Amp Has No Power Transformer

[Tom Phillips]

Check out the video at https://www.youtube.com/watch?v=FGoaXZwFlJ4 to see an extreme example of how one can safely touch a high voltage source if you remain isolated from the referenced current return path.

[The Dude]

...... and how many times have you seen birds or squirrels sitting on power lines?

[Enzo]

137.

[Enzo]

Actually in one of my physics classes we had to calculate the voltage across a bird. We had a high tension wire, I forget the voltage, say 50,000 volts. The wire was of a certain size with a certain resistance per foot. I guess current was specified. The bird's feet were some distance apart, say two inches.

We didn't get into the bird's resistance, we had to calculate the voltage difference between his two feet along that wire. Of course it was tiny. I think they were trying to catch some of us with the 50,000 volts, which doesn't matter.

[Tom Phillips]

There are problems when a big bird completes a circuit by simultaneously touching two energized parts or an energized part and a grounded part of electrical equipment on a power pole such as

If that happens the bird is electrocuted and in some cases the power can be interrupted.

The power companies try to prevent this in some locations by installing structures to prevent the big birds from shorting across the lines, Such as
or

[Enzo]

I actually witnessed a raccoon bite the dust. One night I pulled into my driveway, happened to look up at the power pole, and there was a raccoon climbing over the transformer. He stepped on the top terminal and touched ground and in a purple flash, he evaporated. Also tripped the breaker on the pole and I had no power in the house until the power company could dispatch a truck.

[bobloblaws]

Thanks for all the info guys, very informative. The bottom line is, that amp is a BBQ waiting to happen unless we put a isolation transformer inline.

[darkfenriz]

On paper, a signal transformer (suitably reinforced insulation rated) on the guitar input line plus getting the chassis insulated and floating is just as safe.

[Mick Bailey]

On paper, a signal transformer (suitably reinforced insulation rated) on the guitar input line plus getting the chassis insulated and floating is just as safe.

Maybe, but not in my world. What about the speaker connections, or 'grounded' pot shells that could connect the pot shafts to a live connection? Ever worked on those old TVs or radios where the PCB is live and the pot shafts are too? They can really bite, especially on 240v mains.

The only consideration should be the IEC protection classes for equipment.

[darkfenriz]

That's why I said 'on paper' and mentioned insulating chassis and all things accessible... making it a class II equipment (double insulated).

[g1]

Yes, a wireless system for the guitar is also helpful, but you still have to touch the amp sometimes.

One of the takeaways for bobloblaws should be that voltage is relative and always to some 'reference', in this case ground.
Thus, the 'bird on a wire' etc. examples.
Here are a couple more practical examples:
One fellow I know works on helicopters. They develop voltage while airborne, but it isn't a problem till it comes in contact with a reference. Landing on ground discharges it, but what about on a ship or something? The workers have a grounding device which they must use to discharge the copter before anyone can come in contact with it.
Another guy works for the power company. He told me that to work on high voltage lines way overhead, the worker is put in a special suit that is then charged up to the same voltage as the equipment he is working on. Again, the voltage is not a problem when it is completely insulated from anything else.
One other example. When you encounter downed power lines, they say to always either shuffle or hop. This is so you always stay at one voltage potential.