2. amps-preamps
  3. 126866-10110

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
15,805 posts
 
I've been meaning to put together a blog post about this, please find my latest here, which discusses a range of problems and inexpensive solutions!

http://pqltd.blogspot.com/2016/11/quick-safe-and-easy-fixes-for-ground.html
jetter
2,961 posts
 
In order to make my Dynaco st70 safe to use, I would need to have a three prong plug attached?  Easy to have done, but just asking if that is the solution?
erik_squires
15,805 posts
 
Hi Jetter!

I would be a little careful retrofitting. Designers tried a lot of things before 3 prong outlets became standard and added all sorts of odd solutions to attach the case to the AC line.

I would probably leave yours alone. I'm not an expert, but I can just envision a series of problems. :) I'd talk to other owners or techs who have experience with your particular model.

Possible problems may be that your input grounds are in fact connected to the case ground. This should be disconnected before attempting the retrofit, and if there is any connection it would be star grounded at the transformer's center tap.

Best,

Erik
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