Hi,
I would like to use the same 12V switching power supply for a TPA3110D2-based amplifier and an USB hub. The amplifier board (PUI audio AMP2x15) has both single-ended and differential inputs. It is connected to the headphone output of a monitor and the USB HUB is connected to the same monitor's built-in USB HUB.
My original setup looked like this:
In this case there was a lot of high-pitched, "digital-sounding" noise from the speakers, presumably because of a ground loop created this way. I then changed it to use the differential inputs:
The SGND was not connected to the ground of the headphone output, but is connected to the board's gound plane. In this case, however, there was a different kind of noise (noise.mp3).
If, however, I connect the USB HUB as well, i.e. the grounds of the monitor and the board are actually connected, the noise goes away:
Why does the noise appear in the former case? Isn't the differential input supposed to work with the difference between the signals? Why does it matter that the grounds of the monitor and the amplifier are connected?
In this latter case the digital noise observed in the very first case also goes away, even though some sort of ground loop still exists. If I connect the SGND of the amplifier to the display's headphone output ground, the digital noise reappears:
I would like to use the same 12V switching power supply for a TPA3110D2-based amplifier and an USB hub. The amplifier board (PUI audio AMP2x15) has both single-ended and differential inputs. It is connected to the headphone output of a monitor and the USB HUB is connected to the same monitor's built-in USB HUB.
My original setup looked like this:
In this case there was a lot of high-pitched, "digital-sounding" noise from the speakers, presumably because of a ground loop created this way. I then changed it to use the differential inputs:
The SGND was not connected to the ground of the headphone output, but is connected to the board's gound plane. In this case, however, there was a different kind of noise (noise.mp3).
If, however, I connect the USB HUB as well, i.e. the grounds of the monitor and the board are actually connected, the noise goes away:
Why does the noise appear in the former case? Isn't the differential input supposed to work with the difference between the signals? Why does it matter that the grounds of the monitor and the amplifier are connected?
In this latter case the digital noise observed in the very first case also goes away, even though some sort of ground loop still exists. If I connect the SGND of the amplifier to the display's headphone output ground, the digital noise reappears:
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