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Class D Switching Power Amplifiers and Power D/A conversion

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Old 5th March 2013, 01:07 AM   #51
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I replaced $5k worth of tube monoblocs with the ClassD Audio Spiral Groove Mastering amp. I have been an NPR station manager and classical recording engineer/producer for many years. I think I know what a system should sound like as I use recordings I made with such ensembles as the Chamber Music Society of Lincoln Center. No I do not think class d is perfect, but it is much better than many critics give it credit for. That is why I pay no attention to the "audiophile" rags and blogs. Regards
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Old 5th March 2013, 04:00 AM   #52
xrk971 is offline xrk971  United States
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Originally Posted by bnorrish View Post
I try to keep an open mind and I am not sure the arguments for Class D add up. On one hand not too many commercial Class D gets it right - its a different animal, requires different design skills, etc.,etc. On the other end I can on my own, purchase an eval board with a cheap switching PSU and compete with a Class A design? I suppose my Yamaha Aventage does not sound well because it is 2 years old and does not sport the latest chip or Yamaha does not design Class D very well, yet I can beat it by hooking up a TI eval board?
I am not sure what topology the Yamaha Class D amp uses and if these are better, but given that they are the latest offerings from TI, it wouldn't surprise me if they are indeed better.

The eval board will probably work well but to get the best performance, the main power supply electrolytic caps should be upgraded to a larger size and the input ceramic caps could probably be upgraded with good poly-foil caps. $150 will let you try out the test...

Regarding switch mode PS bricks... Even Nelson Pass says they are fine for supplying class A designs if all you need is 19 volts.

These TI chips are so new that there are very few people who can tell us how they sound. Although there are some diyAudio members who have built one and report very favorable performance. Here is a 50 w/ch TPA3116D2 amp and its bridged mono 100 w/ch sub amp sibling next to some valve amps:

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I have also heard reports that these amps can sound as good as some of the best tube amps.

Last edited by xrk971; 5th March 2013 at 04:07 AM.
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Old 5th March 2013, 12:17 PM   #53
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Originally Posted by johnm View Post
I think there's a lot going on behind the scenes here, as it were. Many are disgruntled at the prospect of a 'simple' little chip giving such good performance, for so little money. There's the typical high-enders snobbery at work here too. Some dislike the idea of anybody being able to afford such high performing amps. High end performance should cost high end money and all that elitist (and thankfully fast becoming a thing of the past) crap! Good performance speaks for itself - all you need is a decent pair of ears and no market bias.

I'm sure some manufacturers are 'scared' too. After all their hard work on discrete designs over the decades, suddenly these new compact Class D upstarts come along and risk taking a huge bite from their market.

I still own the infamous little Sonic Impact T amp. Serves as a reminder of what is possible these days from a budget device. I truly think Class D will eventually topple all others...

Interesting times for Audio!

John.
Class-D amplifier can be made to sound good. In the bipolar transistor ere, it was not possible to go very far with the carrier frequency. The first class-D amp I saw 30 years ago worked with 100kHz carrier.
Didn't sound very good above 200-500 Hz, So I used it for subwoofer.
Now with 2 Mhz carrier frequency, they sound very good to cca 4000 kHz, very well into the upper midrange.
With 10MHz carrier they'll sound good probably up to 20 kHz, but I still didn't hear any with 10 MHz. carrier...
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Old 5th March 2013, 12:59 PM   #54
xrk971 is offline xrk971  United States
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Why does carrier freq need to be 50x audio freq to sound good? Is this to allow more headroom for pwm to have sufficient pulse width modulation depth? 50x seems excessive... especially when THD measurements show less than 0.1% distortion at 20khz fir 400khz carrier.
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Old 5th March 2013, 02:53 PM   #55
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Ones can consider Class A amp as a Class D amp implementation with infinity switching frequency. Moreover some tube amps tend you use electromagnetic field for power energy reservoirs.

There are some real physical and mathematical stuff behind LPs and Class A amplification.
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Old 5th March 2013, 04:39 PM   #56
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There is also real physics and maths behind class-d BTW.

