problem with earth gnd

[maxpou]

That is probably the problem, it should be connected to the chassis at one point, usually the best place is at, or near the midpoint between the PSU reservoir capacitors. See page 57 here http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf Read the whole presentation preferably

thank you scott, i did the test and yes it's my problem, if i connect the audio gnd and earth gnd to the chassis at one point the amp become mute.

Now, i would like to understand why?

Maxpou

 

[scottjoplin]

That's good. 🙂 What have you discovered in your quest to understand why?

 

[Bonsai]

You must have one and only one connection from your amplifier 0 V to the chassis. If you have more than 1 you will get earth loops.

There are lots of circulating currents flowing in a metal chassis from th3 transformer leakage flux, radiation from mains wiring and the speaker cables. It’s a big mess.

 

[maxpou]

There are lots of circulating currents flowing in a metal chassis from th3 transformer leakage flux, radiation from mains wiring and the speaker cables. It’s a big mess.

Thank you Bonsai,
Yes i have only one point connection on the chassis, that's why i did not understand my problem. Can it be a bad earth ground in my electrical main panel?

Maxpou

 

[Bonsai]

No not normally. The reason you get ground loops if you have two connections from your electronics to your amplifier chassis is the transformer leakage flux causes currents to flow in the metalwork so between your two connection points, you will get a voltage drop at the frequency of the transformer, or harmonics. Any cables carrying heavy current will cause this - so even speaker output and return if not dressed properly will cause it as will wires from the transformer to the rectifier and capacitors - you usually take this connection from the central star ground point, or off the 'T' (see slides 56 - 59 here http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf)

 

[scottjoplin]

Does that explain why he only had a buzz when he connected the mains earth to the chassis? Am I missing something?

 

[Bonsai]

I missed that. Sorry.

Likely if he gets hum when he connects the amplifier 0 V to the chassis he has a classic AC ground loop.

 

[scottjoplin]

It's not perfectly clear since, as he says, his English isn't good, but initially the only connection to the chassis was the mains Earth, and with nothing connected to the inputs he was getting hum, when he disconnected the mains earth the hum went. With both mains Earth and audio ground connected to the chassis there was no hum.