I have a Raspberry Pi 4 in a metal case. A Topping D10 DAC is connected to a USB port, and RCA cables connect that to my preamp/hifi. There is also a USB external hard drive connected to the raspberry pi.
The problem is noise - BUT - not when playing music using the raspberry pi. The noise only is heard when I switch my preamp away from the input coming from the pi, to the input from it's own phono section, to play vinyl. When the preamp is switched to phono, there is a background buzzing, that is hard to hear at normal volume levels, but becomes obvious at high volumes. The buzzing goes away as soon as I unplug the raspberry pi/ Topping D10 DAC audio cables from the preamp. I am thinking that low level noise is being introduced into the preamp, via the DAC line level cables, that is only heard because of the high gain of the phono preamp section.
At first I thought maybe a ground loop problem - but the raspberry pi power supply has no ground connection. I tried grounding the case of the topping D10 DAC anyway, just in case, but it made no difference.
The problem is noise - BUT - not when playing music using the raspberry pi. The noise only is heard when I switch my preamp away from the input coming from the pi, to the input from it's own phono section, to play vinyl. When the preamp is switched to phono, there is a background buzzing, that is hard to hear at normal volume levels, but becomes obvious at high volumes. The buzzing goes away as soon as I unplug the raspberry pi/ Topping D10 DAC audio cables from the preamp. I am thinking that low level noise is being introduced into the preamp, via the DAC line level cables, that is only heard because of the high gain of the phono preamp section.
At first I thought maybe a ground loop problem - but the raspberry pi power supply has no ground connection. I tried grounding the case of the topping D10 DAC anyway, just in case, but it made no difference.