Late 2012 Mini Power Supply Causing Audio Crackle?

Discussion in 'Mac mini' started by theoreticalgirl, Mar 21, 2013.

  1. theoreticalgirl macrumors newbie

    Mar 21, 2013
    I work for a small radio station that recently upgraded to a Late 2012 Mini to stream and archive our broadcast signal. (Technically, the machine sends a relay to our external Shoutcast hosting, people do not connect to it directly.) We don't use the machine for anything else. It remains locked away in a room with the equipment used to transmit our FM signal.

    Since switching over to the new machine, we've noticed that our stream develops a clicking sound after a while. (And by "a while," this can mean anything from "after a few hours" to "after a few days".) Similarly, the archived audio degrades in quality.

    After numerous things, we've narrowed it down to a possible power supply issue at the suggestion of a friend. (I know, how terribly unscientific!) He suggested that the crackling might not be audio related, but rather teeny power sparks causing interference with the audio.

    Since the 2012 mini uses a completely different power design than the previous models, has anyone encountered a similar problem? Would having Apple swap out the internal power supply even resolve this? Or is there something else that could be done?
  2. benwiggy macrumors 68020

    Jun 15, 2012
    If you suspect a hardware fault in brand new equipment, then go back to the shop you bought it from and get it fixed or replaced.

    I realise that it might be tricky to take the machine out of use now, though for mission critical stuff, you should always have redundancy.
  3. theoreticalgirl thread starter macrumors newbie

    Mar 21, 2013
    Yes, that is obviously our plan.

    What I'm more curious about is the problem itself for the purposes of research prior to bringing it in for repair. Is this something others have encountered?
  4. SoCalReviews, Mar 21, 2013
    Last edited: Mar 21, 2013

    SoCalReviews macrumors 6502

    Dec 31, 2012
    It could be USB 3.0 RF interference. There were problems with USB 3.0 on the late-2012 interfering with Bluetooth range for the Apple keyboard and trackpad or Magic Mouse. There was a fix to add shielding to the Bluetooth radio tx/rx inside the Mini but that wouldn't solve this problem. If you are using USB 3.0 with external drives or other devices make sure you are using very high quality shielded cabling.

    There is a possibility the clicking still could be from the power supply. You could try having that replaced but it is strange that more late-2012 Mac Mini users haven't reported similar problems before since a large number of them use the Mini for audio and video production and editing. You could try replacing the power supply or the Mini. If you can't solve it with replacement then I would lean more towards this being a problem of RF (radio frequency) noise from inside or outside the Mini. Unshielded lower grade USB 3.0 cable or possibly even lower grade Ethernet cable could cause a problem. RF interference noise from the outside environment can also be drawn into poorly shielded cabling like an antenna. Also check the power plug source that is powering the Mini and devices attached to it...speakers, etc..
  5. theoreticalgirl thread starter macrumors newbie

    Mar 21, 2013

    However, A/V production is not the same as streaming, which is why others might not have this problem?

    I'm also wondering if the FM broadcast equipment in the room contributes to any interference (or to what extent). With that said, we have hooked up other mac equipment to the stream without issue.
  6. SoCalReviews, Mar 21, 2013
    Last edited: Mar 21, 2013

    SoCalReviews macrumors 6502

    Dec 31, 2012
    Macs before 2012 used USB 2.0 which utilized lower frequencies and didn't have these reported USB RF noise problems. The late-2012 was the first Mac Mini to have USB 3.0 and there already have been reported problems with USB 3.0 RF interference being a problem on some of the new Minis. This isn't really a unique problem only to the Minis with there are problems with some PCs using USB 3.0 as well. The RF can effect other devices outside the Mini and bleed over into unshielded cabling nearby. Outside RF can also effect the Mini. Check to see if you have active USB 3.0 devices plugged into the new Mini when this is happening.

    If you can't solve the problem replacing the Mini or it's power supply then the USB 3.0 issue is what I would consider. Better quality shielded cabling can help with this issue. If the problem is effecting the Ethernet cabling you can purchase shielded/shielded twisted pair (S/STP) Ethernet interconnect cable. There are doughnut shaped magnets that can be attached to the ends of the effected cabling that can help. If you suspect outside RF you can try moving the location of the Mini to see if that helps.

    As a reference for the effect of RF noise...on my older flip phones my computer speakers used to make very loud clicking sounds a second or two before I would receive a phone call or a text message. Because of a design change or the move to 3G and 4G cell phone service I don't have that problem anymore with my smart phone. This was simply the cell phone's RF transmission bleeding through the unshielded cabling of my speaker wires and/or into the speaker itself. You could also try turning off the new Mini's internal wireless N radio (which is on by default) in the OS X settings and see if that helps.
  7. scotttroyan macrumors newbie

    Feb 25, 2005
    Is the audio being fed through the analog input? If so, I'd try using an external D/A to get the signal to digital before the mini. The unpredictable but eventual degradation is weird, but feeding it digital bits should at least rule out radio interference. If it's still breaking down, at least you can blame the Mac mini itself (whether hardware or software).
  8. theoreticalgirl thread starter macrumors newbie

    Mar 21, 2013
    So, I've posted a sample of the audio crackle:

    I wish I could say this was old-school cellphone interference, but it's not. I know very well what that sounds like. Using an intermediate audio interface such as an iMic, Mbox et al doesn't resolve the problem.

    We're testing some power options at the moment -- using different outlets, making sure everything's properly grounded/shielded. The thing is, it happens after the machine has been running for a while. Restarting the machine seems to make it stop, but we can't constantly turn on/off our machine (this defeats the purpose).

    I haven't entirely ruled out RF interference since we are inside a radio station and the equipment is close to the rack that sends our signal to broadcast.

    See what I mean by confusing?
  9. scotttroyan macrumors newbie

    Feb 25, 2005
    I don't even know what I'd do in this situation. Listening to it I'd blame analog interference over digital distortion, but if it a) always goes away after a restart and b) happens even when the audio is being digitized before arriving on the Mac I'd look in the direction of the software.

    If it's a new piece of equipment running a updated/different version of OS X (assuming whatever was doing this before was also a Mac) and possibly updated streaming/recording software I'd go through anything that's different from the old machine and see if something resolves it. Downgrade the software on the new machine, if you have access to the old machine try upgrading it to the same configuration the new machine has, and a thousand other obvious things that take a horrible amount of time to do with no guarantee of success.

    The closest I've seen to this was a period when iTunes would start introducing noise into playback and the only fix was a restart until Apple fixed the bug. Software problems are the worse. I much prefer when hardware fails.
  10. Fishrrman macrumors G5


    Feb 20, 2009
    "I'm also wondering if the FM broadcast equipment in the room contributes to any interference (or to what extent)."

    Can you move the Mini to a location OUTSIDE of the room it's currently in, and run it for a few days, to see if the problem persists?

    Could be the USB3 interference that was mentioned above.

    What are you using to get your streaming audio OUT OF the Mini?
    USB3 or ethernet?

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