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TV speaker amplifier

Discussion in 'Electronic Repair' started by micky, Mar 1, 2013.

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  1. micky

    micky Guest

    Well, last night, I finished the first draft of the amplifier for my
    bathroom tv speaker.

    Thanks for the advice earlier

    It works well** except for two problems.

    A) Allong with the TV sound, it blends in the strongest AM station in
    town. The amplifer module I bought just has 5 unshielded wires
    coming out of it, and for the input, I used 20 inches of lamp cord
    connnected to a 1/8" phone plug, which plugged into the earphone jack
    of the tv. I guess the fix most likely to work is to replace the
    lamp cord with co-axial shielded cable. Right?

    Or I could just wrap some kind of shielding around the wire that is
    there. Like heavy duty aluminum foil taped in place. Good idea.
    Easier becaue I wouldn't have to hunt for some shielded cable, or
    solder a phone little plug to the end. .

    B) It's probalby much too loud. I have to turn the tv volume down
    from a maximum of 50 to about 15. Then let it get amplifed again by
    the amp. I'm figuring the TV output has less distorition, and that
    using it at low volume which then gets amped by this thing introduces
    distortion. (Though I caouldn't tell because the AM radio was too much
    of a distraction.)

    The remedy for this seems to be to change wall warts. Right now I'm
    using a 12VDC, 500mA adapter, which I chose mostly because it was the
    first I saw in my box that had the end, the tip, cut off already.
    The spec says it can use 4.5 to 12VDC


    **I'm using a Kemo M031N monaural amplifier module that sells for
    about 8 dollars at MCM Electrronics. Rated at 3.5 watts. I'm glad I
    didnt' get the 8? wattt version that was about 13 dollars.

    It's "box" is open on one side but filled with some sort of hard
    filling. It has 5 unshielded wires coming out of one side. Two for
    the input. And two for the speaker plus two for the power, which
    share one negative wire. Which makes 5 total.

    I paid no attention to polarity, since it's a monaural output, but
    when I put in a shielded input, I could make sure that the shield is
    conected to what the instructions say is the ground, if it matters???

    Unlike their drawing, I don't have the pot wired into the input,
    because the TV is 9 feet away from the bathtub. Rather it's in the
    wires that go to the speakers, from a 1930's record player, mounted
    above the tub (for the last 30 years.) .

    Thanks.
     
  2. A) Allong with the TV sound, it blends in the strongest AM station in
    town. The amplifer module I bought just has 5 unshielded wires
    coming out of it, and for the input, I used 20 inches of lamp cord
    connnected to a 1/8" phone plug, which plugged into the earphone jack
    of the TV. I guess the fix most likely to work is to replace the
    lamp cord with co-axial shielded cable. Right?

    RIGHT!!!

    Story... Back in 1978 I was working at a hi-fi store in Pennsylvania. Around
    this time, fancy speaker cables and interconnects were becoming popular. One
    customer bought some Monster speaker cable, then called us to say that he had
    a hum problem. When I saw his system, I broke into uncontrollable laughter. He
    had attached RCA plugs to the Monster cable, and was using it as an
    interconnect!


    B) It's probalby much too loud. I have to turn the tv volume down
    from a maximum of 50 to about 15. Then let it get amplifed again by
    the amp. I'm figuring the TV output has less distorition, and that
    using it at low volume which then gets amped by this thing introduces
    distortion. (Though I caouldn't tell because the AM radio was too much
    of a distraction.)

    If anything, the TV introduces more distortion than the amp. Keep the TV
    output low and let the amp provide the needed gain.

    Stick with the supply you have.
     
  3. Jamie

    Jamie Guest

    That's gotta be one of the funniest post I've seen in some time now.. :)

    Jamie
     
  4. micky

    micky Guest

    Yes it did, and I read it, but I sort of blew that off in my mind,
    thinking it was referring to very small signals rather than line level
    input. And I did that despite the blurb in the MCM online catalog
    saying it accepted line-level input.
    Aha. Maybe I have a couple of these that I cut off discarded
    equipment, or I'll buy them if the AM is still getting in.

    Aha, I found them for sale at a mail order place where I needed 7 more
    dollars to avoid paying a 5 dollar handling fee (for orders under 10
    dollars) . I still need to spend 4 more dollars!
    Just to be clear, I didn't mean that I had experienced audible
    distortion already, but that was because I kept the tv volume at 20
    out of 50. And I kept the pot low, but after I posted I turned it
    almost to the max and of course the volume didn't seem to go up so
    much in the last third or half of my turning it.

    But I figured there was distortion I wasn't hearing, that would show
    up if I listened to music, or would make my ears hurt after a while
    (even if at one level it sounded okay) .

    I also kept the tv volume down for fear of damaging my 80 year old
    speakers. (BTW, I never take showers or hot baths (only warm baths
    with no steam, not even on the mirror when I'm done) , so the
    environment for them above the bathtub is not so bad. But my brother
    has visited and he takes showers (I don't know how steamy they are)
    and the grill cloth (designer burlap, that is, light tan-colored
    burlap) is water stained, I guess from the steam. I'm lucky the
    speakers didn't get hurt and next time he visits I will have him
    shower in the bathroom off my bedroom.
    Ah, let me ask about these lines from the instructions:
    Parallel to the cables? Not across the cables? I know this is
    translated from German, but still.
    Power will *increase* with lower voltages??

    OTOH, with "highly ohmic" speakers, 8,, 12, 16, more power will be
    needed, right? Or not? But either way, the power won't increase by
    using higher ohm speakers?? So for both situations, they must mean
    "decrease".

    Watts=Volts*Amps=Ohms*Amps*Amps-R*A
    I had planned on using the tv's volume control, but your idea would
    keep it safe when I forgot or when someone else visited. (Though I
    don't remember any of my guests using the tv or the radio in the
    bathroom. They probably think I'm weird.)
     
  5. micky

    micky Guest

    Thanks. I would have thought the word was perpendicular, not
    parallel.
    OK. Still working on this. It may be done in 2 years, in time for
    my Masters Degree in tinkinering. (MST)
     
  6. Leif Neland

    Leif Neland Guest

    micky formulerede spørgsmålet:
    If you think of "Parallel to the end of the cable" it makes sense.

    Leif
     
  7. micky

    micky Guest

    Hmmmm. Thanks.
     
  8. Leif Neland

    Leif Neland Guest

    Den 05/03/2013, skrev Pat:
    Which makes the interesting question: Is a bulb/speaker/motor/whatever
    connected in parallel or in series with its connecting cord? :)

    Leif
     
  9. Which makes the interesting question: Is a bulb/speaker/motor/whatever
    In parallel. Think of stripping the power cord of small sections of insulation
    and attaching additional loads.
     
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