave at 20khz, not a triangle.
Mike
Shouldn't there be a harmonic compromise between speed of amp
and effective slewrate ?
In my amps i often reduce intentionaly the slewrate to avoid overshooting...
My experience/believing is, that all parameters must harmonize to
give a good sounding amp. Otherwise you get stuff like sounding
unprecise, false trebles, harsh sound and so on.
If an amp has given bandwidth, doesn't this result automatically
in high enough slewrate ?
If an amp has bandwidth of 50khz, then it automatically should be
able to reproduce a sinewave at 20khz, not a triangle.
Mike
Personally I don't think enormously high slew rate is needed. It's nice to have a good margin over what is minimally required, and sure it's fun to be able to write some ludicrous number on the specs, but I am confident that it would be impossible to tell the difference between an amp with merely adequate slew rate and one with huge slew rate, all else being equal.
RF gets everywhere. The fact that even the best shielded amp in the world would still need supply decoupling caps is evidence of that.UrSv said:
No. Slew rate and bandwidth are related but one does not always lead to the other. Slew rate determines power bandwidth, as mentioned earlier. However at low amplitudes, the required slew rate is lower and thus does not limit the bandwidth.MikeB said:
Whats the point of such confrontation?
Better approach the question from other angle: what is the bad effect of slew rate limiting as one extreme? What gets better with no limiting? What behaviour fits in between?
Bandwidth limiting is only one piece of the picture.
Good margin. What is good margin? What good does making the margin larger?
What happens to output impedance and damping during high output slew rates? And by corollary, with NFB loop?
I guess that impedance goes up, and at KW levels even very small impedance changes would result in audible differences. Isn't then very high slew rate indirect way of expressing low dependance of output impedance on output power?
I don't know answers, so its just asking, to get the discussion back to interesting exchange of thoughts and experience.
Better approach the question from other angle: what is the bad effect of slew rate limiting as one extreme? What gets better with no limiting? What behaviour fits in between?
Bandwidth limiting is only one piece of the picture.
Good margin. What is good margin? What good does making the margin larger?
What happens to output impedance and damping during high output slew rates? And by corollary, with NFB loop?
I guess that impedance goes up, and at KW levels even very small impedance changes would result in audible differences. Isn't then very high slew rate indirect way of expressing low dependance of output impedance on output power?
I don't know answers, so its just asking, to get the discussion back to interesting exchange of thoughts and experience.
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