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Should I ground my amplifier? Answered

This needs a bit of background info. I found this amplifier a year ago in the streets, by the trash, and I took it with me cause I like to open up things and see what I could get (it was obviously broken).
I opened it up, and started looking at the parts. The connections are old-school, first time seeing those. I noticed that one cable was not connected, so I took care of it, and tried to power it up. For my surprise it worked, and I had to secure the plug, which had only red and black (+ & - I guess).
Fast forward to now, I heard or read that anything connected to a plug should have the ground as well, especially if it had something metal. The amplifier is made of metal on the sides. I'm giving it to my uncle, but I don't want to give him in a dangerous state, so, should I change the plug again and put one with the 3 wires? How or where do I connect the ground? (I saw one connected to a screw in the metal part once) And most important, why?
Thanks a lot, sorry for length and for possible grammar or vocabulary mistakes.
TL;DR: Found an amplifier without plug, should I put one with ground? How? Where? and Why? THANKS!!
I've got answers saying that ground on audio systems are complicated and I've been reading but it's so confusing, and I don't understand it pretty well...


For an mains powered appliance in a metal case, the metal case should be connected to the ground wire of your mains power, via a power cord with a plug that includes a ground terminal. That is a power cord with three wires total, namely: "hot", "neutral", and "ground".

The reason for doing this, is because this offers the user some protection in the event something inside the appliance breaks, in such a way that the "hot" wire gets connected to the metal case.

For a more complete explanation of how this works, with some cute diagram-pictures of a little stick figure person getting shocked, or not, see:


It just occurred to me: I have seen appliances in metal cases, made with a ungrounded cord ( just two wires, namely hot and neutral). In fact that seems to be pretty common for things like audio amplifiers, DVD players, also VCRs, although no one uses those anymore.

I mean the logic that goes into this choice to use a grounded cord, or not, depends on the probability of the appliance failing in such a way the hot terminal (or something connected through small impedance to hot), gets connected to the metal case somehow.

For something like a toaster in a metal case, or a drill press in a metal case, it seems pretty likely that the hot wire could get connected to the case. The toaster is full of uninsulated wire heating elements, closely spaced next to the metal case. The drill press has a motor containing wires that are moving, spinning with the rotor, and they might touch the case if the rotor fell off its bearings.

However for something like an amplifier, the hot wire goes to small number of components (e.g. fuse, RFI filter, transformer, or rectifier stage of a switching power supply) with the vast majority of the circuits in the amplifier NOT connected through small impedance to hot, and this is done via the magic of electrical isolation.


So for something mechanically solid, with layers of heatproof insulation, its hard to imagine how wires connected to hot, could ever possibly touch with the metal case, neglecting really improbable events, like a creative anachronist stabbing your amplifier with a sword, in such a perfect way the sword connects the case with the circuits where the power cord connects.

So if you were wondering about the meaning of these comments about how a transformer protects by providing isolation. Well, that's how it does it. The only wires in the appliance connected through small impedance to hot, are in a small, insulated, and mechanically well protected area, that is unlikely to touch itself to the metal of the case.

This explanation might seem kind of long, but I hope it brings you closer to enlightenment.


The thing here is, I don't know why, it would work only in a specific location, so I had to connect the wires trough "plastic connectors" and stick those to the metal wall. I'm going to try and upload a picture of it, and you tell me if it's more dangerous. Also what could I do to make it safer? (Maybe shrink tubing).


I am not sure what you mean by "it would work only in a specific location". Perhaps your amplifier only works when it's in Vermont, but not when it's in New Hampshire. That would seem strange to me too.

Or maybe you mean to say, the power cord only works when it is bent into specific curve. Bent in a curve to the right, it works. Straight or bent in a curve to the left, it doesn't work. If that's what it is, then that means there is a break in one of the wires in the power cord, and the break gets closed when the power cord is bent a certain way. For something like that you should replace the power cord, or discover where the break is, and cut out that part of the cord.

Regarding the pictures, your connection is not pretty to look at, but it will probably work, and not connect itself to the metal case, under normal circumstances.

By the way, it is important for the the cord to have some sort of strain relief, e.g. tie a knot in the cord before it goes through the hole in the case.


That way if someone decides to yank on the cord, it won't pull the wires out of that bundle of terminal block and hot glue.

I did what you said, sorry for the long response.
I meant the location of the wire, sorry for not clarifying, also english is not my native language.
I send you pictures of how it is now, I added the knot, and a shrinking tube to make it look more beautiful.
Thanks for the info and advice, I really appreciate it :D


If you like to know the ending of this story, it didn't work :(
I tried at home, and it was turning on and the relay was activated. Once i got it to my uncle, it didn't turn on, and we found out that some wires were loose. It was sad...
But hopefully my uncle says he could give it to a friend of his and try to repair it.
Thanks to everyone, especially Jack A Lopez

I am sorry to hear that. I am hopeful you'll have better luck with the next thing you repair.

Amplifiers use a transformer to seperate from mains power, that is why there are only two wires on your plug.
Grounding such equippment is something people discuss all the time but usually for other reasons.
With amp, CD, Blue Ray, vinyl and other things all attached to each other you can get the problem of interference from one to the other.
Mostly with old stuff that does not use optical connections though.
Again, all of those devices need no ground for the plug if there is a transformer seperating the power.
But when "grounding" them together it means grounding the case of the device only.
This way stray interence is mostly cancelled out resulting in better audio signals.
On the other hand people say that eliminating the device causing the problem or fixing it is better than grounding all together.
In any case you have no need to add am earth connection to your plug and amp.

I've been looking at discussions, and as always there's people saying ground it and other saying not to.
I understand the danger it can be to not ground it, but they say that grounding it could make a buzz noise, and didn't want that either.
I think I will leave it like this, without grounding it, just because there's more people saying why it's OK not to ground it.

Chassis grounding is mandatory in the EU and USA, where the metal may become live in a fault.


3 years ago

If it has a real power transformer like the one I see in your pictures then grounding for safety is not necessary.

I agree !! Safety being met, only Downunder was Upto explaining signal grounding ;-)

And happily now, Jack who is renown for word count, has comment upon this double insulated world, where grounding may be very necessary as our coastal cities may be submerged in a highly conductive ocean due to water rising as glacial storage melts twice as fast as it did a lustrum (five years) ago. Shorting out non-impregnated xfmrs and certainly the AC power outlets mandated to be below the knee cap height by the electrical code wizards.

I believe my home in the high desert is one of the last dry land due to be submerged before Denver Colorado which it will ( there is a fossilized ichthyosaur that used to swim this high in Nevada )


Just stream your music from the cloud which really resides in some server farm in California ! So much for grounding, glub glub water dance