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Is it possible to replace a single speaker with an aux port?

KilgoreCemetery

Apr 12, 2017
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Before I dive into this crazy project I want to know if I'm missing anything major. I have an old radio with a built in speaker that I want to continue to use. The catch is, the speaker is blown. Can I simply wire in an Aux cord and plug the unit into a different system?
 

kellys_eye

Jun 25, 2010
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Have you looked to replace the speaker? They are fairly easily sourced and don't even need to be 'exactly' the same size as the original if you use a small adapter plate (thin ply will do) to ensure a good fit.

If you're referring to an 'aux' port on the radio this may be for an external input signal, not an output. What make/model are you using?
 

KilgoreCemetery

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This is a vintage Sony 8F-11W. It doesn't have any sort of extra inputs or outputs naturally, just a button to switch between AM and FM.

I just want to output the signal from the original unit into something else via an Aux cable
 

Arouse1973

Adam
Dec 18, 2013
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I don't see why not as long as you don't go beyond the spec of the devices aux input. You may need to download the manual and check, unless you have it already.
Adam
 

dave9

Mar 5, 2017
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Be Specific. What is "different system"? What is "something else"?

What exactly do you want to do? That determines how to do it.

Being vintage, I would replace the speaker. If you would rather hack it up, then you can run a wire to an external speaker, or get rid of the volume knob to set a fixed signal level then use a resistive divider/dropper on the speaker output to reach line level (~1VAC) to the input of something that takes a line level signal.

If that is what you'd like to do, you'd want the input signal formerly going through the volume potentiometer, at the highest level the amp circuit will take without distortion for high SNR. The pot would be replaced with another resistive divider. Described simply you could just adjust the pot till you get the right 1VAC output then measure the resistance between the 3 pot contacts to pick resistor values to replace the pot.
 

KilgoreCemetery

Apr 12, 2017
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Thanks, Adam. It seemed like it wouldn't be any different than hooking an iPhone up to a car stereo, but I felt like I was over-looking something.

I'm aiming for the 1VAC, Dave. This may be a vintage unit, but it's not what I would call quality. However, the AM/FM works just fine. If I can output the signal into a better quality amp, and also better speakers, I can make this little radio feel useful again.
 

kellys_eye

Jun 25, 2010
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I love the definition of 'vintage' - in this case it being 1975...... I was 16 years old then!!! Darn I feel old!

Anyway, if the radio has any particular value to you then consider purchasing another to salvage parts from - such sets are available on a buy-it-now basis for $25 on eBay.
 

dave9

Mar 5, 2017
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Well then I don't understand. You might as well just use the case for the vintage appeal, put a HQ tuner and amp circuit in it if you were just going to use the low quality tuner and output that to an external amp.

I mean that there's no real reason to have the radio signal go through its internal amp, then lose that voltage gain, just to boost it again, though for purposes of SNR it might be prudent to put a basic opamp, preamp circuit after the tuner. That's bound to have an order of magnitude lower THD than taking the signal after the built in amp circuit, providing you use a suitable opamp.
 

KilgoreCemetery

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Yeah, "Vintage" might be a bit much, but it's not the sort of thing that you can go out and buy new now days. This one's not particularly valuable. I picked it up for $5
 

dave9

Mar 5, 2017
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Well vintage is about the look, some people value that and others think it's silly. There's nothing desirable about the electronics inside, you'd have to go further back in time to get a tube radio for the warmer sound, or more recent for lower distortion.

It's kinda funny though, some songs I remember hearing as a child, on a radio with tons of distortion, then hearing them again in recent years on a much better amp and speakers, they sound so clear and sterile.
 

KilgoreCemetery

Apr 12, 2017
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I know, Dave, it's silly, but the heart wants what the heart wants. That, and figuring out how/where to put in a higher quality tuner and amp sounds like more work than I'm wanting to do. I don't know enough about amps or tuners to build them myself and I only have about a 9 x 9 x 3 space to work with. I have everything else that I need figured out save the switch, which I am currently researching.
 

dave9

Mar 5, 2017
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You can get ready to roll (wire) tuners and amp boards on eBay (direct from China) for cheap, single-digit $. They would easily fit in a 9x9x3 area. Trying to get the vintage case mechanical tuner dial and needle pointing to the number that corresponds to the actual tuner frequency, THAT would be more challenging, might have to involve brackets and gears to get all sorted out, or you'd just lose that aspect of vintage and instead of an analog needle range, there's an LCD display in its place, though a tuner with a display might exceed my claim of single-digit $ cost.

Another option is hack the circuit. It's set to a particular gain, which could be adjusted down till it's far closer to 1VAC. Reverse engineering something from that era would give me a headache, but so would what you want to do instead.

Keep in mind that electrolytic capacitors don't last forever. If you want this to have a decent tour of duty then you may want to replace many if not all of those.
 
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