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Speaker to line-in?

Discussion in 'Beginner Electronics' started by Grumble, Mar 10, 2006.

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  1. Grumble

    Grumble Guest

    I was wondering if there is a way of converting the speaker output of a
    cassette player to a signal suitable for line-input of a PC audio card.
    There is no headphone-out on the device. The intention is to fit a car audio
    cassette player into the PC. Will it even fit? Has anyone tried to do the
    same thing? I know there is a company that makes one but it ain't cheap
    http://plusdeck.com/englishsite/index.asp or at least it ain't as cheap as
    I'd like it to be! I'd like to convert the family tape collection to mp3 but
    I'm sick of all the cables and leads festooning this computer as it is
    without adding any more to it with another piece of stand alone kit.

    Thanks for any help

    Ian
     
  2. default

    default Guest

    I'd just go ahead and try it. Line in is typically rated for one volt
    input (if you over drive, it will clip the signal and be distorted).

    A car system will output a maximum signal of just under its power
    supply voltage. ~12 volts unless it is rated at some very high RMS
    power output - then they may use an internal DC -DC converter to step
    up the voltage - but that is just in those systems that make your ears
    bleed, an inexpensive player won't use a power converter.

    A car tape player may use a bridged amplifier so there is no common
    between speakers - that may cause you a problem. They use two
    amplifiers for each channel to increase the power - one amp is driven
    with an out of phase signal - so its output will be high when the
    other amp is low. Four amps for stereo . . . and it is quite common.

    You might try using ground and one wire from each speaker output to
    the line in and see if that works. Keep the output turned down low.

    If that is still too much a resistor divider on the output will drop
    the signal.

    It may require some experimentation - the car amp is designed for a 4
    ohm speaker load and may not work well on a much higher impedance
    input so you may need a load resistor to keep the amp happy.

    You may find all kinds of hum and hiss that wasn't noticeable with the
    player in a car - you changed the power supply from a heavy DC battery
    to the switching supply in the computer or some other supply that it
    wasn't designed to work with.

    You may have ground loops between the signal paths and supply current
    paths.

    The output of the car player may have a high noise level that will be
    present all the time but only becomes noticeable when driving another
    amp input (a voltage divider may help there).

    All the problems have solutions - but you have to be able to track
    them down and fix them.
     
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