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Class D Switching Power Amplifiers and Power D/A conversion

TPA3251d2
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Old 11th May 2020, 07:43 AM   #1501
ClaudeG is offline ClaudeG
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Thanks a lot for this detailled feedback, Rich!

Eventhough LS aren't dummy loads, it gives IMHO a pretty good idea what coil to chose for your own LS, indeed provided you know their complex impedance (modulus and phase) above 10kHz.

There isn't a lot of music content / density above 10k, but from 10 to 20kHz being a wide band in terms of overall perception it can quite affect our perception in terms of thiness and brillance. It does though IMHO also impact our perception re agressivity and flesh on the bone at lower octaves, so worth considering eventhough the TI calculation is a simple model - at least it is very well detailled.

Rich, what magnitude would you give to your coil mod vs op amp rolling? Is that quite majour, or more a small step? I do understand that op amp rolling was performed whith the old coils, so less clarity and differences between op amps I presume, but nevertheless, would you rate that coil mod a majour must-do step or is it more fine tuning?

Further, I always felt (to my ears) Class D was lacking in terms of 3D imaging and of end of note truncating - whereas details and control were quite OK. I have the feeling reading your comparo with state of the art amp it may also be the case for you. Now that you have a better imaging, how close does it get re soundstage and placement? Is majour field covered, or the gap still quite there - possibly chip or technology limited?

Sorry for the numerous questions Rich - it is your fault, your posts are really that interesting :-)

Last but not least, I really wonder how much 3D image that tiny and presumably very cheap vol pot is robbing... cheap pots do that very often in my experience...

Thanks again for all this interesting stuff

Stay safe

Claude
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Old 11th May 2020, 07:47 AM   #1502
daniboun is offline daniboun  France
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Quote:
Originally Posted by rhing View Post
I installed the Coilcraft MA5173 7uH inductors in the Aiyima TPA3251 amp and the sound quality is further improved in terms of clarity, detail and imaging. The amp with the stock inductors is on the left, and the same amp with the Coilcraft inductors is on the right.
Great ! thanks amigo )
do you have pictures of the PCB with a bottom view? thanks


As Claude already asked : is the tweak worth it in the end?

Last edited by daniboun; 11th May 2020 at 07:51 AM.
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Old 11th May 2020, 07:52 AM   #1503
drMordor is offline drMordor  Russian Federation
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Quote:
Originally Posted by rhing View Post
I installed the Coilcraft MA5173 7uH inductors in the Aiyima TPA3251 amp and the sound quality is further improved in terms of clarity, detail and imaging.
Is not better inductor.
Really better is Wurth 7443630700 and Codaca CSCF2014
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Old 11th May 2020, 08:14 AM   #1504
ClaudeG is offline ClaudeG
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Oh, I am pretty sure Rich knows that already as he read the TI sheet re output filters and it contains a full section on inductors and makes...

But perhaps the Coilcraft was easier to implement than say the Wurth (size and board connection)?
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Old 11th May 2020, 09:01 AM   #1505
rhing is offline rhing  United States
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Quote:
Originally Posted by vacuphile View Post
The upshot of these plots is use 10 uH and any speaker between 4 and 8 Ohm will be just fine.
That's why I included the plots and calculations. Yes, they are based on general assumptions, but the trends still apply in case others want to try inductors themselves.

Thank you for the suggestion to try the inductors. They did make a significant improvement. The best way to describe the improvement is similar to improving the headroom of an amplifier--basically extending power output without increasing distortion, so the audible effect is greater dynamic range and greater depth to the soundstage.

I love the soundtrack to the Spanish movie "Habla con ella" ("Talk to Her"), and Track 4, "La Mesita de Noche," really demonstrated that. There is a drum beat that symbolizes a heartbeat that resonates in the background of the soundstage with a guitar in the foreground and orchestra behind.

I also played "Dream Within a Dream" on vinyl from the 80's German group Propaganda where the conga drums remained distinct as more instruments including synths are added to the mix. I also spun a remastered LP of The Rolling Stones "Let It Bleed," and it rocked my listening room. I enjoyed better separation of instruments and vocals.

Quote:
Originally Posted by daniboun View Post
Great ! thanks amigo )
do you have pictures of the PCB with a bottom view? thanks

As Claude already asked : is the tweak worth it in the end?
I did not photograph the underside of the PCB since it just has through-hole leads poking through. I should mention that in installing any new components inside the Aiyima amps, one should trim the through-hole leads sufficiently enough to keep anything from shorting. There isn't much room underneath.

