Sunday, 3 May 2015

MEASUREMENTS: Corning USB 3 Optical Cable, Ground Loops, and Noise.

Folks, remember, the "Linear Phase vs. Minimum Phase Digital Filter Test" is still running as I post this! Please give it a try and report back in the survey. I want data and hopefully an opportunity to report back on what the readership perceives (or not perceive).


I. Introduction

Indeed, "noise" can be an issue with audio systems. There's little worse that can happen to an audiophile after spending hundreds or even thousands of dollars on new equipment, plugging everything in as per "best practice", getting ready to play your first piece of music, and finding that for some reason, noise has seeped through to disturb the expectation of pristine, clean background silence from which music can blossom...

Before proceeding further, remember that noise can sometimes be subtle, and very importantly, ambient noise must be low in your sound room. It's quite possible that slight hum and low-level noise may not be significant from a normal listening distance if the ambient noise level is high (something we urban dwellers especially do have to consider!).


It is not surprising that the more complex our audio system gets, the more potential there is to experience analogue noise as an issue. Sure, we can have digital anomalies ("digital noise" would be meaningless in this context) that cause errors in the transmission through poor cables as I have previously demonstrated, and I guess one could have so severe analogue noise as to cause digital errors (I suspect very rare and likely due to poor equipment, device failure, or extreme conditions). But those anomalies have characteristic "digital" traits as I previously discussed. What we normally think of as noise is the analogue stuff... Characteristic humming at a certain (often mains resonant 50/60Hz) frequency, constant random "white" noise like a poorly tuned radio, or episodic blips and bursts associated with intermittent electrical circuit activity (EMI from computer activity, hard drive access, intentional transmission from cell phone placed too close to equipment, etc.).

If we look at the "big picture" of how noise contaminates audio systems, we can see two major mechanisms:

1. Noise from without: RF/EMI radiation inducted noise because you put an inadequately shielded device or cable close to a source of radiation like a high power computer. Just take an old AM radio and put it close to one of these radiating devices to "hear" the noise. In this case, we have to either get better shielding (no need for fancy cables or expensive ones necessarily), reduce the chance of a cable from acting like an antenna in receiving the radiation (eg. ferrite beads), and/or move sensitive devices like your DAC or pre-amp away from the source of radiation. There are standards for allowable RF radiation from consumer devices so generally this isn't a huge problem except in confined spaces. The inverse square law; placing devices away from the radiating source is you friend. (My father used to run a 1kW Ham radio transmitter in the basement in my high school years with a large antenna in the backyard - now THAT was how I learned the importance of shielding!)

2. Noise from within: Noise conducted within the electrical circuit / cable originating from the equipment itself. High quality audio demands low noise floor so a good piece of audio equipment should not be a major source of noise itself (this is of course why everyone who does measurements always include evaluation of the noise floor). These days, the device that is most likely to add electrical noise to the system is of course our computer in the sound room (hopefully your computer isn't adding much acoustic noise with loud fans). In modern systems with a DAC, conduction through the USB cable is therefore commonly suspect. Instead of just transmitting the electrical "pulses" down a digital cable, the conductor will also carry with it the unintended electrical signal (noise). If it does not get filtered out, noise becomes amplified and transduced in our speakers/headphones where we can hear the unintended distortion. It is this form of noise which can be extremely difficult to deal with since shielding and fancy metallurgical properties will likely not make any difference irregardless of expense. In other words, noisy electrical currents do not care whether it's travelling down copper, silver, gold, or unobtanium once it's in the conduction path. For these situations, the ideal is galvanic isolation which "breaks" the electrical contact but allows only the intended signals to cross - this is more difficult and costly to solve. Although I'm focusing on USB cables here, there are of course many potential sources of conducted noise such as pollution through the power system (eg. washing machine, fridge, light dimmer switches, etc.) and any electrical interface can be affected in varying degrees (coaxial S/PDIF, HDMI, Thunderbolt, DVI, DisplayPort, SATA, ethernet, etc...)

II. The Situation...

Now I've got a little situation here which I think can provide a nice "case study" of what could happen, and how we can remedy the issues.

Here's a picture of my setup in the soundroom:

As you can see, I have a number of pieces to this system obviously interconnected with all the wires in the back. The Paradigm Signature S8 speakers are powered by the two Emotiva XPA-1L monoblock amps sitting on the floor with my Technics SL-1200M3D turntable in the center. Signals going to the monoblocks are from the center Emotiva XSP-1 preamp (turned off with the amber LED visible mid-center rack).

