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AK4493 DAC
AK4493 DAC
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Old 20th May 2020, 08:56 PM   #91
potstip is offline potstip  Turkey
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Join Date: Oct 2013
Quote:
Originally Posted by nihtila View Post
Archimago (Archimago's Musings) uses the ADC/DAC version for measurements, apparently the ADC in that is great as well.

That distortion is extremely low. May be a particularly good unit as well, of course. I wonder if big elco helps in THD even if not in THD+N. Maybe I should revise some tests as I used THD+N as figure of merit in these and didn't check THD only that often. LT3042 just didn't always seem to like big capacitance at the output but maybe it would be ok.

A few notes on your comparisons though. Datasheet does not give THD but THD+N so it's not 20dB better than DS. THD+N is -115dB which is the same I measure. This is not 0dBFS level yet though and it gets even lower (-117dB) after that in the RME. But often you get better results with higher level. I (and some others) have a knee before 0dBFS so optimal level is slightly lower, here it's also not clear knee although there is a small drop in SINAD at one point.

Nevertheless, excellent results. Seems they have great implementations. In the ADC/DAC one the PCB was I think 10 layers so that pleases engineer as well. Btw, I wonder if they do something in the FPGA and in what mode the DAC is used in.
Hello Tomi, thanks for all that great infos, one thing i want to mentioned the cap you used 100u VCMR. most of the designs even in referance design it is 10u. Is there any particular reason to do that.
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Old 23rd May 2020, 02:05 PM   #92
Joseph K is offline Joseph K  Hungary
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Join Date: Dec 2004
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Dear Tomi,

When I had bumped in this link, Your bypass experience came into mind (in your 4493 'saga')..

Experimental Comparison of 0402 Ceramic Capacitors as Supply Bypasses

Ciao, George
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Old 25th May 2020, 10:36 AM   #93
nihtila is offline nihtila  Finland
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Join Date: Jan 2006
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Quote:
Originally Posted by potstip View Post
Hello Tomi, thanks for all that great infos, one thing i want to mentioned the cap you used 100u VCMR. most of the designs even in referance design it is 10u. Is there any particular reason to do that.
No particular reason. Not sure why I ended up using that I never played with that cap much; think I did try some options in the beginning but didn't see any differences. I don't think that's very critical. It's the common mode voltage and should cancel out in the output circuit anyway.


Quote:
Originally Posted by Joseph K View Post
Dear Tomi,

When I had bumped in this link, Your bypass experience came into mind (in your 4493 'saga')..

Experimental Comparison of 0402 Ceramic Capacitors as Supply Bypasses

Ciao, George
I also tried to measure effects of different capacitors but couldn't really. Doesn't mean there are no measurable differences but I wasn't able to do that. With such low frequencies we have in audio (even with over-sampling converters) it's not easy to measure such things. Should maybe feed the circuits with higher bandwidth stimulus but then again what would we really be after..

But thinking of higher bandwidth stuff, cap performance is mainly set by its inductance which mostly comes from package size. Thus, smaller package works better in higher frequencies. Moreover, if you parallel these caps you reduce the inductance and make it even better; and also increase capacitance of course.

Henry Ott has some good stuff in his EMC book about bypass caps. He measured impedance across frequency. In your link nothing bad happens when all those different caps are used in parallel (although it doesn't help either), but it may cause very nasty impedance resonance spikes and make things a lot worse. According to Ott's measurements, it is better to parallel the same caps than use different values. In any case, the only way to ensure it works in your application is to measure (which may not be easy).

In my odd cap results there are likely also some very subtle effects going on between different caps I just couldn't measure. The distortion levels in high performance audio are so extremely low that I presume even very tiny things may make a difference in.
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