Man, I hear ya! What is important is the final result, with an actual music signal, not some artificial square wave.
To what? All I can say is that yes, distortion and clipping level matters, response with square waves doesn't.
Somehow I feel we are going in circles...
Ok, I understand, al people wich tests amplifier under circumstances of square wave to see ability of rise and fall times, to be able to calculate slew rate of the amplifier ARE STUPID, and you are ten only smart one.
GGGGot it.
Good luck!
Enjoy your classD amp with residues on output and poor rise and fall times, as Hi-Fi one!
GGGGot it.
Good luck!
Enjoy your classD amp with residues on output and poor rise and fall times, as Hi-Fi one!
Some people who test amplifiers with square waves - and now what they are actually testing for - are extremely smart. I am sure there are more than ten smart ones.
I didn't know you had tested the hypex nc400. I am sure we would all love to see your measurements on that one, and hear your conclusions.
Rise time is not the same thing as slew rate. That confusion is the source of your misunderstanding.
Rise time is that time that amplifier needed it to swing from 10% to 90% from his output Vpp excursion.
Slew rate is dependant by 2 factors, rise time, and Vpp of square wave signal, measured on output to an known load, measured 10Vpp under clipping level, to measure correct and acurate.
Let's take by example this amp:
http://postimg.org/image/xz8sibhn3/
If one amplifier is able to offer 2,73uSec rise time with one excursion of 198Vpp, (there are 10Vpp under clipping level to make acurate measurement ) that amp will have 198Vpp/2,73usec=72,52 volts per microsecond.
Higher slew rates are absolutely required for high power amplifier like Powersoft.
Unfortunately as you see in tests rise time of him was around 21-23uSec on this movie
https://www.youtube.com/watch?v=flkGIeehOyY
So let's say for 300Vpp on 10Khz that amp showed for very short period until limiting his slew rate is 300/23=13volts per microsecond wich is TOO LESS for one 5900Watts/2 ohms amplifier.
13 volts per microsecond had Crown Powertech 2 series where for 440Watts/4 ohm that amp have, 13 volts per microsecond are enough to reproduce acurate 10Khz for that amount of power.
But for 5900 watts that claims this Powersoft is much much low just 13-15 volts per microsecond as slew rate measured REAL, not what they said in LIAR specs.
Greater power that amplifier delivers, greater slew rates required to act correctly on entire audio band, especially for high freqs above 8Khz.
Slew rate is dependant by 2 factors, rise time, and Vpp of square wave signal, measured on output to an known load, measured 10Vpp under clipping level, to measure correct and acurate.
Let's take by example this amp:
http://postimg.org/image/xz8sibhn3/
If one amplifier is able to offer 2,73uSec rise time with one excursion of 198Vpp, (there are 10Vpp under clipping level to make acurate measurement ) that amp will have 198Vpp/2,73usec=72,52 volts per microsecond.
Higher slew rates are absolutely required for high power amplifier like Powersoft.
Unfortunately as you see in tests rise time of him was around 21-23uSec on this movie
https://www.youtube.com/watch?v=flkGIeehOyY
So let's say for 300Vpp on 10Khz that amp showed for very short period until limiting his slew rate is 300/23=13volts per microsecond wich is TOO LESS for one 5900Watts/2 ohms amplifier.
13 volts per microsecond had Crown Powertech 2 series where for 440Watts/4 ohm that amp have, 13 volts per microsecond are enough to reproduce acurate 10Khz for that amount of power.
But for 5900 watts that claims this Powersoft is much much low just 13-15 volts per microsecond as slew rate measured REAL, not what they said in LIAR specs.
Greater power that amplifier delivers, greater slew rates required to act correctly on entire audio band, especially for high freqs above 8Khz.
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No, it's not. This is a bandwidth limited sampling system. Rise time (not slewing!) is a function of the input filter. If the amp can deliver full power to >20kHz (which it can), then for audio purposes, there's no problem. If you want to use it for some other purpose, that's a different story.
Man, slew rate tests of an amplifier must be made on squarewave.
That amp cannot deliver not even 30% from claimed power at 20Khz without tons of distortion as showed.
