Trev D
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| posted on 27/10/09 at 07:05 PM |
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Mains hum
Any good electricians around?
I have just bought a 1940/50's record player that has a very bad mains hum and was wondering if anyone new how to get rid of it apart from
disconnecting the loud speaker or switching it off.
Any advice would be much appreciated or if anyone fairly local would be willing to have a look at it, beer tokens waiting.
Atb Trev
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McLannahan
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| posted on 27/10/09 at 07:10 PM |
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Trev - Does it have a separate ground on the rear? Normally older players did - not sure as old as yours though!
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BenB
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| posted on 27/10/09 at 07:13 PM |
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Does it have an intergral amp or are you plugging it into something else? Mistmatched amps / players will hum like crazy due to ground loops.
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iank
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| posted on 27/10/09 at 07:14 PM |
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Are you sure the hum is coming out of the loudspeaker? Sometimes it's the plates in the transformer de-laminating and making the noise.
(I've got a modern digital radio with that problem - which got worse after I dropped it  )
http://www.altavistaaudio.com/hum.html
[Edited on 27/10/09 by iank]
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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splitrivet
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| posted on 27/10/09 at 07:20 PM |
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Probably AC hum off of the motor or a duff smoothing Capacitor on the rectifier stages try temporarily disconnecting the motor first, if it goes away
thats the problem, put a capacitor between the motor connections to get rid.
Cheers,
Bob
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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MikeRJ
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| posted on 27/10/09 at 07:25 PM |
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Has this record player got an built in valve amp? Many older valve amp designs suffered quite badly from hum even when new.
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Macbeast
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| posted on 27/10/09 at 08:27 PM |
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As said, probably the electrolytic smoothing capacitor (s) in the power supply. They should be replaced as a matter of course in anything this old as
they could easily explode.
Probably marked something like 8UF 350 V
Be careful - lethal voltages in there
I'm addicted to brake fluid, but I can stop anytime.
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Trev D
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| posted on 27/10/09 at 08:32 PM |
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Thanks for the replies. I've failed to mention that it has a built in radio, the mains hum is continuous on either the radio or the record deck,
it is definately coming out of the speaker because it is that bad that you can feel the air movement when you put your hand near the speaker, it has
its own valve amplifier built in, I have now looked on the back of the box and have now noticed it has two round sockets, one marked AE and the other
marked E. I presume that the AE is the aerial for the radio and the E is the earth. Could you tell me if it would be best to fit a new 3 core mains
lead and solder the earth to the back of the socket marked E, thank you in advance.
Trev
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tegwin
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| posted on 27/10/09 at 10:14 PM |
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I would put money on the problem being duff antique capacitors on the smoothing circuit for the power supply...
(or a bad earth)..
------------------------------------------------------------------------------------------------------------------------
Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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morcus
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| posted on 27/10/09 at 10:49 PM |
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Fiddle with the balance knobs, it might make it go away. My Bass amp buzzes if its not set up right as the other electrical items interfere with it
but I can get rid of it by adjusting things like the treble.
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ReMan
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| posted on 27/10/09 at 11:03 PM |
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This was the norm in those days.
As mentioned capacitors may have deteriorated, so may have the valves, but it's part of the character, try to ignore it
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Macbeast
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| posted on 27/10/09 at 11:39 PM |
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It was NOT the norm to have hum so bad that you could feel the air movement.
Changing flex and soldering to the E terminal is not going to help. As hum is there on both radio and gram positions, most likely culprit is smoothing
capacitors - as said - you should replace those first anyway for safety. First test is - does the hum go up and down with the volume control, or is it
steady no matter what the position of the control ?
You have U2U.
[Edited on 27/10/09 by Macbeast]
I'm addicted to brake fluid, but I can stop anytime.
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splitrivet
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| posted on 28/10/09 at 12:00 AM |
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Sounds like AC hum for sure, has the mains lead an earth connection though.
Cheers,
Bob
I used to be a Werewolf but I'm alright nowwoooooooooooooo
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