Need a easy to build signal amplifier

Discussion in 'General Electronics' started by Chisvasi Sebastian, Sep 2, 2003.

  1. Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    complex one, my problem is that the input signal is below a millivolt
    and i need to raise it to at least a copple of volts (tenths of volts
    will be perfect) anyway the output signal is going to the mic jack of
    my soundcard (because i intend to use it like an osciloscope).

    Thanks ...
     
    Chisvasi Sebastian, Sep 2, 2003
    #1
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  2. Chisvasi Sebastian wrote:
    >
    > Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    > complex one, my problem is that the input signal is below a millivolt
    > and i need to raise it to at least a copple of volts (tenths of volts
    > will be perfect) anyway the output signal is going to the mic jack of
    > my soundcard (because i intend to use it like an osciloscope).
    >
    > Thanks ...


    This is an ordinary job for opamps. These are universal signal
    amplifiers that have two inputs (labeled + and -) and an output. The
    opamp has a very high differential gain (it amplifies the difference
    voltage between the two inputs) while using almost no current through
    these inputs. When the + input is more positive than the - input, the
    output heads positive.

    You program an opamp for what ever gain you want with a few
    resistors. It can produce a positive or negative output for a
    positive input (called noninverting or positive gain versus inverting
    or negative gain). The input voltages and output voltage are
    constrained to stay within the supply voltages.

    For a basic tutorial on these cheap and useful components and lots of
    circuit ideas, see:

    http://www.national.com/appinfo/amps/0,2175,967,00.html

    --
    John Popelish
     
    John Popelish, Sep 2, 2003
    #2
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  3. Chisvasi Sebastian

    Allen Bong Guest

    This site is cool! I really enjoy it. Thanks

    Allen

    "Baphomet" <> wrote in message
    news:...
    > try this single op amp circuit
    > http://www.uoguelph.ca/~antoon/gadgets/741/741.html
    >
    >
    > "Chisvasi Sebastian" <> wrote in message
    > news:...
    > > Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    > > complex one, my problem is that the input signal is below a millivolt
    > > and i need to raise it to at least a copple of volts (tenths of volts
    > > will be perfect) anyway the output signal is going to the mic jack of
    > > my soundcard (because i intend to use it like an osciloscope).
    > >
    > > Thanks ...

    >
    >
     
    Allen Bong, Sep 3, 2003
    #3
  4. Chisvasi Sebastian

    Baphomet Guest

    try this single op amp circuit
    http://www.uoguelph.ca/~antoon/gadgets/741/741.html


    "Chisvasi Sebastian" <> wrote in message
    news:...
    > Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    > complex one, my problem is that the input signal is below a millivolt
    > and i need to raise it to at least a copple of volts (tenths of volts
    > will be perfect) anyway the output signal is going to the mic jack of
    > my soundcard (because i intend to use it like an osciloscope).
    >
    > Thanks ...
     
    Baphomet, Sep 3, 2003
    #4
  5. "Kevin McMurtrie" <> wrote in message
    news:...
    > In article <3f5537d4$>,
    > "Allen Bong" <> wrote:
    >
    > > This site is cool! I really enjoy it. Thanks
    > >
    > > Allen
    > >
    > > "Baphomet" <> wrote in message
    > > news:...
    > > > try this single op amp circuit
    > > > http://www.uoguelph.ca/~antoon/gadgets/741/741.html
    > > >
    > > >
    > > > "Chisvasi Sebastian" <> wrote in message
    > > > news:...
    > > > > Hello, i need a easy to build signal amplifier (i'm a begginer), not

    a
    > > > > complex one, my problem is that the input signal is below a

    millivolt
    > > > > and i need to raise it to at least a copple of volts (tenths of

    volts
    > > > > will be perfect) anyway the output signal is going to the mic jack

    of
    > > > > my soundcard (because i intend to use it like an osciloscope).
    > > > >
    > > > > Thanks ...
    > > >
    > > >

    > >
    > >

    >
    > I'd avoid the 741 op-amp. It's an ancient op-amp with quirks that can
    > be frustrating unless you know how its internals work. Radio Shack
    > sells a dual JFET input op-amp that's good enough for most uses. Some
    > fancy op-amps are specially made for audio use (low distortion open loop
    > gain).
    >
    > Op-amps are generic term for a generic device that has a differential
    > input of nearly infinite gain. The circuits using them rarely depend on
    > a specific type. Use any basic circuit and any good op-amp.


    Although the OP doesn't specify his needs very clearly, its clear that he is
    working with audio. Are most run of the mill opamps fast enough to handle
    high audio without distortion?

