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I think I found why car cassete adapters have hum -- no ground

Discussion in 'General Electronics Discussion' started by dietermoreno, May 26, 2013.

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  1. dietermoreno


    Dec 30, 2012
    I think I found why car cassete adapters have hum -- there's no ground.

    There are only two wires, red and black, leading into the cassette adapter from the 1/8 inch stereo phone plug, even though the stereo phone plug has 3 contacts.

    I definitely hear a stereo signal. The vocals come out center panned equally out of both speakers and the guitars and bass play around back and forth between the two speakers.

    I hear a stereo signal that has a quiet hum in the background, and when my portable music player is not playing a song, the hum is as loud as having a guitar cable disconnected from a guitar while connected to an amp.

    This leads me to suspect that the device is designed for portable music players that have no ground, like iPhones and iPods, and instead of a true ground connected to the car body it uses one wire as ground at audio frequecies to allow for a stereo signal to be sent over only 2 wires and no true ground needed.

    Would adding what I am calling a "true ground" remove the hum?

    I am considering buying another cassette adapter for $3 from Walmart so I can use the other one in case I mess up on this one.

    Then, with the new cassette adapter I would solder its black and red wires to a 1/8 inch TRS cable and connect the shield to a wire soldered to the car door.

    Good idea?
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