I have a center channel on the rack (Paradigm Signature C3) so this is a surround system (5.1) with the rear channels behind out of view and the subwoofer (Paradigm Signature SUB 1) on the left beside the left S8. Surround processing duties are done by the Onkyo TX-NR1009 receiver situated on the bottom rack (between the turntable and Emotiva XSP-1) connected to my computer through HDMI.

Stereo audio is quite straightforward, I have the TEAC UD-501 DAC (top-left rack) and Squeezebox Transporter (mid-right rack) sending signals to the XSP-1 preamp. The Transporter is just a streaming device so it gets data from the wired ethernet network (which as I have shown is generally immune from issues). The TEAC UD-501 however is connected by USB to the computer to the far left of the image (with the white Logitech keyboard on top beside a GIK Acoustics sound panel at the first reflection point).

I use generic (various Mogami and Monoprice) balanced XLR interconnects throughout the system for both the TEAC and Transporter, as well as the preamp to the monoblocks. The noise floor in stereo mode is measurably very low and I really could not wish for any better! The only times I bother with single-ended interconnects in this system is with the Technics turntable to the XSP-1 pre-amp phono input (which sounds fantastic) and when I connect the Onkyo to the Emotiva XSP-1 preamp when I listen to surround sound through the "Home Theater Bypass" input (which as you will see was problematic) .

As much as I love the Emotiva XSP-1 pre-amplifier, there was one issue I ran into from a sound quality perspective early on. It was exquisitely sensitive to noise in the "Home Theater Bypass" analogue inputs. This is significant only when I enter surround sound mode where the output from the Onkyo is sent to the pre-amp for the subwoofer and two front channels (unbalanced signal). The signal would be polluted by both a hum as well as computer-associated EMI noise. So... How does one remove this nasty noise?

III. Ground Loop Noise (Hum)

First, let's talk about audible low frequency hum. Most of the time, this is due to ground loops. Here's a nice summary from Associated Power Technologies of what happens. Basically, when a number of electrical components are interconnected, the shielding ties the ground potentials of the equipment together. There would not be an issue if the world were perfect and every single outlet potential was exactly the same. Unfortunately, it isn't perfect and variations in grounding point potentials will lead to small currents injecting noise into the system. Typically, this ground loop "hum" will either be 50/60Hz correlating with the mains AC frequency of your local standard or a resonant multiple (eg. 100/120, 150/180, 200/240Hz, etc.).

In my system, with the highly sensitive "Home Theater Bypass" analogue input, here's what it sounds like:


After making the video, I realized the little camera microphone is having a hard time picking up that low hum (maybe even filtering it out?) - trust me, although faint, it was audible in my room... In fact, I can record it and analyze the spectrum to see this:

There it is, the 60Hz ground loop with resonance up at 120Hz and 180Hz. Like I said, it's faint but I'm a perfectionist and I could hear it in late night listening sessions when the world is asleep :-).

Because the ground loop is caused by differing ground potentials, the easiest ways to deal with this problem is to connect all the devices to the same ground tap. This could be the same power outlet or in this case, I'm connecting them all to the same Belkin PureAV PF60 power conditioner I have been using in the system for many years. Thankfully, this fixed the issue for me as per this second video:


As you can see, I also show another "trick of the trade" if needed in the video... The "cheater plug". Basically, an inexpensive <$5.00 adapter plug that disconnects the ground pin hence removing potential for ground loops through that pin (and also I may add removing electrical noise from the computer/power supply through the ground connector). As I said in the video, be aware of potential safety issues. Also, it may or may not work depending on your computer power supply. Consider using a Ground Fault Circuit Interrupter (GFCI) like this one if you intend to do this longer term. As you can see, they're not too expensive (~$20). An even more permanent and esthetically pleasing method would be just to replace the wall socket with something like this. Isolation transformers would be another option but these tend to be more expensive. Another potential device would be the Hum-X - I've never used one but have heard good things.

With the ground loop inaudible, the spectrum now looks like this:

Beautiful humless noise floor :-)!

