Hey guys, I really need some help figuring this out. It's driving me crazy. I have an audible buzzing (around 980 Hz) coming out of my powered monitors when USB is connected to my desktop computer. My setup is as follows:
DX3 Pro is in preamp mode connected with RCA cables (BlueJeans) to Kali LP-6 powered studio monitors. Power for the DX3 Pro (topping provided power cable) and both Kali monitors is plugged into a 3-outlet extension cord which is plugged directly into a wall outlet (US - 120v). The DX3 Pro is, of course, also plugged into my computer (topping provided USB cable). My computer is water cooled so it has a pump and 6x 120mm fans. It has a Z390 Aorus Master motherboard powered by an EVGA SuperNOVA 750 G3 PSU. I have a pair of HD 6XX which playback flawlessly even using USB to my computer. There is no buzzing when using headphone out.
If I switch to any other input and leave the USB connected, the buzzing continues. If I unplug USB from my computer, the buzzing goes away. I can use optical to my computer just fine, but that's not a great long-term solution for me as I have a different source I want to use via optical. Bluetooth is fine; no buzzing. I don't have any coax output devices (that I know of), so not sure if the buzzing is present on coax.
At this point, I've tried so many different things. What's interesting is that the DX3 Pro via USB to two other laptops has no buzzing. That makes it seem like something with my computer. When I plug my HD 6XX or AKG earbuds into my computer, there is no buzzing. Same thing when I use a super cheep USB DAC and any headphones/buds. I had a 3.5 mm to RCA cable laying around so I connected it from my laptop to the Kali monitor and there was no buzzing. I connected the same cable to my PC and it goes straight to crap. The buzzing is at least twice as bad as it is when going through the DX3 Pro. If my computer was the problem, wouldn't I hear the buzzing in any headphones or through the other crap DAC? So, then maybe power related?
My computer was plugged into an APC UPS, but I've bypassed it which did nothing. I started looking into a P50 LPS thinking that would "clean the power" but after reading a little, doesn't seem like it would do much at all (am I wrong?). I even started looking into a DX7 Pro so that I could use balanced XLRs to my Kali monitors which would get rid of any noise introduced on the cable between the DAC and the monitors. I am doubting that's where this buzzing is coming from though and don't want to spend $600 and still have the problem. It seems like there is interference from the computer somehow being sent over the USB cable to my DX3 Pro. Having an external USB DAC is supposed to isolate all types of interference that's going on inside the computer though, isn't it? Back in the day if you could hear your mouse movements through your headphones, the fix was to get an external USB DAC. Which... DX3 Pro.
That got me thinking so I did some more tests. I turned the volume on my Kali monitors all the way up so the buzzing was as pronounced as possible and I was able to hear my mouse movements and scrolling and moving windows around. I then grabbed Cinebench to see if maybe loading the CPU changed anything and it did. The frequency of the buzzing lowered to around 780 Hz and actually got a little quieter. I did a 3D Mark GPU benchmark and it went absolutely crazy. I had the output on the DX3 Pro set to BT (not paired with anything), Windows muted, and the DX3 Pro device disabled under device manager. Even with all that, it sounded like I should have been getting a deep tissue massage.
All that makes me think there's some type of interference or current that is originating inside my computer, hitching a ride on the USB cable to my DX3 Pro, and somehow jumping over to the RCA output even when Line Out isn't selected, then being faithfully reproduced by my Kali monitors. First, how is this even possible, and second, how can I fix it? My motherboard has a feature specifically for audio equipment that won't send the 5v power out the USB port. It will send the data, but relies on the external device to power itself. I've tried that with my DX3 Pro, but it seems to require the 5v in order to function, even though it has its own power source. I just stumbled across USB isolators, but haven't looked into them at all yet. Snake oil or viable solution? Again, it isn't affecting the headphone output at all. I can't hear even the faintest trace of this interference, or whatever it is, through my HD 6XX while USB is connected to my computer. I'm completely lost and would very much appreciate any suggestions.