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Re: Class A, AB1, B, C Operation/Modes [message #96688 is a reply to message #96679]

Tue, 09 May 2023 21:30

gofar99
Messages: 1949
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi, There are several ways to make the chassis to signal ground connections. Everything from the old school way of using the chassis as the signal ground (usually too noisy for me) to huge bridge rectifiers. Any of them can comply with the various electrical codes as long as the user is protected from accidental contact with a live chassis. How we all lived through the 2 wire AC mains days with tube gear is a miracle. What I find is there is a sort of sweet spot when using an X2 capacitor and a resistor in the 120 to 150 ohm range. It is not designed to protect from faults like lightning etc or really any external faults. That is why the chassis is AC mains earth grounded. It will provide a path to the earth ground if there is an internal fault but that is not the main purpose. It is not really all that good at that as the impedance is fairly high. Its purpose is generally accepted as two fold. One it acts as a ground loop prevention measure when other gear is connected that passes signals to the subject device. The signal ground on the one will not find an alternate path through the AC mains and cause hum. Second it allows the chassis to act as an EMI shield without being in direct connection. IMO your one ohm resistor will comply with the codes....but may not provide as much ground loop hum rejection as is possible. And as nearly everyone knows...I hate hum and noise with a passion and the higher value resistor helps. BTW wattage is not really critical (I use 1 watt ones) as fault protection is not the primary function...that is what the chassis and three wire mains connection is supposed to do. Even if the resistor failed, the user is still protected. Now to be difficult...I could make a case for if the resistor and X2 fail open and an internal circuit fault energized the signal ground and it was connected to either an input or output cable that had a circuit ground conductor and the user was touching the ground conductor and something else that really was grounded there could be a hazard. Such a failure would almost always manifest itself as an anomaly in the gear and require attention. But then that sequence can happen with anything attached to the AC mains like lights, appliances etc. Opinions anyone?

Good Listening
Bruce

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[Message index]

		Class A, AB1, B, C Operation/Modes By: positron on Sun, 05 February 2023 20:40
		Re: Class A, AB1, B, C Operation/Modes By: Wayne Parham on Sun, 05 February 2023 20:54
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Mon, 06 February 2023 20:38
		Re: Class A, AB1, B, C Operation/Modes By: positron on Tue, 07 February 2023 16:13
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Tue, 07 February 2023 19:33
		Re: Class A, AB1, B, C Operation/Modes By: positron on Tue, 07 February 2023 20:37
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Thu, 09 February 2023 21:01
		Re: Class A, AB1, B, C Operation/Modes By: positron on Thu, 09 February 2023 21:35
		Re: Class A, AB1, B, C Operation/Modes By: positron on Tue, 28 February 2023 19:04
		Re: Class A, AB1, B, C Operation/Modes By: Wayne Parham on Wed, 01 March 2023 08:28
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Wed, 01 March 2023 19:45
		Re: Class A, AB1, B, C Operation/Modes By: positron on Sun, 05 March 2023 00:33
		Re: Class A, AB1, B, C Operation/Modes By: Wayne Parham on Sun, 05 March 2023 08:05
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Sun, 05 March 2023 08:10
		Re: Class A, AB1, B, C Operation/Modes By: positron on Mon, 06 March 2023 19:01
		Re: Class A, AB1, B, C Operation/Modes By: positron on Sat, 06 May 2023 22:32
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Tue, 09 May 2023 21:30
		Re: Class A, AB1, B, C Operation/Modes By: positron on Thu, 11 May 2023 00:26
		Re: Class A, AB1, B, C Operation/Modes By: positron on Tue, 05 September 2023 23:48
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Fri, 08 September 2023 21:12
		Re: Class A, AB1, B, C Operation/Modes By: BreakneckRedneck on Sun, 24 September 2023 00:42
		Re: Class A, AB1, B, C Operation/Modes By: positron on Thu, 12 October 2023 11:21
		Re: Class A, AB1, B, C Operation/Modes By: positron on Fri, 03 November 2023 12:22
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Fri, 03 November 2023 20:58
		Re: Class A, AB1, B, C Operation/Modes By: positron on Sun, 05 November 2023 01:38
		Re: Class A, AB1, B, C Operation/Modes By: positron on Thu, 07 December 2023 23:12
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Mon, 18 December 2023 20:20
		Re: Class A, AB1, B, C Operation/Modes By: positron on Tue, 16 January 2024 21:32
		Re: Class A, AB1, B, C Operation/Modes By: gofar99 on Wed, 24 January 2024 20:31
		Re: Class A, AB1, B, C Operation/Modes By: positron on Mon, 08 July 2024 20:22

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