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In Reply to: I guess I am missing your point too posted by Russ57 on April 27, 2007 at 09:54:24:
Well, you are saying that the DC power supply establishes *electrical ground* as a current return pathway for the circut. I am saying that your *electrical ground* is actually the circut Common return path, and that no actual connection to an Earth Ground is required for said circut to function as a circut, therefore why refer to such as a ground vs Common? By refering to such as ground, confusion can arrise & in fact did with the OP. Thanks for the English language lesson, but what does that have to do with the topic under discussion? Unless you were making the same point that correct terms DO matter after all.
Follow Ups:
I am simply trying to understand you. Good chance we are saying the same thing in different words. The neutral is considered an "earth grounded" current carrying conductor. So we can't get away from the fact that out power transformer primary has a ground connection.I think I must be missing an important point you are making. The only way I see is with balanced inputs and differential amp stages. Even then any unbalanced stuff can have the potential to go to ground.
Of course it goes without saying that the signal from a preamp goes only to the input tube's grid (and not through said tube) and straight to chassis/signal ground by way of grid leak resistor. If one has a 3-wire cord, or a cap from neutral to chassis, then you have signal connected to electrical ground.
If we wish to avoid electrical ground then best we avoid single ended stuff in general. But home audio, as well as 120VAC in the states, are both single ended in nature. Personally I run 60-0-60 balanced power and avoid a neutral. But I still reference signal ground and chassis to electrical/earth ground for safety reasons.
For instance, if your circut (any circut) were battery powered, then there is no actual Earth Ground connection. Yet the circut still operates, because there does exist a Common pathway for current return. With AC Mains powered equipment, the separate power supply circut derives the DC voltage to operate the audio circut, and again except for Safety with such AC Mains powered devices, there is no audio circut requirement for an Earth connection. But refering to the current Common return as an electrical ground DOES sometimes cause confusion as to how & where to make a Safety Earth Ground connection to the circut. Another example is *ground loops*, which are actually current loops that may exist even when no Earth connection is present. I must wonder if anyone bothered to read my original text, or just the subject header. Anyway, guess old habits are hard to discard, especially after a century of use.
Hi.I know where you come from. This is very common sorta misunderstanding btween signal return reference "ground", & actual electrical "earth" ground, or whatever yu can put it.
You're correct for audio amps DC powered, as long as the signal in & return circuit is completed, the amp functions.
But if the amp is working in an EMI/RFI noisy environment, like in many modern homes today, where tons of computers, notebooks, flat panel TVs are all over the place, the poor amp is subject to HF rash.
So metal chassis of the amp still needs to be earth grounded so that the harmful RF energies can be drained away via the earth path as per my post above despite the in/out signal circuit is completed.
As I posted earlier this week, my SS phonostage, a dual-monaural stereo design, full battery powered, still got its plastic housing full laminated with aluminum foil, which is AC grounded to the turntable chassis ground wire as well as the ground rod of the tube phonostage/line amp where the SS phonostage unit hooked up to its "
AUX" input.EACH of the I/P jacks of the SS phonstage unit is AC grounded to the plastic housing aluminum foil shield via a 0.1uF3KV ceramic disc cap,
an excellent potential RF rash short-cut from the amp return reference ground.c-J
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