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Adding a Headphone Jack

Discussion in 'General Electronics Discussion' started by ennova, Jan 13, 2011.

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  1. ennova

    ennova

    1
    0
    Jan 13, 2011
    Hello,

    First I want to mention that I know very little about electronics. I've always wanted to learn about designing circuits and such, but I've never gotten around to it. Currently I'm working on a project where I've taken apart some simple computer speakers that will be relocated into a custom case I've built. I've realized that I'm missing a headphone jack and will not be able to use headphones, so I'm trying to fix this issue. I first started by trying to find a set of computer speakers that met all my requirements

    #1 - small in size, simple L+R speakers
    #2 - Push button On/Off and Volume control (no knobs as I will be relocating the controls to a place where knobs sticking out would be an eye sore.)
    #3 - NOT USB speakers, the sound will not be coming from a computer.
    #4 - A Headphone jack.

    However after days of searching and finding speakers that almost fit the requirements, only to find out they are USB or don't have a headphone jack was very frustrating. So I decided to explore the option of modifying the speakers I have now and insert a headphone jack. My idea is as follows:

    After the signal leaves the simple audio amp, it goes straight the the L+R speakers. I was thinking of instead sending it to 2 Transistors that in one position go to the speakers and on the other position go to the headphone jack. I was thinking that a simple tactile push button switch would work to control the transistors. As I stated above I don't know very much about electronics let alone diagrams. I guess I should start to explore what all the symbols mean etc. However for know I was wondering if these idea would work? It almost sounds too simple. If it would work, could someone help me find transistors that would work? If it is simple enough I was thinking of printing the basic circuit off on those projection slides with a printer, burning it to a PCB board, developing and then etching it as I've seen done in a video I once saw. Thanks for your time and anything you might contribute,

    Ennova

    PS - is it possible to replace an those knob volume controls (I think potentiometers) with digital ones (push button volume control)? If so is it hard to do?
     
  2. awright

    awright

    10
    1
    Oct 10, 2009
    If I understand what you are trying to do, it sounds like you are making this more difficult than necessary.

    To answer your question about building your own digital volume control - yes, it can be done with special digital pot ICs or with motor controlled analog potentiometers. However, I can't imagine it would be worth the hassle just to avoid using the computer's digital pot unless you have special remote control requirements. And it would take some electronics sophistication that you profess not to possess yet.

    Except for the elimination of knobs on one of the speakers, your criteria are met by the vast majority of "computer speakers" that are not USB speakers. You can pick up these non-USB computer speakers for $5 or $10 a pair at electronic surplus or used computer stores. They have a 1/8" stereo phone plug on a cable permanently attached to one of the speakers. This plugs into the earphone jack on your computer. Unplug the speakers and you have your earphone jack. The computer has a digital volume control built in. Set the volume control on your master speaker at some convenient level and control volume digitally from your computer.

    Typically, one speaker contains a small audio power amplifier powered by an external modular power supply. The second speaker plugs into the speaker containing the power amplifier and the cable connected to the computer. The master speaker does usually have a push-button power switch and a volume control knob on the front panel but these functions can be handled by switching the power to the speakers and using the computer volume control.

    Note that these small computer speakers almost always are contained in plastic cabinets having special acoustical design to enhance and complement the properties of the transducers in the cabinets and are carefully matched to those properties. Taking the transducers out of their special cabinets and putting them into your home-built cabinets is highly likely to lead to disappointing sound quality. If you want to change the appearance of the speakers, I would suggest putting them inside or behind a wire frame covered with speaker fabric (really any lightweight, open-weave fabric) that will not modify the carefully designed acoustical characteristics of the speakers

    Some of these very inexpensive (surplus or obsolete) computer speakers are actually quite sophisticated, like the Klipsch speaker pair with built-in 30 watt power amplifier I picked up for a few dollars. (Unfortunately, the Klipsch has a unique 3-pin power connector for a bipolar power supply that is hard to find.)

    Your idea of using transistors to switch signals can be made to work, this also takes some sophistication in design to minimize distortion. And you'd probably want to use CMOS ICs or MOSFETs. But if you are using a pushbutton to switch transistors, why not just use a pushbutton switch to control the signal directly? One of the important elements of good design is to use the simplest technology that will do the job at hand. Use the pushbutton switch to transfer the signal coming from the computer earphone jack to either a jack feeding the master speaker or a jack for earphones.

    Hope I'm not misinterpreting your goals.

    awright
     
  3. davenn

    davenn Moderator

    13,381
    1,784
    Sep 5, 2009
    Just a little :) in point #3 he comments that the sound WONT be coming from a computer. But I agree with you he seems to be making the project more difficult that it would need to be.

    Ennova .....

    maybe you should start at the start and tell you what the source of the music is ?
    surely it already has an amplifier, vol control and headphone jack ??
    tell us what you are actually trying to achieve :)

    cheers
    Dave
     
  4. awright

    awright

    10
    1
    Oct 10, 2009
    Thanks for pointing out my misreading, Dave. I read that line incorrectly multiple times.

    awright
     
  5. davenn

    davenn Moderator

    13,381
    1,784
    Sep 5, 2009
    no probs mate can hapen to anyone :) but the OP still hasnt bothered to respond :(
    difficult to help if they dont tell us the whole story huh


    Dave
     
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