IV. USB Cable Conducting Electronic Circuit Noise

In a way, what I showed above is a bit artificial... The truth is, in order to just demonstrate the hum problem to show you guys that issue, you may have suspected that in the video above, I had already isolated out what is actually even more problematic - electrical noise from the computer circuitry itself, transmitted in the wiring causing distortion where there is susceptibility such as the analogue "Home Theater Bypass" input of the XSP-1. In the video below, I plugged in a typical shielded USB cable to my TEAC DAC directly to show you what the interference sounds like:


Nasty eh? As you can hear, the pre-amp analogue input is picking up all kinds of computer noise and this is getting amplified and sent to the speakers. You can hear JRiver starting up for example; likely a composite of noises from SSD data transfer and program execution. There's also a distracting high pitched whine which actually the camera picked up very well (it sounds louder in the video than hearing it live in the room). This is the infamous 8kHz "packet noise" originating from the high-speed USB "microframe" rate (1kHz for "full"/slow speed, see here under "Frames and Microframes"). And yes, it can be measured:

As you can see from the data to the left, where I put the cursor (8kHz), there is a -92dB peak measured by my E-MU 0404USB. We'll look at this again a little later.

What to do about this? USB noise isolation of course!

To be honest, I have no idea if specific USB audiophile products work. For example, here's a "review" of products from Schiit, iFi, and UltraFi, without any objective context (ie. measurements of a situation in which the device worked). From reading the article I have no idea what has improved sonically other than rather generic and subjective opinions, so how is the consumer supposed to know what to buy? Since I live in Canada and haven't seen any dealers with these units to borrow and test, I really do not want the hassle of ordering and returning if it doesn't actually work for me.

So, I figured, let's just do this logically myself. We basically need to isolate noise from two places: 1.) the serial data pins of the USB cable (D+ and D-), as well as 2.) minimizing noise from the power pins (+ & -).

For the data pins, the best way I can think of is to use an optical technique. This is similar to using a TosLink cable instead of coaxial for S/PDIF back in the "old days" for galvanic isolation. And recently, Corning has come out with this interesting USB 3 Optical Cable (~$100):

As you can see, it's quite long at 10m (33') and meant to be used as a USB extender. However, it is capable of USB 3 (5Gbps!) speeds and so can be repurposed in the future for other duties if I don't need it for my sound system. Also, since it's capable of very high speed, there should be no issue with transmitting DSD128, DoP, and 24/384 PCM to the hi-res USB DAC. Remember that this can be an issue with some USB isolation devices like the Firestone GreenKey which goes up to 24/96 only.

It's important to realize that the optical USB cable does not provide 5V USB power (and thus noise on the voltage pins will not be transmitted) and so it will not work directly with devices that need it to operate (for example USB stick DACs like the AudioQuest Dragonfly or AudioEngine D3). Because my TEAC UD-501 required the USB 5V to be present for the interface, the straightforward way to do this is therefore using a powered USB hub to provide the 5V. I decided to try a spare USB 3 hub I had along with some cables to connect to the DAC:

Nothing special, just one of these generic USB 3 hubs from a local store. I suspect that USB 3 hubs may be a bit better as electrical tolerances probably are superior to standard USB 2 devices in order to accommodate the higher transfer speed.

So... Did the combination of removing ground loop hum and using the optical USB cable (plus powered hub) work? Yes:


Here's how the FFT spectrum looks now (specifically focused at the 8kHz spike):

Compared to the spectrum above, although the technique did not completely remove the 8kHz "packet noise", it is now down to about -120dB, plus the overall noise floor is down another 5-10dB. Basically, there has been a >20dB suppression of the packet noise which has now rendered it inaudible at normal listening levels. Also, no more audible "processing noise" when I open or close programs like JRiver, or do other tasks on the computer.

Remember, the issues I'm showing in this post were always just when the XSP-1 preamp was in the analogue "Home Theater Bypass" surround mode which was susceptible to noise. Normally, I never have a hum or hear electrical noise from the TEAC DAC output directly or through playback in stereo mode from the XSP-1.

For completeness, here are some measurements of the TEAC UD-501 using RightMark Audio Analyzer 6.4.1 PRO comparing the 33' Corning USB 3 optical cable with direct 10' USB 2 wire cable. As usual I'm measuring off my E-MU 0404USB, at "high resolution" 24/96:

No difference; and a few of the graphs if you care for the details (just click to enlarge):
Frequency Response
Noise Level
THD + N
Stereo Crosstalk
Here's the Dunn J-Test with the Corning optical USB 3 vs. standard USB 2 cable if you're worried about potential for jitter:


I remain unconcerned about jitter with modern asynchronous USB interfaces (not that I was ever really worried even in the S/PDIF days about audible distortion caused by jitter even though measurable).

