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small speaker to auxillary input

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bensimmons_05

New Member
Hey guys,

I'm new to the site, always messing around with electronics. I am putting a car computer in a 1955 chevy truck and I'm trying to iron out some loose ends. This question has nothing to do with the computer itself but rather a blue tooth hands free car kit I am messing with. Here is the problem.


The car kit I bought has a small speaker that acts as the reciever. I cut the wires to the speaker and solder a 3.5mm jack to the leads. In my truck I have an auxillary input on my stereo and I plugged it into there. The sound works most of the time, but is faint. Sometimes it just clicks as if the channel is peaking. Is the Vpp to the speaker too much for the auxillary input, or is there a resistance that needs to be met to make it work better???
any thoughts would be appreciated.

Thanks
Ben
 

MikeMl

Well-Known Member
Most Helpful Member
I'm not clear on what you mean by "a small speaker that acts as the reciever."?

It is possible that the car computer uses a "bridged" audio output, where both ends of the speaker are driven out of phase by two audio amps (to get more audio at a low supply voltage). If you just connected to the two wires that formerly went to the internal speaker, you would have two problems:

1. The input to your main stereo is ground referenced, so connecting one of the wires to the RCA jack AUX input would short to ground the audio amp inside the computer.

2. The other audio amp with got connected to the aux input has a huge DC offset in it. If the aux line input doesn't have a DC blocking capacitor in it (inside your stereo), then you need to put one outside...

I dealt with these exact same issues in extracting the "*****-in-the-box" out of a Garmin 496 GPS. I ended up using an audio coupling transformer to convert the floating, bridged, balanced GPS audio output to the ground-referenced, unbalanced, audio input to an audio system...
I needed to do this to break up a ground-loop to get the alternator whine out the audio, but that is a separate story
 
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bensimmons_05

New Member
Hey Mike,
Everyone will have to excuse my lack of knowledge on some things, I'm learning. By "a small speaker that acts as the reciever" I mean the speaker output is the other persons voice, like what would be against your ear on a normal telephone. What your saying makes pretty good sense.

Like I said this does not directly pertain to the car computer. I will be using a preamp equalizer that this will actually connect to (which I currently do not have) On my other truck I have the aux input and I tried it on there. Where Could I find the audo coupling transformer? This seems like a good solution.

Thanks , ben
 

MikeMl

Well-Known Member
Most Helpful Member
Typical coupling transformer. Wiring shown on top.

Bottom sketch is how to try it single-ended. You will have to find a "ground" in the audio source. This is sometimes hard to do if you are powering the audio source using a plug-in DC cord rather than internal batteries. It can also be the source of getting alternator whine into your car stereo. The transformer coupling is preferred.
 

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