So I can currently think of 2 solutions
1. Speaker cable switch - but I have a 7.1.4 out of the Yamaha 3070 which requires 2nd amp so would need to loose 2 speakers
2. Turn off at the wall the AV receiver and Bluray except when using, when hum isn't really noticeable
Probably not a good idea and I expect to get shot down in flames for this suggestion but would disconnecting the earth in the AV receiver plug be a solution?.....
Any other options?
Have you check your wiring? You may not have your earth connected properly, just use one of these:-
KKmoon Automatic Electric Socket Tester Neutral Live Earth Wire Testing RCD Test UK Plug: Amazon.co.uk: DIY & Tools Shop KKmoon Automatic Electric Socket Tester Neutral Live Earth Wire Testing RCD Test UK Plug. Free delivery on eligible orders of £20 or more. www.amazon.co.uk
If that is OK you probably just need to ground the Denon amps chassis...
Wiring has been checked by qualified electrician - I did the wiring and he fully checked and tested it. HOWEVER
I was scratching my bald patch over there being two grounds when of the 3 components (amp, receiver and bluray) only one had a metal earth pin on the plug.
That got me thinking what else was attached to the amp
USB cable from Mac which is on a different ring main.
Removal of USB from back of Mac also stops hum
Any thought how to solve the hum with the USB still plugged in and AV receiver switched on?
The isolator in post 2 in theory solves the problem but has very mixed reviews, including loss of S.Q.
This may help, It will isolate the USB from the amp, converting the usb to a coaxial connection:-
Schiit Eitr Buy your Schiit Eitr online, directly from Schiit.eu,The Authorised EU retailer offering 2 years warranty /proxy.php?image=https://www.schiit.co.uk/image/favicon.ico&hash=5f48725c2f709f0884f5347c96d7d614&return_error=1 www.schiit.co.uk
Interesting - will contact them to see if it will solve the issue as it states "with complete electrostatic and electromagnetic isolation (via transformers),"
I initially missed your last line. I may try that but not sure how 3 grounds will cure having a problem by having 2 as a loop. Electronics is too complicated for a Numpty...
Anyone care to advise on losing the earth connection on either the AV receiver or Mac plug to reduce down to 1 ground connection for the loop?
Maybe worth trying an isolator on the USB cable - google them, plenty to chose from.
iFi iDefender3.0 External USB Ground Loop Eliminator: Amazon.co.uk: Electronics Free delivery and returns on eligible orders. Buy iFi iDefender3.0 External USB Ground Loop Eliminator - Silence Noise/Hum/Buzz/Distortion at Amazon UK. www.amazon.co.uk
If removing the usb from the Mac gets rid of the hum then that’s (obviously; sorry for being pedantic), the problem, so this is the most likely cure.
You can also add a battery (such as a phone pack) or a clean 5v power supply, should you wish, into the iDefender downline of the Mac’s usb output thereby (allegedly) cleaning up the usb’s signal as well as removing the hum.
So, certainly no signal degradation, a (possible) improvement even, and hum removal.
...alternatively, if your just feeding music through the usb to the amp then one of these will do the job of perfectly isolating the Mac from the rest of your hifi if you have a spare optical input.
Good manufacturer and a good quality Xmos circuit.
/proxy.php?image=https://i.ebayimg.com/images/g/uIwAAOSwtRRdTS1Y/s-l400.jpg&hash=69322ad7838915ecfb702851465c3c83&return_error=1 Douk Audio XMOS XU208 DSD USB to Optical Coaxial Converter Digital Interface OTG| eBay U2 is a USB to Toslink optical and coaxial converter, suitable for PC computer, notebook, android phone(OTG), set-top box, rock 64, raspberry pi and so on, it can bring better listening experience than PC own sound card. www.ebay.co.uk
Look an earth loop is easy to diagnose with a pencil and paper and tape measure. You can assume that each electric item, including usb leads, coaxial tv antennas,power leads HDMI cable and the RCA leads are all earthed somewhere. Just look at the dimensions of the biggest of these loops and that is often the power socket