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741 Op Amp Question

Discussion in 'Electronic Basics' started by BobaMosFet, Jun 8, 2007.

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  1. BobaMosFet

    BobaMosFet Guest

    I used to have a Sony cassette recorder in the early 80s that if you
    wore headphones and pressed record, you could literally here a pin
    drop in the room. I took this apart back then and the circuit for this
    used a 741 op amp chip. I have some of these and have found some
    schematics and put them together on my breadboard, but none of them
    have the gain that the cassette recorder had. Does anyone have a
    schematic that will produce this high gain?
  2. There is more to answering your request than simply providing "a schematic
    that will produce this high gain".

    How high a gain are you trying to achieve? What are your input and output
    devices and what are their characteristics? What supply voltages are you

    You are likely needing different circuits for input and output, and they may
    not both be op-amp circuits.

    To get you started, try a Google search on "op-amp tutorial". There are
    several, including some specifically for the 741. You might even be able to
    find something about frequency conversion (or, at least.
    frequency-to-voltage and voltage-to-frequency conversion) to answer your
    other question. While you are at it, get a copy of the 741 datasheet, if you
    don't already have it.

    Good luck and have fun experimenting.

    Richard Seriani, Sr.
  3. Eeyore

    Eeyore Guest

    I think your perception of it being so quiet that you could "hear a pin drop"
    must have been optimistic.

    741 op-amps are horribly noisy for mic preamp stages. There's far far better.

    Let's start with what kind of mic you want to use. Let's have its source
    impedance, is it balanced or unbalanced, moving coil, capacitor or electret
    etc.... Does it need phantom power ?

  4. YD

    YD Guest

    The 741 can't have been the only active part in it, there must have
    been a lot of other stuff there. If all you want is a high gain phone
    amp with mic input there are oodles of schems on the net, do a search
    and take your pick.

    - YD.
  5. Phil Allison

    Phil Allison Guest


    ** Be a nice Sony electret mic built into that.

    They make professional grade examples too - see the ECM-CS10.

    All these mics have an internal pre-amp, so there aint any 741s doing

    ........ Phil
  6. neon


    Oct 21, 2006
    let me see how about $1.00 for a amp stereo phones hearing spy made in china all packaged into a 3/4" by 1/4". i cannot buy the amp for that.
  7. Guest

    Hello BobaMosFet,

    Bell & Howell Sound Amplifier - Model #: 7667 $20 usd

    These do work good in the forest and ghost hunting. They have a couple
    of other models on that page.

    I bought a toy Spy Tek listener with two ear buds in the toy section
    of Thrifty Drug store. Also check our Walmart if you are in the
    states. For $5 you can get a clear plastic belt mounted enclosure and
    circuit board with one button battery.

    Good luck,

    * * *

    Temecula CA.USA
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