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LCD TVs - What would generate a 1110Hz (audio) pitch?

Posted on 2014-03-28
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Last Modified: 2014-04-16
We have a new soundbar ($200 range, middle of the road as these things go).
Unrelated, due to various factors we must use the Earphone-out jack from the TVs.
We realize that this is not optimal impedance matching, but it's not a high-end home theater situation.

What about two different brands of flatscreen TVs (Sceptre, LG) would BOTH generate the identical 1110Hz pitch picked up by the soundbar amp/spkr?
Is there an internal scan line frequency or refresh rate that coincidentally is the same in both TVs?  (maybe a uproc or switching pwr supply  clock frequency?) -- something whose EM field is unshielded or un-notch-filtered.
I've tried all combinations of off/unplugged, and it's only when the one isolated TV under test (connected to the soundbar) is plugged in that the pitch is picked up WHETHER THE TV IS "ON" of "OFF" (i suspect a standby mode). Also, it's the same regardless of TV input source selected (HDMI vs AUX vs TV RF tuner).  Also high-end earphones pick up nothing.

In trying another non-TV device earphone-output jack (my laptop was handiest), there is no pitch (i would have expected the laptop to have more rogue unfiltered/unshielded emissions going on),  thus it's not the soundbar's fault.

We can live with the SNR mitigated with TV volume loud and soundbar volume low, there's no distortion.

But i'm curious why exactly 1110Hz,  between two brands.
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Question by:willsherwood
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My first suspicion is some sort of grounding problem.  Headphone jacks are typically designed to connect to passive devices that have no ground (or other power) connections.  That would explain why headphones or a battery-powered laptop wouldn't exhibit the problem.

I'm afraid that I can't explain the actual frequency.  My first guess would be that it has to do with the switching power supply in the TV, but I believe that those run at much higher frequencies than that.

Is there any chance you can use a different output, such as line-level or optical?  If not, some sort of audio isolator may be appropriate.
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by:willsherwood
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thanks for your comments- the optical output jack for the TV is broken (we didn't discover until too many months too late), i suspect it would be fine.
i hear you about passive... (low impedance)
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