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Review and Measurements of JDSLabs ODAC Rev. B Compared to Fiio E10K

amirm

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#41
The final step was to solder a cable to the ground of one of the DAC's RCA sockets, then insert the other end of the cable into the amp's ground plug.
That tells me that the Stax's input may be floating. I run into that all the time in my reviews/testing. The RCA inputs on my new Audio Precision analyzer are floating. About half the time, using an alligator wire between the ground terminal on my analyzer and an unused RCA jack substantially reduces mains hum. Sometimes it works better if I just ground things at the analyzer end. That is, just go from its ground lug to its own RCA outer shroud. Other times doing it as you show works better. In other cases, doing this causes much more noise so I don't do it.

Balanced interconnects don't have this issue and hence the reason they are my preference.
 
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#42
That tells me that the Stax's input may be floating. I run into that all the time in my reviews/testing. The RCA inputs on my new Audio Precision analyzer are floating. About half the time, using an alligator wire between the ground terminal on my analyzer and an unused RCA jack substantially reduces mains hum. Sometimes it works better if I just ground things at the analyzer end. That is, just go from its ground lug to its own RCA outer shroud. Other times doing it as you show works better. In other cases, doing this causes much more noise so I don't do it.

Balanced interconnects don't have this issue and hence the reason they are my preference.
Given all the trouble that floating inputs give, what's the reason for expensive gear to use them?

Thanks
 

amirm

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#43
Given all the trouble that floating inputs give, what's the reason for expensive gear to use them?

Thanks
It gives you the choice to ground or not ground. As I mentioned, in some devices I test floating works a lot better.
 
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#44
It gives you the choice to ground or not ground. As I mentioned, in some devices I test floating works a lot better.
Does this mean that if my noise issues are entirely due to the amp? (If I replace the ODAC by something more modern with its own power adapter, the noise will come back unless I mess with the amp's ground terminal again?)

Thanks
 

yue

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#45
Unfortunately he is using a narrow band analysis from 8 to 14 Khz versus my full bandwidth one. Both the jitter and spurious tone that I found is outside of his measurement range:
Probably you can test ODAC again in -5db and see if the problem goes away. JDS does not recommend use ODAC at 0db as it's not designed to be used at that volume.
 

amirm

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#46
Probably you can test ODAC again in -5db and see if the problem goes away. JDS does not recommend use ODAC at 0db as it's not designed to be used at that volume.
The content dictates the max dB and there, there is plenty of content that is at or near 0 dBFS. So user has no control over it.
 

yue

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#47
The content dictates the max dB and there, there is plenty of content that is at or near 0 dBFS. So user has no control over it.
I believe it's the interface chip (such as XU208 in topping's case, SA9023 in ODAC case) that does the multiplication of volume and data, and send the final result to the DAC chip (PCM5102A in this case, which cannot handle 0db). So user can avoid the 0db issue easily by always using a slightly lower volume (and that's what JDS recommends).

So even with max db content, it's still easy to avoid sending full amplitude to the chip.
 

amirm

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#48
Clipping can happen due to digital filters, or analog stage. Either way, there are a lot of DACs that handle 0 dBFS fine. One should not have to change things upstream of the DAC to make it work well when there are alternatives without that issue.
 
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