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Class D Switching Power Amplifiers and Power D/A conversion

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Old 4th December 2017, 05:08 PM   #21
doctormord is offline doctormord  Germany
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I answered to your pm some minutes ago. Judgement based on these cheap class-d boards isn't that fair i think as you then have to compare them against some "low grade" class-a boards as well. (like TDA2003 or so)

Best option is to get yourself a 3251 or 3255 EVM from TI directly (with 50% discount by using their coupon) via Samples-Store.
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Old 4th December 2017, 05:34 PM   #22
dellama is offline dellama  United States
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I read it and responded
Speaking of the mini board linked above, do you think the miniscule capacitance on that board will be a problem for bass response? I think this might be addressed in the main supply but don't know enough about how these operate to be sure. What are the strategies you use to keep the noise floor on these D amps down?
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Old 4th December 2017, 05:42 PM   #23
DPH is online now DPH  United States
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No need for more (the 3255 have 4700 uf on the rails). Large reservoirs and SMPS mean something went wrong. Linear, yeah, worth having more to keep the rails smooth(er).
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Old 4th December 2017, 05:46 PM   #24
FauxFrench is offline FauxFrench  France
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I was somewhat skeptical about cheap class D amplifiers as well (I had heard about ICEPower). I was raised with class AB amplifiers and even a class A amplifier (Linsley Hood). The idea of cutting the nice sound into square-waves did not sound appealing.
Recently I noticed a simple class D amplifier board sold for very little. I bought it just to confirm my prejudice that it was not as good as the "real" class A/AB stuff.
Just trying out this simple class D amplifier made me doubt - it actually sounded surprisingly well. I then bough some ten (rather cheap) class D amplifier boards of different make and tried them out. I have never been disappointed with any of them when I consider the price. It does not mean that in blind-test the class AB/A may not be a bit better for audiophile use. But, a priori the class D amplifiers cannot be discarded even for audiophile use.
Class D amplifiers primarily serve commercial production in the sense that they are attractive for portable use (due to better efficiency) and easier to enclose in a structure (like a sound-bar) with only a small heatsink because of reduced heating.
Tripath took class D a giant step ahead and the improvement has not stop.
Another issue is the ability of the ordinary user to notice the difference and his/her willingness to pay considerably more for a marginally better performance. The human physiology sets important limits (also for the output power you "need").
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Old 4th December 2017, 06:05 PM   #25
dellama is offline dellama  United States
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DPH
I linked the mini board with the low capacitance I'm talking about several posts up. It looks like less than 1mf of supply of very fast capacitance to me but others with better eyes (or a better photo) can correct me.

FauxFrench
Yes, I feel as you did. Perhaps my mind will change when i receive the mini boards described above that I just ordered.
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Old 4th December 2017, 06:06 PM   #26
DPH is online now DPH  United States
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And the 325x series raised the bar on the monolithic IC chip class-D pretty notably (specs wise at least, let's not get into the quagmire of people's opinions).
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Old 4th December 2017, 06:08 PM   #27
DPH is online now DPH  United States
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Quote:
Originally Posted by dellama View Post
DPH
I linked the mini board with the low capacitance I'm talking about several posts up. It looks like less than 1mf of supply of very fast capacitance to me but others with better eyes (or a better photo) can correct me.
Ah, I missed it and thought you were talking about the TI EVM boards. Yeah, local bypass in the ~1000 uF range would be good to have.
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Old 4th December 2017, 07:18 PM   #28
wushuliu is offline wushuliu  United States
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At this point I doubt the credibility of anyone who says Class D isn't audiophile quality. This isn't 2007.
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Old 4th December 2017, 08:00 PM   #29
Kjeldsen is offline Kjeldsen  Denmark
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Class D is also much more than TI EVM boards :-)

There is some pretty expensive hifi amps out there based on class D.
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Old 4th December 2017, 08:20 PM   #30
dellama is offline dellama  United States
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Kjeldsen
I've noticed the great effort to make these class D amps hifi

wushuliu
That's a bit harsh isn't it? I'm sure there are many like me who are uncomfortable with the inherent characteristics/limitations of class D amps. I never said they are insurmountable but they are there. The two that come immediately to mind are their propensity for poor linearity above 6khz and their poor noise floor but there are others. People who live in cities have to deal with the usually poor RF filtering and using tried and true tricks like massive feedback is much more complicated with class D. There are many reasons to suspect this newer technology but the same was once said of crossover distortion with class B. If I hated it that much I wouldn't have ordered those totally SMD boards that I linked above. I share interest in that board with both you and doctormord.

Last edited by dellama; 4th December 2017 at 08:24 PM.
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