V. Conclusion

I hope this little discussion and demonstration using my set-up helps as a practical way to understand noise in a high-fidelity audio system. As expected, suggestions here may or may not work in your situation but I suspect it will help in many cases if you're running into trouble with noise. I have already received E-mail from folks with the Emotiva XSP-1 who have experienced the same noise issue with the analogue "Home Theater Bypass" input.

I repeat. I have never run into these noise issues with the direct DAC output! It is only with the analogue bypass mode on this pre-amp that I hear the noise. Here then is a good example of how the "system" as a whole can be susceptible to analogue noise... The digital transmission itself is fine and in fact the DAC output does not show the 8kHz contaminant nor ground loop hum. And if I did not set up a multichannel system with the XSP-1 preamp, I would never have realized there could be a problem.

A few conclusions then:
1. If you hear a hum; usually low frequency 50/60Hz (+ resonant multiples), think ground loops resulting from the AC power configuration. First thing to do is to reconfigure the power cables and see if you can connect the devices as close to each other as possible. Using a common power bar/power conditioning device worked for me. Even if you don't use a "cheater plug", it's worth having just to temporarily diagnose a problem by "lifting" the ground pin off various devices to have an idea of the "culprit" device. They're cheap. (Another link for those who want to read more about ground loops.)

2. Yes folks, computers are noisy! Indeed, the analogue noise can be transmitted down cables like the USB cable and cause audible interference. I demonstrated how the Corning Optical USB cable can be used to minimize the noise originating from the computer. It's logical. It can be measured. No magic.

3. Despite the use of the optical cable, the 8kHz high-speed USB "microframe packet noise" is still present but much reduced in my "case study". Not audible anymore, so that's good enough. It is possible that this residual signal is originating from the generic USB hub (PHYsical transceiver chipset) I'm using to provide the 5V power. It is possible that a device like the Uptone Audio Regen could result in a better, lower noise outcome. Another possible solution could be a high quality USB card like the oft-mentioned but expensive SOtM product. These solutions need to be objectively tested however and I suggest evaluation using a set-up like what I have here where there really is a noise problem rather than folks just plugging them into a system where there might not have been an audible issue to begin with!

4. Objective measurements of analogue output from my DAC using the optical USB cable shows no difference compared to a shielded 10' USB 2 wire cable. Likewise, no difference in the J-Test FFT to suggest audible jitter anomaly at 16-bit/44kHz or 24-bit/48kHz. Rest easy if you have one of these 10m (33') cables to connect your audiophile DAC. I have been using the Corning optical cable for almost 2 months now and it has worked flawlessly with DSD64/128, and PCM all the way to 24/384 with the TEAC DAC. Subjectively it sounds no different from any other functioning USB cable I have tried.

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For those who may have followed this blog for awhile, you may recognize that this is not the first time I wrote about a device that reduced noise with the "Home Theater Bypass" mode of the XSP-1 preamp. More than a year ago, I bought an inexpensive USB to Ethernet extension device that actually did the trick. I did not measure the 8kHz level with that but I don't believe it attenuated the noise as well as the optical cable shown in this post. It's still a fine solution for my problem until this optical USB 3 cable caught my eye!

If you look at the measurements in that previous post, you will see that I could not find a difference in the DAC analogue output there either between a direct USB feed compared with going through many feet of ethernet cable. Again, just more evidence that a good DAC is likely not going to sound any different between USB cables even when the data is processed through transceivers to convert to ethernet or optical fibres as in today's post. Subjectively I can't say with any certainty that I have heard differences.

I have been planning to write this piece for about a month now so I think it's interesting that this post just came out the other day. There are some interesting links in there, but I'm ultimately unclear of the practical intent other than to remind us that noise can cause problems and can be transmitted through a digital cable. Sure, it's possible. Let us consider this concluding paragraph for a moment:
"One approach is to just shrug this information off based on the belief that EMI and RF noise levels in our home and in our network-connected hi-fi are just not worth worrying about. There's no experience like no experience. Another approach is to try different solutions including different digital cables and see if they make a difference. There's no experience like experience."
Seriously, are those the only approaches? Why so black or white!? May I suggest a third approach, and IMO best approach... Become "more objective" in the analysis. "Experience" is nice but fully made valuable when paired with understanding of WHY something works (or not) especially as regards to scientifically engineered devices. To not explore why something is better than another (eg. Hmmm, it seems my system could be noisy. I tried and I think this fancy cable sounds awesome compared to that fancy one... Don't really know why... Just try it and experience for yourself!) is akin to superficially "shrugging off" an opportunity to learn; to understanding oneself and the technology behind higher fidelity. Nobody needs to enter this endeavour essentially blind using just trial-and-error! Why not try a bit of objectivism and confirm what is "heard"? Yes, develop experience but through understanding the system and showing others in what way a device (like the optical USB cable or if one believes in a $166/m USB cable) provides value. Demonstrate the actual problem and potential magnitude of the problem so the reader can evaluate with some confidence that they should give something a try because of a demonstrable deficiency that was improved rather than vague testimony. That IMO is what a review should be about, especially for passive devices like cables which as we know can be quite a financial "investment"! (I hear the term "accountability journalism" being tossed about; not sure what to make of this for the majority of audiophile "reporting" these days.)

