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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
jea48
4,303 posts
 

jetter said:

kijanki, or anyone who cares to answer, does older equipment such as a Dynaco ST70 that has its original 2 prong plug have a greater shock potential?

Probably more so if the amp’s old AC wiring and power transformer are original. What are the chances of a user receiving an electrical shock if an internal hot to chassis fault were to occur? It all depends on the circumstances of where the amp is located and associated equipment it is connected to. It also depends if the amp and all other associated equipment is plugged into the same wall receptacle outlet.

Examples where a hot to chassis fault has occurred:

First for the user to receive an electrical shock he must place his body, or some part of, in series with the hot chassis and an earth grounded object. In this case the user completes a ground fault circuit path from the Hot chassis through the part of his body that is in contact with the earth grounded object, back to the source the electrical panel grounded service neutral conductor. Current will pass through the user’s body and he will feel the shock.

Grounded objects?

Is the floor bare concrete? As in a basement? In this case if the user was in his bare feet and touched any metal part of the amp the user would receive an electrical shock. On the other hand if the amp was on an insulated floor like wood he would not. His body would be insulated/isolated from a grounded object. Like a bird perched on an overhead high voltage power line.


Back in the day the Dynaco ST70 was first designed what other associated equipment that might be connected to the amp by ICs used a safety equipment ground?

Was there even a 3 wire grounding type wall receptacle back then?

What other grounded objects, within arms length or other parts of the body, could the user come into contact if he touched the hot chassis of the amp?

Say the user has a preamp that uses the wall receptacle safety equipment ground. The outer case/enclosure of the preamp is metal. Maybe the knobs are metal. There is now a grounded object in close proximity of the user for the possibility of the user to come into contact at the same time while touching the metal chassis of the amp. But wait. The signal ground of the ICs will ground the equipment right? Maybe, maybe not.... First I would never rely on the small signal ground wire of an IC to carry the high current of a dead short ground fault back to the source. For a typical 20 amp branch circuit the initial ground fault current can be over 100 amps before the breaker can react and hopefully trips open breaking the ground fault circuit.

What if the user buys a new pair of ICs. What happens when he disconnects the second IC from the first RCA jack? Is there a chance his fingers could come into contact with the outer metal shell of the IC and the metal case/enclosure/chassis at the same time?

So what if the preamp has a ground lift switch that lifts the signal ground from the safety equipment grounded chassis? The false feeling the IC will protect the user from an electrical shock is gone.

Bottom line, just be careful if you are using old vintage 2 wire cord and plug equipment. Especially if the plug is non polarized. When changing ICs unplug the vintage equipment power cord from the wall receptacle outlet first.

.

stringreen's avatar
stringreen
6,371 posts
 
safety is important....but also, using poor quality cheaters (all of them) brings grain and grunge into the system.  I use them only for detection of ground problems, but remove it after the test.  You should fix your ground problem, and use the original plugs as is intended.
jetter
2,959 posts
 
Thank you for the explanation jea48.  Actually I have been zapped once by the unit, but it was my error.  I was setting the bias, which of course you do with the unit running, and touched the wrong part of the amp (i.e. the exposed parts around the 7199 driver tubes).  Its one of those things you only want to do once.  
bpoletti
1,529 posts
 
The only way to safely use a cheater plus is to keep it sealed in it's original package.
erik_squires
15,788 posts
 
There is a little confusion in what "lifting a ground" means.

It’s perfectly safe to lift the signal ground. That is, the ground associated with RCA or XLR cables and plugs. Pro gear or devices with XLR inputs often provide this feature. It’s a very good thing and sometimes the most important reason to use XLR inputs.

The AC safety ground is not the same thing. It starts at the round middle pin on the AC plug and terminates at the metal chassis. Lifting, or removing the AC safety ground is NEVER a safe thing. Not all equipment requires it, but if they do, it should not be removed when present.

Cheater plugs originally had a good purpose. They were designed so you could screw the ground to the face plate screw on wall sockets without having to replace the entire receptacle. However, many of these receptacles weren’t grounded to begin with, so the screw was pointless, and no one uses it correctly anyway. :) So, effectively, @bpoletti is right. Leave them at the store. If you have 2 prong wall outlets then it is time to upgrade them anyway, as your wiring is probably 40-50 years old.

Best,


Erik
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