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Audio Quality Issues when using Headphone switcher

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Marc Cerisier

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Audio Quality Issues when using Headphone switcher

PostWed Mar 04, 2020 4:00 pm

Hi—

I've never had an especially sophisticated method of switching between my speakers and my headphones. To date, it has been to unplug the speakers, and plug in the headphones. I recently thought to look for some sort of mechanical switcher that worked with 1/8" cables, found one, but have had issues that the manufacturer said were "ground loop issues." Hoping that some of you may have dealt with this issue previously, I come asking for your advice. Possibly complicating things, the area of my house where this is located is not grounded.

Setup:

Audio comes from a Mac Pro 2008's internal sound output (1/8") through a M->F 1/8" stereo cable. The female end is where I would make the manual change from speaker to headphones. The headphones are Sony MDR-7506. The speaker setup consists of a Presonus T10 sub, and two Behringer B2031A speakers. The cable to the sub is M <-> M 1/8" stereo to dual XLRs. Then from the T10 to the monitors are another two standard XLR cables. The computer, console, and sub are all plugged into one outlet, and the two monitors (located about 10' higher than the console) are plugged into another outlet.

Diagnostics:

The switch is simple 1-in, 2-out toggle switcher (http://4minds.co/audio-switch-box/). If all three (source, headphones, speakers) are connected, being in the speaker position causes no sound to the headphones, and normal sound to the speakers. The initial issue was that when I then switched to the headphone mode, normal sound went to the headphones, but there was audio "leaking" out to the speakers still... maybe 5–10% of the full volume.

Disconnecting the monitors from the subwoofer (both by unplugging their xlr connections or by removing power from the monitors) does not clear the issue. The T10 does have a "GND LFT" switch on it which reduced the leaking sound to maybe 1–2%, but it was still there. At this point, I listened to the headphones and noticed there was an electrical buzz in the signal.

Questions:

1) Does my non-grounded power situation preclude me from employing a 1/8" switcher to allow me to keep both the headphones and speakers plugged in at the same time?

2) Is there a device that could be employed at some point between the computer and subwoofer to filter out this issue—either on the audio side or the power side—and that would work with my outlets not having a ground wire connected? I'm especially curious about this as I presume the ground lift in the T10 is the equivalent of the protection a direct box or similar would provide. I am not knowledgeable enough, though, to know if my presumption is based in reality.

3) Is there a better way to achieve my goal of keeping headphones and speakers plugged in all the time, and easily switch between them?

Many thanks for reading this wall of text. Any suggestions would be greatly appreciated. I've looked at things like the Furman power conditioners, and the Hum X product, but hate to throw money at possible solutions until I know they might possibly be of assistance.

All the best,
Marc
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tf11972

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Re: Audio Quality Issues when using Headphone switcher

PostMon Mar 23, 2020 9:49 am

Hello Marc,
I think you have named the issue: the non-grounded environment of your house. The next problem is the connection between your Mac and the subwoofer, I suppose. I would give an USB-audio-interface a try, like this one:

https://focusrite.com/en/usb-audio-inte ... arlett-2i2

With such an interface you have also no problem to switch between the speakers and your headphones. Just turning the volume knobs.
Best regards
Thomas

www.forestpipes.de
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dw154515

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Re: Audio Quality Issues when using Headphone switcher

PostMon Mar 23, 2020 4:13 pm

Sounds like ground loop to me. If it's a 60Hz frequency, then definitely so.

A cheap, easy, way around this is to use one of these:
https://www.homedepot.com/p/GE-Polarized-Grounding-Adapter-2-Pack-14404/203684998?mtc=Shopping-VF-F_D27E-G-D27E-27_3_EXT_CORD_WORKLIGHT_SURGE-Generic-NA-Feed-PLA-NA-NA-EXT_CORD_WORKLIGHT_SURGE&cm_mmc=Shopping-VF-F_D27E-G-D27E-27_3_EXT_CORD_WORKLIGHT_SURGE-Generic-NA-Feed-PLA-NA-NA-EXT_CORD_WORKLIGHT_SURGE-71700000033101998-58700003865786276-92700048704092075&gclid=CjwKCAjwvOHzBRBoEiwA48i6Aq0VHOifHs3oVkXo2G8raSBxIsNZnT_BKuUl6s3-ABQDhsFXq1-0_xoC-XEQAvD_BwE&gclsrc=aw.ds

If you're having audio bleed in your switch, then I'd suggest not using that switch. Following tf11972's advice about an interface is also a good option.

