Amp hums in standby mode when TV is on

If your video system is connected to cable you may need to have your cable provider isolate the cable with a devise similar to the Jensen VRD-1FF.

http://www.jensen-transformers.com/iso_vid.html

Thanks! Yes, I do have cable TV service. Also, this amp hummed in the same manner when it was previously used in another room in the house. There is also a cable outlet in that room.

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.
.

Sometimes careful cable dressing/orientation can help mitigate situations like this.

Thanks, yes it is a mechanical buzzing, very loud at times.

It is my understanding that the power standby feature on this amp is designed such that when it receives a signal and switches on, it is supposed to be somewhat in a "warmed up" and stable status for good sound.

I will also see if adjusting the speaker and/or interconnect cables has any effect, which I doubt.

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.
.

You might want to clarify whether your cable TV is actually connected to your audio system and whether the audio components (ie. your stereo) and video components (ie. your TV) are on separate circuits.

Reminds me of that old joke about the guy who visits the doctor, and says, "Doc, it hurts when I do this." The doctor's reply, "Then don't do that."

Don't forget the video and power cords. Component placement can be considered too.

Jim, my e-mail address is sae_2300@optimum.net. You forgot the underscore. :)

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

Jim,you asked an interesting question about something I hadn't thought of before. I tried a quick test with a pair of back-to-back caps bypassed by diodes, between a known source of DC offset (400mV) and mains. I connected a toroid transformer that is susceptible to DC on another branch circuit. The DC blocker reduced the audible level of transformer noise by about 2/3.

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

Jim,
I plan on doing a comparison of the blocker at the source of DC versus at the toroid. I could not do a thorough test the other night because I was working with exposed mains connections and wanted to make it quick. I will try again when I have a blocker properly assembled and enclosed in a box.

Glen

IMO ... the DC offset created by the half wave bridge rectifiers in all the switching power supplies of our equipment is a silent killer

The Humming that is heard at the transformer is only the Symptom ... the real Disease is the loss of head room and reduced dynamics when the transformer’s efficiency is compromised by the DC off set saturating and rattling the transformer when that extra pulse is drawn

When a system is infected with RF you will hear the RF irritating you and effecting the high frequencies ... if your system has issues with EM (the magnetic side) ... you will hear a humming

But enough DC offset and the transformer’s efficiency is reduced and things just don’t sound as dynamic or authoritative ...

I feel you can clearly hear the effects RF and EM .. but a reduction in efficiency and head room is hard to realize until it has been corrected

I use two PS Audio Humbuster III’s in my system and was shocked at how much more powerful and authoritative the system sounded ... the character and tone of the system never changed ... it just sounded more powerful after unplugging everything from my EP15 Exact Power and plugging everything into the two Busters