USB Buss Power?

[mauidan]

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?

[Pim]

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

[Antoine]

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.

[Morten]

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

[mauidan]

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.

[Morten]

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

[mauidan]

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.

[Morten]

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

[Kunter]

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

[gray]

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.