Another options is something like this:
https://www.sweetwater.com/store/detail/HumX--ebtech-hum-by-ground-loop-hum-exterminator?mrkgadid=3308752876&mrkgcl=28&mrkgen=gpla&mrkgbflag=0&mrkgcat=livesound&lighting&&acctid=21700000001645388&dskeywordid=92700046938524719&lid=92700046938524719&ds_s_kwgid=58700005283381343&ds_s_inventory_feed_id=97700000007215323&dsproductgroupid=685951991752&product_id=HumX&prodctry=US&prodlang=en&channel=online&storeid=%7bproduct_store_id%7d&device=c&network=g&matchtype=&locationid=%7bloc_phyiscal_ms%7d&creative=290335234070&targetid=pla-685951991752&campaignid=1465475237&gclid=CjwKCAjwvOHzBRBoEiwA48i6Ai_PMUGfh01meRrjnsrQZmUCa85tFUA48wGj6LY61cNpubg2GRUHUBoC5w0QAvD_BwE&gclsrc=aw.ds

I have never used that particular device before.

I do commercial A/V installations for a living and ground loop hum (especially in older buildings) is a REAL PAIN. And can sometimes be impossible to track down. Most electricians I've worked with, aren't even aware of such an "issue" since it doesn't affect them. It is extremely problematic with Audio and Video gear. The ground lift adapter plug is the most practical solution - just put one on everything. However, are you saying that your outlets are NOT grounded? They are just the two-prong outlets. Also, are you in the US? I must mention that I am not familiar with electrical setups outside the US.

I have also seen situations where the hum can be caused by other devices - seemingly unrelated - plugged in via USB and HDMI! So, you may be able to narrow it down by listening, then unplugging something to see if it goes away - even if it's not a device in the AUDIO signal chain. Do remember, that almost (if not all) grounds will ultimately be tied together internally.
Last edited by dw154515 on Tue Mar 24, 2020 2:18 pm, edited 1 time in total.
Drew A. Worthen
Master of Music in Composition - Butler University
http://www.drewworthen.com
Director of Music & Website Admin - Greenwood UMC
http://www.greenwoodumc.org
Field Engineer - Diversified (Formerly Sensory Technologies)
http://www.sensorytechnologies.com
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murph

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Re: Audio Quality Issues when using Headphone switcher

PostMon Mar 23, 2020 4:52 pm

Go to a car audio website (you don't say where you are, which is a huge problem here) where you live. Look up "ground loop isolater". (It's a twin transformer with male/female phono connectors, like this: https://www.peatswholesale.ie/High-qual ... lator.html ) Put it in-between the output of the switcher and the active speakers (the sub). This will fix things.
Also, how LEGAL is not having a proper earth connection where you live and is your life worth it?
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jkinkennon

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Re: Audio Quality Issues when using Headphone switcher

PostTue Mar 24, 2020 10:47 am

Use a small USB interface with balanced XLR outputs. Connect to the sub with balanced XLR cables and then from the sub to the Behringer speakers with the same kind of balanced XLR cables. Feed the headphones from the USB interface and try as much as possible to keep all of the audio components on the same AC circuit.

I would consider running a dedicated AC line to this equipment if only to have the proper ground and to be sure that nothing else runs on the circuit feeding the electronics. These steps, especially using all balanced cabling will eliminate any audible hum.

EDIT: You are fortunate to have a sub with dual balanced inputs and outputs!
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dw154515

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Re: Audio Quality Issues when using Headphone switcher

PostTue Mar 24, 2020 2:17 pm

jkinkennon wrote:Use a small USB interface with balanced XLR outputs. Connect to the sub with balanced XLR cables and then from the sub to the Behringer speakers with the same kind of balanced XLR cables. Feed the headphones from the USB interface and try as much as possible to keep all of the audio components on the same AC circuit.

I would consider running a dedicated AC line to this equipment if only to have the proper ground and to be sure that nothing else runs on the circuit feeding the electronics. These steps, especially using all balanced cabling will eliminate any audible hum.

EDIT: You are fortunate to have a sub with dual balanced inputs and outputs!


You bring up an excellent point that I failed to consider...

I recommended the LP16 but has UNBALANCED outputs. Please disregard that recommendation. In fact, I will edit and remove that line from my earlier comment.
Drew A. Worthen
Master of Music in Composition - Butler University
http://www.drewworthen.com
Director of Music & Website Admin - Greenwood UMC
http://www.greenwoodumc.org
Field Engineer - Diversified (Formerly Sensory Technologies)
http://www.sensorytechnologies.com
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Marc Cerisier

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Re: Audio Quality Issues when using Headphone switcher

PostThu May 14, 2020 9:40 pm

Thank you all for your very helpful and detailed replies. The current world mess has taken my mind off of the organ, and now I'm being forced to move—so the issue might possibly rectify itself. Sorry to have been away from this thread so long.

To some of the questions... yes, I'm in the US, and yes, I have 2 prong outlets. My house was built about 8 years prior to grounded outlets became part of the electrical code.

While I had never used one because the consensus I received on this forum when I first got my console was that the Mac Pro internal line out was as good as any usb interface (for stereo, anyway), it seems the easiest solution would just be to get an external audio interface and be able to plug the headphones and speakers all into it together.

Now to find one that works with 10.11...

Thanks!

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