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Class D Switching Power Amplifiers and Power D/A conversion

TAS2770 20W Digital Input Mono Class-D Amp, Speaker I/V Sense, I2S input all digital
TAS2770 20W Digital Input Mono Class-D Amp, Speaker I/V Sense, I2S input all digital
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Old 1st January 2018, 10:04 PM   #11
5th element is offline 5th element  United Kingdom
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Happy new year doc!

I am, as we speak, working on a three channel PFFB design with the TPA3244. One part in BTL, one in PBTL. It'll be interesting to see how this one does! Using your cap recommendation for the bulk decoupling. The GPD series from Nippon, a step above Panasonics FC series, what I was using, but of course you pay for this!

One thing I've pondered a couple of times is would a composite amplifier be possible with some of these class D chips? Like the composites that use the LM3886 + opamp for vastly improved performance over what the LM3886 can ordinarily provide. Certainly there'd be a handful of headaches to overcome
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Old 2nd January 2018, 12:50 PM   #12
Windforce85 is offline Windforce85  Poland
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Thanks for great informative post 5th element!

Yes I also considered TPA3244 becouse from points you have mentioned it looks most promising from analogue point of view. It is funny but I also considered the same DAC.

Thanks for SSM3582 part suggestion - great find! On pair or even better than TAS2770...
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Old 2nd January 2018, 02:03 PM   #13
voltwide is offline voltwide  Ireland
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Hello 5th element!
Your findings with distortion of TPA325x look familiar to me. To mask the noise of my soundcard (EMU tracker pre) I decided to measure k2- and k3-levels with ARTA/SPA. These numbers look more informative to me.
Your achievements are outstanding. Would you mind elaborating on stability of postfilter-fb around these chips?
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Old 4th January 2018, 12:56 PM   #14
KaffiMann is offline KaffiMann  Norway
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A composite might prove difficult with i2s/tdm/i2c input amplifiers.
I think the LM3886 is very hard to beat when correctly implemented. TPA32xx family is awesome!

Still really want to try the SSM3582, too much going on so I'm still hoping for a GB or something. Have not touched pcb design since 1999/2000, and then only for small stuff.
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Old 4th January 2018, 10:04 PM   #15
5th element is offline 5th element  United Kingdom
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Quote:
Originally Posted by voltwide View Post
Hello 5th element!
Your findings with distortion of TPA325x look familiar to me. To mask the noise of my soundcard (EMU tracker pre) I decided to measure k2- and k3-levels with ARTA/SPA. These numbers look more informative to me.
Your achievements are outstanding. Would you mind elaborating on stability of postfilter-fb around these chips?
I haven't actually had any problems with stability and pffb. TI have released two application notes for its implementation. The latest includes additional filtering to help prevent instability which the original did not.

For my tpa3251 build this was only done with the first app note but it worked flawlessly and measured stable within TIs guidelines. I did poke the bear, out of curiosity, to see what would happen if the thing did becom unstable though. I omitted the additional zobel and tried the amplifier without a load connected. All that happened was the amp quickly went into protection and shut itself down. Good to know.
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Old 4th January 2018, 10:09 PM   #16
5th element is offline 5th element  United Kingdom
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Quote:
Originally Posted by KaffiMann View Post
A composite might prove difficult with i2s/tdm/i2c input amplifiers.
I think the LM3886 is very hard to beat when correctly implemented. TPA32xx family is awesome!
Yeah a composite would be ridiculously hard to implement using one of the digital input amplifiers. You'd need an ADC for post filter measurements coupled with a DSP. They'd all need to be high speed too, enough to have the bandwidth to correct for higher order harmonics.

I was thinking of composite using the tpa3116 or something from the tpa32xx family. Just out of interest, rather than necessity really.
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Old 5th January 2018, 07:09 AM   #17
KaffiMann is offline KaffiMann  Norway
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I am a bit curious as to why the TPA3116 sounds bad to me, my hearing is not that good. May there be some noise issue fed back into the power bank? Even with batteries? Could the TPA3116 feed noise to itself?

