Jump to content
Sign in to follow this  
Dayjob Dave

New Audio Buzz from MBP

Recommended Posts

I have the headphone jack audio out connected to a stereo and just recently it began an annoying buzz. The exact same cable chain is plugged into an iPod cradle with no problems, so the trouble is with the Mac Book Pro itself. Sounds like something not grounded, but never had a problem before. Any ideas?

Share this post


Link to post
Share on other sites

Depending on the sound of the buzz and your setup... My first guess would be a 60-cycle hum, leaking in from the power system, possibly due to a ground loop.

Test: remove all other connectors from the MacBook (disconnect power, run on battery; disconenct ethernet, USB, firewire, video out, everything except the headphone jack.) Place MacBook on non-conductive surface (so it isn't touching any metal). See if hum persists. (If the hum goes away, plug other stuff back in one at a time to isolate the circuit with the ground loop.)

Share this post


Link to post
Share on other sites

Thanks - it is the Bookendz docking station. No problem when connected directly.

Share this post


Link to post
Share on other sites

Oops. Wrong! I tried removing the dock, plugged everything back directly into the MBP and the hum is back.

Share this post


Link to post
Share on other sites

OK, this is weird. I ran through the steps you recommend and it turned out to be the USB cable from the Cinema Display power adapter. But the buzz continues even with the adapter UNPLUGGED.

Share this post


Link to post
Share on other sites
OK, this is weird. I ran through the steps you recommend and it turned out to be the USB cable from the Cinema Display power adapter. But the buzz continues even with the adapter UNPLUGGED.

In that case, perhaps it's one of the peripherals conected to the USB on the Cinema Display ? E.g., if your MacBook USB connects to the Cinema Display power adaptor, and the power adaptor is connected to the Cinema Display, and the Cinema Display is connected to a USB disk drive or hub or scanner or printer, and that's connected to a power adaptor that's plugged into the wall, then that's another possible path for a ground loop.

 

Ground loops are one of the great wonders of electronics. Ground is supposed to be "zero potential" in any electric circuit. It's the external sleeve of any shielded RF, audio, video, ethernet, TV, USB or Firewire cable (or an ADB or AppleTalk cable, for that matter! Anything but fiber). Ground spreads like a web through your home: from every power socket, from your ISP, through the cable/DSL modem, the router, all the computers on the router connected by ethernet, all the peripherals connected to all the computers by ethernet, USB, Firewire, and then over to your TV set, its cable/satellite box, its audio amp, the DVD player, the CD player, the VCR, whatever, it's one giant tapestry of "ground". If any one of those isn't completely grounded where it should be, if there's minor resistance someplace along a path (a corroded connector or plug, cold solder joint, sloppy crimping) then a small current can flow through what should be "ground" to equalize the small voltage difference. US power being 60Hz, this often shows up in analog devices as a low hum leaking into the audio, or a couple of horizontal bars rolling up an analog NTSC TV screen.

Share this post


Link to post
Share on other sites

Wow. Fascinating and very educational. I had no idea that one bad solder could affect another device so easily. Thank you.

Share this post


Link to post
Share on other sites
In that case, perhaps it's one of the peripherals conected to the USB on the Cinema Display ? E.g., if your MacBook USB connects to the Cinema Display power adaptor, and the power adaptor is connected to the Cinema Display, and the Cinema Display is connected to a USB disk drive or hub or scanner or printer, and that's connected to a power adaptor that's plugged into the wall, then that's another possible path for a ground loop.

 

Ground loops are one of the great wonders of electronics. Ground is supposed to be "zero potential" in any electric circuit. It's the external sleeve of any shielded RF, audio, video, ethernet, TV, USB or Firewire cable (or an ADB or AppleTalk cable, for that matter! Anything but fiber). Ground spreads like a web through your home: from every power socket, from your ISP, through the cable/DSL modem, the router, all the computers on the router connected by ethernet, all the peripherals connected to all the computers by ethernet, USB, Firewire, and then over to your TV set, its cable/satellite box, its audio amp, the DVD player, the CD player, the VCR, whatever, it's one giant tapestry of "ground". If any one of those isn't completely grounded where it should be, if there's minor resistance someplace along a path (a corroded connector or plug, cold solder joint, sloppy crimping) then a small current can flow through what should be "ground" to equalize the small voltage difference. US power being 60Hz, this often shows up in analog devices as a low hum leaking into the audio, or a couple of horizontal bars rolling up an analog NTSC TV screen.

 

Wow, sounds quite unsolvable. While I normally have a couple peripherals plugged into the Display, I ran the experiment with nothing but the Display USB cable plugged into the MBP - still 60HZ buzz. Ok, let me add another piece to the puzzle. The problems seems to have coincided with removal of a malfunctioning APS battery backup unit. It was sensing power dips that were not happening so I plugged the power strip directly to the wall and disconnected the APC. But still... without the Cinema power supply even plugged in, I'm getting the buzz?

 

BTW, thanks for all the info!

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

  • Recently Browsing

    No registered users viewing this page.

  • Who's Online (See full list)

    There are no registered users currently online

×