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Thread ID: 47652	2004-08-02 00:05:00	Off Topic: Hi Fi Speaker Hum	tbacon_nz (865)	Press F1

Post ID	Timestamp	Content	User
257345	2004-08-02 00:05:00	I have my TV and VCR connected to my Kenwood Compact component HiFi so I can get better sound through the speakers. Most of the time it is all OK, but sometimes I get a low-frequency hum coming from the Kenwood. It happens whether the TV and or VCR are powered on or not, and happens on all the Hifi inputs - Video, Tuner, CD, Tape, etc. It is not the speakers, as I have tried different speakers and cables. I can't identify any other reasons why it might be happening - and why it happens for a period, and then it doesn't. Any ideas? I might say I am highly ignorant about sound systems/electronics, so if anyone mentions ohms or imepdances or stuff my eyes will probably glaze over! :D Tony Bacon	tbacon_nz (865)
257346	2004-08-02 00:07:00	If anyone uses the microwave at my house i get a low hum through the speakers :_| Possiblly something else on the circut running at the same time?	metla (154)
257347	2004-08-02 00:41:00	sounds like an earth loop. unplug the aerial(s) and see if you still have it. if so you may need an isolator.	tweak'e (174)
257348	2004-08-02 00:54:00	> sounds like an earth loop. unplug the aerial(s) and > see if you still have it. if so you may need an > isolator. Pardon ?:| :?| :?| :?| R2	R2x1 (4628)
257349	2004-08-02 00:55:00	>Possiblly something else on the circut running at the same time I wondered about that, and when it last happened I turned off everything I could think of but it didn't make any difference.	tbacon_nz (865)
257350	2004-08-02 01:08:00	> > sounds like an earth loop . unplug the aerial(s) > > and > > see if you still have it . if so you may need an > > isolator . > > Pardon ?:| :?| :?| :?| > R2 what part of that didn't you understand ??? ?:|	tweak'e (174)
257351	2004-08-02 01:43:00	after the word sounds :D An earth-loop is where current can flow through the earth side of a signal lead . As signal levels are low, current flow can cause the "hum" . Induction and that kind of thing . Usual procedure is to unplug each input to the amp, to find out which one is causing the problem . If everything is disconected that is external to amp (apart from speaker outputs) then it most likely to be coming up the power, or an internal fault such as dry caps . Cure can be quite tricky . Clear as mud?	Pheonix (280)
257352	2004-08-02 01:56:00	An earth loop via the aerial would be rather novel, as well as an oxymoron ;-) It is somewhat more likely if different peripherals run from seperate mains circuits, and try to equalise via the signal lead ground or shield connection. Via the signal leads, I would agree, but via the aerial, well, I would take a power of convincing on that score. It makes a good pub argument though. :D R2	R2x1 (4628)
257353	2004-08-02 02:22:00	<sigh> earth loops via an aerial is not comman but they do happen. aerial system have a voltage and current and is on a comman earth to the tv/vcr/stereo not to mention tv in the other room (and houses in some cases). very easy to check (unplug aerial and see if the hum stops). an extremely bad earth loop can cause lines on the tv. isolators are advailable should they be needed. btw some places like harveynorman stores have isolators on the FM connections for their stereo display stands to stop earth loops.	tweak'e (174)
257354	2004-08-02 02:57:00	I am with tweak'e on this. Aerials are often an "earth" in nature (attached to a metal roof etc). Many TV sets and most VCR's do not have a mains earth (2 core flex) at all, and you can often get stray capacitive earth currents flowing in the aerial circuit, via the sheath of the co-axial antenna cable. The stereo may not have an earth either, so it could be providing stray earthing currents via the connection to the TV/VCR. The TV antenna cabling in this house will give quite a nasty bite if you get between it and ground, while the TV's and VCRs are connected. Not enough current to injure, but enough to feel.	godfather (25)
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