One final and I hope obvious comment on this noise "issue". Don't worry unless you hear a problem! I've read comments over the years from some and you'd think unless someone invested in thousands of dollars of power conditioning, dedicated electrical lines, expensive cables, esoteric devices (cable lifters?) and removed every switching power supply within sight of the system, one would never achieve a system free from noisy distractions! Nonsense. I bet that the vast majority of setups employing reasonable equipment, decent cables, connected together in a logical fashion are just great as is. It's the systems with numerous components hooked up (like mine with both a pre-amp and surround processor switching between modes of operation with some vulnerability to noise), or maybe highly sensitive systems like very low voltage phono cables, step-up transformers, and phono-preamps that are most susceptible.

Okay. I hope this post has been useful. Let me know of corrections you would suggest and other interesting links. I'm sure there are many things missed and other ways to control noise I have not mentioned; remember, it is a "case study" so what I discussed here works for me and I bet the techniques (like using the optical USB 3 cable) will work for many out there also.

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I recently watched an interesting documentary from BBC - "When Albums Ruled The World" (2013). Lovely archive footage and historical review:


The sun's out and the Springtime temperatures are gorgeous on the West Coast... Time to head off...

Enjoy the music and please don't forget the ongoing Digital Filters Blind Test! Get me your results and tell your high-resolution audiophile friends to try! Come, experience...

33 comments:

  1. If I understand the way the Corning works correctly:
    - It has power lines but they are only used to power the optocoupler hence there is no galvanic connection between the PC and the DAC over the power lines
    - Likewise as it is optical, no galvanic connection over the data lines

    In this experimental setup you replace the noise generated by the PC by the noise generated by the hub. A different hub might yield different results.

    I wonder if you can get rid of the packet noise completely by not using a hub but using a PSU like this one: http://www.aqvox.de/usb-power_en.html or any other source of clean DC.

    An alternative would be a DAC that doesn’t require external USB power.

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    Replies
    1. Thanks for the link regarding the AQVOX Vincent!

      Yes, indeed the reasoning makes complete sense and that's how I believe the Corning works as well.

      Hmmm, for some reason the TEAC UD-501 was listed as "not compatible" with the AQVOX. I'll look around.

      Does anyone know if there's a simple USB (B) adaptor that has a power plug on one end where I can just plug in whatever power supply I have? That would be cheap and easy! I guess I can just make one with a few parts just to try and see if it works... I also have some of these 5V USB batteries usually meant for phones and remote charging that should be really clean as power source.

      Delete
    2. DIY solid core audio USB cable with linear power injection http://grizzlyaudio.blogspot.ro/2015/08/diy-solid-core-audio-usb-cable-with.html

      But why would you need to inject power if on the bottom of http://www.aqvox.de/usb-power_en.html for TEAC-UD501 there's written:
      << Inside the above devices, the USB-chips are powered from the DAC´s internal powersupply. The 5V from the computer are not connected to the DAC, and as they are not connected, no "evil-computer-power" can affect or alter the USB-datalines or the DACs electronics.>>?

      Delete
  2. They call it "incompatible" because it is self powered hence supplying clean DC won't make sense according to Aqvox.
    I wonder is the USB receiver of the UD-501 really self powered?
    If it is, might it be the Corning doesn't work because the PC expects a current to detect an external device?
    Have you tried plugging the Corning straight into the DAC?


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    1. Yup. I have tried it straight. DAC not detected.

      Delete
  3. Great post!!

    I'm in the process of building a good HTPC for movies and music (maybe even multi-ch DSD), and i'm dealing with some noise issues, but not with USB. My problem is HDMI. It's some annoying hiss.
    I'm using my AV Receiver to do the DSD conversion through HDMI and i intend to use it for multi-ch decoding. I'll see if the receiver can do a good work. If not, i think i'll have to go to some USB multi-ch audio DAC.

