if I unplug the usb cable, that annoying sound goes away, (when I run audio out into my DAW). But sometimes, I want to be able to have audio going from the op1 and at the same time be sending midi from it, hence I don’t want to unplug the sub/midi cord. Anybody know a workaround for this problem?
Turn off USB charging?
What’s on the other end of the USB cable? What’s on the other end of the audio cable? Some laptops and switching psu-s are electrically noisy, and USB, being the low-cost architecture that it is, makes no provision for such quiet. (Also, Intel CPUs 
) It may be difficult to address that in the end device, if the host is noisy, it eventually gets into the sound outputs. Check if unplugging the laptop from the mains has any effect too.
Welcome to the OP-1… This is a famous problem which has never been rectified since the birth of the OP-1. There have been threads on how to reduce the sound. Turning USB charging helps.
I am going from the op1 directly into an external sound card (presonus audio box), running man do into ableton live. I saw something somewhere about turning off usb charging but haven’t figured out how yet. So… Uh, yeah, how:)? Thanks for the feedback and assistance everyone.
Shift + COM and then T4 iirc
Shift + Com from memory.
Shift + COM, select OPT and then you turn the blue knob counter-clockwise until the green lightning bolt symbol changes into a red X.
Except that does not eliminate the noise.
I think TE should just “go for it” and advertise it as a feature. Maybe coordinate the announcement of this feature with a new line of “distressed” or dirty clothing?
Should move a few units at the new price point.
I think it’s in stock too!
This is a general problem with unbalanced audio connections (google "ground loop" if you're interested in a technical explanation), which unfortunately is especially noticeable with this setup since the OP-1 doesn't have its own power supply. It gets its power from the computer, but the returning currents pass through both USB and audio cable ground where it can cause audible noise.
http://www.monacor.co.uk/products/carfi-accessoriesmisc/vnr/212420
This is a general problem with unbalanced audio connections
this
For US people:
If you’re DIY inclined and have a few old dial up modems laying around they have isolation transformers you can re-purpose.
Awesome. Thank you!!!
This is a general problem with unbalanced audio connections (google “ground loop” if you’re interested in a technical explanation), which unfortunately is especially noticeable with this setup since the OP-1 doesn’t have its own power supply. It gets its power from the computer, but the returning currents pass through both USB and audio cable ground where it can cause audible noise.The best solution is to use an audio isolation transformer such as this one between OP-1 and computer:
I was trying to attach a not to this, saying, yes, jon got it right. I ordered the groud loop isolator from the Amazon link he posted and it arrived two days later, works perfectly. Thanks to the community and especially jon for the speedy solution to an annoying issue!
Anyone know how these compare? It has a suppressor, but no idea how it works.
I too, bought the the ground loop isolator linked by @krism, but I can't see myself lugging this little box around- for portable wise sake.
http://www.ebay.com/itm/380745043260?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
I wonder if clamping these things both on the USB and audio cables would help… I read they filter out high frequencies. Using my Apogee One I have a steady tone at 3KHz and a few quieter overtones, definitely not higher than the music’s range.
^ Ya I have a suppressor on a USB I randomly found, but never realized what it was. Is it the pressure from the clamping force that helps reduce the noise with these things? It’s interesting since no soldering is involved.
On a side note the Pac isolator that Krism linked works very well with a pair of my headphones. My ATH-M50s are incredibly noisy cans with the OP-1, EVEN with the OP-1’s volume cranked all the way down. Now, with the isolator, it’s greatly reduced and the same goes for my AKG-702s. To my ears the isolator sounds like a low pass filter, cleaning out the noise, but unfortunately flatting out the entire range as well. Maybe more drive will balance it out.
Interesting… I’ll have to make some tests myself - as soon as my OP-1 arrives today! 
Will report on that later.