    Thanks,
    Bob Monsen
     
    Robert Monsen, Sep 3, 2003
    #5
  6. (Chisvasi Sebastian) wrote:

    >Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    >complex one, my problem is that the input signal is below a millivolt


    What is the signal source?

    >and i need to raise it to at least a copple of volts (tenths of volts
    >will be perfect) anyway the output signal is going to the mic jack of
    >my soundcard (because i intend to use it like an osciloscope).


    The mic input is already made for very weak signals, below and above
    1mV, so maybe you do not need any amplifier, just use the volume
    control on the mic channel in the computer.

    If you really need an amplifier you should know that amplification is
    not the main problem with such weak signals, an op-amp can deliver a
    lot of amplification, keeping unwanted noise out is the big problem.

    You should look for microphone pre-amplifiers for good low noise
    designs.

    You need a low noise op-amp, like the 5534/5532, and you need to be
    very careful with how you arrange the input cable, shielding of the
    circuit, etc..

    For such weak signals you need to shield the signal source, the cable,
    the pre-amp, and the cable into the mic input.
    Coaxial cable and metal boxes for the circuits, battery driven or use
    the voltage output available in the mic jack.
    There are 3 contacts on a mic connection on a sound card, ground,
    input, and 5-9Volt output which is used to drive an electret mic.

    That voltage output can you use to drive your pre-amp, if you do not
    need so much current. Otherwise use a battery, and shield the battery
    too.

    If you want to use the sound card as an oscilloscope there are
    problems with using the mic input, by the way. It often has an
    automatic gain control and that will make the gain adjust
    automatically, which means you cannot rely on the values you get.

    If you want to use the sound card as an oscilloscope you should use
    the line input instead, and then you really need a pre-amp for such
    weak signals.

    Your best option to begin with is to use the mic input without any
    pre-amp, and see what results you get.
    Check the soundcard docs to see if you can disable the automatic gain
    control. If not you cannot trust the values you get on the strength of
    the signal, but maybe it is not so important.

    If you need to measure the signal strength, and the automatic gain
    control cannot be disabled on the mic input you need to build a
    sensitive mic pre-amp and use the line input instead.


    --
    Roger J.
     
    Roger Johansson, Sep 3, 2003
    #6
  7. Chisvasi Sebastian

    Bill Sloman Guest

    "Baphomet" <> wrote in message news:<>...
    > Chrisvasi Sebastian wrote:
    >
    > " Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    > Complex one, my problem is that the input signal is below a millivolt
    > and i need to raise it to at least a copple of volts (tenths of volts
    > will be perfect) anyway the output signal is going to the mic jack of
    > my soundcard (because i intend to use it like an osciloscope)."
    >
    > To which Kevin McMurtrie indirectly replied"
    >
    > " I'd avoid the 741 op-amp. It's an ancient op-amp with quirks that can
    > be frustrating unless you know how its internals work. Radio Shack
    > sells a dual JFET input op-amp that's good enough for most uses. Some
    > fancy op-amps are specially made for audio use (low distortion open loop
    > gain)."
    >
    > "Op-amps are generic term for a generic device that has a differential
    > input of nearly infinite gain. The circuits using them rarely depend on
    > a specific type. Use any basic circuit and any good op-amp."
    >
    > Kevin -
    >
    > I'd be interested in what quirks in particular you experienced with the
    > 741. While it's true that the 741 has been around for awhile (I think it was
    > a follow up of the 709), it is still made because it is such a good,
    > reliable general purpose device. While I wouldn't use it for precision
    > instrumentation, it is admirably suited for the purpose intended in
    > Chrisvasi's original post. I think you would be amazed at how much military
    > and Fortune 500 equipment the 741 wound up being designed around. Would I
    > use it today for non critical applications? You betcha!


    The LM324 quad and the LM358 dual op amps are cheaper, more compact,
    just as crummy and work as single supply op amps. Using a 741 is pure
    lazyness.

    The guys who design for the military had an excuse - it takes a long
    time to qualify an integrated circuit for high reliability military
    applications, and their choice of op amps used to be limited.

    Fortune 500 equipment represents a different problem, not unlike high
    end audio, where the customer wants something idiosyncratic to
    indicate their unique capacity to throw money down the drain, and that
    market is too small to pay for good design - whence loads of 741's.

    ------
    Bill Sloman, Nijmegen
     
    Bill Sloman, Sep 3, 2003
    #7
  8. Chisvasi Sebastian

    Baphomet Guest

    Chrisvasi Sebastian wrote:

    " Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    Complex one, my problem is that the input signal is below a millivolt
    and i need to raise it to at least a copple of volts (tenths of volts
    will be perfect) anyway the output signal is going to the mic jack of
    my soundcard (because i intend to use it like an osciloscope)."