    But this post was incredibly helpful for me! No doubt there are many ways to workaround our noisy problems without going bankrupt!

    Best regards!

    ReplyDelete
    Replies
    1. Hey VK, let me know how this goes with the HDMI system! Thankfully my HDMI receiver seems OK in terms of noise rejection from the computer...

      There's a paucity of "audiophile" focus on HDMI. Would also be very curious about multichannel USB; are you thinking an exaSound DAC?

      Delete
    2. Good to know that your receiver is ok with noise rejection. I dont know yet, but i think that my problem isn't my receiver. I will do some more tests and try to isolate the source of noise.

      And yeah, HDMI seems to be totally forgotten by audiophile community. Sadly, royalties and constant change in the standard seems to contribute to keep HDMI out of stage for Hi-Fi market.

      About the multi-ch via USB, i really didn't think in any specific gear. exaSound e28 MkII seems to be a fine jewel, but it costs like a jewel to me (the dollar is strong in economic market, and import fees are way TOO much high in Brazil).
      To be honest i haven't bought the center and surround speakers yet. I don't know if i go to multi-ch setup or if i go to some better front speakers. Dilemma!! But if i go to multi-ch setup, and decide to use USB, i will have to look for some more budget friendly multi-ch DAC.

      Best regards!

      Delete
    3. Yeah the strong US$ at the moment has been tough on international buyers (including myself here in Canada).

      Dilemma indeed :-). A shame that HDMI hasn't gotten more hi-fi attention but like you say, many factors going against it including the royalties. I must say that I very much enjoy the multi-channel presentation for music (not always of course), but the number of titles I have that's MCh is low compared to stereo so if there's significant room to move up in terms of stereo speaker quality, I'd probably spring for better stereo speakers (and a nice sub!).

      Of course... If you watch many movies and want TrueHD and DTS-MA... There's more incentive for the surround package!

      Delete
  4. Isn't the USB noise a problem with the DAC not isolating itself? Does the TEAC not have galvanic isolation for its USB input?

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    1. Good point... I haven't check other DACs like my ASUS Essence One and see how that works out in comparison in terms of noise.

      I didn't think high-resolution USB DACs were typically galvanically isolated at the input... Most of the USB galvanic isolator devices seem to only allow (slow) "full" speeds like up to 12Mbps such as this:
      http://www.cesys.com/products/usb-isolator/

      or the Firestone Greenkey I mentioned above. Probably fine up to 24/96. I have not seen isolation devices capable of the full high-speed 480Mbps USB 2.0 specification.

      As an aside, note that Gigabit Ethernet is galvanically isolated and can run faster than USB 2.0. BUT it does so with 4 wire pairs rather than the single data pair with USB. I suspect the USB-ethernet adaptor I tested before (and linked to above) parallelizes the USB signal (and each wire pair running slower can be galvanically isolated by the usual ethernet components) and of course the optical cable is capable of transmitting at the very high speeds up to USB 3.0.

      If anyone finds a galvanic isolater that's relatively inexpensive and can handle 480Mbps USB 2.0 speeds - let me know!

      Does the "Uptone Audio Regen" do this in a way? Anyone with one of these to comment on?

      Delete
    2. I did read somewhere that galvanic isolation was limited to USB 1.1 and was not supported for USB 2.0 and later. I could not find any explanation for this though. I would be very interested in the answer. I use the DAC inside my Classe CP-800 (v1) which is indeed limited to 24/96. The v2 board they came out with goes to 24/192 and trades off galvanic isolation.

      Personally, I prefer the isolation as I really can't see/hear any benefit beyond 24/96.

      Delete
  5. Looked into the Corning fiber USB cable when it was first announced a couple of years ago thinking that it would provide the galvanic isolation of the DAC from my PC-based music server. After numerous email exchanges with Corning, their Tech group finally advised that it DID NOT provide isolation since there was a very fine power wire in the cable.
    Instead I opted for the Adnaco Fiber/USB device ; available from Amazon at the time. Not only does it provide galvanic isolation but also avoids noise transmission of these connections which seems to be getting more and more press recently.
    The only change I made was to replace the OEM SMPS wallwart with a Linear Regulated Power Supply.
    Have been happy with this connectivity and have not looked back.
    FRANK

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    1. Cool Frank! Looks like the price is pretty steep on the Adnaco? I don't specifically see the USB set on Amazon at the moment.

