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Help needed to get rid of hissing in monitors
Old 4th May 2019
  #1
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Help needed to get rid of hissing in monitors

I have the following home studio setup: a pair of Yamaha HS50 monitors (powered with ground plugs), plugged into a Motu Track16 (powered without ground), itself connected to a Mac Mini (powered without ground). A display (powered with ground plug) is plugged to my Mac Mini.

Now, the display is a cheap one and, with my current setup, it produces some hiss in my HS50s. If I unplug the display, everything is back to normal. Until now, I used a adaptor which goes to female plug with ground to a male plug without, but it's dangerous (and probably illegal where I am).

What would be clean solutions to that problem? I was considering buying a Furman M10-X but I'm not 100% sure that it would solve my issue.
Old 6th May 2019
  #2
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Try to keep the power supply cable/adapter of the display as far away as possible to the audio cables. Might help.
Old 6th May 2019
  #3
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Richard Crowley's Avatar
 

It seems unlikely that the noise you are talking about is "hiss". It is more likely "hum" or digital "hash". If it IS "hiss" then how far down is it from normal audio levels? No audio gear is completely free of hiss. All active (powered) gear has some "noise floor" which is always there. The question is how far "down" it is? This is known as the "signal-to-noise ratio". (SNR). You will hear hiss from ANY audio gear if you turn the gain up far enough. Can we assume that you are not talking about "normal" noise levels?

If the noise goes away when you lift the ground to the display, that suggests ground-conducted noise or perhaps a ground loop. You did not reveal how you are powering all the components (computer, audio interface, display, speakers). Are all the system components plugged into a common circuit (such as using a power strip or equivalent).?

You also did not mention what display you are talking about? Does your display have an external "line lump" (or "wall-wart") power supply? Or is the display power supply integrated inside the display? (The power cord plugs directly into the display)

As @ MPrinsen suggests, does the noise change if you move the display power supply around? (If your unidentified monitor uses an external power supply?)

Good detective/troubleshooting skills, discovering that lifting the ground from the display kills the noise.
If you disconnect the audio interface and speakers and power them off, and listen on headphones plugged directly into the computer, do you still hear the same noise and absence of noise when you lift the display ground? Do you hear the same noise if you plug headphones into the audio interface but with the speakers disconnected?

We don't know where you are on the planet because you have not completed your user profile. It is likely true that lifting the ground is not properly following the rules for mains power. However, I would not be terribly worried about lifting the ground from the display. IMHO, it is very low risk. Its not like you were using electric power tools outdoors in the rain.

Of course, we are assuming things about your situation because we don't know about your display or power distribution. And we are assuming that you are not taking audio out of the display. And we are assuming that you are using HDMI or DVI (or VGA?) video connection.

Without knowing what your power distribution situation is, it seems unlikely that Furman M10-X will solve your problem. If you can get one with the option to return it, you could try it, but don't get your hopes up.

If you really want to try a commercial remedy, I would try an Ebtech "Hum-X". That will give you a safe equivalent of lifting the power mains ground to the display. Although, to be honest, you seem to already have the most cost-effective solution. It is not completely without risk, but you are probably at greater risk of being run over by a concrete-mixer.

Last edited by Richard Crowley; 6th May 2019 at 02:08 PM.. Reason: spelling
Old 6th May 2019
  #4
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Thanks both for your answer, I'll try to give a bit more details

First, about the naming, English is not my native language but I'm sure that it's not "hum". I didn't know about the term "digital hash" and that sounds appropriate in that case. Anyway, the level of the noise is very low, hardly audible when loud content is playing but definitely audible when not playing anything. And it's surely loud enough so that we're not talking about "normal" noise levels, especially that it disappears when I unplug the display.

About powering the different element, all are plugged into a power strip, but even if I plug them in different power outlets, the problem remains, as all outlets in my flat share the same circuit.

The display has and integrated power supply and the noise doesn't change if I move the cable or the display.

The hiss is audible only on my loudspeakers and not on my headphones. I haven't tried, but I wouldn't be surprised if lifting the ground from the speakers and not from the display worked as well.

I'm based in Germany but I'm not German, so I don't know the regulations super well, but I would expect that it's "forbidden", although I'm not too worried either. (Sorry for not completing my profile, I'm a long time lurker but never felt the urge to participate I'll add more info soon!)

Finally and maybe one of the most interesting thing: I'm connecting my display with an HDMI cable and I discovered yesterday that if I disconnect the cable from my Mac Mini, but leaves the display on, the noise disappears. I've tried another HDMI cable and the problem remained; unfortunately, I don't have other cables (VGA or DVI) to try out at the moment, so I can't report on that. However, I have the feeling that the problem would disappear if my Mac Mini was grounded.

Let me know if that gives you more concrete ideas to solve the problem
Old 6th May 2019
  #5
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You can try to put a DI box between your audio interface and your monitor speakers, like this:
https://www.thomann.de/nl/behringer_microhd_hd400.htm
Old 6th May 2019
  #6
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Richard Crowley's Avatar
 

Your experiment with the HDMI cable rather suggests you have a ground-loop problem from your display mains power ground, through the HDMI cable, through the computer, through the audio interface, and out to the speakers which are also grounded through the mains power cords. If lifting the display mains ground solves the problem, I would just go with that and proclaim it "resolved".

As @ MPrinsen suggested, breaking the ground using a transformer is another potential solution. Note that Behringer product that @ MPrinsen suggested is actually an isolation transformer (which tend to have equivalent input and output impedance and operate at line-level). Technically, a "Direct Box" has a very high impedance (for electric instruments like guitar or bass) and a very low output impedance (to simulate a modern microphone) and operates at a very low signal level.

If lifting the mains ground on the display solves the problem, then using a transformer seems like a rather undesirable overkill. Undesirable because all transformers introduce distortion into the audio signal and that seems worse to me than the digital hash noise-floor. But that is just my personal opinion.
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