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Getting rid of ground loops: What is the best option? - Page 3

post #31 of 38

Okay, here's a related question for you guys:

I have a pair of old mono tube amps with metal chassis that were serviced and a grounded cable added to them for safety purposes.  But... I want to plug these in via the switched, non-grounded outlets on my pre-amp.  The power switch for the amps is the treble tone control, and it is known to fail through regular use.  The switched outlets would prevent that from happening.  Of course, I do not want to lose the grounding.

 

I've thought about getting an extension cord and routing the grounding tab on cheater plugs to the hacked up extension cord, cutting off the live portion of the extension cord's plug.  But is there something similar commercially available, perhaps with plastic prongs in place of the metal ones?

post #32 of 38

You can also use a single ground wire that you attach to the amp chassis using an existing screw, then attach the other end to "ground", whatever that is in your case. You won't be using the third pin on the power cord, so a cheater plug would be fine. Might be a little less messy than a hacked apart extension cord.

post #33 of 38
Quote:
Originally Posted by anetode View Post

The Ebtech Hum X works well and isn't too much of a rip-off. Alternately, I haven't heard any degradation with a cheapo ground loop isolator.


Ditto, perhaps the best option available today.

post #34 of 38
Quote:
Originally Posted by jaddie View Post

You can also use a single ground wire that you attach to the amp chassis using an existing screw, then attach the other end to "ground", whatever that is in your case. You won't be using the third pin on the power cord, so a cheater plug would be fine. Might be a little less messy than a hacked apart extension cord.

 

I'm not sure how I would ground the amps without using the existing electrical infrastructure (i.e. the wired ground), and to tap into that I'm either going to need to hack up an extension cord, make my own, or buy a commercially available product to do the same thing.

 

It's not like I can go sink a 6 ft long copper pole in the ground outside my balcony and run a wire up to my apartment...

post #35 of 38
Quote:
Originally Posted by BlackbeardBen View Post

 

I'm not sure how I would ground the amps without using the existing electrical infrastructure (i.e. the wired ground), and to tap into that I'm either going to need to hack up an extension cord, make my own, or buy a commercially available product to do the same thing.

 

It's not like I can go sink a 6 ft long copper pole in the ground outside my balcony and run a wire up to my apartment...

Your basic problem is you have a nice 3-pin grounded plug on your amps, but your switched outlet on your preamp is only 2 pins.  So, the Ebtech Hum X won't help you.  You want to use the two pin outlet and still ground the amps. 

 

One question, though first: does your preamp have a 3 pin grounded plug too?  If not, you may actually be creating more of a problem by grounding your amps.  Any ground leakage in the preamp will flow back through the shield of the output cable to the amps, then from their chassis to ground (assuming you find a way to ground them).  Might want to just try it without the ground first.  

 

The center screw that holds the cover of any outlet is tied to the conduit, which is grounded. That's what the small metal eyelet on the "cheater" is supposed to be screwed to, and that screw is at the same ground potential as the third pin.  If you don't want to hack up an extension, you can just run a wire from a screw on the amp chassis to the center screw on an outlet.  However, if you ground your amps this way, you'll probably want to ground the preamp that way too.  Could end up with quite a knot of wires on that outlet screw.

 

Or, like I say, just float them all.  Unless there is a problem with leakage to the amp chassis, it'll be fine.  

post #36 of 38

There are some outlets strips available with a control receptacle. When the component plugged into the control position is turned on, all the other receptacles are turned on.  Decades ago even Radio Shack sold one.

post #37 of 38
Quote:
Originally Posted by jaddie View Post

Your basic problem is you have a nice 3-pin grounded plug on your amps, but your switched outlet on your preamp is only 2 pins.  So, the Ebtech Hum X won't help you.  You want to use the two pin outlet and still ground the amps. 

 

One question, though first: does your preamp have a 3 pin grounded plug too?  If not, you may actually be creating more of a problem by grounding your amps.  Any ground leakage in the preamp will flow back through the shield of the output cable to the amps, then from their chassis to ground (assuming you find a way to ground them).  Might want to just try it without the ground first.  

 

The center screw that holds the cover of any outlet is tied to the conduit, which is grounded. That's what the small metal eyelet on the "cheater" is supposed to be screwed to, and that screw is at the same ground potential as the third pin.  If you don't want to hack up an extension, you can just run a wire from a screw on the amp chassis to the center screw on an outlet.  However, if you ground your amps this way, you'll probably want to ground the preamp that way too.  Could end up with quite a knot of wires on that outlet screw.

 

Or, like I say, just float them all.  Unless there is a problem with leakage to the amp chassis, it'll be fine.  

 

No, my preamp is non-grounded.  I see what you mean about the potential ground leakage problem.

 

Yes, I know about the grounded screw on outlets without the ground pin.  I'm plugging everything into a surge protector/power strip - but it never occurred to me to run a wire to the screw even on a three-prong outlet.  Do you know if three-pronged outlets typically still have the screw grounded?

 

 

Quote:
Originally Posted by Speedskater View Post

There are some outlets strips available with a control receptacle. When the component plugged into the control position is turned on, all the other receptacles are turned on.  Decades ago even Radio Shack sold one.

 

Hmm, that sounds like a very interesting idea, if I can find one.  Thanks for the idea!

post #38 of 38
Quote:
Originally Posted by BlackbeardBen View Post

 

No, my preamp is non-grounded.  I see what you mean about the potential ground leakage problem.

 

Yes, I know about the grounded screw on outlets without the ground pin.  I'm plugging everything into a surge protector/power strip - but it never occurred to me to run a wire to the screw even on a three-prong outlet.  Do you know if three-pronged outlets typically still have the screw grounded?

Yes, the screw is grounded by design and necessity.

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