Question on ground and earth

DIY STUFF
1

Hi everyone,

I have trouble understanding a certain concept that gives me trouble often and don’t know how to deal with it.

The question is simple, wether common ground of lets say a typical DIY half wave rectification dual rail supply can be connected to earth.

This time i am wondering for a specific project, that is putting two class d amplifiers in a metal casing with their power transformer inside, a meanwell 24V 211W. normally the earth from the transformer should be connected to the chassis, but also the jack or RCA inputs will connect the common ground of the amp and of the input signal to the chassis and therefore to earth.

Thinking that earth and ground might have a potential difference that would lead to a short circuit and an unknown current flow, is somewhat scary.

On the other hand, while doing service on a few marshal guitar amplifiers i notice on the schematics that is clearly shown the common ground being tied to earth and I saw it also on the PCB.

Screen Shot 2025-03-14 at 12.11.28
Screen Shot 2025-03-14 at 12.11.281920×1359 251 KB

Even thought the input and output jacks are plastic, their sleeve obviously is connected to com ground. therefore every time i plug my diy modules in the amp, the com of my dual rail is shorted to the amps com and earth at the same time… and it works fine!

Its just that I am scared to try it DIY even though it seems i have done it countlessly…

So is it ok to connect com ground to earth?

Cheers!

NM

2

The answer is no. The ground at the rectifier output should not be directly connected to the earth. If you do so, you will get hum. The only thing that should be connected directly to the earth is the metal chassis (unless your transformer also has an earth mounting point).

The ground is a reference point for the DC side. The earth is a safety measure, for if anything live touches the chassis, it goes to earth.

In the end, you will connect all the grounds together at a star point, and that will be connected to the chassis. This should avoid the hum problem (although not always, in which case, you can modify the star connections to solve the issue).

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