lordvader82 Posted May 24, 2021 Share Posted May 24, 2021 (edited) Hey all, I'm trying to diagnose some noise that I hear on my HiFi. I've attached an image of the topology, so I don't need to overly explain everything in words, but the tl:dr is: There is some low level hissing noise coming through my speakers (definitely not 50 or 100Hz hum) If I disconnect my 4K player, the noise goes. Stepping though the chain ... If I disconnect the HDMI between 4k player and TV, the noise also goes ... If I disconnect the HDMI between the TV and Raspberry pi, the noise also goes If I remove power to the Pi (powered by POE), the noise is gone So, logically, there is a noisy ground originating on my Pi, that's polluting the rest of my system (my assumption). But would like to hear your thoughts on this. Most discussions I've come across relating to noisy HDMI on a Pi have all spoken about ground loops. Which is why I've included the image. I don't beleive there's a ground loop, as when the Pi is taken out of the equation, the system is dead silent. Edited May 24, 2021 by lordvader82 Link to comment Share on other sites More sharing options...
andyr Posted May 24, 2021 Share Posted May 24, 2021 If it's not 50/100Hz hum ... it's not a ground loop. Can you power your Pi with a dedicated PS, rather using PoE? I'd be suspecting that is the problem. Andy Link to comment Share on other sites More sharing options...
Telecine Posted May 24, 2021 Share Posted May 24, 2021 19 minutes ago, andyr said: If it's not 50/100Hz hum ... it's not a ground loop. Can you power your Pi with a dedicated PS, rather using PoE? I'd be suspecting that is the problem. Andy Might also be the TV. Link to comment Share on other sites More sharing options...
bob_m_54 Posted May 24, 2021 Share Posted May 24, 2021 the arrows are pointing the wrong way.. Link to comment Share on other sites More sharing options...
lordvader82 Posted May 24, 2021 Author Share Posted May 24, 2021 Thanks for your replies (and thanks for pointing out my powerpoint skills @bob_m_54!) Definitely not the TV - as when the pi is disconnected the noise is gone. I built a linear PSU (a Salas L-Pad) for a PiCorePlayer that's also there (not illustrated), and when I used that supply, the noise was much higher (though the POE hat was still there). Might play around more with how I power that pi. Link to comment Share on other sites More sharing options...
bob_m_54 Posted May 24, 2021 Share Posted May 24, 2021 Just now, lordvader82 said: Thanks for your replies (and thanks for pointing out my powerpoint skills @bob_m_54!) Definitely not the TV - as when the pi is disconnected the noise is gone. I built a linear PSU (a Salas L-Pad) for a PiCorePlayer that's also there (not illustrated), and when I used that supply, the noise was much higher (though the POE hat was still there). Might play around more with how I power that pi. Sorry mate, but when you said you added a diagram to clarify... it just did my head in... Link to comment Share on other sites More sharing options...
davewantsmoore Posted May 25, 2021 Share Posted May 25, 2021 Temporarily power the Pi from a (standard, no frills) 5v supply connected to the same power board as the SACD.... what happens then? Link to comment Share on other sites More sharing options...
lordvader82 Posted May 25, 2021 Author Share Posted May 25, 2021 (edited) Just tried it with one of those 5 port usb charger hubs - definitely quieter! I'll double check when there's less background noise (kids). Interesting that the linear PSU which also powers another pi (same power board) adds noise to this pi. Edited May 25, 2021 by lordvader82 Link to comment Share on other sites More sharing options...
Grizaudio Posted May 28, 2021 Share Posted May 28, 2021 (edited) On 25/05/2021 at 8:17 PM, lordvader82 said: Just tried it with one of those 5 port usb charger hubs - definitely quieter! I'll double check when there's less background noise (kids). Interesting that the linear PSU which also powers another pi (same power board) adds noise to this pi. I suspect your SMPS is not grounded. Most aren't The SMPS transformer isolates primary and secondary supplies, meaning a ground isn't "theoretically required". This can typically help provide isolation/less noise in devices. Maybe try powering the PI from one of the TV USB ports? If you have a double USB lead you could parallel USB ports to supply more power to the PI. Edited May 28, 2021 by Grizaudio 1 Link to comment Share on other sites More sharing options...
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