Hum from amplifier

Numpty112233

Will look into the iFi
Confused whether or not the 5v supply is required?
Just to check if this is suitable with an 8 metre USB (Supra) cable which I understand is powered as it's longer than 5 metres

Many thanks to all for the help!

Paul7777x

It doesn’t need the power supply to make a galvanic isolation, (the additional downline power supply is supposed to decrease any usb power supply noise before it gets to a dac).

It’s easy enough to find out if it does. Any old phone charger you have hanging about will do the job, or you can get an inexpensive 5v phone add on battery for about eight quid to test the claim.

But for your specific needs the iDefender itself is all you need. Or any other galvanic isolator for that matter.

Paul7777x

Ps, I’m not familiar with the Supra powered cable and I can’t find a reference to it.

But, they’ve dropped the ball if they haven’t included isolation built in if it’s supposed to be an ‘audio’ usb cable.

Numpty112233

                                                Supra USB 2.0 Cable Type A To B Plug 8m - USB Cables - AV Online - UK Home Cinema and Hifi Specialists                                                                                                        Supra's stunning USB 2.0 is a rewarding impedance-matched cable that offers a dynamic, rich and detailed music experience. Suitable for high-quality DACs.                                                                                                                                                                                                                                                                                                                www.audiovisualonline.co.uk                                                                                My understanding is all USB cables over 5 metres require power to work

Paul7777x

Ah. I see, I thought you meant that Supra had a powered cable.

In the case of usb cables over 5mtrs, some receivers will require a short cable. Others don’t. However, with the iDefender, you can use a charger or battery that has a 2 or 2.5 amp output capability.

I’m not sure if that will suffice for a recalcitrant receiver to draw from, but I’d expect so.

The only other way to to do it is to go through a powered repeater.

Ps, just to check I’ve got this right, is the usb output from the Mac feeding a usb input on your receiver?

Numpty112233

No
the USB cable goes from Mac to stereo amp
the Av receiver pre out goes via twin analogue RCA to stereo amp HT bypass power amp section
remove either the USB cable from the Mac or RCA from the stereo and the hum stops and everything works as it should so I guess either cable could have an isolator gizmo fitted to solve. Whichever one is least likely to affect sound quality.

Paul7777x

I assume both the optical inputs on the Denon are taken, so the usb input it is.

In which case I’d suggest fixing the hum from the usb end. It seems simply to be a case of detaching the usb earth using the iDefender (or similar) which won’t affect the sound.

Adding cheap isolators to the analogue cables is more likely to.