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Solving three different hum sources (2 solved, 1 in progress)

TomekNet

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After hooking up NAD c298 with my Denon x3700 I've discovered a hum noise in my speakers.
I also had another source of hum caused by a 12V trigger cable (either triggering SVS sub or NAD power amp).
Then I've identified a third source of hum coming from my music source device connected to S/PDIF Coax input of Denon...

1)
The last one was easy to solve. I've just used a cheap digital S/PDIF Coax to S/PDIF Optical converter (see attached photo).
Plugged in 1m Toslink cable to Denon and that hum is gone.

2)
NAD power amp and SVS sub are grounded, Denon AVR is not.
12V trigger cable was clearly making a ground loop:
Denon out --> trigger cable --> NAD in = hum
Denon out --> trigger cable --> SVS in = hum
Denon out --> trigger cable --> Emotiva ET-3 --> trigger cable --> NAD or SVS in = hum
NAD out --> trigger cable --> SVS in = no hum
So my solution to brake the ground loop was is to isolate ground in cable between Denon and Emotiva ET-3:
Denon out --> modified trigger cable --> Emotiva ET-3 --> trigger cables --> NAD in and SVS in = no hum
This configuration without Emotiva also works fine:
Denon out --> modified trigger cable --> NAD in, NAD out --> trigger cable --> SVS in = no hum
But I need third 12V out anyway for a second power amp.
I've received tips on this matter in this thread (thanks again guys).

3)
I'm still fighting the first hum source.
In this thread I've identified it to be coming out of HDMI, out of my DVB-S STB and finally out of SAT antenna cables.
This is out of my control as SAT signal is centrally distributed in my apartment building and is grounded somewhere else (than my apartment).
I've ordered some galvanic isolators for band 5-2400MHz but it doesn't work in my place, unfortunately.
I've found out that a cable running to my flat is up-linked to a sat multi-switch (SatMatrix MS 5/12) and it needs to be controlled with DC power delivered by coax cable.
So unless I figure out anything else (ideas?) the only solution that comes to my mind is using some kind of HDMI opto isolator, but I haven't found any so far.
I've found some HDMI 2.0 extenders (I need 4K@60p), but they are pretty expensive (at least for this purpose):
a) AV Access HDMI extender (483 EUR)
b) Foxun EX-EF04 (195 EUR)
Are there any better ideas to isolate antena potential in my case?
 

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Matias

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Lift the ground of the NAD?
 
OP
TomekNet

TomekNet

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Lift the ground of the NAD?
Then I'd need to lift the ground on another power amp (on delivery) and on my SVS sub also.
I'm not sure if this is safe with class I equipment.. (that power amps are, at least)
 

eduardw

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There are several optical hdmi cables but I think a lot of them have one copper lead wire in there for the audio return (ARC)
If you look for optical hdmi you will find plenty for less then $100
 
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TomekNet

TomekNet

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There are several optical hdmi cables but I think a lot of them have one copper lead wire in there for the audio return (ARC)
If you look for optical hdmi you will find plenty for less then $100
Are there any pure optical HDMI cables? Can you recommend any?
I've been reading on different forums that so called "optical" HDMI cables still have standard conductors and pass electrical potential.
 
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TomekNet

TomekNet

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I've finally solved the last hum with a fiber.
Can't say it was a cheap solution.
But at least the device actually does what it says (4K60p 4:4:4 - HDMI 2.0 / HDCP 2.2)

20210204_202450.jpg20210204_202520.jpg20210205_052702.jpg20210205_052630.jpg
 
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