Quote:
Originally Posted by drMordor View Post
Is not better inductor.
Really better is Wurth 7443630700 and Codaca CSCF2014
Unfortunately, I don't have the equipment to test Class D amps adequately, but my ears tell me that these were an improvement over the stock inductors. You won't get any argument from me regarding the Wurth and Codaca inductors. I am sure these are better than the Coilcraft MA5173 inductors with their greater linearity and current handling.

Quote:
Originally Posted by ClaudeG View Post
Rich, what magnitude would you give to your coil mod vs op amp rolling? Is that quite majour, or more a small step? I do understand that op amp rolling was performed whith the old coils, so less clarity and differences between op amps I presume, but nevertheless, would you rate that coil mod a majour must-do step or is it more fine tuning?

Further, I always felt (to my ears) Class D was lacking in terms of 3D imaging and of end of note truncating - whereas details and control were quite OK. I have the feeling reading your comparo with state of the art amp it may also be the case for you. Now that you have a better imaging, how close does it get re soundstage and placement? Is majour field covered, or the gap still quite there - possibly chip or technology limited?
The Coilcraft inductors cost $24 USD, which was almost half of what I spent on the original Aiyima amp. The change of the inductors was a significant improvement as were the op amp upgrades. As I've said before, I am finished with spending any more money on this amp. As you've pointed out, the volume pot (presumably an Alps) and the constrictive space to upgrade the volume pot is a limit to how far one could go with this amp. Where I am at now with this amp is that it is better. I will find out how much better when I receive another one of these amps to modify for my friend in Brazil. I will do a side-by-side comparison with the stock unit in both my systems.

Compared to my higher performance amps, the Aiyima is still not as good. It still can have some of the Class D glare on more complex music and it isn't rock solid like a really well executed Class A amp, but for $50 USD, I would spend the extra money and invest a little soldering time to upgrade the wiring, touch up some of the solder joints in the signal path, and roll a few op amps. It is more quiet than my TI TPA3255EVM amp and sounds better. For a complete amp, I still contend that this is a bargain. If one wants a significantly higher level of Class D performance, then I would invest in some of the better DIY offerings out there or the Hypex Ncore amps (which I have not heard yet).

I hope the manufacturer has not started to skimp on components as sales have picked up. From what I've read on the TPA3255 amp, it appears that they've changed some of the electrolytic input caps.
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Last edited by rhing; 11th May 2020 at 09:12 AM.
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Old 11th May 2020, 09:11 AM   #1506
daniboun is offline daniboun  France
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Quote:
Originally Posted by rhing View Post
I did not photograph the underside of the PCB since it just has through-hole leads poking through. I should mention that in installing any new components inside the Aiyima amps, one should trim the through-hole leads sufficiently enough to keep anything from shorting. There isn't much room underneath.
THanks anyway amigo. I have some of those Coilcraft in stock. I will try asap but I am not good in soldering.... I will share my opinion when it is done )

Many thanks for your effort )
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Old 11th May 2020, 09:31 AM   #1507
LeeHibbert is offline LeeHibbert  United Kingdom
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Thanks Rich for a great series of posts. I sold all of my measuring kit when I lost interest in hifi 15yrs ago, so will rely on other people like yourself.
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Old 11th May 2020, 09:32 AM   #1508
LeeHibbert is offline LeeHibbert  United Kingdom
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Quote:
Originally Posted by drMordor View Post
Is not better inductor.
Really better is Wurth 7443630700 and Codaca CSCF2014
Those being smd, I assume they would be a bit trickier to mount?
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Old 11th May 2020, 09:50 AM   #1509
vacuphile is offline vacuphile  Netherlands
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Quote:
Originally Posted by rhing View Post
That's why I included the plots and calculations. Yes, they are based on general assumptions, but the trends still apply in case others want to try inductors themselves.

Thank you for the suggestion to try the inductors. They did make a significant improvement. The best way to describe the improvement is similar to improving the headroom of an amplifier--basically extending power output without increasing distortion, so the audible effect is greater dynamic range and greater depth to the soundstage.
This is an acute observation which is born out by measurements. I don't think the TI engineers would have taken this inductor if there were better ones on the market. In spite of what Mr Mordor may believe, I am only swayed by measurements and this one I did myself. There may be better ones out there, but please provide proof.
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Old 11th May 2020, 09:50 AM   #1510
rhing is offline rhing  United States
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The Coilcraft inductors wire and leads are slightly larger in diameter than with the stock inductors, and the through-holes are somewhat tight, so you will need to use a good solder sucking tool and technique to thoroughly clear out the holes. Otherwise, it will be next to impossible to properly install the Coilcraft inductors.

You also have to be careful with your solder iron not to touch the adjacent components like the Epcos output filter caps. The space is very tight.
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