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Cleaning USB for Bus Powered Audio Devices: Discuss

DWPress

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I'm the guy who made the split DIY USB cable referenced in the first post and along this thread. I tried the Dragonfly USB cleaner device, no improvement nor did a powered USB hub help. I had occasional problems after my cable solution as well.

Real solution: I bought a Macbook Pro to replace the 2013 iMac that was giving me the dirty USB power and all good now. (was not the only reason I upgraded computers)

That's a pretty drastic solution, I know, but it just seems that some implementations of voltage via USB is just plane bad or aging components on the MB may be the cause. Other DACs weren't affected using the same iMac but over the years I've had similar issues with DACs on other machines Mac & PC. It seems to me galvanic isolation is something that was known of 20 years ago and is so easy to implement in a build that all digital audio devices should include it by default. The D10 just seems to be more sensitive somehow.

Still happily using the D10 though
 

Krunok

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Take a USB cable and cut the +5v (red) cable. Run an external +5v power supply into the device-side of the UBS cable red wire that has just been cut.
I know how to do it, but why would I want to do that? It works perfectly well when powered from USB port.
 

L5730

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I mentioned some time earlier that (a) the issue for me was found to be a ground loop (b) it was cured by breaking the ground connection from DAC to powered speakers. This maintains the USB common ground and thus means there is no risk of damage to either USB device or host.

If folks suffer from a flaky power supply, in the form of a shoddy implementation of USB power from their computer device, then using a Y-cable, whereby only the +5v (normally red) wire is connected to an external +5v power supply and no other power source, but the ground cable (normally black) is connected to both the PSU and the USB host device, should result in a trouble free experience.
USB host to device needs a common ground - it might work for a bit without a common ground connection (broken after initial handshake/enumeration/initialisation) but it runs the risk of causing damage as there is no longer a common reference voltage to which the data voltages are compared to. Additionally, as soon as sample rate is changed or PCM/DSD is switched the DAC will probably stop connecting properly.
Further, breaking the ground between host and device does cause some narrow band noise in the 8 kHz range.

For a real nice solution, the USB chip (XMOS etc.) should have a proper and direct connection to the USB host, and then the IIS data should be sent over galvanic isolation. It no longer becomes so much of a two-way communication, so fast one-way isolators can be used. The IIS signal would then enter the DAC chip and so on. DC-DC isolators can be sued for power, although it would then create additional losses, and may require more current, and thus an external DC PSU may be required. Jitter maybe an issue too.
Something like the Singxer F-1 board coupled with an ESS DAC chip instead of the HDMI and S/PDIF outputs would be a nice solution for a Galvanic isolated USB DAC. Price could be interesting though.
 
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