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+--- Thread: USB Buss Power? (/Thread-USB-Buss-Power)
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USB Buss Power? - mauidan - 09-Nov-2014
My Auraliti PK 90 has a SOtM Audio USB card with an on/off switch for the 5v buss power.
I set the switch to the off position, and the Auraliti PK 90 and D200 communicate just fine.
USB cable is a Nordost Blue Heaven.
Anyone else tried their Devialet units without the 5v buss power on the USB input?
RE: USB Buss Power? - Pim - 09-Nov-2014
I've got an old print USB cable; worth trying to cut the power cables and see how it goes with a Mac. I'll keep you posted
RE: USB Buss Power? - Antoine - 09-Nov-2014
Oops, I think I'll have to go and correct a few posts on this forum as it seems I was wrong!
(edit: I've corrected hopefully all my posts on this topic)I own a motherboard for which I can disable the power feed to some of the onboard USB ports. If I disabled the power and connected the Devialet to such a port the Devialet wouldn't play music.
Also I bought a dual-headed USB cable, which is a USB Y-cable that on one side has a USB connector for data only and a second connector for power. Only connecting the data connector wouldn't let the Devialet play music through it's USB input.
After both tests I concluded that the Devialets need the +5V power active. But after reading your post, Mauidan, in which you stated the Devialet does work without the power active this didn't add up so I found a standard USB cable for some extra tests.
A standard USB cable has four (or five if you count the shield around the four leads)
1. VCC (+5V)
2. D- (data -)
3. D+ (data +)
4. GND (Ground)
If the cable is shielded the shield is connected to the metal case around the USB connectors.
I removed the insulating plastic of the cheap USB cable laying the leads bare and one by one I cut the leads inside while playing music. I started with the red +5V lead and music kept playing. Then cut the black ground lead, music still kept playing. Finally I cut the shield and only then the music stopped. Reconnecting the black ground lead resulted in music playback again. The Devialets look to have tied the shield/USB plug metal casing to ground, either directly or indirectly, I can't tell through this test.
Conclusion: the Devialets don't need the +5V power lead active, they need the USB ground connection active either through the shield or ground lead.
So the Auraliti/SoTM USB interface card only cuts the +5V connection and not the USB ground.
For me, except knowing the real workings now, I think this doesn't change anything as I want to isolate both the dirty PC power and ground from the Devialet so I'll keep powering it using both my JCat USB interface card plus Kingrex uPower battery supply.
RE: USB Buss Power? - Morten - 09-Nov-2014
Cool, now I will have to find the insulation tape and try to disable to 5V leg.
Is there any feedback of sonic differences?
Kind regards
Morten
RE: USB Buss Power? - mauidan - 09-Nov-2014
Nice to know that we've confirmed the Devialets don't need USB buss power.
Morten,
When I turned off the buss power on the SOtM Audio USB card, I was listening to Cecile McLorin Salvant's Woman Child and I thought I heard a small improvement in the focus of her voice.
Since the SOtM Audio USB card already has a power line noise filter, individual ultra low noise regulators and my PK 90 is powered by the optional linear PSU, disconnecting the 5v buss power may produce a bigger improvement for those feeding their Devialet USB inputs from a PC or MAC.
RE: USB Buss Power? - Morten - 09-Nov-2014
Thanks for the feedback.
I have tried to tape over the 5v leg on my USB cable, and yes it plays. But if I power off the Dev. and power it up again it dos not work, only a real bad noise.
Have you tried this on your setup?
Kind regards
Morten
RE: USB Buss Power? - mauidan - 09-Nov-2014
(09-Nov-2014, 20:05)Morten Wrote: Thanks for the feedback.
I have tried to tape over the 5v leg on my USB cable, and yes it plays. But if I power off the Dev. and power it up again it dos not work, only a real bad noise.
Have you tried this on your setup?
Kind regards
Morten
Tried it yesterday.
Powered off/on the PK 90 and Devialet, and the USB connection works fine.
RE: USB Buss Power? - Morten - 09-Nov-2014
Strange that it doesn't work for me...
And you have tried to leave the USB power off, and then do a power cycle on the Devialet?
Kind regards
Morten
RE: USB Buss Power? - Kunter - 09-Nov-2014
Great info guys...
For the ones with dual head USB cables, trying to connect the ground to a clean ground like Entreq is an interesting experiment.
This is what I will do once my PPA USB comes along...
Cheers
RE: USB Buss Power? - gray - 10-Nov-2014
I have an Antipodes DX server that has 2 USB out terminals - one powered, one unpowered.
I find that the Devialet works best with the unpowered.