is the length of a USB cable a factor?
Apr 28, 2006 at 12:49 PM Thread Starter Post #1 of 11

stryker

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Didn't know how else to word the thread.

I am considering getting this to finally try my computer as a source. The device will convert the USB signal to S/PDIF.

Problem: My computer is about 15' away from my DAC & 2-channel setup and is not going to be moving closer anytime soon. Therefore, I am considering running a 15' USB cable to this device which will sit on or near my setup.

Given that cable length is an issue with other formats like digital coax (jitter) and single-ended analog cables, etc. I was wondering if USB has "cable length issues"? My guess is that, from what I've read, USB is generally jitter-free so the issue is more of signal strength (voltage/current/whatever) loss or something like that.

Anyone know anything? I've searched around here and not found anything but I admit I've not done an exhaustive Internet search on the issue.
 
Apr 28, 2006 at 1:30 PM Post #2 of 11

lmilhan

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According to the usb.org FAQ:

"In practice, the USB specification limits the length of a cable between full speed (12 Mbps) devices to 5 meters (a little under 16 feet 5 inches). For a low speed device (1.5 Mbps) the limit is 3 meters (9 feet 10 inches)."

So, on 'paper' assuming your DAC is of the high speed device category (12 Mbps), you should be good to go with a 15 foot USB cable. Since I have never tested a setup like this personally, I can't guarantee anything though. I suppose the good news is that it would be cheap to try (USB cables can be found for cheap on the internet).

If you have trouble with a regular 15 foot USB cable, perhaps something like this will solve your problem.

Finally, your question would probably be best asked to the manufacturer of the USB you wish to purchase.

Good luck.
 
Apr 28, 2006 at 1:48 PM Post #4 of 11

stryker

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Thanks, I didn't even think to look on the USB trade site (duh). Now I have to figure out what brand of port is low speed and high speed. I need a front panel port.

Mshan, I'll assume I can use this instead of a port and then just use a shorter length cable.

Still wondering if shorter cable=higher sonic fidelity regardless of hubs repowering the signal. After all, I am conditioned like a Pavlovian dog to spend much more on cables for my setup. Less than $10 for a cable does not compute.

I see a market for an all-silver, shielded USB cable and Cardas USB jacks and connectors.
 
Apr 28, 2006 at 2:00 PM Post #5 of 11

mshan

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Have you tried contating Hagman about optimal and maximal usb cable lengths?

I am going to be using the 25 ft cable with an USB NOS dac, which are supposed to be more resistant to jitter than spdif units.

Like you, I would be comfortable with a more standard usb cable length, but this is only a temporizing measure till i get an Apple Mac Mini or MacBook as a dedicated source for my usb dac.
 
Apr 28, 2006 at 2:08 PM Post #6 of 11

stryker

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I have an email to him. My problem is that I understand enough about typical coax/optical PCM signals, but I have no idea of the signal format of USB cables and what makes for a robust, accurate, and clean USB signal. I'll assume as long as there's enough voltage going through the USB cable that the USB>S/PDIF converter will do its job and give me a nice robust S/PDIF signal for my DAC.
 
Apr 28, 2006 at 3:03 PM Post #7 of 11

pburke

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if you need a long USB 1.1 cable, this will do the job very well staring at 30 feet and $169...

http://usbstuff.com/longcable.html

Added benefit ( and a huge deal with my USB DAC ) is that you also isolate the computer from the DAC glvanically (no ground loops).

I changed the receiver end power supply to a SLA battery supply with nice regulators, etc - kicked it up another notch.

Not cheap, but definitely THE cable for a USB DAC connection. See talk about it in the PC audio forum over at the asylum. I bought it mostly because of the ground loop issue, but it also allows me to locate my noisy RAID5 music server in the basement while directly driving the DAC.

Peter
 
Apr 28, 2006 at 3:10 PM Post #8 of 11

stryker

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Hey Peter, oh great builder of my DDDac! You know that my DAC receives a S/PDIF signal so will this fiber optic USB cable make a difference? If not, I sure would like to spend $20 instead of $150.

Also, would you know if galvanic isolation is achieved by the above-captioned USB>S/PDIF converter? Or if it even matters since it's converted?
 
Apr 28, 2006 at 4:29 PM Post #9 of 11

Don Quichotte

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With my Apogee Mini-Dac, an ordinary USB cable made of two pieces (1.8m long and 4.5m long, respectively) sound somewhat less defined, more rounded around the edges compared to the stock, short (less than 1m long, I think) Apogee USB cable. I don't know why. Otherwise, it works very well. Also, Apogee advices against any active USB cable, hub, or passive cable longer than 5m, but I think the reason is the stability of the connection, not the sound quality.

Quote:

Originally Posted by pburke
I changed the receiver end power supply to a SLA battery supply with nice regulators, etc


Could you get into detail a bit? I would like to try something like this for my Mini-Dac, but I don't have the expertise (the bare SLA has nice warmth, but also sounds slightly undynamic, with obscured finer details and rolled off treble). You can answer me by PM or in the thread I posted here, so that we don't hijack this one.
 
Apr 28, 2006 at 5:31 PM Post #10 of 11

stryker

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Okay, Mr. Hagerman says...

Brian,

There is no problem using USB up to 5 meters. Works just fine.


Who'da thunk it? That's what the USB people have on thier site! I'll assume there's some wiggle room but until I can make my own USB cable, I guess I'm limited to what I can buy. At this point, I'm going the cheap route and just getting a quality cable I guess from the site the pburke referenced. 5m is *just* long enough.
 
Apr 28, 2006 at 7:46 PM Post #11 of 11

Akathriel

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It should be fine. However if you are going to do a ridiculously long run it couldn't hurt to get an active USB cable.
 

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