Raspberry pi, with USB DAC, noise affecting phono playback??

[0bs3rv3r]

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.

 

[flatmax]

It is possible that the noise is coming over the audio lines from the Pi. Unfortunately ground loops can form over the non ground pins in a supply.

One sure way to get rid of noise in the audio from a Pi is to use an isolated sound card, such as the one here : http://audioinjector.net
As the isolated sound card is only magnetically connected to the Pi, no noise can pass from the Pi to the acoustics of the DAC.

If you want good quality audio and no noise, you can try that solution.

Matt

 

[somebodyelse]

Any details about the preamp? What frequency is the buzzing at? Is it constant or modulated? Does the external HDD make a difference, and does it have its own PSU?

 

[flatmax]

Touching base again on this topic, after rereading your message again. If the type of noise is a lower frequency noise, then it is definately the phono preamplifier - which would have around 50 dB of amplification at lower frequencies. I guess this suggests that the ground path is pushing noise over the phono lines back to the input stage or ground plane of the phono preamplifier.

Just in case you are still interested in using phono with this system of yours, we have a new phono preamplifier on offer for our soundcards which fit the Pi. At the moment it is in the kickstarter phase, but you can access it from our site : http://www.audioinjector.net