If that is the case: Maybe it is possible to use op amps to negate the noise? Would probably require another isolated low noise power supply though, maybe two, one for + and one for -.

At any rate, you already have the '3251 going. How much does it gain from 0 noise psu? PSSR is rated 60db, so there should be some benefit at least. BTL shows lower integrated noise than SE (60uV vs 115uV), maybe there is some cancellation because of small internal/external difference in track lenght? Does noise change with switching frequency? Which influences noise floor most; VDD/DVDD/AVDD or PVDD?

It's getting difficult to measure the low noise on this stuff already, but who knows, there might be some benefit getting to -200db noise floor...... *insert manic smile*

But as I've recently started to experience (the last 4-5 years or so), 1db here is not 1db over there. Signals, filters, gain setting, absolutely everything seems to change with just tiny variations. I feel I'm starting to get crazy, for instance: it seems to me that sometimes q of dsp filters change with gain settings. 1 db of difference completely ruins the whole thing in one place, and 3db difference in another place is not perceived at all. Maybe some data is missing, there must be something relevant we are not measuring somewhere.

Sorry about the OT.

Last edited by KaffiMann; 5th January 2018 at 07:16 AM.
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Old 7th January 2018, 12:13 AM   #18
5th element is offline 5th element  United Kingdom
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Quote:
Originally Posted by KaffiMann View Post
I am a bit curious as to why the TPA3116 sounds bad to me, my hearing is not that good. May there be some noise issue fed back into the power bank? Even with batteries? Could the TPA3116 feed noise to itself?
Typically speaking power supplies are quiet, even switching supplies, unless they are of poor construction, or have been designed with gross compromises in mind, due to the tolerant nature of what they are powering.

What makes supplies noisy is noise feeding back into them from the various devices that they are powering. Keeping noise from one device, from feeding into another device, both on the same supply, is often something that needs specific attention being paid to.

Directly in line with this are issues with keeping the other side of the supply clean, the ground, or return paths. Just like supplies these start out clean but end up noisy because of the devices they are connected to. Again, lots of effort is usually put into PCB design and layout to make sure that problems aren't encountered, or at least minimised to within acceptable levels.

Now the TPA3116/8 is relatively simple and, in general terms, doesn't have particularly low levels of distortion. I doubt that systemic noise, being apparent as noise on the outputs, would be any major concern, nor would I expect any systemic noise to be be responsible for causing excessive distortion here either.

This isn't to say that it's not possible, but it's unlikely, at least from the point of view of severely compromising the devices potential.

Quote:
Originally Posted by KaffiMann View Post
If that is the case: Maybe it is possible to use op amps to negate the noise? Would probably require another isolated low noise power supply though, maybe two, one for + and one for -.
This isn't where these problems tend to show up. The kind of noise that we're discussing here is switching noise, generated by the output stage of the TPA, finding its way back into the input stage of the TPA itself.

TI are aware of these issues themselves and making devices easy to use is important to them. If any special requirements were necessary to extract the performance that the device is capable of then it would be written in an application note or the datasheet.


Quote:
Originally Posted by KaffiMann View Post
At any rate, you already have the '3251 going. How much does it gain from 0 noise psu? PSSR is rated 60db, so there should be some benefit at least.
As with any circuit a noisy PSU has an impact on the overall performance. The sensitive analogue side of the system needs a clean supply. The output stage also needs a relatively clean supply but it also needs a low impedance supply for the absolute best in performance.

Quote:
Originally Posted by KaffiMann View Post
BTL shows lower integrated noise than SE (60uV vs 115uV)
Yes because the bridged nature of BTL configuration helps to cancel out noise and some forms of distortion.

Quote:
Originally Posted by KaffiMann View Post
Does noise change with switching frequency? Which influences noise floor most; VDD/DVDD/AVDD or PVDD?
DVDD and ADVV are internally generated. These are supplied by VDD, which needs to be clean and needs isolation from GVDD.

Generated system noise essentially changes with everything relevant to what the part does. Correct design and usage of the part helps to make the noise sensitive parts of the chip immune to these changes.
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