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volume attenuator

Discussion in 'Electronic Basics' started by [email protected], Jul 27, 2006.

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  1. Guest

  2. Tom Biasi

    Tom Biasi Guest

    If you mean replace the 300 Ohm resistor with a potentiometer, you will not
    get the expected results.
     
  3. Chris

    Chris Guest

    Nope. Keep the 300 ohm resistor where it is (a 270 ohm may be easier
    to find at Radio Shack -- that's OK). Get a 25 ohm 3 watt rheostat
    from Radio Shack (Catalog #: 271-265, $3.99 ea.) and hook up the
    handset speaker like this (view in fixed font or M$ Notepad):

    | o-----.
    | |
    | |
    | .-.
    | | |<-.
    | 25 ohm| | |
    | '-' |
    | | | __ /|
    | | '-| | |
    | o-----o-----|__| |
    | \|
    |
    (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

    Good luck
    Chris
     
  4. Don Bowey

    Don Bowey Guest

    That will likely upset the hybrid balance, which will increase the volume of
    the local talker to his own handset.
     
  5. Chris

    Chris Guest

    Yup, it's ugly. I was thinking a pot on both sides, too, and didn't
    mention that. It's not pretty, but at least it will kinda work.
    Replacing the 300 ohm resistor with a pot probably won't.

    Thanks for the spot, Mr. Bowey.

    Cheers
    Chris
     
  6. Guest

    Why did you choose 25 ohm? Will 100K work?

    Thanks.
     
  7. Simoc

    Simoc Guest

    Please write your reply _below_ the quote, not above.

    The 25 ohm was chosen because it won't have too high attenuation which
    would make most of its range useless. So in other words, you will have
    an useful adjusting range. If you chose 100K, it'd work, but would be
    pretty useless, as you'd have just the first millimeter of the pot's
    range useful (after it there would be so high attenuation that u won't
    hear anything anymore).
     
  8. Guest

    If it is a linear pot, isn't the useful range the same regardless of
    the total resistance? (assuming the pot is the only thing between TIP
    and RING)
     
  9. Chris

    Chris Guest

    Hi, Mike. Standard Google practice is to click "Show Options", click
    "reply", and then put your response under the prior responses (which
    are conveniently shown in Reply to Topic).

    The pot isn't just a voltage divider -- it's also a series resistance.
    Looking at the Radio Shack product, you don't have many choices below
    5K (except for a 1K 0.1W micro tweaker pot). If you use that 5K pot,
    and set it in the middle of the adjustment range, there won't be any
    power going to the speaker.

    The business of using the two phones with the 9V battery and the 300
    ohm series resistor is supposed to be a curiosity, and a way to show
    that it works. It's not supposed to be a practical intercom system. I
    think the OP might have better results with something like this:

    http://www.repairfaq.org/ELE/F_ASCII_Schem_Tel.html#ASCIISCHEMTEL_010

    Although it's a little more complex, it is worth it.

    Good luck
    Chris
     
  10. Guest


    I bought that 1K 0.1W micro tweaker pot at Radio Shack this morning.

    I guess that should work if I put it between tip and ring?
     
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