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Improving AK4490 THD(+N) figures
Improving AK4490 THD(+N) figures
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Old 9th February 2019, 06:23 PM   #61
nihtila is offline nihtila  Finland
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Quote:
Originally Posted by JensH View Post
Besides the THD+N it could be interesting to see the THD, so without the noise.

Have you considered making the PCB compatible with the AK4493? It only requires a small additional effort.
I have not but I should check it, I did notice its existence a while ago.

I do have THD results as well. Here is a graph from the VREF=5V case, from the same run I posted before the THD+N. At 0 dBFS THD+N is pretty much dominated by THD as can be expected, below that noise contributes more.

I could maybe extract more numbers from there but the lowest values are somewhere in the -116..-118 dB ballpark (and again, I forgot to change % to dB..).

Jens, you got to the better side of -120 dB with your analyzer?

In fact, I did not check THD only numbers with large extra capacitors so this is something I should still check. Too many variables!
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File Type: png THD_vs_Amp_TB_5V.png (119.4 KB, 131 views)
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Last edited by nihtila; 9th February 2019 at 06:27 PM. Reason: Added answer/comment to Jens
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Old 9th February 2019, 08:13 PM   #62
JensH is offline JensH  Denmark
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Improving AK4490 THD(+N) figures
Yes, at -20dBFS I typically get just below -120dB THD.

Perhaps you are limited by the AP analyzer? It looks like your results are limited by noise. I normally use a large FFT window (512k) to suppress the noise floor in order to see the harmonics.
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Old 10th February 2019, 05:45 PM   #63
ojg is offline ojg
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Quote:
Originally Posted by nihtila View Post
However, this is the first project for me that I am thinking of running a small batch assembly of so BOM cost is one figure to pay attention to here.
I'm interested. I would buy two and use it together with a SigmaDSP in an active loudspeaker I'm working on. Then the modular approach with a DAC PCB with just I2S inputs would work great.
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