any words of wisdom for usb noise problems?

i thought usb connections would be trouble-free after placing waveterminal u24 between my desktop pc and the dac in my panasonic reciever (office system). itunes runs dead quiet there. i am trying to implement a pc feed into my levinson preamp in main system. when the usb cable makes contact between my laptop pc and the u24 running into the preamp i get substantial noise, which is substantially worse when a usb hard drive is also attached.i googled "usb noise" and saw references to some midi users' and photo printer issues and some filter products (argh!- hope to avoid this step). also mention of computer screens as possible culprits any suggestions or similar experiences?
Yours is not the only case of this that has come up. Even using the Belkin Gold USB, if I touched the cable on the PC side, I could hear it in the system - proving to me at least that the two were connected. Since the Waveterminal takes its power from the USB...

I have been very pleased with the Opticis USB cable. It is a powered fibre cable. Technically it achieves total isolation between the computer andthe audio system. Plus of course it is immune to RFI/EMI.

Price is very reasonable in the context of Levinson level gear.

The only screen problems I am aware of are the traditional shielding problems which focus on the interaction between the speaker and the displays.

Also worth doing a search on Asylums PC Forum under Opticis for some other user perspectives and experiences.
My PC is connected to a Wavelength Cosecant USB DAC by 60 feet of optical USB cable. The DAC feeds a Levinson 32 preamp. The optical USB cable is outstanding as I am unable to hear any noise. The Opticis is highly recommended. I also run the Opticis with a battery power supply (lithium). Additionl improvement is heard with the battery supply.
thanks for the lead. i will investigate. with regard to ckrody's comment that the u24 gets its power from the usb, is noise less of an issue with self-powered usb dacs, and do many other usb dacs have the sample rate conversion ability to operate without the u24?

If you want to experience fabulous digital playback, consider the Wavelength Cosecant. I am able to select and control my musical selections with NetRemote-J. River Media software with a pocket PC using a Wireless LAN. A dedicated power supply would be superior for a USB DAC.

Yep -saving up for the next great thing... Steve and Gordon both have some nice things to consider =)

For Wkraft - please forgive me if you know this....

The Waveterminal is just a device for converting USB to SPDIF/Toslink. Actually it has a DAC built in too, but I have never seen anyone comment about using one. It was developed and marketed to the semi-pro audio recording market

As a general point of info, USB devices come in two flavors - those that require a dedicated power supply (because they need more juice), and those that can draw their power from the USB cable. In fact the Opticis needs a power supply and what Steve has done is create a DC one instead of the AC wall wart. The U24 is an example of a device that does not need its own power source. But effectively that leaves it connected to the computer...

I would assume that any USB DAC (certainly all that I am aware of besides the Waveterminal) require a dedicated power source, though some (like the RedWine units) are battery powered since the DACs tend to operate at 5v.
to elaborate- the waveterminal running into the coax digital input of my panasonic sa-xr55 (i know many will turn up their noses at this class d based unit) results in dead quiet speaker and headphone output. this prompts me to wonder what in the receiver prevents the noise transmission. i see that most audiophiles are not using the u24 dac function, and i am thinking ahead- would implementing certain kinds of dac obviate the need to uncouple the u24 from the dac.
I have used the Waveterminal for almost two years now. It a a great device but I am sure one f its short comings is that it draws its power from the PC via the USB cable. I have spent a lot of time listening to it as a DAC and it is phenomenally good sounding given its price. I am awaiting one of Empirical Audio's new wirless USB offramps. You can find info at their site.
This is clearly a design fault of the U24. They should have put a circuit inside to clean the power via usb and/or add the possibility to connect the U24 to an dedicated external power supply.

I tried an external USB-hub with it's own external power supply. Unfortunately the U24 isn't recognized by the computer when connected via the hub but maybe this is just a matter of reinstalling the U24 drivers.

I am thinking now of modificating the U24 to make it work with an external power supply. The easiest way is probably to cut the USB cable in two and connect pins 1 and 4 of the part which leads to the U24 to an external power supply.
Not a design fault - more likely a design decision, and by modern standards by now an old design. The U24 was built as a semi-pro recording studio product, not as an audiophile product. Recording studios are filled with all sorts of devices using less then optimum electronics.

BTW the hub may not be able to power it.

Using the Opticis fiber optic USB may give you that last degree of quiet you are looking for.
There are two fundamental problems with the Waveterminal:

1) it uses the power from the USB cable
2) it does not have any isolation to break the ground from the computer to the audio system

These things are difficult to get around without modding the thing. The Opticis will help with (2), but not (1).

steve N.
Empirical Audio

Problem "1" pontentially solved utilizing a battery powered USB hub
For a $17 gamble I'm game to investigate a possible improvement to an already excellent device - love my U24!
My prevoius post may have been premature... here is an interesting product I stumbled upon as well. It's basically a 5V battery pack built in the middle of USB cable. I can't seem to find the power requirements for the U24 in the manual but this product looks like it may work with the Waveterminal. I may bite and report back with my results. The battery powered hub that I came across but may not be powerful enough.
I found the solution for the noise problem and it is amazingly simple and totally free, at least in my case, but I think also for a lot of other users of external soundcards in general.

The problem was not the quality of the power supply.
The digital noise was created by a ground loop between my laptop, the U24 and my audiomixer. All noises disappeared instantly by plugging the laptop's power adapter in an unearthed AC outlet. Bye bye ground loop, bye bye noise!

If you don't want to leave your laptop (or computer) without an earth connection, the other solution is to add a line level DI-box in your analog audio in/out lines.

Best regards,

Or, instead of a DI-box, an inexpensive ground loop isolator:-)
The problem is likely a solid connection between PC ground and audio system ground. This is an issue with many USB DACs. A lot of them do NOT offer galvanic isolation, hence, much of the noise from one system enters the other.

This is EXACTLY why I use s/pdif transformer isolation in my USB dacs and converters. You won't need to unplug your PC wall-wart.

As long as we are all advertising here, I'll pipe in too.

This is precisely why I use pulse transformers to galvanically isolate the PC from the Audio System.

Steve N.
Empirical Audio