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Class D Switching Power Amplifiers and Power D/A conversion

TPA3255 - all about DIY, Discussion, Design etc.
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Old Yesterday, 04:52 PM   #3591
opc is offline opc  Canada
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Join Date: Oct 2004
Location: Ottawa, Ontario, Canada
TPA3255 - all about DIY, Discussion, Design etc.
Hi cdsgames,

So you're using a post-SMPS linear reg to achieve that noise figure. Understood. I'm still not convinced that level of output noise is possible at those power levels, so it would be nice if you could provide some details around that, specifically an FFT of the output under light load.

The absolute best regulators in the industry struggle to get down to 1.7uV of output noise and that's at a fraction of the power you're claiming (LT3045 is good for 7.5W). If what you're saying is true, then color me impressed, but a claim like that does require some evidence to back it up.

The best I've managed to achieve with linear regs at those power levels (>250W) is about 15uV of RMS noise from DC to 22kHz and that was with a quartet of LT3081 regs and quite a lot of heatsink.

Regards,
Owen
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Old Yesterday, 06:32 PM   #3592
cdsgames is offline cdsgames  Canada
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First, I am coloring you impressed. Thx you for understanding what we have achived.

Second, I agree that some measurements are fake. I won't say anything further and let you all make up your own mind.

Third, I am not using linear regulators, but a 4 Gen capitance multiplier with 0.6v drop. I do use AP so I am rather sure that achiving 0.00012(latest) thd 1khz 5w 4r needs a psu that's very, very quiet. Battery like quiet.

As I said before Tpa3255 has no real psrr. Class d, has a " fake psrr" on Btl.Psu noise should be canceled, it is, on btl phases. However the analog signal on each phase , is modulated by direct psu noise and cannot be canceled on same btl.

Of course, by using llc power, psu ripple its not modulating analog signal. Noise floor however, definitely is ( but you can hear it less)

That's the main reason that all Tpa3255 have thd+n of 0.002 around. We improved by at least 11db.

Can you hear it? I don't know, but I will not stop trying to improve all measurement including thd,/ap, switching noise/spectrum a...and some more that I am not willing to discuss at this time.

Does it make more sense now opc?
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