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Help for hooking radio speaker to 3.5mm headphone jack

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Wader8

Nov 20, 2014
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Hello


I have an old Nokia E72 phone with standard 3.5mm headphone/line-out/etc jack and I've like to hook up a spare external speaker I found from an old 220v FM clock-radio which got it's clock messed up so I put it away.
I already detached the speaker from the radio, I thought it would work but I guess it needs external power,

Specs:
F - F
0.5 W 8ohm
2

and it has a yellow and blue wire.

I do have a local special electronics shop not far that has all kinds of DIY stuff that big markets never have, like resistors, so I rather do something DIY with a battery

But I have zero electronics knowledge, I have no idea what's the voltages, ohms, ampers needed, but I do have a small multimeter at home if needed so it should be easier.

I do have 220-240v line at the location, but there's no any PCs so I would ignore the whole USB speaker thing that I just came across, I can also find an old phone charger to convert to a more managable voltage out of that i could crate a DIY setup.
 

KJ6EAD

Aug 13, 2011
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You have a few issues to deal with. The phone output is designed to drive two channels of a high impedance, low power load such as earbuds, not a single low impedance speaker. However, if connected correctly to one of the channel outputs, you should be able to hear a small volume of sound from your speaker.

A set of amplified speakers such as are commonly used with computers would be ideal but if you insist on using the speaker you have, you need an amplifier. A circuit or kit that uses an LM386 may appeal to you.

You will need to sum the left and right channels together to have both feed into a single amplifier channel and speaker.
 

Wader8

Nov 20, 2014
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Is combining left and right channels necessary? Because I don't need both.

Do you have any idea on how much would this cost me approximately, for the parts I would need, to see if it's worth it.

That said, I don't really know anything about wiring either, and what amplifiers are, so I would need a step by step visual tutorial unfortunately.
 

davenn

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Sep 5, 2009
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Is combining left and right channels necessary? Because I don't need both.

if you don't, you will likely notice missing sections of audio, due to a stereo recording often has different bits of the music coming out different channels
 

Wader8

Nov 20, 2014
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Oh yeah ofcourse, but I don't think the radio show I'm listening to has and special left-right channel stuff, unless they're playing an external clip but probably it goes through the systems to make it stereo if it's not, i don't know really, I might try it on the PC a few times to see if there's some missing stuff.
 

KrisBlueNZ

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Nov 28, 2011
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The PAM8403 is an efficient stereo amplifier that can drive 4Ω loads with as much as 3W from a 5V power source. Available on a PCB very cheap on eBay. http://www.ebay.com/itm/DC-5V-Digit...895?pt=LH_DefaultDomain_0&hash=item4adbe6d09f

I've seen a comment that the PAM8403 is noisy - a constant background hiss. But at that price it might be worth trying.

I agree with Dave that you should mix the two channel audio signals together if you have only one speaker.
 

BobK

Jan 5, 2010
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Mixing the two signals simply means putting a resistor (say 10K) between each and the input to the amplifier, it is no big deal.

Bob
 
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