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Chassis ground and balanced mode - please help me

Plinius SA 102 has a ground switch (open vs. chassis) that they specify should be set to Chassis when running in balanced mode.

1. I assume that this has to do with achieving proper noise cancellation - but if not can someone straighten me out?

The problem: I am trying to run the Plinius with a Pass Labs X1 pre in balanced mode. There is a LOUD ground loop hum when ground is set to chassis that goes away in open position. Floating one of them does not help.

2. If I power the Plinius and the Pass using two separate lines back to my panel, will this ground loop problem be removed?

3. Will I be able to solve this problem?
jsteigert
marakanetz's avatar
marakanetz
5,473 posts
 
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.
sean
6,229 posts
 
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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ed_sawyer
588 posts
 
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
gs5556
769 posts
 
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.
jsteigert OP
14 posts
 
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?
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