      As I showed, the Corning indeed made a difference although with some limitations... Because of that small power line, it's likely not providing FULL galvanic isolation like a pure optical cable like the Adnaco but not bad from what I can tell and so long as it's inaudible (especially that 8kHz tone), I'm happy given that it's not expensive!

      Delete
    2. The Adnaco is very well developed hardware. Also allows you to do a long run to your HiFi. It allows me to run my Vega DAC in EXACT clock mode, which is very demanding on source hardware.

      Delete
  6. Hello Archimago

    Thanks for a great article….I am thinking of ordering a Corning myself to use in my system which includes a TEAC UD-501. I have designed and built a dedicated 5V linear USB PSU along with a Silver USB Cable which improves sound quality significantly.

    I can confirm that the UD-501 is not self-powered. Vincent Kars is correct in his thinking that the PC expects a current to detect an external device. My original design was developed using a Windows PC and a LED was soldered across the 5V pin and the Ground pin of the USB A plug, enabled the cable to function correctly. Testing the cable/PSU on a Mac resulted in no sound! The LED trick would not work on the Mac; the answer was to remove the LED and solder a ground wire with resistor in line between the USB A and USB B plug, with this set up all was well both on Windows and Mac PCs.

    From your positive comments I shall go ahead and order a Corning this afternoon. My thoughts about improving the performance of the USB cable through galvanic isolation, thus reducing electrical noise levels are confirmed through your excellent graphs and description.

    While I await the arrival of the Corning, I shall make a USB A to USB B (with 5V and Ground wire) convertor to enable the use of the dedicated Linear Power Supply.

    I will do a follow up post in a few days’ time to let you know my findings.

    Best regards

    Chris

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    Replies
    1. Thanks Chris!

      Awesome! I was going to do the same thing with a little DIY converter for external power. See if I can get away from that USB hub...

      Let me know how it goes.

      Delete
    2. Guess I missed it on the first pass but, rereading, noted that the Corning cable is USB3.0.
      My Mytek DAC can take either a USB1.0 or USB2.0 input. I thought this was typically the case.
      Did not think USB3.0 plug was backwards compatible with a USB1.0/2.0 jack?!

      ARCHIMAGO: Confirm that Adnaco not (currently) on Amazon.
      This is device that I installed: http://www.adnaco.com/products/s3a/

      CHRIS C: Is the 5V linear power supply regulated? What is the output Amps? I need 1.5-2.0 amps.
      Desktop LRPS's are rare as hens teeth so would be interested in the design for your DIY supply. Link or home grown?

      Thanks.
      FRANK

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    3. Frank:
      USB3 connector on the Corning that I have is just a female USB A connector. Essentially this makes it an extender cable so whatever can plug into your computer will plug into this whether USB 1/2/3 capable.

      I've not run into any compatibility issues at all over the years between USB 2 plugged into USB 3 connector. In fact, no issue plugging this into a computer USB 2 and it'll act just like USB2.

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  7. Hi Archimago,

    Many thanks for another comprehensive dig into another fascinating audio related subject. Although interested, I'm firmly in the "If you can't hear it, don't worry" camp. Noise isn't a problem for me.

    I have an observation on a noise matter of a different sort: I couldn't help but notice that you have your turntable a few feet away from a pretty hefty subwoofer and pair of large front speakers. From my turntable days I would have thought that layout was about as bad as you could get when considering acoustic feedback. How do you isolate your turntable? (As a further aside, have you chosen to isolate the power amps, but not the t/t?). I digress, I realise, but this article is about noise, albeit of a different sort.

    Thanks and regards,

    Bob

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    Replies
    1. Hi 24BB,
      I'm in the same camp :-). If it weren't for the audible noise, I would not have even thought about the optical USB cable.

      OK, the monoblocks are just sitting on slabs of solid birch (?) butcher blocks! The reason is they get hot especially in 35W Class A bias mode and I didn't want to cause any discoloration/warping, etc. for my hardwood floor! This raises them another inch or inch and a half and protects the floor. Isolation wasn't a prime consideration (nor did I hear a difference).

      In terms of scale, the front width is about 13'. I crossover the main speakers to the sub at 50Hz so the really pounding bass comes from the sub about 5' away. The TT is also recessed a little from the front baffle of the speakers and protected somewhat from the 2 monoblocks + wooden bases. Sure, I could look at a little TT base for better isolation and this should sound better (also reduce a little back strain from switching vinyl!). But the feet on the Technics appear good enough that I haven't had any issues with major problems like LPs skipping even with bass-heavy dance music. On the cheap, maybe I can get another one of those butcher blocks and put some vibration-absorbing feet under them!