For bass purpose is OK, also here I have some retains because very hard clipping on output showed at 103Vrms on 2 ohms wich in any way of measurement ISN'T 5900 watts as claimed
Then instantly after 103Vrms hard clipped, limiter cuts off until 67Vrms/2 ohms wich is a little under 2500watts RMS/2 ohms, more than 60% less than claimed (5900 watts/2 ohms)
POINT.
That amp cannot deliver not even 30% from claimed power at 20Khz without tons of distortion as showed.
For bass purpose is OK, also here I have some retains because very hard clipping on output showed at 103Vrms on 2 ohms wich in any way of measurement ISN'T 5900 watts as claimed
Then instantly after 103Vrms hard clipped, limiter cuts off until 67Vrms/2 ohms wich is a little under 2500watts RMS/2 ohms, more than 60% less than claimed (5900 watts/2 ohms)
POINT.
You're still stuck on two problems:
1. You're still conflating slew rate with rise time. And using an inappropriate test signal- it's telling you that there's an input low pass filter. THAT is what you're measuring.
2. You don't understand what the EIAJ rating means.
The measurements I posted before indicate that these amps meet and exceed their specs.
1. You're still conflating slew rate with rise time. And using an inappropriate test signal- it's telling you that there's an input low pass filter. THAT is what you're measuring.
2. You don't understand what the EIAJ rating means.
The measurements I posted before indicate that these amps meet and exceed their specs.
Man, please read what we write.
Do you know what a bandwidth limited sampling system is?
Some tests that might be relevant to a class A or class AB amp are less relevant to class D amps.
What has that to do with slew rate or square waves?
Ok, accepted. Mostly.
Let's use the wording slew rate really only for the full signal sloping. Fine with me.
I just do not agree on linear operation , because usually many internal gain stages are already fully overdriven and not at all in operation any more.
That's not distortion, that's gibbs phenomenon. When you chop harmonics off a square wave, you get exactly that.
Looks like DJLeco is analyzing the output only in time domain and connot think in the frequency domain.
Man, as long as that amplifier is between 20Hz and 20Khz, on that domain of freq, the amp must act perfectly on sinewave and squarewave.
From as seen on test, that amp was not able even to sustain his official power from specs 2x5900Watts/2 ohms, even for 3-5 seconds that's minimum for heavyest program material dubstep or reggae (deep prolonged bass) ; the amp limit in less than 500mSec to under 2500 watts per channel, less than half claimed.
Those amps are good for bass only, for short bursts power and for making noise on mid-hi freqs above 3Khz because no details on sound, regarding poor rise times of output stage, an rise time of 23uSecs are unacceptable for modern quality amplifiers, in mine opinion.
On outputs alot of artefacts at low power because underdamping output filters, even if is not audible, the original input signal will be altered at output on entire audio band.
In squarewave, response is worse above 1Khz with poor rise and fall times, no matter if internally limited or not, for me one amplifier is a good one, when input signal matches output signal as waveform, that means quality audio amp.
That's enough for me.
Thank you for attention and comments.
Wanna see a good amp in mine opinion with real sustained output power?
on entire audio band without limitings
https://www.youtube.com/watch?v=Y4hmtKZ0Tn8
an good overload clipping limiter, signal stays almost perfect sinusoidal even amp overload by 7Vrms on input:
https://www.youtube.com/watch?v=K8kWbcDJgmg
End of discussion.
From as seen on test, that amp was not able even to sustain his official power from specs 2x5900Watts/2 ohms, even for 3-5 seconds that's minimum for heavyest program material dubstep or reggae (deep prolonged bass) ; the amp limit in less than 500mSec to under 2500 watts per channel, less than half claimed.
Those amps are good for bass only, for short bursts power and for making noise on mid-hi freqs above 3Khz because no details on sound, regarding poor rise times of output stage, an rise time of 23uSecs are unacceptable for modern quality amplifiers, in mine opinion.
On outputs alot of artefacts at low power because underdamping output filters, even if is not audible, the original input signal will be altered at output on entire audio band.
In squarewave, response is worse above 1Khz with poor rise and fall times, no matter if internally limited or not, for me one amplifier is a good one, when input signal matches output signal as waveform, that means quality audio amp.
That's enough for me.
