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Old 22nd January 2010, 01:02 PM   #1
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Default No Ground = Great Sound

I recently upgraded from an old Hafler (DH110) preamp to a new Linn. The new pre uses a three prong grounded AC plug...the Hafler was a two prong ungrounded unit. The new pre has a very faint humm ( down 70db? ) when plugged into a grounded power strip. When I Ungrounded the preamp, the Linn was dead quiet ! I mean it was like it was not even turned on ....SUPER quiet.

Is there any risk running a preamp "ungrounded" ? My Halfer was happy being ungrounded for 20 years. I know grounded equipment has less risk of shock hazzard, but other than that is there any other consideration?
 
Old 22nd January 2010, 01:12 PM   #2
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There's a reason that Ground Lift Adapters exist.... to avoid ground loops and hum.

The only consideration is safety (risk of electric shock). 110 V like you have in the US is not really that dangerous anyway....
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Old 22nd January 2010, 01:40 PM   #3
Salas is offline Salas  Greece
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Use a back to back diode safety floating scheme. What you do is you employ two 5A diodes in parallel with their strap marked ends joined in opposite. You put those at the grounding point you lifted the cable from, and you attach that grounding cable on the new end. Now you got a ground lift but in case of a problem, current can run in the safety ground since the diodes are going to conduct in any 0.7V and over incident. Else, if any chassis develops a potential due to a fault in any system, the house safety trip relay that senses ground will know nothing about it and its against any safety rule. Be generally cautious.
 
Old 22nd January 2010, 02:10 PM   #4
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Originally Posted by Salas View Post
Use a back to back diode safety floating scheme. What you do is you employ two 5A diodes in parallel with their strap marked ends joined in opposite. You put those at the grounding point you lifted the cable from, and you attach that grounding cable on the new end. Now you got a ground lift but in case of a problem, current can run in the safety ground since the diodes are going to conduct in any 0.7V and over incident. Else, if any chassis develops a potential due to a fault in any system, the house safety trip relay that senses ground will know nothing about it and its against any safety rule. Be generally cautious.
Does this actually work? Have you tried it?

By the way, the GFI/GFCI should still trip even if ground is isolated at an end point. Yes, it stands for Ground Fault Interrupter, but it actually trips when current out through hot doesn't match current returned through neutral. Ground doesn't enter into it.

A common source of ground loops I've seen is the difference between the ground of AC power and the ground provided by a cable TV cable. These come together in AV systems. One solution for this is to get a 75 Ohm isolation transformer, or make one by using a 75-300 Ohm balun connected to a 300-75 Ohm F-Plug adaptor. Adding this in-line with the incoming cable separates the ground but couples the signal.
 
Old 22nd January 2010, 02:21 PM   #5
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Does this actually work? Have you tried it?
Yes, it does work. I install them in every pro amp I build. But use a heavy duty full wave bridge. Strap + to -, then use the AC as the loop breaker. A high current bridge will handle very large fault currents without failing open, and will provide two diode drops instead of only one. Voltage rating does not matter so a 50V part that you can't use for an amp power supply will work.
 
Old 22nd January 2010, 02:22 PM   #6
Salas is offline Salas  Greece
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Originally Posted by SQLGuy View Post
Does this actually work? Have you tried it?

By the way, the GFI/GFCI should still trip even if ground is isolated at an end point. Yes, it stands for Ground Fault Interrupter, but it actually trips when current out through hot doesn't match current returned through neutral. Ground doesn't enter into it.
Yes I have it in some of my DIY builds. It works. Its fairly known from some power amps.

GFI/GFCI works as other schemes globally? Is it totally safe without ground?
 
Old 22nd January 2010, 02:22 PM   #7
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Yes I do have a SAT TV ( sound ) in the loop so to speak. But with EVERYTHING ( 3 power amps; 1 electronic crossover; 1 CD player) all turned OFF the results are the same.

It just seems so much easier to run the preamp ungrounded and have black hole silence like it was with my ungrounded Hafler for the past eons. I'll keep reading your posts on safety and possible fixes. THANKS !
 
Old 22nd January 2010, 02:25 PM   #8
Salas is offline Salas  Greece
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Originally Posted by wg_ski View Post
Yes, it does work. I install them in every pro amp I build. But use a heavy duty full wave bridge. Strap + to -, then use the AC as the loop breaker. A high current bridge will handle very large fault currents without failing open, and will provide two diode drops instead of only one. Voltage rating does not matter so a 50V part that you can't use for an amp power supply will work.
Yes its good. I use lighter 5A diodes or bridges in line level equipment.
 
Old 22nd January 2010, 02:37 PM   #9
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GFI/GFCI works as other schemes globally? Is it totally safe without ground?
Yes. For example, the ABB GFCI modules (in the breaker box) I installed when upgrading the electrical supply in my apartment don't connect to ground. The main one was three phases hot plus neutral. The bathroom one was one phase hot and one neutral. Further, in that apartment, in Belgium, we actually didn't have neutral; all 220V power was two hot phases. So, in that case, the correct wiring was to jumper the neutral on the main GFCI to one of the hot phases, while the bathroom GFCI gets hot/hot.

I added ground to all the outlets (original wiring was from 1966 and didn't have ground), but ground still had nothing to do with GFCI.

The basic idea is that if you have a device that's leaking current to some non-standard return path, the GFCI will trip. E.g., a hair dryer dropped in the bathtub, where current will be flowing from hot to the ground of the tub/plumbing, rather than coming back through neutral.
 
Old 22nd January 2010, 02:43 PM   #10
SY is offline SY  United States
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I know grounded equipment has less risk of shock hazzard, but other than that is there any other consideration?
Other than potential death to you or some innocent person? No, not really.

NEVER NEVER NEVER operate equipment with the safety ground disconnected. NEVER!
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