Hum through audio on Mac Mini

Core Machine (Operating system/System info/Roon build number)

MacOS 10.14.6/Roon 1.8 Build 756

Network Details (Including networking gear model/manufacturer and if on WiFi/Ethernet)
Not connected to network in this configuration

Recent Roon convert.For testing I was running Roon Core (latest version) on my iMac with an audioquest cobalt DAC connected to USB or the same DAC connected to my phone running the remote app and listening either on headphones or connected to my HiFi. All worked well.

This week i moved my roon core over to a 2014 Mac Mini. Same OS as my iMac. Now when I connect the AQ DAC i get a mains hum through the head phones. This reduces a lot if I touch the metal body of the mac. If I plug the head phones directly into the 3.5mm jack I also get this.

I am assuming it is because my mac mini is not grounded. Is this correct or do I have a duff power supply? If it is a grounding issue does anyone have any suggestions as to how fix? Would a ‘proper’ powered DAC solve the issue or make it worse?

The other oddity is that through the iMac the volume in Roon is fine - set to around 25 for headphone listening. Connected to the Mac mini beyond 3-4 it is unlistenable loud!

Audio Devices (Specify what device you’re using and its connection type - USB/HDMI/etc.)


Description Of Issue


I think you may have a couple of things going on. I also use an AQ Cobalt from time to time with my Macbook Pro. You didn’t mention the headphones that you are using. I’m using Campfire Audio Andromeda or Lyra II. Both are IEMs that don’t need much power. I’ve found that the volume slide on the Mac doesn’t need to be turned up much at all to get full scale. I’m wondering if your set up is amplifying a bit too much. You might try using DSP volume and setting Roon to a low volume setting so that the Mac volume is less sensitive. Maybe play around with Roon volume and the Mac volume.

With the Cobalt in Device Volume mode set in Roon, it would sometimes jump to max volume so I always use DSP volume for safety purposes.

When using the Cobalt connected to a raspi streamer I would have ground loops if I was also using my laptop for general use and the laptop was plugged into the wall using the plug with ground pin. I switched to using the charger without the ground pin.

And lastly, I also hear a bit of hum using the Cobalt with my iphone (using the camera dongle for USB to lightning). That hum goes away when playback starts. This might be happening with the Mac too. I don’t have that hum with the AQ Dragonfly Red so it’s likely the Cobalt.

Long post but the above has been my experience with the AQ Cobalt in my Mac/Roon/Raspi universe.

Hi Douglas, thanks for the quick reply.

Im using Audeze LCD-X - so sensitive and low impedance so that could be an issue. Except that none of this happens with the iMAC (with has a 3 pin power supply, mac mini has 2 pin). I will investigate to see if it goes when playing starts.

You’re probably on to something with the change from 3 pin to 2 pin. In my case the mix of 3 pin and 2 pin was the problem but only if I was physically touching the devices like working on my laptop while listening to headphones through the Cobalt connected to the raspi on a 2 pin power supply. 2 pin worked fine for me.Best of luck to you. If it is a grounding problem then those can be a challenge to deal with. Hopefully others will chime in with some tips.

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Something you can buy to try is this.

Use the USB grounding adapter in a USB port of your Mac Mini.

Do you then plug into a spare input on the pre amp to ground?

This end goes into wall plug. Use with your own country’s AC (IEC connector) power cable. Inside there is only the earth pin as you can see in the photo.

This end below connects to that adapter above (RCA) and goes into a spare USB port on your Mac Mini:

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Ah! That makes sense now! Cheers that look great.

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Let us know how you go!

Fingers crossed for you.

Will do. Cheers!

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I’ve done it DIY with parts like below (country specific grounding plug of course) but the iFi product looks nicer and has additional adapters that may come in useful in future setups you have, even if you don’t use them all right now…

Screen Shot 2021-02-19 at 11.59.15 pm

I’m not great at diy so I’ll stick the to ifi stuff. :slight_smile:

I hooked the Mac min/dac to the preamp and the hum disappeared. Grounded through the RCA I guess.

WHen I replace the dac I’ll maybe need to get the ifi kit.

Thanks again for all the help folks!

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