I have a outboard dac which also doubles as a headphone amp. Build quality is very good with large toroidal psu plus a discrete output stage capable outputting up to 4.5v...   However the designer has informed me that the output impedance of the headphone out is 50ohm... This seems very high...

http://www.head-fi.org/t/560940/teac-ud-h01-usb-dac/90#post_8952791

I've not idea on mac support but it uses Tenor's TE8802 chip which is notoriously bad - the Asus c-media usb interface chip is far less problematic! I personally would say it's worth the difference... I returned the TEAC and kept the Xonar despite the £100 cost difference.

I had the TEAC very briefly.. Drivers were terrible so if you need usb support i'd look elsewhere personally (on Windows 7 at least). Sound wise it was OK but the Asus is a better built unit with superior support + the opamp upgrading option offers greater potential again.

If you don't measure using the soundcard inlut you are just measuring the output from rightmark, it will having nothing to compare against..?

It is easiest to hook it up to your computer via usb. Connect rca outputs using phono>3.5mm jack wire or headphone output using 6.3mm>3.5mm jack wire to your sound card's line input. Rightmark will then use these connections as a real time monitoring "loop"

Why not hook it up to your computer's line input and measure the r/l volumes using rightmark audio analyzer? I did the same test with mine due to channel imbalance Ive read about and the pot is balanced fine above 9-10 o clock.

It did cross my mind that it may of been related to Windows Update, but two of the computers rarely go online... Just one of things I guess, if I find the cause I'll be sure to post!

Yes Ive made sure Im in the latest version. Manually uninstalling the driver via device manager along with multiple reinstalls of the driver suites has finally cleared it up! Still weirded out by it though, how strange that its happened to 3 computers at once. Thanks all

New issues with W7 x64 machine... Applied same fix (manually updating driver to asus xonar STU) but now I get a new error code   Windows cannot verify the digital signature for the drivers required for this device. A recent hardware or software change might have installed a file that is signed...

Now I am getting somewhere! Deleting the device/restarting did not do anything, but I noticed something on-screen when plugging the usb cable in. In the systray, a balloon tip immediately recognised it as an ASUS ESSENCE XONAR ONE but a few seconds later the device changed to "USB Audio Device"...

I have tried that (+disabling and re-enabling the offending device). Also, I hooked up the keyboard & mouse via ps2 adapters and uninstalled every USB controller listed in device manager - no change after restart.   FWIW, I haven't been able to get it working again on my main Windows 7...

Both of these computers are not connected to the internet so the possbility of a virus hitting either (yet alone both) are next to 0.   Never seen anything like it really... The DAC is working 100% at the moment over usb, but as soon as switch ports.. Error code 10 (Device unable to start). So...

Made some progress but my findings are very strange indeed! On two of the computers Ive got it working via USB. BUT it only works on ONE particular usb port!! How strange is that?? Regardless of cable used and restarts etc this is 100% repeatable... On 3 of the 4 usb ports, I get error code...

It looks like my E1's USB input has developed a fault   "Error code 10 unable to start device"..   Any ideas guys? Luckily it's still functional over toslink/coax inputs.   More info here:   http://www.head-fi.org/t/696701/error-code-10-dac-no-longer-recognized-by-windows