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Old 17th February 2009, 12:18 AM   #1
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Join Date: Feb 2009
Default 4 Pin Amp output to 3 Pin headphone jack?

Hello- I'm new here and wondering if anyone can help me out with making a small circuit...

I have a four pin amplified audio output on a prototype motherboard and I am looking to convert this to a 3 pin output so I can then attenuate and use standard headphones.

The one caveat is that the amplifier is push/pull. Therefore, there are no grounds- AC is fed to each speaker as the polarities have opposite sin waves. I understand they make 4 pin headphones but this will not suffice. Using one channels ground will not work either as it sounds quite distorted.

Is this possible? If anyone can point me in the direction of a component or circuit that would do this I would be SO greatful! It seems simple but in reality....its over my head!

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Old 17th February 2009, 07:10 AM   #2
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Join Date: May 2008
It would help to have a schematic of your amplifier.

One possibility is to use an op amp to convert the symmetric signal into an unsymmetric one. Then you will have to find op amps that can withstand the output voltage of your amplifier and depending on your headphones might need to add a current booster. You might be better off building or buying a dedicated headphone amplifier.

Another possibility is to cut the connector off your headphones. You will find that the cable has four wires. Prepare them to fit your amplifier output.

Be warned that your amplifier might be able to destroy your headphones and your hearing.
If you've always done it like that, then it's probably wrong. (Henry Ford)
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Old 17th February 2009, 07:26 AM   #3
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Sounds like the amps are BTL.

I'm gonna guess that this will work-
Connect an electrolytic capacitor (220uf?) in series with each output + terminal,and connect the negative side of the capacitors to the headphones + wires.
You can then ground the headphones to the circuit ground.
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Old 17th February 2009, 04:46 PM   #4
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Join Date: May 2008
Depends on how they are bridged. If it works that way, it will do that without the capacitors as well. But we won't know without a schematic.
If you've always done it like that, then it's probably wrong. (Henry Ford)
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