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Adding a timer to a stereo amp

Discussion in 'General Electronics Discussion' started by abunaitwo, Dec 4, 2014.

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  1. abunaitwo


    Dec 4, 2014
    First post here. Hope I can get some help.
    I'm making a count down timer.
    I'm using a battery kitchen timer, old home stereo AMP, and a RCA wire.
    The plug is going into the mic jack on the AMP.
    I've wired the timer with the power(red) to the core and the NEG(black) to the shield.
    The plug is wired with the RED to the core and the NEG to the shield.
    It's working, BUT, I am getting buzzing from the speakers.
    I suspect feedback of some kind.
    The speaker in the timer is not connected.
    I did add a on/off mini slide switch in line of the RED wire in the timer.
    Any ideas on how I can get rid of the buzzing??????
  2. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Welcome to Electronics Point forums.

    Really? Making a count down timer, or trying to use "a battery kitchen timer" as a count down timer?

    Wow! What is RCA wire? Does the stereo AMP have stereo speakers connected to it?

    Would that be the LEFT stereo channel or the RIGHT stereo channel of that "old home stereo AMP?"

    What, exactly, in the "battery kitchen timer" have you wired (presumably to RCA wire)?

    May we assume this is the plug that is inserted in a "mic jack on the AMP?"

    Please define "working". What do you expect this arrangement to accomplish? Can you provide a circuit diagram of the "battery kitchen timer?"
    Probably power line pickup rather than feedback.

    What was "the speaker in the timer" originally used for? Does your connection with the "RCA wire" replace "the speaker in the timer?"

    It is likely that the mic input to the stereo amp is a high impedance input and more sensitive than you need. Try loading the source end with a 100 ohm resistor. You can just solder this in the RCA plug between barrel pin and shield, or connect it in the "battery kitchen timer." Either place should work to lower the mic input impedance and help prevent AC line pickup.
  3. abunaitwo


    Dec 4, 2014
    Thanks for the help.
    I'm just a tinker with things like this.
    Don't have any kind of wire diagram for the timer.
    It's a 1.5v kitchen timer made by LUX.
    I'll try the resistor.
  4. davenn

    davenn Moderator

    Sep 5, 2009
    hi abunaitwo

    you haven't really given enough clear info about how you have connected it all up ?
    how about several photos sharp and well lit so we can see clearly what wires are going where

    what were you actually wanting the timer to switch on/off when it completes its countdown ?
  5. abunaitwo


    Dec 4, 2014
    Sorry, I know my description is not to good.
    How's this.
    1) I want to connect a 1.5v kitchen timer, to a 120v stereo amp, through the mic jack.
    2) I connected the mic plug to the timer with 1/2 of a RCA wire. Two wire, shield and center wire only.
    3) I cut off the ends of the RCA and soldered the it to the plug and timer.
    4) The plug is a three wire plug. Only the outer and center connections are used.
    5) The shield of the wire is connected to the outer of the plug.
    6) The center of the wire is connected to the center of the plug.
    7) The timer had two wires going to a beeper in the unit.One red and one black.
    8) I connected the red to the center wire and the shield to the black of the wire. Beeper is not connected.
    9) It works. Beeps through the amp/speakers.
    10) I'm getting a buzzing sound when it is plugged in. I'd like to get rid of the buzzing.
    11) The mic works fine with the timer plugged in. No buzzing with only the mic connected.
    Would it help if I get a two wire plug instead of using the three wire plug????
    Is the RCA wire ok????
    The mic has only two wires.
    Am I trying to do something that's not possible????

    The timer is used to signal the start and end with a beep.
    Press the button, it beeps, to start. Beeps when the set time ends. Reset when button pressed again.
    We've been using a stop watch, whistle, and a mic. It's a pain for one person to do all together.
  6. BobK


    Jan 5, 2010
    The mic input is not the best one to use for this. Is there an aux input you could use instead? That input would be better for the level coming from the timer's beeper, and would be less likely to pick up a hum.

  7. abunaitwo


    Dec 4, 2014
    There is an AUX RCA in the rear.
    I'll try that.
  8. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    I would venture to guess that the original "speaker" in the timer is a high-impedance piezoelectric transducer. If so, there probably isn't enough power or signal amplitude to drive the 100 Ω resistor I originally suggested connecting across your two wires connecting to the amplifier. In other words, 100 Ω will probably attenuate the signal too much. Try increasing the value to 1kΩ or 10 kΩ or even larger until the signal is large enough for the amplifier to use. If the "hum" returns, perhaps a non-polarized film capacitor applied to the amplifier input across the input terminals will attenuate the "hum" without adversely affecting the signal from the timer. I would start with 0.1 μF and work up from there. You will still need the 1 kΩ or larger resistor to provide a lower impedance to the amplifier input. And do try the AUX input first before making any changes.

  9. abunaitwo


    Dec 4, 2014
    Sometimes the simplest solution is the one you should start with.
    The AUX jack works like a charm.
    Thanks for all the help y'all
  10. BobK


    Jan 5, 2010
    <Puffs up chest>

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