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Make an intercom without IC 741

  1. Sep 9, 2009 #1
    I am making a project on linear circuits and am planning to make a basic intercom circuit. But I dont wish to use the 741 IC in it, which is generally used. so please suggest an alternative OP AMP for the same.
     
  2. jcsd
  3. Sep 9, 2009 #2

    vk6kro

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    By far the best opamp is one you can get locally. If it is gold plated but only available in Timbuktu, it isn't much good to you.

    Radio Shack carries the TL 082 which is actually a double JFet input op amp. Costs about $2.
    This seems to be half as noisy as a 741 and has a bandwidth of about 4 MHz vs 1 MHz for the 741.

    I'm sure there are better OPamps out there, but this is an intercom circuit so how good does it have to be?

    Another possibility is the LM386 which is a power amp, but with quite high gain that you can adjust.
     
  4. Sep 9, 2009 #3
    Also LM 358 is very handy, it has two op-amps, just like TL 082, but is not fet based.
     
  5. Sep 9, 2009 #4

    dlgoff

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    I kind of like working with the LM324 quad. op-amp. You can use a single voltage power supply with them.
    "www.national.com/ds/LM/LM124.pdf"[/URL]
    You can get some application notes here:
    [PLAIN]http://www.national.com/mpf/LM/LM324.html" [Broken]
     
    Last edited by a moderator: May 4, 2017
  6. Sep 9, 2009 #5

    vk6kro

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    I like the TL 072 too. They always seem to work immediately and sound great. Never heard any noise from them.

    The 324 is great too. I like to string a number of the opamps in them together with low gain rather than have a lot of gain in one opamp. So, 3 lots of times 10 gives a gain of 1000 and with much better bandwidth than just using one stage.

    Also, having 4 opamps means you can have a couple just making a BEEP noise for an intercom.
     
  7. Sep 10, 2009 #6
    so do I need to change something else in the remaining circuit or everything else remains the same?
     
  8. Sep 10, 2009 #7

    vk6kro

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    There is always a risk with substituting parts, but opamp audio amplifiers are pretty standard, so it is worth a try.

    You could attach your circuit here and maybe something will ring alarm bells. Or, you could just build it and see if it works.

    The pin connections will be different and most of these chips mentioned don't have offset nulling, so omit anything like that.

    Try not to have power from batteries powering the intercom all the time. If you have the two speakers connected to the line all the time nobody is talking and the power only applied to the amplifier when the sender wishes to talk. At that time, he switches his own speaker from the output and possibly uses it as a microphone.
    This way, batteries will last a long time.
    If you can power it from the mains, it doesn't matter if it is powered all the time.
     
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