op amp?

Discussion in 'The Projects Forum' started by ale2121, Apr 10, 2009.

  1. ale2121

    Thread Starter Active Member

    Mar 20, 2009
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    0
    hi.
    i have some oscillating toy sound circuits built. I want to plug them into my amp. Some of them use the lm3909 chip. I don't know where I got the LM3909's, but they're hard to find and expensive, so I'm also using some 555 timers. the lm3909 seems ok to plug straight into the amp, though could use some help. The 555 gets fried when I do. What do I need to place in between the amp and the toy circuit to protect the amp, and help the sound out a little? I'm not so concerned with modifying the sound a little, I'd prefer simple to accurate. Is an op amp the way to go? I have an LM358. Is this the same thing as a pre amp? Any help is greatly appreciated.

    OH! or could I even just put some transistors in between the amp and the circuit? or would this seriously effect the sound?
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Do you have schematics of the circuits you want to connect?
    I think the signal from the 555 is to strong for the amplifier.

    Here is a link to the "music from outer space" site:
    http://www.musicfromouterspace.com/analogsynth.php?page=ANALOG
    Here all kinds of oscillators, mixers and amplifiers can be found.

    Greetings,
    Bertus
     
  3. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    this is basically the toy organ.
    http://www.elecfree.com/electronic/wp-content/uploads/2008/07/toy-organ-by-lm3909.jpg

    i also made another with a photoresistor that works like a theramin.

    the 555, i don't have finished yet. I basically blew it out before I got a chance to test out different frequencies. but this is it, basically
    http://6382195692882002992-a-180274...nx4LrCtC59WKPP2oE8LqhTepzk4RMR5w8imh5aeYeZq7q

    also, this is a really dumb question, but I'm new to all this sound stuff. I don't really understand why a preamp is needed in some cases. is it precisely for what i'm trying to do?
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    The output of the 555 almost swings from 0 to the powersupply (there is some headroom).
    If the amplifier only needs say 0.7 Volts and the 555 will give several volts, you can see it is to much.
    You will need a voltage divider to lower the voltage for the amplifier.
    This can be dome with a potentiometer.

    Here is a site with some information on the 555.
    http://www.uoguelph.ca/~antoon/gadgets/555/555.html
    Here you will finds some schematics with the 555.

    Greetings,
    Bertus
     
  5. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    ok, so are you saying that i don't need to put much of anything in between? cuz even the lm3909 wasn't putting out that much sound.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    When you look at the LM3909, it works on 1.5 Volts.
    The output of the LM3909 will be much less as the 555 will give.
    See also the LM3909 datasheet.

    Greetings,
    Bertus
     
  7. ale2121

    Thread Starter Active Member

    Mar 20, 2009
    71
    0
    ok! this makes sense to me. i think i can add up to 6 volts on the lm3909 before it fries. thank you.
     
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