2. amps-preamps
  3. 1347156354

Amp hums in standby mode when TV is on

Hi, my Sherbourn 5/1500A power amp starts humming whenever the TV in the same room is operating. This occurs even when the amp is in its standby state, and also happens when using the amp(although you can't typically hear the humming at that point because of the sound from the speakers). What's more, as the image on the TV varies in brightness, the intensity of the humming/buzzing also varies. If the TV is off, the amp is dead quiet. I am assuming this is some kind of ground loop problem.

Should I try to plug the amp in with a "cheater plug"? There is a sticker on the back of the amp that indicates that the amp must be used with a grounded power cord.
mtrot

Showing 4 responses by jea48

jea48
4,707 posts
 
Gbart,

My bad.
Thanks for the heads up.
sae_2300@optimum.net.

Gbart, I have a question for you.... Assuming the TV's SMPS is putting DC back out on the mains what would happen if a DC blocker was installed between the TV and mains power receptacle? Would it block the DC offset voltage from the TV from going back out on the mains?
.
Jim
jea48
4,707 posts
 
Hi, my Sherbourn 5/1500A power amp starts humming whenever the TV in the same room is operating. This occurs even when the amp is in its standby state,
Mtrot
Mechanical hum heard from the amp not through the speakers?

If yes then I would assume the power transformer of the amp is energized in the standby mode.

Good chance the sound you are hearing is coming from the power transformer of the amp.

If the buzzing, mechanical noise, is coming from the power transformer (only when the TV is turned on) then there is a good chance the switching power supply, SMPS, of the TV is putting DC offset back out on the AC mains.

Verify the sound is indeed coming from the amp's transformer and not through the speakers.

If that is the case You will to buy a DC Blocker.
.

jea48
4,707 posts
 
Mtrot,

Send an email to member Gbart,
(Email address), sae2300@optimum.net

Explain your power xfmr mechanical buzzing problem to him.
Good chance he can help you solve it.
.
jea48
4,707 posts
 
Gbart,

Thanks for setting up and running the bench test experiment.

The reason I asked the question is so the user of a DC blocker could install the blocker on the known offending device or piece of equipment. In this instance the OP's TV instead of the power amp.

For those out there that are feeding their amp from a high dollar after market power cord would not have to add the DC blocker into the mix. The extra connections of another plug and receptacle plus the power cord or in the case where the DC blocker has an IEC inlet connector, another high dollar after market power cord.

The DC blocker reduced the audible level of transformer noise by about 2/3.

The million dollar question?

How does that compare to the audible noise lever of the toroid xfmr connected directly to the DC blocker?

Thanks,
Jim
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