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Class D Switching Power Amplifiers and Power D/A conversion

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Old 22nd March 2013, 09:53 AM   #351
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Originally Posted by ChocoHolic View Post
Measuring an amp is just half of the game. Listening to it is of same importance (or even more?). This design allows tons of variations of OP amps and comparators.

I would have expected that the comparators would play a dominant role for the sound, but to my ears the differences were just very marginal and sort of diffuse – still giving a personal preference on the MAX913.

The OP amps showed a stronger impact and they are changing the sonic character to the amp.
Here my ranking:

1. AD8620:
Very vital and voluminous. Impressive soundstage (despite being mono!) and surprising air. Details unlimited.

2. OPA 1612:
Also vital, but less voluminous. Less soundstage and gradually less air.

3. LT1364:
Vital, but shows no mercy with the shortcomings/harshness of internet radio and some poor MP3.
Pretty OK, when listening to a higher quality source like 192kHz flac.

4. OPA2134:
Very decent. Very comfortable. Not annoying at all. But for my taste sometimes slightly to thin.

5. LM4562:
Slightly pressed. Reducing the ease of music, giving it more a character of hard work.

6. NE5532:
Has similarities to LM4562 ( sorry TI/National guys, please don't shoot me..), but less contours.
In 1980 NE5532 must have been an amazing OP amp.

7. TL072:
Despite the fact that the amp is still working trouble free - the TL072 is the right choice to avoid audiophile satisfaction after spending a lot of efforts and money.

To me it was very surprising to find the character strongly influenced by the OP amps and less by the comparators. Also I would have expected the LM4562 somewhere in the Top3.

Chasing for a correlation between measurements and listening perception, I went for multiple comparative measurements of NE5532 vs AD8620, comparator was always MAX913.
To ensure that my measurements reflect a similar situation like my listening tests, I used the real speakers as load and performed the measurements at a similar level like listening ==> 4Vp.

First picture:
Again the list of alternative components

Second picture:
Spectral noise density

Third picture:
THD at 1kHz and 5kHz

Fourth picture:
Spectrum of 1kHz THD

Fifth picture:

Sixth picture:
IMD over frequency

Seventh picture:
Step response.
Both measurements in one picture by using the fluorescent storage of the scope. Amazing they equal even in each HF cycle!

By the end of the day I must admit:
Either I am a believer, or my measurements are not covering all relevant properties.
Im curious if you were blind folder-ed would you be able to make these statements ?
There’s nothing worse than the smell of burned output transistors!!
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Old 22nd March 2013, 05:55 PM   #352
Join Date: Jan 2005
This is my interpretation of your Dynamic Hysteresis D-amp circuit.

Currently a simulation is running using a short wave file as the signal input, the output is beeing written as another wave file.
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Old 22nd March 2013, 06:48 PM   #353
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Location: Munich
Double blind tests... definitely to much of an effort.
I am not even sure if I could tell the type in a single blind test.
The described sound characters are my perception from listening while I knew about the DUT. Strange enough that even there my perception was different from what my audisoteric opinionated mind told me before....
Sound is like gourmet food.
It tastes better when you can see it and it's looking nice.
There is no clue in killing subconsciously generated feelings, by blind tests.

Still I am doing blind tests once and a while. Unfortunately you always need a second person who is interested in the matter and agrees to spend time for the test.
My last blind test was with cables, because I wanted to prove to myself:You cannot hear it.
I had moved to a new apartment and had positioned the stereo set for an acceptable WAF ==> 12m speaker wires. Ignorant me did this with 2x1mm˛. The sound was alien, because of the new apartment, but not just alien, also annoying. For some silly reason I thought about the wires and changed the set up to shorter (3m) and multiple paralleled with 2x3x1mm˛.
Still alien, but less annoying.
In the blind test I had 10 correct out of 13.
From measurements and theory it should have been ignorable...
No it was not the bass which had changed, because of the damping factor.
The bass was unchanged to my ears.
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Old 22nd March 2013, 07:12 PM   #354
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Originally Posted by Tekko View Post
This is my interpretation of your Dynamic Hysteresis D-amp circuit.
Yup, I think you took it right.
Your power stage is different, so also your propagation delay (==> fs) and distortion figures may differ from my power stage. But basically it should fit.

WAV files?
You mean you are chasing music through your sim in order to listen to your sim? Playing the output WAV with your normal stereo?
That's a cool idea!!
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Old 22nd March 2013, 08:11 PM   #355
Join Date: Jan 2005
Well yeah but its a slow process, about 100mS worth of audio takes about 10 hours.

My power stage is a little different as i only have spice models for the IR2110 and the others available at this site:

I might try this out together with the UcD in my other post above and see if i can tell them apart from each other.

Last edited by Tekko; 22nd March 2013 at 08:28 PM.
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Old 22nd March 2013, 09:17 PM   #356
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Old 23rd March 2013, 02:27 AM   #357
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Tekko is in serious mode Choco.......!!!!
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Old 23rd March 2013, 09:35 AM   #358
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Just for the fun of it, i did a sim with and without the dynamic hysteresis.

i did modify the circuit alittle toward the kinda voltages i was going to use and what zeners i have in stock.
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File Type: png 5yNhFYM.png (133.8 KB, 540 views)
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Old 23rd March 2013, 10:02 AM   #359
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Hi Tekko,
yes that's the way how it should act.
Nice to see that you use the idea to experiment with your own adjustments to fit voltages, components and personal taste.
I have to admit, I did not investigate in detail which adjustment I really prefer, but just stayed with one reasonable setting so far.

I really like the idea to listen to a sim

Which switching frequency do you get with your output stage?

Last edited by ChocoHolic; 23rd March 2013 at 10:03 AM. Reason: see Edit
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Old 23rd March 2013, 10:09 AM   #360
Join Date: Jan 2005
390-450kHz with the values given in the pics in the post above.

Last edited by Tekko; 23rd March 2013 at 10:22 AM.
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