Playing with QC25 and airplane adapter


Since i bought them, when i connect my QC25 to my Yamaha amplifier there is a medium pitched humming.
It is barely noticeable when noise cancellation is disabled, but very present when active.

The low end DSO scope confirms that :

There is a small 180 hz signal on the wire, some noise generated by the amplifier.

That signal  is amplified a lot by the noise cancellation circuit of the QC25 and is really annoying.

Since it is 180 Hz, it cannot be simply filtered out, else we'll damage the input.

Solution : Use the airplane adapter, the buzzing becomes not noticeable.



But what's inside ?
It's actually very basic :




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