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add headphone jack to APA150?

I've got several of the Dayton APA150 amps, and would like to add a headphone jack to them.
Is that just as simple as grabbing a feed from the speaker output terminals and adding a suitable resistor
so I don't blown the headphones?

https://parts-express.com/Dayton-Audio-APA150-150W-Power-Amplifier-300-812

Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"
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  • Not sure, but I imagine you would want to tap into the line level side. There are several nice headphone amp boards out there, the APA150 might even have a suitable tap on the tranny to power them. Add a small high quality toggle switch to the front panel along with a bulkhead 1/4" stereo jack.

    I think anticipating how much resistance to add to the output stage might be tricky.

    Honestly, I guess I would splurge for a small pre-amp with built-in headphone amp and switch between headphones and speakers that way.

    I have a signature.
  • Lots of commercial equipment, old receivers and such just had an L-pad from the amp output over to the headphone jack. Not the best solution but functional.

    I'm not deaf, I'm just not listening.
  • Is part of the goal to grab some of the 'warmth' of the class AB amp section in the amp?
    I don't know how its supposed to be done, but if you have some crossover resistors to fiddle with, I would think you could get close by trial and error with a cheap tiny speaker as a test driver, then use cheap cans once you get close.
    TomZ

  • Looking at some vintage silver Pioneer schematics, they just used a 150 ohm resistor in series with the positive speaker outputs.

  • One thing to check - are the negative terminals floating or grounded? If they're floating and you tie the channels together with a 3 wire headphone cable, you could let the magic smoke out. :o

  • @Tom_S said:
    One thing to check - are the negative terminals floating or grounded? If they're floating and you tie the channels together with a 3 wire headphone cable, you could let the magic smoke out. :o

    I'm not the tech y'all are, so I think that means I would check to see it I got continuity from the negative terminals to chassis ground, correct? Or would I need to open up the amp and check for continuity between the negative terminals and the circuit board ground?

    Don, Donno, or "Hey you" all work for me, But never "Mr Johnson"
  • Yup - just see if they are both grounded. I'm guessing they are. Fingers crossed!

    rjj45
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