UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

TonyDuell · 31st Oct 2018, 5:55 pm

I really dislike the idea that the screen of the audio cable should be the safety earthing conductor. It can be disconnected too easily, and may not carry the current anyway. I wonder why balanced (differential) inputs are not common on hi-fi amplifiers. This would go a long way to solving the earth loop problem. But anyway.

Some valve tuners which drew their HT+ voltage from the main amplifier used the audio cable screen as the HT return. Meaning that if you unplugged the audio cable the tuner chassis would get up to the HT+ voltage (albeit somewhat current-limited) relative to the amplifier chassis. ARGH!

31st Oct 2018, 5:55 pm	#4
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Philips N4407 etc double insulated? I really dislike the idea that the screen of the audio cable should be the safety earthing conductor. It can be disconnected too easily, and may not carry the current anyway. I wonder why balanced (differential) inputs are not common on hi-fi amplifiers. This would go a long way to solving the earth loop problem. But anyway. Some valve tuners which drew their HT+ voltage from the main amplifier used the audio cable screen as the HT return. Meaning that if you unplugged the audio cable the tuner chassis would get up to the HT+ voltage (albeit somewhat current-limited) relative to the amplifier chassis. ARGH!