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Class D Switching Power Amplifiers and Power D/A conversion

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Old 1st May 2014, 08:25 PM   #21
ungie is offline ungie  Canada
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Quote:
Originally Posted by ChocoHolic View Post
You mean you see in your FFT a fuzzy -100db floor?!?!
CDA-224, which is a clone of the IRAUD7 is 20-30dB better, but still to noisy.


THD of the CDA-224 was IMHO OK. May be not perfect, but OK.
Have a look here in posting #42 (comparison of different dead times).
With the original dead time setting of 45ns the CDA-224 is not so bad and
close to the IR promises.
Can you show your measurements?
FFT of noise floor is exactly as shown in IR's published measurements of IRAUDAMP7S. I have confirmed this be repeating their measurements on a sample of the actual reference design board using AP 2722. I'm curious how CDA-224 can possibly be 20-30dB better, unless the gain has significantly been reduced from the 36dB of the reference design, and even then I find it unlikely. All of IR's reference designs utilizing the IRS2092 seem to have a similar noise floor.

THD is also as shown in the reference design measurements. Not bad, but not exceptional.
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Old 2nd May 2014, 03:40 PM   #22
ChocoHolic is offline ChocoHolic  Germany
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Quote:
Originally Posted by ungie View Post
I'm curious how CDA-224 can possibly be 20-30dB better, unless the gain has significantly been reduced from the 36dB of the reference design, and even then I find it unlikely.
The -100db noise floor in the application note is related to a 1Vrms output signal. My measurements on the CDA-224 have been with 10W/4R means 6.3Vrms.
I will have a look the at 1Vrms, most likely results will come closer there.
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Old 2nd May 2014, 05:56 PM   #23
ChocoHolic is offline ChocoHolic  Germany
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Here the measurements with 1Vrms into a 4R load.
The absolute voltages in the display of the QA400 do show the level at the input of the QA400, not the absolute value of the amp output.
Between QA400 and DUT I have a filter and adjustable buffers, running the QA400 always in its sweet spot around 700mV (500mVrms single tone).
Please also note that this sweet spot means the peak of my 1kHz is at -6db (while the AP2 scales the peak to 0db), so the floor also is shifted by 6db...
IMHO the findings with the CDA-224 fit acceptable to the application note of IR.

First picture:
CDA-224, please ignore the hum - it is a short coming of my placement in the specific enclosure.

Second picture:
The LiteAmp with a voltage gain of 10.

Third picture:
The LiteAmp with a voltage gain of 5.

Would you prefer to go for the low voltage gain of 5 in order to achieve the lowest possible noise?
Please note that this would require to use the optional gain stage daughter board in most applications.
For me it would be OK to go for the lowest noise.
Attached Images
File Type: jpg 1Vrms_CDA224.JPG (63.3 KB, 1350 views)
File Type: jpg 1Vrms_LiteAmpGain10x.JPG (62.9 KB, 1314 views)
File Type: jpg 1Vrms_LiteAmpGain5x.JPG (63.0 KB, 1288 views)
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Old 2nd May 2014, 06:41 PM   #24
ChocoHolic is offline ChocoHolic  Germany
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...and here the gain 5 with A weigthing...
The -84dbV (A) fit nicely to the noise which I get visualized with my noise amp and scope: 65uVrms
Related vs intended full output power (22,4Vrms) this translates to a normal advertising specification of SNR:110db

I think we should go for the low gain, because with this we achieve
noise figures which are normal for class A/B amps.
Attached Images
File Type: jpg 1Vrms_LiteAmpGain5x._AweightedJPG.JPG (62.9 KB, 1257 views)
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Old 3rd May 2014, 07:34 AM   #25
Baldin is offline Baldin  Denmark
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Cool project
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Visit www.sensibleaudio.dk or read latest news on Baldin's Blog
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Old 3rd May 2014, 11:15 AM   #26
Khron is offline Khron  Finland
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I doubt line-level gains should be an issue Even if the input impedance is low, slap a good ol' NE5532 in front of that, and call it a day
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Old 3rd May 2014, 11:33 AM   #27
ChocoHolic is offline ChocoHolic  Germany
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Quote:
Originally Posted by astx View Post
Would need 4 bridged channels.
This is sounding like you are intending something which I would not recommend. It is not helpful to run everything in bridged mode without need.
Despite the fact that I expect for the LiteAmp similar trouble free operation like in my 2kW amp in bridged mode, I generally do expect inferior performance in bridged mode.
In bridged mode the load brings a noticeable impedance between both amp outputs, means you couple them. Switching residuals from one amp now can enter the feedback signal of the other one, and vice versa.
The amount of impact will depend very much on your particular set up / load parameters. Typically such effects turn visible in FFT by increased distortion and a more fuzzy noise floor.

Even if I expect trouble free bridged operation - for best audiophile performance I do recommend to use the unbridged for most chanels and
bridged only where you really need the power. I.e. for the sub.

P.S.
Regarding bridged mode IMHO post filter solutions are generally more picky than pre filter. And self oscilating again more picky than clocked.
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Old 3rd May 2014, 11:37 AM   #28
ChocoHolic is offline ChocoHolic  Germany
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Quote:
Originally Posted by Khron View Post
I doubt line-level gains should be an issue Even if the input impedance is low, slap a good ol' NE5532 in front of that, and call it a day
True, even if I prefer the AD8620 - basically any normal OP amp will do the job.
The nice thing with the intended daugther board is that it opens an uncritical area to experiment according personal taste.
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Old 3rd May 2014, 03:11 PM   #29
astx is offline astx  Austria
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Quote:
Originally Posted by ChocoHolic View Post
...
Even if I expect trouble free bridged operation - for best audiophile performance I do recommend to use the unbridged for most chanels and
bridged only where you really need the power. I.e. for the sub.
...
Yes - bridged for sub to get > 200W8R. Mid speaker and tweeter will be driven by single amp with adapted gain.
But bridging would be obsolete for me if we get > 200W@8R with
two paralleled IRFI4019 or IRFI4020, running from about +/-70V ... ?
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Old 3rd May 2014, 03:21 PM   #30
astx is offline astx  Austria
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If we go for gain 5 we should think about output performance of used opamps delivering high output voltage swing. I have done some test some months ago with gain 20dB and output 600R with 7Vrms:

opamp_comparison_20kHz_at_7Vrms

BR, Toni
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