[Closed] Background hum from speakers

Probably a decoupling capacitor in one of the units, if they're unhappy they take a few mins to warm up and start showing it.

Probably a decoupling capacitor in one of the units, if they're unhappy they take a few mins to warm up and start showing it.

Ck: In one of the speakers? (wish i knew what a decoupling capacitor was :oops:)

In one of the speakers?

no, he means inside the TV! I've never heard of this, but it is plausible I suppose. The good news is that they're easy to replace, as they're big, easily identified and not expensive

As Simon says, it'll be in the amp unit (TV, or home theatre amp) It's just something I've found in the past. Also found it noted here:
http://tinyurl.com/yjfhn54

However it does mean taking the units apart and knowing what you're looking for and able to open up a TV/amp without killing yourself.

I'd start by disconnecting all items and seeing if they make the noise while they're not interconnected, but it sounds like you're just attaching speakers to the TV, in which case you can't do that, and it must be the TV in some way.

OK. Thanks guys. The guy I bought the panel off is a proper whizz at this sort of thing so I'll leave it to him.
He's been using the TV until the other day with no problems (via home cinema) so maybe I'll just chuck an amp onto the TV audio outputs and run the speakers off that - I'd rather not though.

Sounds like like earthing incompatibility with the rest of your system... 😥

You could try a ferrite choke, I did on my surround system (I had loads of "spare" cable, all looped round on the floor, nr a power supply). It definitely helped reduce hum

http://www.maplin.co.uk/Module.aspx?ModuleNo=32792&TabID=1&C=SO&U=strat15

Aha! I know exactly what's wrong here!

Back in the early 90's I bought a stack system and it was lovely. Except after a few weeks the left hand speaker started making an eerie whistling noise. Even when the power was switched off! Now having spent a few quid on this system I was promptly onto the shop and put through to their engineer. He confessed that he'd never heard of this problem before and was keen to jump in the van and come over to check it out.

Whilst waiting on him, I decided to pull the speakers away from the wall to give him easier access. That's when our kitten's toy ball, which flashed and whistled when a sensor was pressed, fell out from where she's jammed it behind the speaker. It was a rather embarrassed Beagleboy who phoned up the engineer to cancel his visit. 😳

B. 😆

Sounds like like earthing incompatibility with the rest of your system

no it doesn't - plugging speakers into a standalone TV cannot be "incompatibilty"! And ferrites are for RF interference, not hum, and will have zero effect.

simon - RF can cause hum, can't it?

simon - RF can cause hum, can't it?

hum is 50Hz, RF (radio frquency) is 50kHz +, though it's true that it might in some circumstances be modulated at 50Hz, though that begs the question why it would start only after several minutes and not instantly

We had this when I got a new (to me) surround sound set up, the hum only appeared when the virgin box aerial was plugged in. Got virgin out and they put in a new coax cable in with some sort of extra installation on it.

begs the question why it would start only after several minutes and not instantly

Yep, unlikely to be an earth loop if it only starts humming after a few minutes. Try leaving the speakers connected, then switching the TV off and on quite quickly. Does the hum come back instantly?

i would agree with Mr Woppit.

My PC speakers hum when plugged into my laptop.
its VERY annoying.
if u unplug them, it goes away,
connecting various peripherals too the computer affects the hum, which indicates its to do with the earthing i think...

it indicates that you are amplifying a signal from inside a small metal box containing thousands of un-insulated and electrically noisy components. very few PC peripherals will have an earth anyway.

containing thousands of un-insulated and electrically noisy components. very few PC peripherals will have an earth anyway

electrical noise sounds like a hiss

components was the wrong word, there are motors and all sorts in a computer. PCs and especially laptops make some stunning noises appear in audio signals

oh and the vast majority of plasma TVs with removable speakers come with ferrite choaks on the short speaker cables

My own similar experience was that, trying to run an Arcam CD player with a NAIM amplifier, I got speaker hum when trying to use the TV sound that was switched through the amp.

When I upgraded to a NAIM CD player, the hum dissappeared. It turned out that this was because NAIM equipment is earth-routed through the CD player. The Arcam, of course, did not match this requirement.

If the other suggestions do not work out, it might be worth pursuing this as an option, despite simonfbarnes' opinion...

despite simonfbarnes' opinion...

with respect, my remarks were addressed to the scenario where there was a TV and some speakers and no 3rd party equipment involved, where your solution would clearly be irrelevant - unless some were connected and were able to inject just the right amount of hum in antiphase ?

I reckon some directional cable would sort this out

Quick update - I found a ferrite chock (spare that came with our other telly and put it on the power cable but this made no difference. I then disconnected the aerial feed and connected a dvd player and the hum was still there so it must be coming from the internal amplifier.
Connected a spare old amp to the line-out port and the hum has gone 🙂

So the decision is whether to keep the amp attached (bit big really but may be able to find a smaller/cheap one) or to stick with the speaker attached to the TV and just ignore the hum. Seeing as this TV is mainly just for the kids room (I only paid £100 for the set), and they didn't notice the hum anyway, I may just go with the latter.

Connected a spare old amp to the line-out port and the hum has gone

try just inserting a shorted plug, or even better one with say a 1K ohm resistor soldered across the terminals