Input selector - switching the ground

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karatestu
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Input selector - switching the ground

Unread post by karatestu »

I have been thinking about switching ground as well as signal when selecting sources.

Having all the 0V wiring connected to various sources is surely a bad thing ? Switching it out would surely remove all that potential antenna ? It could also prevent unwanted earth loops if you have more than one source with signal 0V connected to mains safety 0V. On the other hand, if you only have one source with a signal to safety 0V connection then there will be no connection when not using that source :think: .

I need to look into this more. Maybe it is not even worth doing. Has the potential of producing loud noises when changing source via the selector. Maybe a make before break switch is required.

Any input :grin: appreciated.

Stu
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Chopsaw54
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Re: Input selector - switching the ground

Unread post by Chopsaw54 »

Martin Clark over on PFM did explain it to me a long time ago and said it wasn't a good idea but I can't just remember the full reasoning. It's to do with rising levels of dc or something from whatever equipment is plugged into the preamp. However I seem to recall that a resistor from the ground tag of the phono socket to amplifier ground keeps dc from rising from whatever is plugged into that input once the ground is disconnected from the preamp. I can't remember the resistor value but it must be big enough that it doesn't constitute an ground connection but small enough to bleed dc to ground. A make before break switch is essential I would have thought. I hope that some sense lol.

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karatestu
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Re: Input selector - switching the ground

Unread post by karatestu »

Cheers Chopsaw. Martin certainly knows his stuff. Another of my brilliant ideas filed in the bin :grin:
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Geoff.R.G
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Re: Input selector - switching the ground

Unread post by Geoff.R.G »

May I recommend that you Google "The pin 1 problem". You will find a wealth of information, and unfortunately misinformation, on the subject.
You may end up thoroughly confused but I can assure you that reducing the ground resistance does make a difference, even if my experience did involve audio source selection on a 747-100.

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karatestu
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Re: Input selector - switching the ground

Unread post by karatestu »

Hi Geoff.

One of the mods we did on naim equipment yonks ago was to make the 0V connections as low impedance as possible. I did make a difference for the better.

Pin 1 problem - i have read about that before but didn't take much notice :grin:
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Geoff.R.G
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Re: Input selector - switching the ground

Unread post by Geoff.R.G »

karatestu wrote: Fri Sep 06, 2019 6:41 pm Hi Geoff.

One of the mods we did on naim equipment yonks ago was to make the 0V connections as low impedance as possible. I did make a difference for the better.

Pin 1 problem - i have read about that before but didn't take much notice :grin:
Essentially the Pin 1 problem is that pin 1 can be significantly above earth, when it is there is a resistance across which a noise potential can exist. Get pin 1 down to earth potential and the problem goes away. Well my crosstalk on the 747 did.

Pin 1 on an XLR is signal ground by the way but, as my experience on the Classic 747 illustrates, the "problem" it isn't just applicable to balanced audio systems.

keepitsimplestupid
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Re: Input selector - switching the ground

Unread post by keepitsimplestupid »

Pin 1 on xlr should be chassis bonded at both ends if done to spec. All commoned in all devices with shortest path to clean side of 0v return in psu

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Re: Input selector - switching the ground

Unread post by keepitsimplestupid »

Search for the 'g word' by Bruno putzeys for an in depth discussion of ground vs earth as it pertains to audio, especially differential balanced circuits.

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