2. amps-preamps
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Cheater plug safety

So I recently decided to swap out my subwoofer amp for another one I had to see if it worked better with the driver. It did, but I have run into a slight problem. My old sub amplifier had a captive two prong cord. The new one has a 3 prong cord.

The subwoofer amp resides on a different AC circuit than the rest of the system. (Can’t be avoided)

Although the new amp is an upgrade for the sub, there seems to be a ground issue that is hazing up my transparency and sound stage. The system looses some air when the sub amps ground isn't lifted. There is no hum problem through any speaker per se, but just an overall sonic degradation when the ground is left in place. Using a cheater plug just on the sub amp brings back The transparency and it sounds absolutely beautiful.

I read that this can be dangerous, though. (Then why are these created plugs made?) anyway, I also read that as long as the amplifier with lifted ground is connected to the rest of the system via interconnect , and the other components are grounded, then the amp will use the ground from the other circuit that the other equipment is connected to and you are "safe", and only some very unlikely happenings, such as an internal ac wire becoming loose and touching the chassis and standing in a puddle of water should cause a concern. I even had a parasound 750 amp in my college dorm that even suggested using a cheater plug if needed for hum, sooooooo.........

At any rate I am addicted to the sound at the moment and going back without the cheater plug just sounds dull and fuzzy. The system is resolving and shows just about anything you do to it. Mind you, it’s not a night and day difference that would say that there is something wrong with any of the equipment, just a subtle but very tangible improvement that I definitely like and desire. The equipment is working 100% properly.....

It sounds so much better than the old amp and the transparency and air I’m getting right now are rediculous, but I don’t want to get shocked, but the chances seem to be very slim. Can anyone advise?
audiolover718
erik_squires
5,268 posts
 
Only a qualified tech should attempt this, but it appears possible that the signal uses a floating ground and that the chassis and power supply ground are not bonded together. If this is true, then I would recommend:

  • Use standard 3 pin plug
  • Use shielded IEC cable. Most IEC cable is 3 conductor but not shielded. Connect shield at plug, not amp. Connect ground at both ends, of course.
  • Move switch and fuse to the same "hot" side of plug.
  • Bond chassis to AC safety ground.
You don’t want any voltage inside if either the switch or fuse is open. Having them on opposite sides of the incoming AC allows for the small possibility of one or the other opening, but still having 120VAC inside.

Best,


Erik
jea48
2,944 posts
 
but it appears possible that the signal uses a floating ground and that the chassis and power supply ground are not bonded together.
Eric,

What power supply ground?

Equipment today that have a 2 wire power cord and polarized plug, that use double insulated AC power wiring, does not have an earth ground. In the world of this audio equipment the metal chassis and metal enclosure that houses the chassis is it’s ground for the power supply of the secondary and signal ground is all it knows. Am I wrong?

You don’t want any voltage inside if either the switch or fuse is open. Having them on opposite sides of the incoming AC allows for the small possibility of one or the other opening, but still having 120VAC inside.

Agree.

That could be a possible problem, IF.....

Jim

.

arcticdeth's avatar
arcticdeth
179 posts
 
my sunfire sig has only  the  two prong plug, no ground plug.
 so putting a three prong adapter will essentially do nothing ? correct?

 also the house wiring from box to outlet is basic thin stuff, commercial wire.
 adding an expensive power cable will also do nothing. as if theres 300 feet of garbage wire, how do you expect to get better sound by adding another 4 foot of high quality wire? don't make sense, now if you wired your house with all 8 gauge to your dedicated 20 or 30 amp breakers, and used a good power cable, i can see an upgrade. other than that, its a waste of money
gbmcleod
396 posts
 
I haven't read all the posts, but I've been lifting grounds for 35 years, and have not had a problem. From what I was taught (in High End audio), the ground should be at the preamp, and you lift the ground at other places. 
The thing is, all cheater plugs now are made with one side polarized. That didn't start happening 'til the late 90s, I could always find a cheater plug with two small prongs, so I could turn them whichever way I needed. 
erik_squires
5,268 posts
 
GB,

You haven’t had a problem because fortunately equipment is reliable, but you are defeating a built in fail-safe. Please don’t do it and don’t suggest it to others.

It's like the guy who never wears a seat belt, because hes' never had a problem without it. :)

There are much better ways to do this.

Best,


Erik
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