I have a new, 2015 MacBook Pro 15" retina. The headphones port is producing a LOUD HUM to my external sound system plugged into the headphones port. I know it's not the ext sound system because the system works perfectly when other peripherals are played plugged into it. What's causing the hum and how do I prevent it?
LOUD HUM produced by headphones port.
- Thread starter Arthur09
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Cory Cooper
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The hum you are experiencing is a ground loop.
-IS the MBP running on AC or battery?
-If on AC, is it plugged into the same outlet as the amplifier//sound system?
It is a fairly common issue and doesn't mean there is an issue with the MBP or the sound system. The hum should go away if the MBP is running on its internal battery. This hum can also be caused by a bad audio cable.
You could also try a ground loop isolation audio cable or an optical cable. You sound system would require a TOSLink optical input to use an optical cable from the MBP to the inputs.
C
-IS the MBP running on AC or battery?
-If on AC, is it plugged into the same outlet as the amplifier//sound system?
It is a fairly common issue and doesn't mean there is an issue with the MBP or the sound system. The hum should go away if the MBP is running on its internal battery. This hum can also be caused by a bad audio cable.
You could also try a ground loop isolation audio cable or an optical cable. You sound system would require a TOSLink optical input to use an optical cable from the MBP to the inputs.
C
Thanks for your reply to my post, Cory. There is no fibre optic port on the MBP, is there? If there is a way of using fibre optics from the MBP, I'm open to more advice. I'd still need an adapter to go from fibre optic to RCA/1/4" inputs on the Yorkville 812.
The weird thing is, the sound output from the MBP headphone port was perfect for the first 2 days after bringing the MBP home from the store and wiring it up to the Yorkville 812. Then on the 3rd day came the hum without, to the best of my knowledge, making Any changes to the wiring hookups!
I'll try changing the hookup combination to see if I can eliminate the HUM.
How could a ground loop be absent for 2 days and then suddenly appear on the 3rd day?
Cory Cooper
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There is an optical output on the MBP - the audio out is a combo jack that supports analog 1/8" phone plug and TOSLink optical with an adapter. However, there isn't a converter that will go from optical to RCA or 1/4" directly. You would need D/A converter.
I am not sure why the ground loop appeared after a few days. It can happen though. Pro audio gear can be very sensitive to ground loops. Faulty cables can cause ground loops as well.
-Is the Yorkville you mentioned the AP812 12 input mixer/amp?
-Did you try running the MBP on battery instead of using the AC adapter?
-Do you have any fluorescent lighting or dimmer switches in the room?
You could try something like this:
Radio Shack Ground Loop Isolator
C
I am not sure why the ground loop appeared after a few days. It can happen though. Pro audio gear can be very sensitive to ground loops. Faulty cables can cause ground loops as well.
-Is the Yorkville you mentioned the AP812 12 input mixer/amp?
-Did you try running the MBP on battery instead of using the AC adapter?
-Do you have any fluorescent lighting or dimmer switches in the room?
You could try something like this:
Radio Shack Ground Loop Isolator
C
Thanks for your continuing interest in the HUM problem, Cory! Yes, the powered amplifier/mixer is the Yorkville AP812. I was unaware that the headphone port on the MBP was also an optical output. I do have a D/A converter (optical to RCA) but no adaptor for the 1/8" plug. Do you know where one is available?
If I use an optical cable out of the MBP, then convert it back to analog to plug into the 812, will there be any improvement in the quality of the sound to justify the cost of still another 1/8" to Toslink adaptor?
I have solved the HUM problem though, with your suggestions from your first reply, Cory!
I had inadvertently plugged the MBP into the SAME power bar as the 812 on the third day in the middle of changing some other connections.
When I reconnected the 812 to a separate circuit in my recreation room, the HUM magically disappeared and has never returned!
Thanks for your suggestion, Cory Cooper!!!
Arthur.
If I use an optical cable out of the MBP, then convert it back to analog to plug into the 812, will there be any improvement in the quality of the sound to justify the cost of still another 1/8" to Toslink adaptor?
I have solved the HUM problem though, with your suggestions from your first reply, Cory!
I had inadvertently plugged the MBP into the SAME power bar as the 812 on the third day in the middle of changing some other connections.
When I reconnected the 812 to a separate circuit in my recreation room, the HUM magically disappeared and has never returned!
Thanks for your suggestion, Cory Cooper!!!
Arthur.
Cory Cooper
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Glad that it is working. Strange that plugging the MBP AC power into another outlet solved it - usually, ground loops are caused by using different AC circuits.
I don't believe there wouldn't be any noticeable difference in going the optical-to-analog route. It would depend on how good the D/A converter is. What brand/model is the one you have?
If you want the TOSLink adapter for the MBP, here is a link to one:
S/PDIF Digital Optical Audio Adapter, Female Toslink to Male Mini Toslink
Enjoy the quiet
C
I don't believe there wouldn't be any noticeable difference in going the optical-to-analog route. It would depend on how good the D/A converter is. What brand/model is the one you have?
If you want the TOSLink adapter for the MBP, here is a link to one:
S/PDIF Digital Optical Audio Adapter, Female Toslink to Male Mini Toslink
Enjoy the quiet
C