Long USB cable


#1

Is it OK to run a 50’ long USB cable to the DS DAC without worrying about sound quality?
I re-watched Ted’s video and he mentioned that DS DAC has very large buffer, and ignore the incoming clock, which makes me think cable type and cable length isn’t very important to the PSA DirectStream DAC, as long as no data drop out and data speed is fast enough to keep the buffer fed.

Ted, Paul, if you can chime in?

Thanks ahead.


#2

The limit on a simple USB cable’s length is set by the speed of light and the time to get a signal to the end and back of a cable and is approx. 15’. Going just a little over that and things will start to get flaky. If it’s not a certified USB cable the limit may be smaller depending on what changes have been made.

If the cable has active repeaters (which turn out to be USB hubs with only one downstream connection) then you can have 15’ per section. I have some 30’ active USB 3.0 cables that work great, but you can’t have as many hubs chained with it. There’s also the Corning 3.Optical cable which uses optical fiber to extend the length of the cable up to 150’. It’s a little more twitchy to get working, but it does work well after you get it to work the first time.


#3

Thanks Ted.

I bought this one here:

Seems to be working well with PCM 44/48k. Sounds OK to me. I haven’t tested higher rest or DSD yet.

This one has an active repeater built-in to the cable. Going to compare it against Bridge II this weekend.


#4

If it works at one sample rate it will very likely work at all USB Audio 2.0 supported sample rates (e.g. with the DS up to 24/352.8k PCM and DSD128 (via DoP.) I used a similar cable for a long time before I upgraded to USB 3.0 (mostly for performance on USB 3.0 drives.)


#5

Thanks again Ted.

Am I OK to assume that sound quality compared to Bridge II should be similar thanks to the way you designed it? large buffer, and internal re-clocking and all.


#6

Things are a little more complicated: all inputs can be made to sound good. Some feel that getting great sound quality from the bridge is easier (on the other hand configuring your favorite player to work with any network connected DAC (including the bridge) can be frustrating.) Also some prefer the user interface of the kind of software that drives the bridge and others prefer other user interfaces.

The technical downside of USB is that it has both a power and a ground wire in parallel to the data for a long distance. That can induce high frequency noise on both of them. Calling the VBUS line in a USB cable “power” is slightly confusing because even if you don’t use any current from the VBUS line it’s also used to signal when a device comes online or goes offline and whether it’s a hub or not. If you don’t connect the VBUS line on a USB cable the connection becomes flaky and may or may not work in any given system on any given day. Also USB does 8000 packets a second so tho everything works out well for 48Hz and its multiples, 44.1kHz and its multiples have to have a varying number of samples in each USB packet. Processing the packets therefor takes different amounts of current and generates colored noise at the sums and differences between multiples of 8000 and multiples of 44100… Tho everything is well buffered and the DS isn’t very sensitive to jitter the noise coming from USB may need special attention. As a quick hack I use an externally powered hub just before the DAC with no other units using the hub but the DAC. With a modestly good power supply for the hub a lot of the upstream noise from the computer, etc. is attenuated. Another approach is using the Corning 3.Optical cable: it uses an optical connection for the data and very fine wires for ground and power. Keeping these lines high impedance adds filtering to them and since the data isn’t interfering with the VBUS and ground they stay a lot cleaner.

My advice is to pick the interface you want to use and then optimize the sound quality of the connection if you like tweaking.


#7

Thanks Ted,

Very informational, I appreciate the detail response.

Just wanted to add a bit on why I’m doing this for background info.
The reason I like to use USB is that it’s the only way I can get to use the DAC with video. I enjoy watching music videos and wanted to use my system to listen, no reason not to :slight_smile:

I went out and bought a USB over Ethernet adapter, since I already have cat6 cables running inside the wall. I got this one:

From my initial testing, I find that it’s much better than the 50’ cable. Compared to BridgeII, the BridgeII is a little bit more open, a little bit clearer, sound stage is a little bit larger. Not that going through the USB converter is bad, just different, it has more weight to the sound, a tag veil compared to BridgeII, but I’m pretty happy with it right now, allowing me to listen to my system while watching the music videos.

If I listen to exclusively audio, then I’ll probably still use BridgeII.


#8

The converters that go to Ethernet and back (or perhaps just good Cat 5, 6, … cable or optical cable) can work well and isolate your DAC from some of USB’s worse problems. Some can’t really do USB Audio 2.0 (they don’t support anything above 24/96), but that’s not a problem with the one you chose. I like how they work in my system, I just don’t need the extra length, etc. for my test bench :slight_smile: