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Please help me solve my ground loop issues - Pics and layout attached.
Please help me solve my ground loop issues - Pics and layout attached.
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Old 23rd April 2013, 11:38 AM   #11
CopperTop is offline CopperTop  United Kingdom
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Join Date: Feb 2009
Location: UK
Do we know which transformers are suitable for 'Class II' and which aren't? All we need to know is that the secondary cannot become live. We can earth the enclosure as long as we keep the connectors isolated, and ensure that even detached mains wires cannot physically touch anything after the transformer. I could live with this arrangement.

As an example, would this transformer be suitably approved?
MCTA250/40 - MULTICOMP - TRANSFORMER, 250VA, 2 X 40V | Farnell United Kingdom

It says in the data sheet
Quote:
Termination:
All leads tri-rated UL1015 style cable rated 600 V / 105C VW-1
Primary leads double insulated with PVC sleeving for a minimum of 20 mm
Lead lengths 5 mm approximate all leads ends tinned to 6 mm
Pri / Seconds leads O

Standards:
Designed and manufactured in accordance with:
EN60742 (Non short circuit proof),EN60065 (IEC65), EN60950
UL recognised to UL1411, 2601-1 and UL1950 under family approval file E115159
All we need for peace of mind is to know is whether the primary->secondary insulation is approved, but the words 'Class II' or even 'double insulated' with respect to this, are very hard to find anywhere.
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Old 23rd April 2013, 12:00 PM   #12
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
Coppertop,
ask your house and contents insurance company if they will insure you against the risks of your version of ClassII equipment becoming faulty and killing someone?
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Old 23rd April 2013, 12:42 PM   #13
CopperTop is offline CopperTop  United Kingdom
diyAudio Member
 
Join Date: Feb 2009
Location: UK
Quote:
Originally Posted by AndrewT View Post
Coppertop,
ask your house and contents insurance company if they will insure you against the risks of your version of ClassII equipment becoming faulty and killing someone?
As I suggested in my first post earlier, the dogmatic "All exposed metalwork must be earthed" line is easy to say, but doesn't actually offer a solution. If the home constructor is going to build an amplifier and use it with an earthed computer, say, is there an approved way of doing it that doesn't give rise to ground loops?

In the absence of anyone telling them how to do it properly, they're going to come up with their own potentially risky solutions.

You know about this stuff. Just tell us how to do it!! :-)
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Old 23rd April 2013, 08:57 PM   #14
Fusion916 is offline Fusion916  United States
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Join Date: Feb 2012
... Does anybody have any suggestions for my setup/layout/etc? So far the discussion has centered around the theoretical, but is the only solution to not use the earth ground in my active crossover?
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Old 23rd April 2013, 09:17 PM   #15
Conrad Hoffman is offline Conrad Hoffman  United States
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Join Date: Mar 2007
Location: Canandaigua, NY USA
Maybe I'm just lucky but when my system was tri-amped, the preamp, the crossover and all three stereo power amps had the line ground connected directly to the chassis, all circuit grounds connected to the chassis and there was no hum problem. The trick is where those connections should be made.

There should never be current flowing in shields, one of which is the chassis. I connect mains ground to the chassis right where the module is, or the cord comes in. Everything else connects to a master ground point, which is usually located at the power supply, and that point also connects to the chassis at a single point close to the power supply. Most RCAs have ground wires that also run to the PS master ground, though my power amps usually mount the RCAs right to the chassis. Finally, everything plugs into a power strip, never into widely separated outlets.

Probably not to the best theory, but it works without fancy ground breaks using resistors or diodes.
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