noise on sound system

petertearai · July 2012

Hi when operating my laptop connected to the stereo sound we get an annoying noise while the lap top is connected to the power. If we run the lap top from the laptop battery there is no noise.
Some sort of earth loop???
Thinking of putting either the stereo or laptop on an isolating transformer.My isolating transformer is rated at 1.5 kva.
My inverter is a xantrex puresine 1800. Will the inrush current on the transformer be ok for the inverter?.
Soon to get a proper tv but may have the same issue.
Regards peter

boB · July 2012

Re: noise on sound system

I would definitely try the isolation transformer.

Another thing that should work would be to isolate the line level audio signal with an
audio transformer. Stereo 2 channels of audio transformer of course.

Also the audio transformer will be smaller and lighter weight than the power isolation
transformer and you won't have to worry about startup surge of the power transformer
if it did become an issue. I don't think it would, but who knows ??

boB

waynefromnscanada · July 2012

Re: noise on sound system

I had the same symptoms when using a 12 volt powered speaker system with my lap top running off inverter. The speaker system came with a wall wart power supply, and when using that, all was fine, but if I ran it off the same 12 volt source that powered the inverter - - buzzzzzzz. Tried a lot of things, but the only thing that worked was to go back the the wall wort, which acted as an isolation transformer.
Inrush for you're 1.5 kva xformer should not be a problem for that inverter, as they have no problem starting 1/2 HP and larger induction motors.
I like Bob's idea of using audio transformers to isolate. That's one thing I didn't think of trying.

petertearai · July 2012

Re: noise on sound system

Thanks for your reply's. Is there an off the shelf audio transformer or is it something I would have to wire up my self?
Thanks again for your ideas and input.

john p · July 2012

Re: noise on sound system

Audio isolation transformers are available at any good electronics parts store they have RCAinputs ond outputs .. They are used a lot in car sound systems so any place that sells good car amplifiers should have them.. they are not expensive

techntrek · July 2012

Re: noise on sound system

+1, what John said. I've installed multiple car audio systems (in my younger years) and an audio isolation transformer helped more than once with irritating ground loops that couldn't be traced. Ones I used were slightly smaller than a closed fist. In fact I ran across one the other day in my electronics parts pile - too bad you aren't a little closer or I would give it to you.

TheBackRoads · July 2012

Re: noise on sound system

I've used some of these for car installs, very small inline units, and they only minimized the buzz, never had one fully eliminate it. Worth trying however. Should be able to find Stinger or Scosche one even at like wallmart or somewhere... ground loop isolators... who woulda' thunk!

petertearai · July 2012

Re: noise on sound system

Thanks . Looked at our local Jcar and they have a unit for around 12 dollars.Will try that .Thanks .

H2SO4_guy · July 2012

Re: noise on sound system

I have the exact same problem with a laptop power supply inducing noise into the sound system, but not when on battery power. My solution is to take the audio out and put it into a direct box which is a pro audio device, but not expensive, I think a stereo version was less than $40 or so, and lift the grounds. It also has the option of sending out a balanced signal via XLR connectors.

Worked every time,

Skip

ggunn · July 2012

Re: noise on sound system

H2SO4_guy wrote: »

I have the exact same problem with a laptop power supply inducing noise into the sound system, but not when on battery power. My solution is to take the audio out and put it into a direct box which is a pro audio device, but not expensive, I think a stereo version was less than $40 or so, and lift the grounds. It also has the option of sending out a balanced signal via XLR connectors.

Worked every time,

Skip

I'm confused. The 1/4" connectors on a DI are just connected in parallel; lifting ground won't do anything to that connection. Lifting the ground just separates the shield on the balanced side from the shield on the unbalanced side. You cant separate the shields on an unbalanced connection because the shield is part of the circuit.

inetdog · July 2012

Re: noise on sound system

ggunn wrote: »

I'm confused. The 1/4" connectors on a DI are just connected in parallel; lifting ground won't do anything to that connection. Lifting the ground just separates the shield on the balanced side from the shield on the unbalanced side. You cant separate the shields on an unbalanced connection because the shield is part of the circuit.

So, if you use a DI box which does not provide the feature of isolation via a transformer between 1/4" input and output (which would allow you to separate the grounds but would use insulated 1/4" jacks in the box), you can use the 1/4" or RCA (unbalanced) to XLR (balanced) feature of the box, run an XLR cable, and use a simple XLR to 1/4" adapter (balanced to unbalanced) at the other end, and then use the "ground lift" feature of the box to completely isolate the two systems. If all you were concerned about was avoiding the presence of ground loop voltage on the signal leads, you could just use an XLR to 1/4 adapter at each end of the balanced cable. But that would still allow the ground difference to cause problems inside the circuitry of the computer.

ggunn · July 2012

Re: noise on sound system

inetdog wrote: »

So, if you use a DI box which does not provide the feature of isolation via a transformer between 1/4" input and output (which would allow you to separate the grounds but would use insulated 1/4" jacks in the box), you can use the 1/4" or RCA (unbalanced) to XLR (balanced) feature of the box, run an XLR cable, and use a simple XLR to 1/4" adapter (balanced to unbalanced) at the other end, and then use the "ground lift" feature of the box to completely isolate the two systems. If all you were concerned about was avoiding the presence of ground loop voltage on the signal leads, you could just use an XLR to 1/4 adapter at each end of the balanced cable. But that would still allow the ground difference to cause problems inside the circuitry of the computer.

On all the passive DI's I have seen, the two 1/4" jacks are simply in parallel and have no isolation between them. The ground lift only affects the balanced output.

You could certainly use a pair of adapting transformers as you say, but you'd also need a ground lifting adapter or you could just cut the shield connection in one end of the mic cable which connects them. Otherwise the shield is contiguous and the ground loop is still there.

H2SO4_guy · July 2012

Re: noise on sound system

In my case I always hooked the laptop to a mixing console with XLR (Balanced) inputs with the ground lifted at the direct box. When I only used a 3.5mm trs (The standard laptop audio out jack) to the dual 1/4" phone plugs the ground was there if using the power supply. If I was on the laptop battery the buzz was not there. Are you wanting to use an XLR type input or unbalanced RCA / Phone 1/4" type?

Skip

inetdog · July 2012

Re: noise on sound system

H2SO4_guy wrote: »

In my case I always hooked the laptop to a mixing console with XLR (Balanced) inputs with the ground lifted at the direct box. When I only used a 3.5mm trs (The standard laptop audio out jack) to the dual 1/4" phone plugs the ground was there if using the power supply. If I was on the laptop battery the buzz was not there. Are you wanting to use an XLR type input or unbalanced RCA / Phone 1/4" type?

Skip

Either balanced XLR or *balanced* 1/4" phone should work as long as the connection between the laptop and the mixing console is balanced and there is no connection between the grounds. But to get a balanced output from the laptop will take a transformer. Either in the form of a 1/4 to XLR Adapter or a DI box.

noise on sound system

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