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Thread: Audio shield headphone out connected to amplified line-in

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  1. #1
    Junior Member
    Join Date
    Mar 2019
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    11

    Audio shield headphone out connected to consumer stereo amplifier line-in

    Hi;
    I was working through some of the Tutorial material for the Audio shield and Teensy 3.2 over the weekend. Things were going great but I found that the next morning I was not able to get ANY output from the headphone connector using the same tutorial material, even the first Hardware Test tutorial that generates the beep. The shield is not completely dead as I can read the floating input values from the button and pot inputs and talk to the SD card. Tried a couple of different sets of headphones.

    After quite a bit of pondering I got to thinking about the silkscreen note on the board warning not to short the headphone VGND to the board GND (if I'm interpreting that correctly). While working with the board previously I had connected the headphone output to the line in of an AC powered stereo receiver to play output on the speakers. Seemed to work ok but since realized that probably connects the headphone GND back to the board GND via my computer's AC GND and USB cable. I was being lazy and didn't use the line-out on the shield, figuring headphone out should have been ok given the relatively high input impedance of the stereo AMP line-in, but had not thought of the ground connection implications.

    Is connecting the headphones to the line-in on an AC connected stereo amp something that could wipe out the headphone output HW in the SGTL5000 due to the GND path back through the wall outlets and computer's USB, or is that warning just about preventing ground loop noise?
    Thanks for your time.
    -AG6GU
    Last edited by AG6GU; 03-25-2019 at 09:35 PM. Reason: Typo in title

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