Chassis ground and balanced mode - please help me

hahaha.... as they say, it's the simple stuff that'll kill ya : ) Glad to see that it really was simple : ) Sean
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Mystery solved. I was working with a dealer on these speakers when this event occurred, getting ready to bring them home. He was behind the amp operating the switch. It turns out that things were actually working as they should have. The big hum came when he switched the amp into OPEN mode and went away when he switched to chassis ground, exactly as SHOULD have happened. The only thing backward here was the communication between us. Thank God for little things.

J: I think that a phone call to both manufacturers might offer you quite a bit of info. I'd be curious as to what you find out, so please, share the wealth once it falls into your lap : ) Sean
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PS... I was not talking about Pass or Plinius gear in specific, but all audio gear in general.

Sean, If you look inside the Plinius it has two HUGE toroids separated by a metal horizontal divider from the compartment containing the circuit boards. This is already beginning to look like a pair of Faraday cages to me. J.

J: While i don't know how common it is in audio gear, some RF designs make use of two different "grounds". One is a board ground and the other is a chassis ground. In some instances, it is beneficial to have these two grounds separated and in some instances, it works better to have them tied together. I don't know if this is what Plinius is doing with their switch, but it might explain some things.

Personally, i've always wondered why audio components tied circuit ground to chassis ground ??? If audio engineers were "smart" ( some really are, some ... ), they would use the chassis as a "Faraday cage". In effect, the chassis would be tied to electrical ground but NOT to circuit ground. This would increase the rejection of RFI and minimize the potential for damage via inducing stray voltage ( static shocks ) into the circuitry. While this would mean that all of the external signal connections ( RCA's, XLR jacks, etc.. ) would have to be isolated from the chassis electrically, that is not really a big deal. It might raise the cost of a product slightly, but hell, we're already paying too much as it is yet we come back for more with every purchase. Sean
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Ed, Both pieces are true balanced designs. I am not clear why Plinius lays out their spec in the way that they do. I need to ask them.

Sean, Since the ground at the panel is common to all circuits, I am not surprised to find out that dedicated lines won't help. I think you are right - I need to determine whether there is a basic mismatch between Pass and Plinius. So a call to Pass is also in order. The good news is that both companies are very responsive.

Gs5556, I think it it interesting that the Plinius open ground switch achieves isolation that floating the power cord ground does not. Any thoughts on this?

It sounds like that the Pass preamp is providing the signal ground that the Plinius "chassis/open ground" switch provides. So by opening the ground on the Plinius, you are eliminating multiple ground paths which caused the hums. Multiple paths remain along the signal path so floating the power cord ground doesn't help. Like it's stated above - it works, so enjoy.

If switching the ground switch on the plinius to open solves the problem, then you already have your answer. Just leave it on open! No need to make it more complicated than it is. Whether the ground switch is set to the chassis or not doesnt' affect whether the signal is transferred as balanced signal or not. That comes from the design of the gear - and likely both are truly balanced pieces. If it sounds good it is good - leave it at that. And if there is a ground loop hum it's more likely to do with the lines in your house than the gear per se.

-Ed

I would suggest calling Pass Labs up and see what they have to say. Other than that, running dedicated lines for each component would not correct the problem if there was a difference in ground potential between the lines. Since you've floated the grounds on both / either component, it does not appear that it is an Earth ground based problem but is simply a conflict in impedances / loading between components. Sean
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1. most-likely there is no problem
2. if this occures i believe either plinius or pass is not true-balanced and actually uses balanced receptacles in unbalanced cicruit.