Electrician's advice wanted: safely lifting ground

The danger from electric shock depends on several factors including but not limited to the persons own electrophysiology, the impedance of the person at the time, and the current path through the body. None of these depend on the potential. For example, an arm to arm path will result in more current flowing through the heart than most other paths and put you at more risk of vfib - not a fun thing. While a GFCI provides protection (in a different manner than a grounded chassis) the question to really ask is why are you using equipment that is so poorly designed that you have to lift the ground to avoid hum? And, no, hum is not unavoidable and "just part of the unique, wild and dangerous life of the audiophile." In short, there is no excuse or valid reason for placing yourself at any additional risk in this regard. Remember, there are those who in bygone days would use pennies rather than fuses in their panel. Just because something works (look ma, the lectrics on and ain't never gonna blow that penny, plus we done saved 14 cents on the fuse) doesn't mean its a good idea (darn ma, the house burnt down, with junior long with it - oh well, them's the breaks). Do not defeat safety grounding, don't smoke, use your seat belt, avoid crack - just common sense.

is why are you using equipment that is so poorly designed that you have to lift the ground to avoid hum?

Thanks for your opinion, but did you read my last two posts?

The only ground lifted is the chassis ground to the INPUT connectors. The chassis is still grounded at the power input to the amps. There is no safety issue with my solution.

Dan ed, your solutions is good only for components in which the input and output jacks are isolated from the chassis. I have seen few where there is such isolation.

Lifting the chassis ground is dangerous if there is a hot wire in contact with the chassis and you are grounded and can complete the circuit, such as being barefooted or touching the defective chassis and another grounded one.

My line stage only operates at it max if all other components have no ac ground but it does. Would Underwriters Labs take exception to this and deny certification to a manufacturer doing this? Yes. Would you city electric department? No. Do I feel unsafe? No.

Tbg,

IT is not the chassis ground! Chassis ground is intact, still there, grounding away, at the AC input. The inputs to both amps are grounded back to the preamp.

The lift is to the input connections ONLY, and they are tied to the power supply ground. Everything is grounded! Why doesn't it hum anymore?

One amp had an ADDITIONAL ground from the inputs to the chassis, one did not, simply due to different type of connectors.

Take a look at Rogue, Bryston, any other manufacturer that provides a ground lift. This is what they do also.

I'll try to explain, which means I just may botch this up. :-)

The hum was only between the two amps. Everything upstream unplugged. Only the amps were on. Ground loop between the two amps. The cheater plugs proved this.

Now, amp A had a ground connection from both input (-) rings over to chassis ground as well as the (-) wire going back to the power supply. Amp B had no such chassis ground on the inputs. Both amps have chassis ground from the transformer.

The transformers in the power supplies of the two amps don't tap to identical potential. So you get a ground current between the transformer taps on both amps and it hums like crazy because there are two paths to ground through both amps due to the leakage. Remove the connector ground to chassis (which is really the transformer tap) and no more leakage.