My very first Class D pwm (switching) amplifier. - Page 12 - diyAudio
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Class D Switching Power Amplifiers and Power D/A conversion

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Old 20th June 2003, 02:52 PM   #111
JohnG is offline JohnG  United States
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Gotcha. I'm familiar with basic analog linear feedback methods, but your response clarifies what you meant.

It is difficult with an analog loop to take the feedback before the filter, because you need to get rid of the switching ripple somehow. I suppose a separate filter might be easier to design since it does not need to handle the power, but then you are not including the output filter in the loop. This may be fine

I have little familiarity with discrete methods, although I'm doing some studying up on them. The self-oscillating amp in the link mentioned earlier looks more like a delta-sigma converter to me. Is this correct, or am I missing the boat somewhere?

I have designed self-oscillating resonant inverters whose frequency was quite stable, but these used a different method than that referred to here.

John
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Old 20th June 2003, 02:56 PM   #112
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To me, such a self-oscillating PWM amp looks more or less like a high-power square-wave generator having a duty-cycle-control- voltage input.

Regards

Charles
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Old 20th June 2003, 03:08 PM   #113
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The following old Sony patent describes quite well how the feedback of non-self-oscillating PWM amps works (including mine).

http://l2.espacenet.com/espacenet/vi...h&LG=de&DB=EPD

Regards

Charles
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Old 20th June 2003, 03:29 PM   #114
JohnG is offline JohnG  United States
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"To me, such a self-oscillating PWM amp looks more or less like a high-power square-wave generator having a duty-cycle-control- voltage input."

Charles,

I will have to take a closer look. I admit not having analyzed the circuit. As much as I try, my company has little interest in audio-band amplifiers, so it will be a while before I get to it.

Thanks for the additional link.

Best regards,
John
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Old 21st June 2003, 09:06 AM   #115
koldby is offline koldby  Denmark
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Charles;


"The frequency of most self-scillating designs is quite independant of input signal.
The switching frequency of delta-sigma amplifiershowever is heavily signal dependant."

How would you describe the difference between a self-oscillating PWM amp and a delta-sigma PWM amp.?
And the "soerensen" amp would then be a delta-sigma , right??



"To me, such a self-oscillating PWM amp looks more or less like a high-power square-wave generator having a duty-cycle-control- voltage input"


Do I detect a certain less positive attitude towards this technology



Well ,as I see it, it is a rather elegant way of dealing with the problem regarding nonlinearities in the triangular waveform, and this I belive is a major problem in digital amps.

For what it is worth, iI have auditioned the TacT at several occasions, but at shows and with unfamiliar equipment and surroundings, and it was very good sounding. Just how good I canīt say.
I have in house the ICE power modules, and I had the oppertunity to compare these with the LC-audio modules and a High-end tube/MOSFet hybrid under controlled conditions and known equipment:
BOW ZZ-8 CD player
DVD-rom with upsampling prototype DAC (sounded best)
The original developed prototype of the Gryphon loudspeakers

The two PWM amps. were sounding suprisingly good AND suprisingly different: ICE power was a little lazy/undynamic sounding, but with excellent bas.
LC-audio was very energetic, but also a bit flat and strident sounding.

None of them, however, could match, overall, the tube/MOSfet hybrid even though the ICE power was the best in the bass.

The hybrid is , I should mention, a VERY good sounding amp.!!


I belive that the technology has very great potential even when it comes to sound quality per se, as the ICE power modules uses less than stellar op-amps and passive components and has not been developed from an audiophile standpoint.
I still hope I havenīt turned the focus of this thread away from the original subject??





Koldby
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Old 21st June 2003, 10:52 AM   #116
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Hi Koldby

A delta-sigma amp like the Sharp SM-SX100 for instance is outputting an RF-noise like switching signal and not a pulse-width modulated rectangular of constant frequency.
I once posted such apattern within another thread but I have to find it again.
The "sorensen" amp is an ordinary self-oscillating PWM amp IMO.

Quote:
Do I detect a certain less positive attitude towards this technology
What I wanted to express is just a short and simple description of how such a self-oscillating PWM actually works like.

I personally don't think that the triangular linearity is the main culprit for the class-d problems, since this can be generated with quite good accuracy.

Regards

Charles
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Old 21st June 2003, 11:08 AM   #117
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The simulated DS signal can be found here:

http://www.diyaudio.com/forums/attac...&postid=179974

Be aware to watch it at 100% size or it will look quite strange.

Regards

Charles
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Old 22nd June 2003, 09:03 AM   #118
koldby is offline koldby  Denmark
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Charles,

Quite good accuracy is not nearly enough.
It has to be better than the source and here we are talking about maybe 20 bits accuracy. The triangular waveform should at least have this kind of accuracy to be out of the equation - IMHO.


Koldby
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Old 22nd June 2003, 11:11 AM   #119
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Quote:
It has to be better than the source and here we are talking about maybe 20 bits accuracy.
Could you please show me any gain-stage for instance with 20 bit accuracy ?

Regards

Charles
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Old 22nd June 2003, 03:55 PM   #120
koldby is offline koldby  Denmark
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Charles;

No this I cannot do, but that is irrelevant in my oppinion, as the errors from a gain stage is nonlinerarities that is very difficult for the ears to detect (second order harmonics can be quite high in an gain stage and be very accurate sounding all the same) but nonlinearities in the triangular wave form is not related to the musical signal an thereby much more detectable to the ear.

To go from 16 to 20 bits of resolution in a PCM signal is easily detectable for the ear, even through an amplifier having .1 % harmonic distortion!!

Koldby
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