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Thread: Noise from speakers when MacBook Pro plugged into mains???

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    Noise from speakers when MacBook Pro plugged into mains???

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    I have a really frustrating issue which I can't seem to solve. Also I don't know why no-one else seems to have this issue?

    So I have a Macbook Pro using a Scarlett 2i2 which is conneted to my genelec monitors. When my macbook is running of battery power my monitors are crystal clear but as soon as I connect power to the macbook I get a constant distortion background sort of crackle. So bad that I cant use them...

    Anyone got similar issues or solutions?

    Any feedback would be much appreciated

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    Quote Originally Posted by music_man View Post
    I have a really frustrating issue which I can't seem to solve. Also I don't know why no-one else seems to have this issue?

    So I have a Macbook Pro using a Scarlett 2i2 which is conneted to my genelec monitors. When my macbook is running of battery power my monitors are crystal clear but as soon as I connect power to the macbook I get a constant distortion background sort of crackle. So bad that I cant use them...

    Anyone got similar issues or solutions?

    Any feedback would be much appreciated
    Sounds like you have a classic case of a hum, aka ground/earth loop problem.

    This comes about because the Genelecs are earthed via the mains connector...WHICH MUST NEVER BE REMOVED! and then earthed again from the audio cables from the F'rite which are IN TURN eathed when you power the macbook from the mains.

    First question. Are the AI to monitor cables balanced and thus feeding the Genelec's XLR inputs? If not you need TRS (stereo) jack to XLR cables. May NOT solve the problem but usually does and is in any case "the right thing to do" .

    Assuming you are balanced the next step is to break the sceen connection in both cables. Most easily done in the XLR but if you have a nice pair of such cables it always seems a shame and a pity to "butcher" them and in any case you never know when you might need the screen intact? Better IMO to make up two XLR-XLR* "slugs" of about 300mm with disse'd screens...And MARKED UP as such!

    Lastly you can buy a dual transformer earth lift box (NOT a DI box!) but good quality ones are expensive and even the best have some effect on audio quality.

    *It might be possible to buy inline XLR screen lifting adaptors? Cannot recall seeing such but be bloody handy if they exist! Will have an extensive varder...
    Hosa GLT-255 XLR3F to XLR3M Ground Lifter Adapter: Amazon.co.uk: Hi-Fi & Speakers

    Well! ^ Whaddaya know! (that's putthat right!)

    Dave.
    Last edited by ecc83; 4 Weeks Ago at 03:52.

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    Hum on a Mac is unusual, because they are NOT grounded. Their power supply has a metal earth pin, but is double insulated and the case of the MacBook floats which makes the guilty party more likely to be the 2i2. The test is to disconnect the 2i2 fro the Mac with the speakers powered up and see if the noise comes back. I note you said "noise" and not "hum". I think I'd be sticking a meter onto the three devices and seeing if I can spot stray voltages and currents that can upset things.

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    Quote Originally Posted by rob aylestone View Post
    Hum on a Mac is unusual, because they are NOT grounded. Their power supply has a metal earth pin, but is double insulated and the case of the MacBook floats which makes the guilty party more likely to be the 2i2. The test is to disconnect the 2i2 fro the Mac with the speakers powered up and see if the noise comes back. I note you said "noise" and not "hum". I think I'd be sticking a meter onto the three devices and seeing if I can spot stray voltages and currents that can upset things.
    Did not know mac PSUs were Classll Rob. Maybe it is possible the OP has a non-OEM charger? I am at pains to think what the 2i2 could be doing?

    Dave.

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    The Mac power supplies have a 3 pin 13A plug part that slides onto the power supply housing, that has a fig 8 style connector. The foreign sockets have a different connector that can be used in place of the 13A version - quite a neat idea really. In contrast PC PSUs tend to have the negative line earthed to the mains and this causes regular and really big problems. It's very rare on a Mac - which is always treated as pretty silent. I wonder if the PSU on the 2i2 is grounding the interface, which then causes grief through the audio grounds.

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    Rob, the 2i2 is entirely bus powered and has no provision for other power.

    I have read of other odd problems with macs, audio interfaces and USB? Not likely here but an email to Focusrite could do no harm.

    Dave.

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    So the only mains ground is the speakers? Then I think maybe we’re not talking hun at all. Best guess now is usb carried bus noise which has been a subject on 2i2 this interfaces before. We need a sample of the noise to hear it.

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    Quote Originally Posted by paulears View Post
    So the only mains ground is the speakers? Then I think maybe we’re not talking hun at all. Best guess now is usb carried bus noise which has been a subject on 2i2 this interfaces before. We need a sample of the noise to hear it.
    I know they did a lot of BAD THINGS but I don't think we can blame the Nazis for this problem?

    Heh! If indeed macs are earth free maybe we have a "no earth at all" situation? But then did OP not say all was well with the mac on battery power?

    Dave.

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    He did - so we have switch mode PSU floating on the Mac making the difference? I've had trouble with numerous windows laptops, but Macs normally are hum and interference free. Till we hear the problem and identify it, not much w e can do.

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