Thank you for attention and comments.
Wanna see a good amp in mine opinion with real sustained output power?
on entire audio band without limitings
https://www.youtube.com/watch?v=Y4hmtKZ0Tn8
an good overload clipping limiter, signal stays almost perfect sinusoidal even amp overload by 7Vrms on input:
https://www.youtube.com/watch?v=K8kWbcDJgmg
End of discussion.
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Do you understand that a square wave has all the odd harmonic frequencies from it's fundamental till infinity? And do you understand that when you accept that an amp has a bandwidth till 20kHz is it physically impossible to reproduce a good square wave? ALL amps are low pass filters, they only differ in the cut-off frequency and the roll off rate.
If you want to test your 20kHz amp with a 1kHz square wave, run the square wave through a 20kHz low pass first, if you're serious about this.
Jan
That already exists in the amp. That's what he's measuring and is misinterpreting as slewing behavior.
The thread is 8 pages long talking about slew rates etc., only to conclude that the DJ is not able to distinguish between slew rate and BW limit, what I suggested on page 1 of this thread on 12th of June:
"A typical slew rate issue is occurring when big 10kHz signal gets more distorted into an almost triangle waveform than small signal because of higher dv/dt.
In this case, it might not even be slew rate issue, since the small signal bandwidth of Powersoft K series is "only" ~23kHz. So the lowest harmonic of the 10kHz square is 30kHz and that is filtered away by the bw limit so no wonder almost pure sinusoidal wave remains. Acoustically that makes NO difference at all as there is NOBODY on earth who can tell the difference between 10kHz square and 10kHz sine wave by ear as long as there is no oscilloscope."
Amp-testing should really be forbidden for all guys that do not understand the spectral composition of non-sinusoidal waveforms. Like driving is forbidden w/o license or posting should be forbidden if someone can quote only with "" (like myself) ;-)
"A typical slew rate issue is occurring when big 10kHz signal gets more distorted into an almost triangle waveform than small signal because of higher dv/dt.
In this case, it might not even be slew rate issue, since the small signal bandwidth of Powersoft K series is "only" ~23kHz. So the lowest harmonic of the 10kHz square is 30kHz and that is filtered away by the bw limit so no wonder almost pure sinusoidal wave remains. Acoustically that makes NO difference at all as there is NOBODY on earth who can tell the difference between 10kHz square and 10kHz sine wave by ear as long as there is no oscilloscope."
Amp-testing should really be forbidden for all guys that do not understand the spectral composition of non-sinusoidal waveforms. Like driving is forbidden w/o license or posting should be forbidden if someone can quote only with "" (like myself) ;-)
A rectangle can be synthesised from many summed sine waves of various increasing frequencies.
To produce a 20kHz rectangle with 80Vrms the amp has to produce the following sine waves at the same time:
70.7Vrms/20kHz + 23.6Vrms/60kHz + 14.14Vrms/100kHz + 10.1Vrms/140kHz + 7.86Vrms/180kHz + 6.43Vrms/220kHz + 5.44Vrms/260kHz + 4.71Vrms/300kHz + .... + .... + .... +
If you stop the synthesis at 300kHz the wave shape looks like the attached picture.
Reproducing anything which comes close to a rectangle demands from the amp to reproduce substantial amounts of much higher frequencies than the fundamental of 20kHz in the example above.
Filter functions of real amps do not exactly reflect the theoretic fourrier coefficients for the synthesis, so often the ripple in the roof is not there, often just round corners- but this depends on the specifics of different amps.
Regarding audibility:
If you compare the sound of 1kHz sine vs a 1kHz rectangle it will sound very different.
If you compare the sound 15kHz sine vs 15kHz rectangle you won't hear a difference, because the signal portions which make the difference are above the human limits.
Try it with your signal generator and earphones.
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I agree. In this case we do seem to have an OP who is a repair technician, pretty experienced with traditional class AB amps, but without the theoretical background to understand class D.
DjLeco, we do recognize that you are probably a very experienced repair technician when it comes to class AB amps. As you might have realized by now, class D is a different animal, and by adopting a slightly less confrontational attitude, you could probably learn a lot from the people here who have a solid theoretical and practical background with class D.
It us your choice...
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