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  1. #1
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    Stereo 1/4" jack Y-adapter

    Hi Everyone. I am trying to make an adapter that will link two audio sources to a single set of headphones. I am working on a Y-adapter with two male 1/4" jacks that link to a single female 1/4" plug. In essence, I want to be able to listen to two different audio sources at the same time.

    My problem is that a friend of mine came over and looked at what I was doing and mentioned that if I just solder the wires together at the female connector, I might end up damaging either of the amplifiers in the audio sources. He suggested that I put a resistor in the signal line at both of the male ends of the adapter. The reasoning here is that a small resistance (8-16 ohms maybe) in the line at these points will protect the amplifiers from 'feeding' each other.

    I'm not sure if this is the right way to go about it or if I should give up on this project all together! If anyone could offer some advice on this, it would be appreciated. I'd be more than willing to supply more info if you need it.

  2. #2
    By the sound of it i think he thought you was going to use in to plug two mono audio sources into one stereo input on an amplifier.

    you should be fine without the resistors as long as the two audio sources don't mix.

  3. #3
    This is a common problem. Power amp outputs should never be connected in parallel because each amp will try to ram its signal backwards into the other amp's output.

    Generally, unless you're using headphone outputs to begin with, you need resistors between a power amp's outputs and the headphones anyway. Headphones are so much more sensitive than speakers (because they're coupling directly to your ears) that the background noise coming from the amps would drive you nuts. Not to mention potential damage to your hearing.

    Common values for series resistors are 33 ohms to 100 ohms. I'd start with 100 ohms and if you can't get it loud enough, reduce the resistors. Better than starting at the other end and blowing your ears out.

  4. #4
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    I am pretty sure I am working with headphone outputs. If that is the case, is 33 - 100 ohms too much? Or should I just give it a go and find the right value by trial and error?

    Thanks for the explanation of the problem. This is pretty much what I needed to know.

  5. #5
    Nowadays headphones are almost all 32 ohms. I'd say you're safe with 18- or 22-ohm resistors. This will cause a little attenuation, but when you sum signals, the result is a few dB higher so a little attenuation may not be a bad thing. Lower resistors, like 8 ohms, could possibly overtax the outputs if you get a strong out-of-phase signal. This is unlikely, unless polarity gets flipped in one channel, but best be safe.

  6. #6
    Quote
    Quote: 3d_matty
    View Post
    I am pretty sure I am working with headphone outputs. If that is the case, is 33 - 100 ohms too much? Or should I just give it a go and find the right value by trial and error?

    Thanks for the explanation of the problem. This is pretty much what I needed to know.
    If your planning on wireing the two inputs together then add a resistor but i thing that it's best to keep the channels separate so you can monitor both inputs separately.
    For example.
    Code:
    Headphones out 1         Headphones Out 
           L    G             G    L   
           |    |______________|   |         +==================+
           |         |             |         |  Key             |
           -------   |      --------         |------------------|
                 |   |      |                | G - Ground       |
                 L   G     R                 | L - Mono Channel |
                   Headphones                |    usually Left  |
                                             +==================+

  7. #7
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    Unfortunately, smifis, wiring it that way doesn't suit my purpose. I'll try putting some resistors in and see how I go. Thanks for the help guys!

  8. #8
    bahhhh

    Good luck and dont listen to my advice

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