Plasma TV, Line Noise

[shawn]

Hello,

It has been literally years since my last post, but I am still listening to my Bottlehead gear (Foreplay and Paramours). I was thinking the other day that my Foreplay might be 10 years old by now. It's still going strong.

We bought a plasma TV last weekend and I mounted it on the wall over the stereo gear. The TV shares a power outlet with the power strip that the stereo uses. When the TV is on, I can hear a buzzing from the stereo speakers when I put my head close to the driver. If I unplug the Paramours or disconnect the speaker cables the buzz stops. This does not disrupt my record listening- I don't listen to the stereo when the TV is on or send television audio to the Foreplay. Still, the buzz is a little annoying... mostly because I know it is there and want to get rid of it.

Am I hearing line noise created by the TV? If line noise would ferrite choke cores or a power conditioner help kill this buzz?

Thanks!

[Grainger49]

Shawn,

Welcome back!  Seems you are looking for a buzz kill (I couldn't help myself!).

Do you get buzzing in your speakers with the Paramours off?  If so, there is a large field around the Plasma, stay away.  Probably not, but do you need to have your Paramours on while watching TV?  I wouldn't waste the tube life.

And now to answer your question.  Ferrite cores can seriously attenuate line noise.  I would bet the plasma has a switching supply in it.  They can have a lot of noise produced by them.

Luckily two turns through the core is as good as two cores.  Wind the incoming hot lead through a core 10 times and you get quite a bit of attenuation.  Using one core is cheap and easy to see if it will help.

Good luck.

[Paul Birkeland]

Putting the TV on a power conditioner would very likely kill the buzz (this is somewhat dependent on the power conditioner).  The choke that Grainger suggested is a good idea, I would use the filtering for the TV/digital only if possible. 

[shawn]

Grainger,

Thank you for your response! To be clear (if it makes a difference): I can hear the buzz when the amps are off. The buzz disappears when I unplug the amps or disconnect the speaker cables.

In any case, thank you for your advice- I am going to give the ferrite cores a try, first thing.

Paul,

Thank you as well for your reply. Jon Risch's power conditioner has been in my project queue for a while. Maybe this is a good opportunity to build one. Retail power conditioners all seem to be very expensive. I would be curious to learn if Bottleheads have had good experience with sub-$200 conditioners. Belkin makes an AV conditioner that retails for about $99. As you suggest, I would filter the TV, not the stereo gear.

Thanks again!
-shawn

[Paul Birkeland]

So the buzz comes through the speakers (plugged into the Paramours) when the Paramours are off and the TV is on, but this buzz vanishes when the TV is switched off?

[Grainger49]

Shawn,

That is scary!  Imagine the field that must be there to cause this. 

To do as Paul Birkeland suggests, you can use the ferrite on the Plasma only you might buy a small box and put an power cord, to the ferrite to a single outlet on the box.  The plug the plasma into this.

[shawn]

Yeah, so I am not alone in thinking this is a little crazy? Here is an image that should give you an idea of my setup (you can see the Paramours in the bottom right hand corner):

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Ffarm3.static.flickr.com%2F2763%2F4516867328_3f7521a94a.jpg&hash=5c8dab4f91b9d09582494bfff23592d6a9d74dda)

I get buzz in the speakers when the TV is on and the Paramours are *off*

The buzz disappears if I: disconnect the speakers or disconnect the Paramour power or turn off the TV.

My thinking was that the source of the noise is coming through the power line since that seems to be the only common factor- and the buzz disappears if I unplug the amp.

Thanks again for your replies!

[Grainger49]

Just one more question, what if you unplug the preamp to power amp interconnects at the Paramours?

Since unplugging the Paramours makes it go away I don't expect that the interconnects will help. 

[Maxdd]

Is your Plasma a Samsung PN50B850 or B860?
If so, put your ear up to the TV to make sure the buzz isn't coming from the Display itself.

[2wo]

I have my gear plugged into an conditioner/isolation transformer. Sometimes when everything is switched off I can still here a slight buzz from the speakers. I

[shawn]

Hey guys,

Thanks for the replies. Some follow up information.

Grainger: I did try unplugging the interconnect to the preamp, thinking that the source is the preamp. Buzz persists.

Maxxdd: My plasma is indeed a Samsung. Specifically it is a PN50C550. The TV does have a slight buzz that I can hear when I am up close to it or the room is totally silent. The Samsung FAQ states that this is true of just about all larger plasmas. (I admit that I am a little disappointed with this "feature"). There is definitely a buzz coming through the speakers- it disappears when I unplug the speaker. It *is* interesting to note that both of the buzzes sound the same. Thankfully none of this noise is perceptible unless I have my ear at the equipment. My wife claims to hear no buzz   I can live with the noise from the Plasma; but I would not mind silencing the noise in the speakers.

I have often read about this devil- line noise- on audio forums and until now have yet to encounter it myself. I am going to keep wrestling with it for a little while. I found a ferrite core cord noise suppressor last night and attached it to the TV's power cord at the outlet. This did not completely kill the noise in the speakers, but it did dampen it. I should be able to get my hands on another suppressor tonight. I am going to try attaching it at the TV end. I should be able to wind both ends through the clamps once. As Grainger says, I believe this makes the equivalent of 2 ferrite cores on either end. I get paid this week and think I will pick up a power conditioner for the TV line. It certainly can not hurt.

Thanks again!

[Paul Joppa]

Here's another experiment to try: When you disconnect the speakers from the amp, no current can flow. But if you short the speaker cable at the amp end after removing it from the amp, then the speaker and its cable can make a current loop, and if you hear buzz then it's the speaker and cable picking up some magnetic field-induced loop current.

The cable loop area is usually small, so the speaker internal wiring would be the most probably pickup point. Crossover inductors would be especially susceptible.