      These days as I've been experimenting with impulse responses and digital room corrections, I've realized just how impressive the technology can sound! Even though I still love collecting vinyl and listening, I'm down to maybe 24% vinyl + 75% digital listening in the last couple months so the TT isn't grabbing a lot of priority :-).

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    2. Having spent several days trying all combinations of set up for the adaptor, I have come to the conclusion that what looked relatively straight forward to solve is in fact a “very hard nut to crack”!!

      Many computers will not allow the data signal to pass until a power draw is active and measurable. Using a resistor and LED to trick the computer into thinking it is powering the usb device did not work no matter what way it was set up.

      From my time experimenting with the Corning cable and the adaptor, I have come to the conclusion that even if I could get the cable and adaptor to work together there will always be an electrical link between them hence not galvanic isolation.

      With the existing cable there is no electrical connection between the units just the data + and data -, so at the USB A plug there is the LED/resistor and at the USB B plug the 5V linear power supply is connected to power the UD-501 USB chip. Improving the 5V supply to the DAC can result in considerable gains in sound quality…. Increase in detail and less grain and a lowering of the noise floor to very low levels. This set up will only work with a Windows PC unfortunately, a completely different arrangement would be required for a Mac PC.

      I liked the idea of fibre optic between USB’s but after my experimentation I have decided to revert to the powered USB cable I designed and abandon the Corning USB .

      If you would like further information about my USB PSU and cable www.thedigitalmusicbox.com

      Hello Frank, yes, the 5V linear power supply is indeed regulated, but the bad news is that it is only 1 amp output.

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    3. Thanks for the comments Chris... Wondering, for your set-up, were you able to get some measurements to show changes in the sound quality?

      I'm going to try making an adaptor to try out various USB power sources and see if I can improve my measurement anomalies like that 8kHz noise. Already it's not audible for me so I'm satisfied with the improvement (even though measurable), it would be great to drop it even further!

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    4. From your site, looks like you make some very nice products, Chris. Looking forward to checking out your software optimization guides once up and running.

      Since my Mytek Manhattan, and previously the192-DSD, DACs are self-powered and do not need to see 5V for handshake, I have defeated the power pin on the USB umbilical connecting the ADNACO Fiber/USB receiver module and the DAC. Actually have the materials for a purpose built USB cable which will not have a 5V conductor at all but have not got around to the build.

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    5. Thanks for the comments Archimago and Frank, you both should get on and build the adaptor/cable as they will definitely improve your sound quality and lower the noise floor of your systems.

      I am away for a week from today, but on my return if you need any advice on the builds I will be more than happy to help, I will also post some measurements for my system.

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  8. This comment has been removed by the author.

    ReplyDelete
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  11. Hi Archimago
    Your question
    Does anyone know if there's a simple USB (B) adaptor that has a power plug on one end where I can just plug in whatever power supply I have? That would be cheap and easy! I guess I can just make one with a few parts just to try and see if it works... I also have some of these 5V USB batteries usually meant for phones and remote charging that should be really clean as power source.

    The answer not precise but coming near is this solution, see http://www.aqvox.de/usb-power_en.html

    Johan Kraus

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  12. Hi Archimago,

    A user of our Vbus2 isolator has pubished an interesting post on the Computer Audiophile forum regarding the Corning USB 3 Optical Cable & the Sbooster Vbus2 isolator. According to his post, the sound quality improvement is impressive. The post can be found here;

    http://www.computeraudiophile.com/f27-uptone-audio-sponsored/uptone-audio-regen-22803/index143.html#post548857

    Are you interested to make some measurements of this setting?

    If yes, please contact me on info@sbooster.com

    Regards,

    Wiebren Draaijer

    ReplyDelete
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  15. I'm a bit late to the party, but still would like to clarify and confirm some things.

    - The Corning cable does not provide galvanic isolation. I am a bit amused that all these complicated and time consuming measurements made you forget somnething simple like grabbing an Ohm meter and checking the - power pin on both ends of the cable - they are connected.

    - The Corning cable does provide 5V voltage on the other end. This is necessary to wake up many USB devices. But the available current is limited (below 100 mA). I can only speculate that the Teac's USB port needs too much current so it didn't work for you. You could easily measure this with a cheap USB voltage/current dongle.

    - The only device currently providing full galvanic isolation at full USB 2 speed is the Intona isolator (wasn't available at the time this blog was written). And it works perfectly.

    Hope this helps!

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