m1 24-inch iMac, possible Ethernet/Thunderbolt/ground noise issue

[jonljacobi]

So I borrowed a 24-inch iMac over the weekend to kick the tires on for music use. The good news is it's really quick, I like the smaller display, it produces way less heat. All things being equal, I'd love to have one. But they weren't equal.

My biggest issue was that with the Ethernet connected to the power brick, I got a background modem-like digital whine through my Yamaha HS5's. Like you'll hear from some internal sound chips. RF.

I tried both my Clarett 4Pre Thunderbolt and the Apollo Twin X thunderbolt. Same deal with both. There was no noise from the internal speakers. I tried pulling grounds from everything, and all of this stuff is plugged into an isolation transformer.

Using Ethernet from a dock or adapter caused no noise. I didn't try a USB interface as I sold all of those.

My guess is that the Ethernet next to the power cable is creating RF that's traveling through the Thunderbolt bus.

Has anyone else had the same experience. And if you have an iMac with a USB interface, have you experienced RF noise?

[Weasel-Boy]

Just a shot in the dark. It may be something as simple as the CAT5 cable causing the issue. Not all CAT5 cables are constructed the same way regarding grounding/shielding.

https://www.cablesandkits.com/learning- ... lded-cable

I’m only suggesting your cable might be the issue when in use with the iMac power supply Ethernet jack.

[BertKoor]

Who needs cables. Doesn't it have wifi? Doesn't your home wifi do 5GHz and up to 300mbps? (at less than 4m range ofcourse)

[jonljacobi]

Cables are more reliable, and Ethernet is much faster. I run 2.5Gbps between most of my stuff and 10Gbps on the main trunk. Not subject to interference or router location or barriers in between. That's not really the point however.

I doubt it's the cable as it's not really in contact with the power supply or running across the power cord wire. Also, it's cat 7, I have them all over the place, and it doesn't occur with the same cable and other Ethernet connections. That said, I could

I'm guessing it's RF from the Ethernet traveling up the power cord and across the Thunderbolt power connection. I never got around to attaching a ground to the interface. There's more trouble-shooting I could do, but I no longer have the iMac.

[Schmidi]

I've experienced that noise situation when running USB to external gear that has a lot of LED lights: A few DJ controllers, and most notably, the Zoom ARQ 96.

Was it possible that anything else was plugged into it?

[S950]

I've experienced that noise situation when running USB to external gear that has a lot of LED lights: A few DJ controllers, and most notably, the Zoom ARQ 96.

Was it possible that anything else was plugged into it?

Have a similar situation that took me a while to pinpoint the source. I seem to get digital noise whenever I have a USB output of a synth (non-audio, midi/data only) connected to the PC. Plugging a usb device with LEDs into the PC adds more noise. For me it seemed to happen predominantly with synths that had 2 prong wall warts instead of an integrated power supply.

[jonljacobi]

I'm pretty familiar with ground noise and RF and have taken many steps to get rid of it in my setup. My apartment wiring sucks and some of it's not grounded, but all this stuff was behind an isolation transformer which has a real path to ground.

This seems very much to me that the noise is being introduced by the Ethernet via RF inside the power brick or cord which leaves no real solution other than not using it.

I have solved this on occasion by running a ground wire from the audio interface enclosure, but I didn't get around to it and now I'd have to drag all my stuff down to the office to test it.

Note that this was one of the loudest incidents of this type of noise I've heard.

[jonljacobi]

As to the question was nothing else plugged into it. Yes, there was other stuff, but disconnecting the Ethernet from the power brick immediately eliminated the noise. It's dawned on me that this is in the wrong forum. I'm just so used to posting here, I didn't think about it.

[BertKoor]

Sounds like you had a ground loop: multiple paths exist to ground which really is not grounded. You broke it by disconnecting ethernet. It's possible it were also broken by disconnecting usb. Or the computers mains power. Or whatever else contributed to the loop.