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Class D Switching Power Amplifiers and Power D/A conversion

What is wrong with TPA3255?
What is wrong with TPA3255?
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Old 25th September 2018, 04:36 AM   #391
errcl65 is offline errcl65  Canada
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In looking a the TI 3255EVM manual, I discovered they are using a single +12V
to power the 5532. 3E is doing likewise with their NJM4580 front end op-amp.

This is essentially giving it only -/+6V rails. Most of the published specs for these
op-amp are based on -/+15V rail. I have to wonder how optimal the front
end is running at < 50% of its rail and without the benefit of wide band
regulation like (HxR style regulator).

Without the proper rails and regulation, throwing the $10 AD8599 opamp may
do nothing to SQ.

I have been listening to both the stock version of the 3e and TI EVM boards.
They have different sonic qualities and are providing hours of comparative listening.

I am running a good 500W (setup for 51VDC) SMP from Connex. This has
improved the listen-ability a great amount.

NCore NC400 has nothing to worry about from the two 3255 examples.
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Old 25th September 2018, 05:11 AM   #392
chermann is offline chermann  Austria
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Quote:
Originally Posted by chermann View Post
thanks doc !

if i am not totally stupid for soldering ......
i wonder that sybic wrote nothing about this.

yes this 22pF caps are normal stlying.. no smd caps at home on stock

business trip...maybe end of the week...

to make it more clearer:

sybic did his surround amp with 3 boards and he wrote nothing about problems with the original 22pF + Ad8599 or Performance problems (50% rail)

Last edited by chermann; 25th September 2018 at 05:15 AM.
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Old 25th September 2018, 05:35 AM   #393
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by errcl65 View Post
This is essentially giving it only -/+6V rails. Most of the published specs for these
op-amp are based on -/+15V rail. I have to wonder how optimal the front
end is running at < 50% of its rail and without the benefit of wide band
regulation like (HxR style regulator).
Plenty of opamps run fine on +/-6V with only slight changes to their parameters. The AD8599 is one such - its fully characterized for +5/-5V operation and only gives up a couple of volts of slew rate at the lower voltage that I can see. GBW is unchanged.

Quote:
Without the proper rails and regulation, throwing the $10 AD8599 opamp may do nothing to SQ.
I agree about the necessity for high quality power rails - have you provided external regulation for the TPA3255's signal processing rail voltage? I suspect if you do, it'll leave the NC400 behind. My own board improved immensely from just adding additional caps to that rail, regulation I've yet to try as it requires some trickery to override the internal reg.
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Old 25th September 2018, 04:50 PM   #394
t-minik is offline t-minik  France
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Hi all

I'm thinking to give a try at one of those TI Evm or 3E-audio boards but I've got a question.

I seen on TI EVM and 3E-Audio datasheet that input impédance is 10k, that's set with input and feedback loop on opamps, as 10k is a bit low for my setup, do you think changing those resistors (and feedback caps accordingly) will reach the noise up to high ?

to avoid using one more opamp between my passive LDR volume and that amp i would like to reach it to 47k at least.
any advice on that point ?

best regards
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Old 26th September 2018, 07:01 AM   #395
linuxfan is offline linuxfan  Australia
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Quote:
Originally Posted by abraxalito View Post
I agree about the necessity for high quality power rails - have you provided external regulation for the TPA3255's signal processing rail voltage?
Has anyone here actually tried improving the 12V rail? Was there much SQ improvement?

The EVM uses an LM5010A switching reg to step down the supply voltage to 15V, then on to an LM2940 linear regulator to provide 12V.
I suppose a basic upgrade would be to divert the existing 15V to a better 12V regulator, such as - LT3042/LT3080/ADM7150/TPS7A4700 etc.
And a more advanced upgrade would be to give this new regulator its own transformer and rectifier, such that it becomes a completely separate supply.

But is any of this worthwhile?
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Old 26th September 2018, 07:13 AM   #396
abraxalito is offline abraxalito  United Kingdom
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Without attention to the 7.75V rail first, IME I'd say no its not. That AVDD is the bottleneck.
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Old 26th September 2018, 07:35 AM   #397
linuxfan is offline linuxfan  Australia
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Thanks abraxalito.
Sorry for the potentially dumb question, but to improve the AVDD what is involved - better cap(s), different value cap(s)?
I see that the EVM's AVDD pin has a 1uF 0603 cap to GND.
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Old 26th September 2018, 07:41 AM   #398
abraxalito is offline abraxalito  United Kingdom
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Bigger caps is what I've used so far - a couple of Nichicon HZ 1800uF/16V. I'm not sure this is optimized but it does clean up the HF substantially.
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Old 26th September 2018, 08:31 AM   #399
linuxfan is offline linuxfan  Australia
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Thanks. By "couple" I suppose you literally mean that you are using 2x 1800uF/16V in parallel.
It seems the Nichicon HZ series caps are difficult to obtain, and maybe in depletion - Mouser only has 1000uF in 16V.
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Old 26th September 2018, 08:57 AM   #400
abraxalito is offline abraxalito  United Kingdom
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The type you use I doubt is very critical, I use the HZs because they're the lowest ESR ones I have. If you can't get HZs try Nichicon HM or NCC KZJ or Rubycon ZLH. Failing those almost any polymer type will have low ESR.

Yes I'm using them in parallel.
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