Ground loop/USB noise

[nicari]

Hello everyone,
today I tried to connect my Crack (with Speedball) directly to the ObjectiveDAC output (which is USB powered), excluding the Objective2 Amp from the chain.
The setup is  PC --(USB cable)--> ODAC ---(RCA cables)---> Crack. In this situations it gets very noisy event at low volumes.
If I connect the ODAC to the laptop the noise goes away even if the laptop is powered only with the power adapter (battery pulled out).
I read something online about ground loop, but my noise is not a constant 50Hz buzz, it has higher frequencies components (I made a recording to let you hear, but I cannot post external links or upload audio files here) and gets worse when the CPU use is intense.
Do you have any (cheap) idea on how to solve?

[2wo]

I have found that the ODAC is sensitive to noise over the USB power. You need to break the chain, so to speak.
 If you have some kind of USB hub that would probably do it. In my early experiments. I split off the 5V and used a battery to supply power.
 It seems to vary from system to system. I had trouble with my PC but plugged into my Vortexbox (a dedicated Linux PC), or my laptop it works fine     

[kgoss]

You could try all available USB ports on your computer. One might be on a different USB bus and be quieter. It ask might not make any difference but it won't cost anything but some time to try.

[nicari]

I already tried to switch USB port. Didn't work. Even connecting it to the LCD monitor's hub.
I was thinking to try to isolate the Crack power with an isolation transformer or an EMI filter..do you think it will work or the problem is only in the USB line? Then maybe an optocoupler?

[2wo]

I think the noise is on the USB. You could test by disconnecting the power to the Crack while listening, you should get a few seconds of music as the power supply runs down but the noise will stop instantly if it is AC power related...John

[nicari]

Yes, the noise stop immediately if I unplug the power cord, while the music fades away. At this point it should be a ground loop problem.
Still don't know if an EMI filter would work

[adydula]

I use two odacs with multiple pcs.... Gateway. Lenovo, DIY, HP, Dell and attach via USB port with a ferrite bead USB cable, nothing fancy just a good grade Belkin from Amazon..has beads on both ends... mainly for RF interference if there is any or radiation coming out from the PC.

I have never experienced a noise issue of any kind.

The ODAC in rare cases with certain pc/usb electronics/chips etch have caused issues.... there is a Rev B that just came out that address's this.

You might want to try the pc in a different room, different power source.... and a different cable one with ferrite beads.

Also try on a friends pc etch if you already haven't....

Good Luck
Alex

[Paul Birkeland]

Yes, the noise stop immediately if I unplug the power cord, while the music fades away. At this point it should be a ground loop problem.
Still don't know if an EMI filter would work

This sounds a lot like dirty power over USB.  One way you can tell is to have the computer do something really arduous, which may change the nature of the noise as the processor ramps up to crunch numbers.

An optical connection or decoupling the 5V rail are both generally good solutions to this problem.

[mcandmar]

The ODAC is particularly susceptible to noise, i used to run mine though a USB isolator to cure the problem, but its not a guaranteed cure for everyone.  Laptops are generally a lot noisy then desktops due to the small power adapter, have you tried it with the laptop running off battery?

Also make sure the power adapter for the O2 is disconnected.

[nicari]

One way you can tell is to have the computer do something really arduous

[..] and gets worse when the CPU use is intense.

have you tried it with the laptop running off battery?

If I connect the ODAC to the laptop the noise goes away even if the laptop is powered only with the power adapter (battery pulled out).

decoupling the 5V rail are both generally good solutions to this problem.

How?

[nicari]

Ok, I solved replacing the ground wire  between the chassis ground screw and the ground terminal on the power entry module with a 21Ω resistor. It's a compromise between lifting ground (unsafe) and stay with the noise. Wikipedia suggested a 10Ω resistance, but the smallest I had was 21. It sould be small enough to keep the ground "connected" in case of short.
Now my Crack is dead silent event at full volume, better than how it was with Objective2 amp still in the chain.