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Old 12th June 2017, 12:31 AM   #11
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Its not the distance in itself that's responsible for adding jitter, its the noise voltage between the grounds of the oscillator and the DAC. Which is increased by distance normally, but is also increased by larger noise currents and is decreased by having lower ground impedance.
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Old 12th June 2017, 12:34 AM   #12
Eldam is offline Eldam  France
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It means a standalone digital plain ground and a sota voltage reference (chip?) to power both the XO and the ladder with such high precision résistors ?
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Old 12th June 2017, 12:37 AM   #13
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More importantly it means having no currents in the ground plane between the oscillator and the DAC. Of course not worth taking such steps without also a very low noise supply to both oscillator and DAC.
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Old 12th June 2017, 12:48 AM   #14
Eldam is offline Eldam  France
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Thanks Abrax for those inputs.

Not sure I understand ? Do you mean zero current or at least the two active devices should not share/cross the same currents on the Gnd plane because those last having different impedance despite number is very low ?

So maybe Gnd islands tied together more than a plain Gnd plane or cuts in the plain Gnd plain to drive the currents and avoid crossings? Or XO close to the DAC chip area ?

Is such a targett can be achieved by isolator chips, or are they just for noise in voltage domain ?

Btw sorry, totally off topic

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Old 12th June 2017, 01:06 AM   #15
soekris is offline soekris  Denmark
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Originally Posted by abraxalito View Post
Filtering out normal-mode noise is fairly easy, enough chokes and ceramic caps ('lytics for damping too) and you're done. Presumably that's what you're referring to. Common-mode noise on the other hand....

The Denafrips does have a most impressive capacitor array. I wonder what circuit aspect is so sensitive to PSU noise that they need that many?

SMPSUs have unreliable electrolytics inside too, probably running at much higher internal temps than the array visible in the Denafrips.
Yes, the electrolytic capacitors is the first part to fail in a SMPS, can tell you that from experience.... But those new Meanwell SMPS have a MTBF of 1.5M hours, very very impressive. And people tell me that they really are good. Time will tell of course....

But MTBF goes down as part count goes up, that's the issue with all those electrolytic capacitors on the Ares....
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Old 12th June 2017, 01:08 AM   #16
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Quote:
Originally Posted by abraxalito View Post
The Denafrips does have a most impressive capacitor array. I wonder what circuit aspect is so sensitive to PSU noise that they need that many?

SMPSUs have unreliable electrolytics inside too, probably running at much higher internal temps than the array visible in the Denafrips.
Isn't this done to lower the esr to a minuscule amount?

Agree, the single worst component in SMP's are the caps, they s**t themselves, no matter what the quality.

Cheers George
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Old 12th June 2017, 01:41 AM   #17
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Quote:
Originally Posted by Eldam View Post
Not sure I understand ? Do you mean zero current or at least the two active devices should not share/cross the same currents on the Gnd plane because those last having different impedance despite number is very low ?
Its tricky to visualize - the oscillator has its own power supply, the DAC has its own power supply. Normally both will be regulated with low-noise devices. Both regulated supplies normally come from the same transformer winding which is what leads to noise being introduced in the 0V. One way to solve the problem is to have the oscillator run from its own dedicated winding then join the two 0Vs at the DAC, this ensures no external ground currents can pollute the 0V between the DAC and oscillator. So yeah, isolated supplies are the best solution I think.
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Old 12th June 2017, 01:44 AM   #18
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Well for the price, one really can't complain.
Don't see any sub $600 dac build this way
right ?
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Old 12th June 2017, 01:45 AM   #19
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Isn't this done to lower the esr to a minuscule amount?
Yes, that's why I've done such arrays in the past. The ESR and the ESL get so much better than a few large caps. Better still though understand why the circuit's so sensitive to PSU noise and design better PSRR into the active stages.
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Old 12th June 2017, 01:47 AM   #20
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Well for the price, one really can't complain.
Don't see any sub $600 dac build this way
right ?
Agreed, I don't think I've seen any DAC with an isolated supply for its clock oscillator no matter what the price. This Denafrips looks like a bargain, the cap array certainly impresses me
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