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Class D Switching Power Amplifiers and Power D/A conversion

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Old 12th March 2013, 11:16 AM   #271
AP2 is offline AP2  Italy
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Hi,
Another confusion with PSRR.
the drop in voltage transients (perfectly audible to an audiophile, which certainly does not want to hear), has nothing to do with the PSRR.
some audio measurements are ... intelligent. does not show in the case of FFT, to segment under 1Khz, or 10Hz-50Khz at 65% power referred to the class D obvious.
if it is a good amp, it is normal that I can use in loudspeaker crossover, perhaps high cost. then it is very easy to listen to 75% modulation with high output current, depending on the type of music I'm listening.
Or, why the manufacturer of the amp must say that it is perfect, but only if coupled directly to a speaker (multi-way).
With the words, we're all good, this is the problem.
In many smps, I see how easily, the engineer has the 2200uF filter cell high voltage, it is necessary for me to explain what catastrophe happens to the AC line? it is "power factory (PF), or" cosine of f ".
@ Choco: I think that can be constructive for others who read, if you show the dynamic measurements on smps fast that you have. We discuss the problems that can be solved (if any).

regards
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Old 12th March 2013, 11:50 AM   #272
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Quote:
Originally Posted by AP2 View Post
then it is very easy to listen to 75% modulation with high output current, depending on the type of music I'm listening.
75% modulation? with real speakers and real music?
I have done my measurements and I don't think that ever happens with real music. I think 75% modulation would be very visible even on quick visual inspection of the waveform.
I'm not saying it can't happen but I'd have to come up with the worst case conditions to achieve that.
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Old 12th March 2013, 12:19 PM   #273
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First of all I'd like to know what he actually means with 75% modulation ? Is he talking of the PWM duty-cycle or the voltage drop of the PSU ? And how do we listen to a duty cycle ?

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Charles
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Old 12th March 2013, 12:33 PM   #274
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Quote:
Originally Posted by mr_push_pull View Post
75% modulation? with real speakers and real music?
I have done my measurements and I don't think that ever happens with real music. I think 75% modulation would be very visible even on quick visual inspection of the waveform.
I'm not saying it can't happen but I'd have to come up with the worst case conditions to achieve that.
I do not understand why you want to push me, to explain old things in some way resolved by the manufacturers of professional audio, already many years ago, the class AB.
Problems increase when the speed is added to the current.
at 30w, what issues you want to see?

When I listen to a good jazz in my living room (at volume that do not disturb), the B & W 802 II, passing 8-10Amp on load, repetitive peak.
Bass and vocals are warm and dry attacks really.
This effect of realism gives you immense pleasure. How do I get this? ... smps normal or psu with simlpe 2x10.000uF?, or with nfb?

In what measure audio traditional you can understand this?
Explain to me please

sorry, i mean 75% of modulation or 65% (volume amplitude) just create current at output.

Last edited by AP2; 12th March 2013 at 12:36 PM.
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Old 12th March 2013, 12:34 PM   #275
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@phase
I would very much expect duty cycle to change with power supply sag I'd be worried if it didn't, because likely I'd be able to hear it. but that is PSRR too, isn't it?

@AP2
out of curiosity, I have measured instantaneous current with my speakers using a shunt. I have to push them to the limit (way above decent levels) to reach the theoretical predicted value of 4 amps. and that is using full scale orchestral music, like Reference Recordings' version of Bolero, taiko drums etc. speakers have 83dB W/m sensitivity and max tolerable levels in my living room are reached @ 100-150W in 4 ohms.
looks like phase accurate which is obviously more schooled in EE and signal theory compared to me failed to understand exactly what you meant.

the 802's are known to be a difficult load. nevertheless, a good amp should be able to drive them too.
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Last edited by mr_push_pull; 12th March 2013 at 01:02 PM.
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Old 12th March 2013, 07:50 PM   #276
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Quote:
Originally Posted by AP2 View Post
@ Choco: I think that can be constructive for others who read, if you show the dynamic measurements on smps fast that you have. We discuss the problems that can be solved (if any).
regards
Hi Roberto,
you did not look seriously to my posted screen shot.
It shows multiple dynamic load steps.
The 900W are applied for 1.8ms, then 3ms no load, then again 900W for 1.8ms...
The red line is showing the AC-voltage of the rail with 200mV/grid, in order to magnify the load step response.
The loop gain structure is PD, no integrating portion. Consequently the rail saggs a little bit (less than 500mV) and remains there.
As you can see the regulation reaches the stable situation within few hundret us almost free of regulation over shoots.
If you are asking for more measurements - I cannot serve. I just designed and built a single proto for a friend and handed it over.
In any case I cannot involve deeply into public discussions about SMPS any more. My work has drifted more and more into this direction, so I must limit my contributions to a very basic level.
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File Type: jpg 1kW_load_step.jpg (60.2 KB, 265 views)
File Type: jpg PSU.jpg (82.3 KB, 263 views)
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Old 12th March 2013, 10:53 PM   #277
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..to avoid misunderstandings.
At the beginning of the screen shot there is no load.
The dips of the red trace are the times when the smps is loaded with 900W.
The dip stabilizes fast with moderate undershoot and remains stable until the load is switched off. When the load is turned off, the rail steps up back to the no load level without any overshoot.
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Old 13th March 2013, 02:34 AM   #278
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Quote:
Originally Posted by mr_push_pull View Post
hi Kal

I'm using a DIY UCD180ST implementation with a SMPS made for audio.

just received an Audio Refinement Complete (YBA design) amp for evaluation. it was praised in many reviews, including by Stereophile. judging by the measurements, it seems to be a low NFB design. I'm curious how it compares to the switching amp. I wish it wasn't -3dB @20kHz, but... who knows.

Audio Refinement The Complete integrated amplifier Measurements | Stereophile.com
I have no idea. Never saw/heard it.
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Old 15th March 2013, 01:15 PM   #279
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EDN beginning a series of articles on Class-D:

New approaches to switched-mode audio power amplifiers (Part 1) | EDN
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Old 15th March 2013, 01:33 PM   #280
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Quote:
Originally Posted by Kal Rubinson View Post
I have no idea. Never saw/heard it.
I promised to give some comparison results and I guess it'll be obvious that bias is not a factor.
in short, the ARC wipes the floor with the UCD180 modules. night and day difference. I'll refrain from blurting the usual audiophile adjectives, because the difference is way too big.
only thing in favor of the UCDs I can find is that with some very hot mixes it sounds better. but with the majority of the music, not. at first listen the ARC seems on the euphonic side, but the more you listen you realize it's the exact opposite, recordings start to sound more different from each other than with the UCD.

and boy, does it measure horribly...

too bad I'm an engineer and that makes me even more curious as to what explains the major difference
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