Hum when receiver is off

[yusuf]

Please help me in resolving two problem below:

My subwoofer produces hum when receiver is off. As soon as I turn ON the receiver, hum goes away and subwoofer sounds as it suppose to. So this is not a very big problem but really like advice on how to get rid of it.

Also, I have a treadmill in same room as subwoofer. As soon as I turn on treadmill, subwoofer starts humming heavily and almost unusable. This is a big problem as I can not turn ON subwoofer when using treadmill. Please guide.

Btw, this is DIY subwoofer based on LM4780. There is no ground connected so far.

Thanks
Yusuf

[Jan Dupont]

Seems like you have a problem with radiated hum.....
Are your LM4780 placed in a metal chassis (shielded box)?
Do you have the chassis connected to PSU Ground ?

[yusuf]

Originally posted by ACD
Seems like you have a problem with radiated hum.....
Are your LM4780 placed in a metal chassis (shielded box)?
Do you have the chassis connected to PSU Ground ?

No, it is not in metal chasis. Amplifier is placed in a partition of same wooden subwoofer enclosure.

Yusuf

[Jan Dupont]

Seems like one or more circuits in your LM4780 amp are picking up noise from the air
Make sure that all Mains wires are placed far away from the amp.
If that doesn't help, then try to place a metal plate (shield) connected to the PSU Ground over the amp.....