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2018年7月に発売された、モデル番号{A1989 / EMC3214}のMacBook Pro13インチモデルにはクアッドコアi5と i7 を搭載しており、グラフィックにIntel Iris Plusが統合されています。

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Difference Between 13" MacBook Pro 2018 and 2017 Power Adapters

I recently purchased the 2017 MB Pro 13" and saw your new teardown of the 2018 version. Had a scenario regarding the power adapter and was hoping you could shed some light.

When I connect my Bose QC15 headphones to the MacBook Pro (using the headphone jack) while the power adapter is plugged in (not using the grounded extension cable), the headphones reveal a slight buzzing noise that dissipates when touching any metal part of the laptop. However, when using a grounded extension cable to connect the power adapter, the buzzing noise disappears without the need to touch a metal part of the laptop.

After taking my laptop to Apple about a month ago, we tried using multiple power adapters, and multiple battery-powered headphones. When this didn't resolve the issue, they advised that the machine was defective and to get a replacement, which I did. However, the issue still recurs with the replacement 2017 MacBook Pro I received.

Here are my questions: (1) is it possible for you to recreate this issue with 2017 MacBook Pro and charger?; (2) Is this issue resolved when using the newer power adapter with the 2017 MacBook Pro?; and (3) Does this issue occur on the new 2018 MacBook Pro with the old power adapter or the new power adapter?

Thanks for your comprehensive look and hope this is something your team can do.

All the best!

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I think you’ve already go your answer here.

The difference between the duck head and the 3 prog cord is the grounding pin and its connection to a proper ground point.

I’ve seen similar issues with stereo speakers when the deck was not grounded you could hear the hum of the power supply (using a cheater plug).

While the new power adapter may have additional shielding, this shielding is useless until its tied to ground to dissipate the energy.

This gets into a floating Faraday Cage Vs grounded Faraday Cage.

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Thanks for the informative and prompt answer, Dan!

I agree that the solution is most certainly related to grounding. I was just curious as to whether or not this issue may have been addressed in the newer power adapter and/or MacBook. I'm definitely no electrical engineer by any means, but my basic understanding leads me to question whether the newer battery/power adapter may somehow insulate the electrical current being passed through the outer metal casing of the laptop.

I figured it couldn't hurt to ask if someone might be able to recreate the issue with the 2017 model, and see if it recurs on the 2018 model!

さんによる

For safety reasons, the chassis would most likely be tied to the ground on the laptop and not be insulated.

While grounding is definitely the issue, the headphones can also make a difference. More sensitive drivers may pick up the noise whereas others won't. Out of curiosity, do you hear the buzzing sound both in wired mode and wireless? And does the buzzing disappear both in wired and wireless when you ground the laptop?

さんによる

Thanks for the response, Arthur!

The Bose QC15 headphones are not wireless, but using a compatible bluetooth modification, I am able to make them wireless. When using the bluetooth mod, the buzzing does NOT occur, regardless of whether the MacBook Pro is charging without the grounded extension, with the grounded extension, or on battery power. That is, using bluetooth resolves the issue entirely.

However, I can confirm that when using a wired cable from the Bose QC15 headphones to the MacBook Pro's headphone jack while using battery power, the buzzing noise also does NOT occur. Yet, whenever I use the wired cable to connect the Bose headphones to the MacBook Pro, the issue only seems to disappear when on battery power OR using the grounded extension with the power adapter. That is, the issue will only occur when the headphones are physically plugged into the MacBook Pro, AND the MacBook Pro is charging using the non-grounded power adapter.

Thanks for looking into this, Arthur!

さんによる

Thanks for indulging me with details @jzmacman !

It sounds like the MacBook charging circuitry generates electrical noise while charging, though the noise is usually eliminated by grounding the MacBook.

さんによる

Yes! Thats the simple answer. The MagSafe transformer creates the noise and the shielding when not connected to ground leaks the noise. If you have the shields connected to ground the noise is bleed to ground.

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Jay さん、ありがとうございました！
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