Laptop Power Supply electrical noise

#1

Hi, I have a question for the group. At about 30% of the venues I play at, an electrical noise is introduced to my audio chain if my laptop’s power supply is plugged into wall outlet. However, If I unplug the power supply from my laptop, the noise goes away. Noise is similar to a DI that has ground/lift switch set to wrong position. Here’s my hardware chain:

Laptop to Behringer UMC204HD (USB powered) using TS 1/4" main outs to Radial stereo DI to XLR’s to sound system. My laptop power supply is connected to a Furman AC-215A power conditioner which is connected to venue’s power outlet.

Any ideas what is causing this, and if I have a way to clean up the venue’s power on my end?

#2

That depends on your region.
Where are you from? US?

#3

Yes, US

#4

It is probably a power supply ground loop problem. If your laptop power supply has a connector with ground, try to put some adhesive tape on it to isolate it from the ground.

#5

From people in the US, I often hear thatcher are using special power conditioners to avoid these problems. A known brand for that is Furman.

#6

If isolating the ground of the laptop power supply brings something, you can use something like an Ebtech Hum X

#7

I’m an electrical engineer, and after messing with these ground hum problems for 30 years the only useful insight I’ve come away with is to carry around a couple transformer isolators.

The ART DTI boxes work well for me. They handle a stereo pair and will take XLR, 1/4", or RCA. They’re built like tanks. “Ground lift” approaches sometimes work, but I’ve had better luck with the DTIs.

[edit: those Ebtech (Morley) products David-san mentioned above do the exact same thing, electrically speaking, as the ART DTI I mentioned. I looked at those and bought the ART just because I had positive prior experience with other ART devices.]

#8

Back before I switched my entire rig to all balanced cables and using a full-out UPS, I used an ART DTI box as well with good success. The DTI is still not QUITE as noise free as all balanced cables and a UPS but a solid second choice.

X

#9

I have had excellent results with the Behringer MicroHD HD400. I was hesitant at first because it didn’t really seem to cover the type of noise that laptop power supplies emit (that bits and bytes high pitch stream), but because of the relatively low price I gave it a shot. I have to say I was amazed by the difference! From a pretty much unbearable stream of high pitch noise to virtually nothing.

https://www.amazon.com/gp/product/B000KUD2G4/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

#10

Thanks for all the suggestions. It sounds like a need a hum eliminator, so I’ll pickup one of those. Also, I will probably retire my Direct Box and use balanced outs of my audio interface (trs to trs) into stereo hum eliminator and then trs or xlr out of hum eliminator into mixer’s xlr inputs. Hopefully that will fix the strange pc noise that happens at some venues only. Again, thanks for the suggestions.

#11

I’m a little late to the party, but my experiences touring Asia and dealing with the multitude of different power situations there taught me to carry three things with me to deal with electro-static or electro-magnetic interference (different and kind of the same):

  1. Always carry a passive and powered D.I. with ground lifts (though… I rarely find any success with ground lifting)
  2. I always carry a hum-eliminator PLUG from Eb-Tech (this is what I use to power my laptop/Muse receptor rig)
  3. Always carry the stereo hum-eliminator from Eb-Tech. One thing to note about the hum-eliminator… you HAVE to match the balanced cables to balanced cables. If you try to combine balanced (TRS) and unbalanced (TS) you will induce a phase relationship that basically eliminates 50% or so of the gain you can send to the FOH mixer. I always test this before heading out on tour.

This combination of capabilities has let me fix a good number of squirrely power issues coming from “dirty” AC power (and what I believe is a bad chassis ground inside my Receptor) despite the fact that we run through one of the 150lb big-boy Furman conditioner/converter units.

Just my 2 cents :slight_smile:

#12

Cool. With who do you tour? What kind of music?

#13

I serve in a military music unit playing everything from solo piano for dignitaries to big band in Tokyo to pop covers in theaters to dragging my rig into a dirt lot plugged in to wacky power in Cambodia and hoping everything doesn’t blow up while we play pop music for schools in places that almost never get to hear live western music.

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#14

Thanks! I ordered an ART DTI and will get a chance to test it this weekend. Thanks for the other great ideas as well.