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Making use of a spare car radio

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  • 02-04-2008 12:38pm
    #1
    Max_Damage
    Closed Accounts Posts: 5,461 ✭✭✭


    Well, this probably isn't the most 'technical' of ideas, but I had a spare JVC car CD/Radio lying around the house for ages, so I thought of using an AC adaptor (the ones with the adjustable voltages) to power it and use it as a radio in my shed. Cut the wire on the adaptor, and put two push-on connecters on the ends of the wires (best to have a multimeter or similar to make sure the polarity is correct). Pluged it into the radio, along with two old stereo speakers I had lying around in the attic, and bobs your uncle, it worked. However, there is a bit of a problem. There is a slight humming noise from the speakers. It is a constant hum, that doesn't go up or down with respect to adjusting the volume. My uncle done a similar setup a few years ago and it is apparently due to a insufficient earthing of the radio (the 'earth' on the radio is connected to the negative wire on the adaptor). I was thinking, would it be possible to connect the 'earth' on the radio directly to the earth on a plug socket, and leave the negative on the adaptor disconnected from the radio? Any suggestions welcome.


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    #2
    Magown3
    Registered Users Posts: 697 ✭✭✭Magown3


    Good idea.

    On the earthing tho. I wouldn't use the same plug as the one you're getting electricity from. Would probably work, but i'd rathere stick it in to the pin of another socket and use another plug...


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    #3
    Max_Damage
    Closed Accounts Posts: 5,461 ✭✭✭Max_Damage


    Magown3 wrote: »
    Good idea.

    On the earthing tho. I wouldn't use the same plug as the one you're getting electricity from. Would probably work, but i'd rathere stick it in to the pin of another socket and use another plug...

    Thanks for the reply.

    Yeah, I think I might try that. I just want to make 100% sure that I don't fry the radio's internals, although I can't see that happening.


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    #4
    Cmar-Ireland
    Registered Users Posts: 2,340 ✭✭✭Cmar-Ireland


    Could look good in a kitchen, if the radio was mounted under the wall cabinets. Bang a couple of speakers on the top of the cabinets and away you go....


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    #5
    Max_Damage
    Closed Accounts Posts: 5,461 ✭✭✭Max_Damage


    I tried earthing the radio directly, but it didn't work at all. I guess I'll just live with the interference.


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    #6
    Magown3
    Registered Users Posts: 697 ✭✭✭Magown3


    Max_Damage wrote: »
    I tried earthing the radio directly, but it didn't work at all. I guess I'll just live with the interference.

    What way did you try to earth it?


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    #7
    Max_Damage
    Closed Accounts Posts: 5,461 ✭✭✭Max_Damage


    Magown3 wrote: »
    What way did you try to earth it?

    Connected the earth terminal on the radio directly to the early on a plug socket. I left the negative on the adapter unconnected. The radio failed to work though, so I wired it up back to the way it was.

    Maybe there is some high-bandpass filter I could get to remove these hums?


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    #8
    digiking
    Registered Users Posts: 487 ✭✭digiking


    Try connecting the radios negative terminal to earth rather than transformer


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    #9
    Max_Damage
    Closed Accounts Posts: 5,461 ✭✭✭Max_Damage


    digiking wrote: »
    Try connecting the radios negative terminal to earth rather than transformer

    You obviously didn't read my previous post. That's what I done, and it didn't work at all.


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    #10
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 90,908 Mod ✭✭✭✭Capt'n Midnight


    sounds like the AC adaptor isn't regulated , what is it off ??

    you may need a capacitor in parallel
    or an inductor in series to reduce the mains hum - does it sound like one of the big ESB transformers


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    #11
    Max_Damage
    Closed Accounts Posts: 5,461 ✭✭✭Max_Damage


    Capt'n Midnight wrote: »
    does it sound like one of the big ESB transformers

    Indeed it does.


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    #12
    Capt'n Midnight
    Moderators, Recreation & Hobbies Moderators, Science, Health & Environment Moderators, Technology & Internet Moderators Posts: 90,908 Mod ✭✭✭✭Capt'n Midnight


    You need a better power supply that has less mains ripple.

    or run it off a battery


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    #13
    Charles Bronson
    Closed Accounts Posts: 21 ✭Charles Bronson


    The negative wire from the wall wart to the radio is coming from a transformer. When this is disconnected you break the circuit so no current will flow. You need to connect both the negative and the positive sides of the wall wart for the power to flow through the radio. You can then connect a capacitor from the negative wire or the radio chassis to a ground wire in the in the three pin plug to remove the hum. Hope this makes sense.


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    #14
    jayok
    Registered Users Posts: 1,907 ✭✭✭jayok


    Charles Bronson wrote: »
    The negative wire from the wall wart to the radio is coming from a transformer. When this is disconnected you break the circuit so no current will flow. You need to connect both the negative and the positive sides of the wall wart for the power to flow through the radio. You can then connect a capacitor from the negative wire or the radio chassis to a ground wire in the in the three pin plug to remove the hum. Hope this makes sense.

    This is essentially a bypass filter for the noise to ground - would work well. Alternatively a a Capt'n'Midnight said you could remove the ripple, tough you'll need some extra caps in parallel with the power rails.


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    #15
    Max_Damage
    Closed Accounts Posts: 5,461 ✭✭✭Max_Damage


    Thanks for the replies again. If I turn the radio up moderately loud, the music drowns out the hum, so I don't really hear it at all, so I've just learned to live with it.


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    #16
    watty
    Registered Users Posts: 32,417 ✭✭✭✭watty


    I used to buy Sanyo Cassette Car Radios in mid 1970s and package them with PSU and two speaker cabinets based on cheap TV speakers and surplus Courtalds packing cases.

    People were very happy with them. They used a whip aerial as that is best for VHF and a difficult to add ferrite rod aerial only works on MW/LW and needs switched too.

    A CB base PSU would be hum free and correct voltage (13.8).

    Historically 12V batteries were 13.8 while engine running or fully charged. The modern maintenance free ones rise sharply to 14.2V.

    Generally things designed for car use don't cope with main hum at all, need very good linear or switch mode PSU. A charger is no use. Operational absolute limits are usually 10.5V to 16V with reliable operation from 11V to 15V


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