Running headphones from a speaker out jack?

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soccerman58
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Running headphones from a speaker out jack?

Post by soccerman58 » Mon Nov 28, 2016 11:47 am

Hi
I'm looking into buying an old Solid State bass head that does not have a headphone out jack. I'm wondering if it would work if I plugged phones into the speaker out please? The phones are 24-Ohms so the amp will see plenty of resistance but not a large amount of resistance (like 300-Ohm phones I've owned).
I know many years ago a buddy of mine put a headphone jack on a TV for me by having the headphone plug simply bypass (or short I guess) the internal speaker - he may have put a resistor across it; it was a long time ago.
There are two speaker outs on this amp - if I need a resistor or cap I could leave one as is for speakers and modify the other as necessary. Naturally I will need to build an adapter to send a mono signal to stereo headphones, but that's no big deal - it will change the impedance at the amp I suppose, but not drastically.
I don't see why it wouldn't work. Opinions please?
Thanks
Phil

byacey
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Re: Running headphones from a speaker out jack?

Post by byacey » Sun Dec 11, 2016 10:47 am

Usually a headphone out jack has a resistive voltage divider because the speaker output is pretty hot for headphones. It only takes milliwatts to drive a set of headphones to reasonable volume. You might try a 300 ohm series resistor from the speaker output to the headphone hot, and perhaps a 100 ohm across the headphone hot to ground.

Classic30inCincy
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Re: Running headphones from a speaker out jack?

Post by Classic30inCincy » Sun Dec 11, 2016 11:16 am

The other issue is output jack is MONO versus headphones STEREO.

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byacey
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Re: Running headphones from a speaker out jack?

Post by byacey » Sun Dec 11, 2016 4:25 pm

The stereo / mono issue is easy to deal with. If using stereo phones, wire the TRS jack with the tip and ring jumpered together.

AlexianaBritmonkey
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Re: Running headphones from a speaker out jack?

Post by AlexianaBritmonkey » Sun Aug 13, 2017 5:27 pm

Doing that would turn it mono and half the impedance the amp sees. If there's a common ground, then tap left into the left channel and right into the right channel. And watch the gain.

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