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Thread: Noise goes away when I unplug my laptop during recording

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    Noise goes away when I unplug my laptop during recording

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    Hi!

    For our podcast recordings, we typically use Skype as the transport. My Dell Precision 5510 laptop is the hardware platform, with a Heil PR 40 mic going into a Mackie ProFX8 for my voice and the laptop audio going into the mixer through a mini jack to 1/4 inch splitter. The main outs from the mixer go to a Zoom H6 for recording.

    Generally the sound is good but the thing that drives me a bit batty is that there's a hiss noise that I only know one way to get rid of: unplug the laptop. Poof.

    Some sources seem to indicate it's a known motherboard issue (I'm not likely to send it in for replacement).

    Thoughts? Recommendations? Thank you!

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    https://www.amazon.co.uk/AV-Link-Gro...MD7HG1B53WQ50K

    Connect between laptop out jack and mixer. The H/P out is at a low enough impedance to drive such a transformer. Not "hi fi" at that price of course but good enough for Skyping I would aver? I have had a couple and they are not at all bad so long as you keep the level under a volt or so.

    Of course, if it fixes the noise you can always buy better from Art or Jensen.

    Dave.

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    Whenever you get this, you always discover it's a Dell. I've had two that did this VERY badly. Even worse, you cannot use alternative power supplies because the damn things notice! One thing that can work is wiring the output to two XLRs, wired sleeve to both pin 3's, and the two audio lines to the pin 2 of both plugs. This (and success depends on the preamp design for total silence) can produce workable results. If you stick a sensitive meter between computer ground and real ground, there can be surprisingly high circulating currents.

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    Quote Originally Posted by rob aylestone View Post
    Whenever you get this, you always discover it's a Dell. I've had two that did this VERY badly. Even worse, you cannot use alternative power supplies because the damn things notice! One thing that can work is wiring the output to two XLRs, wired sleeve to both pin 3's, and the two audio lines to the pin 2 of both plugs. This (and success depends on the preamp design for total silence) can produce workable results. If you stick a sensitive meter between computer ground and real ground, there can be surprisingly high circulating currents.
    So you are saying Rob that OP has a hum loop and the Dell takes the mains earth through to the negative, chassis, connection on the laptop?

    If so, my cheap'ass traff unit will fix that. I am obliged Rob BTW! I am presently looking for a refurbed W10 laptop, just for internet and "office" duties for whan I turn my W7 machines off line. I don't really need audio capability on the W10 PC but good to know to avoid Dell!

    Dave.

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    Taking a punt...The Mackie ProFX8 is mains powered?

    If so, I've experienced a similar thing in the past.
    The issue, at that time, was that the laptop power supply was completely isolated from the earth in the household wiring, by design, and, as it turns out, was floating a volt or so above.
    The mixer, however, has its chassis tied directly to mains earth. (UK Mains - 3 pins)
    There mustn't have been a direct path between the laptop chassis and the mixer chassis, and that difference caused hum/buzz.

    I tested the theory by taking a guitar lead and touching one tip to exposed external metal on the laptop chassis, and the other to exposed external metal on the mixer.

    If you have a multimeter you could set it to read DC voltage and take a reading between laptop chassis and mixer chassis.
    Finding exposed metal on a laptop might be trickier these days?
    ---------- Steenaudio Website ----------

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    Thank you so much for the responses! Very much appreciated. I'm going to try a ground loop isolator. Once again, I appreciate your advice.

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    Quote Originally Posted by People&Projects View Post
    I'm going to try a ground loop isolator.
    The Ebtech Humex solved a similar problem for me.

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    Thanks for the heads-up about the Ebtech Hum X.

    While looking at that on Amazon, I saw this in the reviews:

    "I have a 12" Harbinger P.A. speaker thats plugged in the wall. My laptop is plugged into a power strip. When I connect the auxillary cable from the speaker into my laptop, there is a constant annoying HUM. When I unplug my laptop and run it off the battery, the HUM disappears. Anyhow, I was gonna buy something like this that I was told solved the problem, a Furman M-8X2 Power Conditioner, $65 from Guitar Center. The salemen ask what if I needed help, I stated my issue. He said that Conditioner wasn't gonna solve my problem and told me to buy a $1 3-prong to a 2-prong adapter for my laptop plug. Sure even it solved my issue and I called him to thank him profusely!! Case Closed!!"

    Does this make sense technically?

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    The cheap adapter will get rid of the hum but, based on what I've read here and there, running a laptop without a ground pin is ill advised from a safety point of view.

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    It depends on the design of the switch mode PSU. Introducing circulating currents as a result of poor design in a PSU where the - supply is connected to mains ground/earth is problematic, and of course lifting the ground when the ground is a safety feature is stupid. Most however are class II devices and don't actually need a ground. these leave the chassis and grounds of the ins and outs floating. Connecting these to ground via typically the audio connector can introduce the hum - the reverse of the usual 'solution'. Breaking the circuit with transformers is the most suitable solution, but the devices are not that commonly found. I don't believe the Dell phenomena has been really solved. these don't seem to just introduce hum, via grounds at different potentials, but actual noise superimposed on the line, triggered by the ground differential. people have tried isolation, direct grounding and all things in between, but Dell PSUs seem to generate the worst possible combination when you want clean audio. I note that Dells also seem to have the ability to identify the model and brand of the PSU, preventing users buying cheaper off the shelf ones. You plug them in and can power the computer fine - but the computer refuses to allow the battery to charge. I cannot prove it, but I assume this could be part of the problem. Clearly some communication takes place to allow ID - and maybe this induces the noise? I really don't know.

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