Z

zfrenchy

Audiophyte
I had a very bad ground loop on my system. Here is some REW measurement, all hum on the 60Hz. Worst curb with amplifier ON, woofer at full gain, no isolator. Best curb amplifier ON and isolator, woofer full gain.

SubW humm test.PNG


I tried a lot of things, at the end, this circuit eliminated all hum.

GND Loop.jpg


Just to be safe, can a EE tell me if that will cause any problem to my electrical circuit or my equipment ?
 
mtrycrafts

mtrycrafts

Audioholic Slumlord
No, it will not but all those sharp corners on your drawing may be an electron leakage point. That could be catastrophic. ;) :D
 
TLS Guy

TLS Guy

Audioholic Slumlord
I had a very bad ground loop on my system. Here is some REW measurement, all hum on the 60Hz. Worst curb with amplifier ON, woofer at full gain, no isolator. Best curb amplifier ON and isolator, woofer full gain.

View attachment 47661

I tried a lot of things, at the end, this circuit eliminated all hum.

View attachment 47660

Just to be safe, can a EE tell me if that will cause any problem to my electrical circuit or my equipment ?
According to the information you provided you did NOT have a ground loop.

Neither the Yamaha or the sub have grounding pins on their AC plugs. So both units must be double insulated.

So if there is a ground loop it is some place else. So my question is, do you hear hum without the transformer if only the sub is connected to the Yamaha and all other connections are removed?

This is important as there are no grounds that you have in your diagram to cause a loop.
The first thing to check is that the AC receptacles that those units are plugged into are wired correctly. I'm suspicious that one of those AC wall receptacles has the live and neutral reversed.

If they are correct and you still have hum with only the sub corrected, then the sub has a potentially dangerous fault and has current leakage somewhere there should not be.

Lastly a small transformer in the RCA lead to a sub is less than ideal. I suspect some attenuation of the lower frequencies form a device like that. So you still need to find the root cause of this problem. Absent more information, it is not a ground loop.
 
Trell

Trell

Audioholic Samurai
This is important as there are no grounds that you have in your diagram to cause a loop.
The first thing to check is that the AC receptacles that those units are plugged into are wired correctly. I'm suspicious that one of those AC wall receptacles has the live and neutral reversed.
I'm a not an electrician but why should the reversal of the neutral (not earth) and the live matter? Here in Sweden we can insert the AC plug either way.
 
TLS Guy

TLS Guy

Audioholic Slumlord
I'm a not an electrician but why should the reversal of the neutral (not earth) and the live matter? Here in Sweden we can insert the AC plug either way.
Because in the US, the neutral is bonded to ground at the panel, and the live swings at 120 volts 60 Hz above ground. The plugs are polarized, with the end of one larger than the other, so you can only insert it the correct way round.
 
Z

zfrenchy

Audiophyte
I will checked that over the week-end then comeback to you with the result.
I am just worried about the safety of the AC circuit and the devices connected to it, now my hum is completely gone no worries about sound anymore.
 
Eppie

Eppie

Senior Audioholic
I'm a not an electrician but why should the reversal of the neutral (not earth) and the live matter? Here in Sweden we can insert the AC plug either way.
Even though European plugs can be inserted either way, there is still a hot (brown) and neutral (blue). To reverse the plug safely, you need a floating chassis (a chassis with no connection to the hot or neutral). In old tube radios, it was common to connect the metal chassis to one side of the line cord on the assumption that it went to neutral, but if someone reversed the cord the chassis could become live relative to ground and create a shock hazard. Some old guitar amps have a ground polarity switch that allows switching the chassis ground between the two sides in case the chassis becomes live. Not a fun feeling when standing on a damp stage outdoors I tell you!

Should not be an issue with modern equipment but if connecting the phono ground and subwoofer input ground to earth ground eliminates hum, that indicates that something else is going on there.
 

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