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Old 1st November 2011, 05:30 PM   #1
veteran is offline veteran  Poland
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Default USB digital isolator for audio DACs

Some time ago I designed a USB isolator, with ADUM4160 as the base of the project, for my sound card measurement system . I also added a dedicated power supply and, to make it more universal, isolated DC/DC converter (ADUM5000). ADUM4160 supports 12Mbps communication which is sufficient for 96kHz/24bit sampling rate.

Isolator works very well. Red line represents the measurement of the EMU soundcard connected directly to the USB port of my laptop and black using isolator. As you can see 50Hz hum and the second harmonic is filtered better. There is also less noise in the 2kHz - 20kHz band.
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Old 1st November 2011, 05:41 PM   #2
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Nice!

I've had both these IC's for a couple years now and still haven't attempted to make a board. Do you plan on selling PCB's?
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Old 1st November 2011, 07:03 PM   #3
4nradio is offline 4nradio  United States
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I've used this USB Isolator Board from Circuits@Home for a few months now and it works great. You can really hear the improvement in the audio quality as the USB-borne noise is stripped off. It uses the ADUM4160 also:

USB Interfaces « Circuits@Home
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Old 2nd November 2011, 09:21 AM   #4
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Originally Posted by theAnonymous1 View Post
Nice!

I've had both these IC's for a couple years now and still haven't attempted to make a board. Do you plan on selling PCB's?
If there will be a few people interested I see no problem in doing more PCB's.
The next version will be smaller (without switches - I used them only for testing).
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Old 2nd November 2011, 11:18 AM   #5
Koenjer is offline Koenjer  Netherlands
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Default nice

This all looks really nice, but with all of the high resolution Dac's at the moment, everybody is waiting for ADUM devices that support more then 12Mbps.

Does anybody know if somethings is on the roadmap?
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Old 2nd November 2011, 12:47 PM   #6
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If there will be a few people interested I see no problem in doing more PCB's.
The next version will be smaller (without switches - I used them only for testing).
Well, count me in.

I still might keep the dream alive of building my own design some day. I would like a version that is as small as possible without any provisions for external power.
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Old 2nd November 2011, 02:50 PM   #7
Koenjer is offline Koenjer  Netherlands
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is allready there, with PSU isolator included.

It works fine, i have one. But does not work above 88,2 Khz

USB Isolator, Galvanic Isolated USB 2.0 - Electronics-shop.dk
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Old 2nd November 2011, 04:57 PM   #8
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Originally Posted by 4nradio View Post
You can really hear the improvement in the audio quality as the USB-borne noise is stripped off.
For me, how would the "50Hz hum" on USB digital connection getting into the DAC is a magical mistery...
More useless stuff.
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Old 2nd November 2011, 07:47 PM   #9
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For me, how would the "50Hz hum" on USB digital connection getting into the DAC is a magical mistery...
More useless stuff.
Remember that all devices (computer → USB → DAC) share the same ground which causes flow of small currents, and these can cause the appearance of distortions in the analog part of DAC.
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Old 2nd November 2011, 11:12 PM   #10
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Hmmm... NO. Digital levels are way higher than those "noises", therefore are immune. You are thinking in analog terms.
Also FYI, currents CANNOT flow on just ONE conductor. They need a return path to source, a closed circuit.

Last edited by SoNic_real_one; 2nd November 2011 at 11:16 PM.
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