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Discussion in 'General Electronics' started by nntp.broadband.rogers.com, Jul 23, 2005.

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  1. I have a cordless phone which I am hoping to modify. It has no volume
    control for the handset, and it is much too low volume. I was wondering
    what I would have to do in order to be able to add a volume control or at
    least increase the volume of the phone. I do have very basic electronics
    skills, but I do need the help of the experts out there ;)

    Please reply to the group.


    Greatly appreciated.

    Thank you.
    Dave
     
  2. default

    default Guest

    Adding a control (a potentiometer) won't necessarily increase the
    volume. The audio gain stage has to have the voltage and power gain
    to increase the volume.

    How you go about it would be dependant on a lot of conditions you
    don't mention here.

    Do you have a schematic? Do you know the impedance of the earpiece?

    With a sufficiently high impedance earpiece a single transistor power
    amp would probably work (at some sacrifice of battery life). Another
    possibility might be to use one of the IC audio amps (LM386 if my
    memory serves me), a power op amp, or op amp with external power
    boosting transistors. More complicated, but the battery life would be
    better.

    Then there's the problem of shutting down the amp when you're not
    using it (to conserve battery power). Is there a mechanical switch
    that controls power when you use the phone? If not, you may need to
    use an amplifier with built in sleep/mute function and would need a
    way to (de)activate it.

    There may already be enough gain there and it is just not used - the
    gain may be set with a voltage divider (like a volume control - or it
    may actually have a control in there somewhere). Gain may also be set
    at an internal IC with a single external resistor.

    The best options - hope there is some way to increase the output by a
    tweak to the existing circuit, or find an earpiece transducer with
    higher efficiency than the one in there and replace it.
     
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