Those advocating very high switching frequencies should keep in mind that a given absolute timing error is resulting in a bigger relative timing error when the switching frequency is higher. So there is not much to be gained IMO with exorbitantly high switching frequencies.

The problem with low switching frequencies OTOH is getting enough negative feedback. With higher-order Loops this can still be achieved like the nCore example shows. But one is restricted to self-oscillating topologies. With carrier-based amps (i.e. natural sampling PWM) it is getting trickier because performance doesn't continue to improve above a certain feedback factor due to the so-called ripple aliasing effect which is causing a distortion mode that doesn't exist without NFB. There are ways around that but they are not always simple.

Regards

Charles
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Old 5th March 2013, 05:04 PM   #57
glt is offline glt  United States
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Originally Posted by xrk971 View Post
...Here is a 50 w/ch TPA3116D2 amp and its bridged mono 100 w/ch sub amp sibling next to some valve amps:

Click the image to open in full size.

Greater Toronto Area DIY meetup

I have also heard reports that these amps can sound as good as some of the best tube amps.
Where is the source for those nice little modules?

I am going to experiment with the older brothers of this amp and gathered some documentation here: Dual-Mono TPA3122D2 AMP | H i F i D U I N O

From the older chips to the latest chips, they all have the same "THD signature" even though the latest chips can be run at 1 MHz or higher.

They have better specs if configured in BTL mode with balanced input

And they are incredibly simple to implement: good power caps and bypass, output LC filter and input coupling capacitors.
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Old 5th March 2013, 06:21 PM   #58
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Originally Posted by phase_accurate View Post
There is also real physics and maths behind class-d BTW.

Those advocating very high switching frequencies should keep in mind that a given absolute timing error is resulting in a bigger relative timing error when the switching frequency is higher. So there is not much to be gained IMO with exorbitantly high switching frequencies.

The problem with low switching frequencies OTOH is getting enough negative feedback. With higher-order Loops this can still be achieved like the nCore example shows. But one is restricted to self-oscillating topologies. With carrier-based amps (i.e. natural sampling PWM) it is getting trickier because performance doesn't continue to improve above a certain feedback factor due to the so-called ripple aliasing effect which is causing a distortion mode that doesn't exist without NFB. There are ways around that but they are not always simple.

Regards

Charles
I agreed with you post absolutely. However the fact that Class D amp is heavily DSP based does not mean it has superior BW then Class A. It is quit opposite. You have explained why BTW.

Obviously there is no way that manufacture can provide a couple of billion consumers with gear that stuffed with audio trafos, chocks and foil capacitors. So Class D is the future for mass prodcution no wonder.

But few audiophiles who can afford a pair of good speakers, turntable or class A decoding computer could benefit from Class A amplification gear.

BTW several watts Claas A would consume less energy then 400 Watts Class D module while playing music. Hi Efficiency speakers is the way for Green route anyway. That is what experienced audiophiles are running for many years already.
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Old 5th March 2013, 09:35 PM   #59
xrk971 is offline xrk971  United States
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Originally Posted by glt View Post
Where is the source for those nice little modules?

I am going to experiment with the older brothers of this amp and gathered some documentation here: Dual-Mono TPA3122D2 AMP | H i F i D U I N O

From the older chips to the latest chips, they all have the same "THD signature" even though the latest chips can be run at 1 MHz or higher.

They have better specs if configured in BTL mode with balanced input

And they are incredibly simple to implement: good power caps and bypass, output LC filter and input coupling capacitors.
Those modules were built by @Dug - his own pcb design. They are indeed simple, the parts list is quite short and inexpensive.
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Old 5th March 2013, 11:04 PM   #60
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Originally Posted by xrk971 View Post
From TI directly - pricey at $150 ea but a deal compared to what a class A will cost you for similar performance. I am building it with a custom made pcb and parts from Digikey, I am also building smaller TPA3118D2 using smd dead bug wiring in progress now on another thread. Total BOM about $17 not including $8 ps laptop brick.
There is also a $10 job @ PE:

2x8W @ 4 Ohm TPA3110 Class-D Audio Amplifier Board Only 320-329

Hook it up w a 12v battery and play! I wouldn't so readily dismiss it because it is sooo cheap!

Duc
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