CM6631 USB Audio 2.0 to Isolated I2S - diyAudio
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Old 8th September 2012, 05:06 AM   #1
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Join Date: Feb 2009
Default CM6631 USB Audio 2.0 to Isolated I2S

listening by different person is always subjective

using a Oscilloscope to check the output waveform is always a good idea
it's suprise to see the ground noise from USB inject to the DAC,

here is a battery powered Oscilloscope waveform compare of the same DAC output
one is USB pluged + windows volume mixer muted
one is USB unpluged

Conclusion:
All USB DAC are BAD sound without Isolation, joke for audiophile.

The only way is DIY a USB Isolated DAC
PCM2707 USB Audio 1.0 + ADuM4160 USB isolation (finished)
CM6631 USB Audio 2.0 + I2S isolation (in progress)
XMOS USB Audio 2.0 + I2S isolation (wait for the new XS1-SU1 chip to start)

The PCM2707 without isolation will stop/halt immediately when any main line power house appliances switch on/off
after using the ADuM4160 USB isolation, the PCM2707 don't stop/halt anymore.
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Old 8th September 2012, 10:04 AM   #2
marce is offline marce  United Kingdom
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Vias in pads
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Old 8th September 2012, 01:01 PM   #3
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Quote:
Originally Posted by marce View Post
Vias in pads
via in pad is good for high speed design i.e. low inductance.
but additional complexity to manufacturing process and the underlying material cost for conductive fill when mass production. Only manufacturer don't like it
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Old 10th September 2012, 01:20 PM   #4
marce is offline marce  United Kingdom
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Location: Blackburn, Lancs
It aint that high speed and it makes soldering hard, for proper via in pad use microvias or have them filled, both expensive like you say and not realy required for these speeds.
isolating any power lines is a good ideaif you use them then you get total isolation.
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Old 12th September 2012, 05:19 AM   #5
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Quote:
Originally Posted by marce View Post
It aint that high speed and it makes soldering hard, for proper via in pad use microvias or have them filled, both expensive like you say and not realy required for these speeds.
isolating any power lines is a good ideaif you use them then you get total isolation.
there is no enough for Audiophile, only beyond
for 192khz 384fs, the mclk is running at 73.728Mhz,
that speed should affected by little via inductance.
as the I2S is a one way transfer protocol, no CRC, it should be designed with the highest standard to avoid any signal loss
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Old 12th September 2012, 08:49 AM   #6
marce is offline marce  United Kingdom
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Join Date: Jun 2007
Location: Blackburn, Lancs
Yes, but micro vias not big vias.
For those speeds a multi layer design with stripline routing would be best if you want to get the ultimate signal integrity for the digital, or even HDI board layout, even better with the outer layers full ground.
but then having done many high speed designs using both normal and HDI teqniques with DDR interfaces I never use via in pad when using normal mechanical drilled vias.
I also use signal integrity simulation software, if I have any concerns over a signal and its possible routing.
The vias them selves do not have much of an effect on signals, it is changes in impedance that is critical, and he ultimate cause of problems is the signal rise time, it is this that ultimetly determines whether a signal is high speed or not.
I have just done a HDI board which if you want the ultimate layout for signal integrity then multi layer microvia (HDI) design is the way to go.
This is worth looking at:
The HDI Handbook
and for the ultimate guide to high speed design try (if you all ready havn't):Signal Consulting, Inc. - Dr. Howard Johnson

The picture is via in pad (0.1mm laser drilled via) 0.4mm pitch BGA, now thats when things get fun.
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