    To which Kevin McMurtrie indirectly replied"

    " I'd avoid the 741 op-amp. It's an ancient op-amp with quirks that can
    be frustrating unless you know how its internals work. Radio Shack
    sells a dual JFET input op-amp that's good enough for most uses. Some
    fancy op-amps are specially made for audio use (low distortion open loop
    gain)."

    "Op-amps are generic term for a generic device that has a differential
    input of nearly infinite gain. The circuits using them rarely depend on
    a specific type. Use any basic circuit and any good op-amp."

    Kevin -

    I'd be interested in what quirks in particular you experienced with the
    741. While it's true that the 741 has been around for awhile (I think it was
    a follow up of the 709), it is still made because it is such a good,
    reliable general purpose device. While I wouldn't use it for precision
    instrumentation, it is admirably suited for the purpose intended in
    Chrisvasi's original post. I think you would be amazed at how much military
    and Fortune 500 equipment the 741 wound up being designed around. Would I
    use it today for non critical applications? You betcha!
     
    Baphomet, Sep 3, 2003
    #8
  9. Chisvasi Sebastian

    Baphomet Guest

    "Bill Sloman" <> wrote in message
    news:...
    > "Baphomet" <> wrote in message

    news:<>...
    > > Chrisvasi Sebastian wrote:
    > >
    > > " Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    > > Complex one, my problem is that the input signal is below a millivolt
    > > and i need to raise it to at least a copple of volts (tenths of volts
    > > will be perfect) anyway the output signal is going to the mic jack of
    > > my soundcard (because i intend to use it like an osciloscope)."
    > >
    > > To which Kevin McMurtrie indirectly replied"
    > >
    > > " I'd avoid the 741 op-amp. It's an ancient op-amp with quirks that can
    > > be frustrating unless you know how its internals work. Radio Shack
    > > sells a dual JFET input op-amp that's good enough for most uses. Some
    > > fancy op-amps are specially made for audio use (low distortion open

    loop
    > > gain)."
    > >
    > > "Op-amps are generic term for a generic device that has a differential
    > > input of nearly infinite gain. The circuits using them rarely depend

    on
    > > a specific type. Use any basic circuit and any good op-amp."
    > >
    > > Kevin -
    > >
    > > I'd be interested in what quirks in particular you experienced with

    the
    > > 741. While it's true that the 741 has been around for awhile (I think it

    was
    > > a follow up of the 709), it is still made because it is such a good,
    > > reliable general purpose device. While I wouldn't use it for precision
    > > instrumentation, it is admirably suited for the purpose intended in
    > > Chrisvasi's original post. I think you would be amazed at how much

    military
    > > and Fortune 500 equipment the 741 wound up being designed around. Would

    I
    > > use it today for non critical applications? You betcha!

    >
    > The LM324 quad and the LM358 dual op amps are cheaper, more compact,
    > just as crummy and work as single supply op amps. Using a 741 is pure
    > lazyness.
    >
    > The guys who design for the military had an excuse - it takes a long
    > time to qualify an integrated circuit for high reliability military
    > applications, and their choice of op amps used to be limited.
    >
    > Fortune 500 equipment represents a different problem, not unlike high
    > end audio, where the customer wants something idiosyncratic to
    > indicate their unique capacity to throw money down the drain, and that
    > market is too small to pay for good design - whence loads of 741's.
    >
    > ------
    > Bill Sloman, Nijmegen


    Bill -

    Laziness is not exactly how I would characterize it. I think hermetic
    sealing and reliability may have just had a little something to do with it
    :)
     
    Baphomet, Sep 3, 2003
    #9
  10. Chisvasi Sebastian

    Bill Sloman Guest

    "Baphomet" <> wrote in message news:<>...
    > "Bill Sloman" <> wrote in message
    > news:...
    > > "Baphomet" <> wrote in message

    > news:<>...
    > > > Chrisvasi Sebastian wrote:
    > > >
    > > > " Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    > > > Complex one, my problem is that the input signal is below a millivolt
    > > > and i need to raise it to at least a copple of volts (tenths of volts
    > > > will be perfect) anyway the output signal is going to the mic jack of
    > > > my soundcard (because i intend to use it like an osciloscope)."
    > > >
    > > > To which Kevin McMurtrie indirectly replied"
    > > >
    > > > " I'd avoid the 741 op-amp. It's an ancient op-amp with quirks that can
    > > > be frustrating unless you know how its internals work. Radio Shack
    > > > sells a dual JFET input op-amp that's good enough for most uses. Some
    > > > fancy op-amps are specially made for audio use (low distortion open

    > loop
    > > > gain)."
    > > >
    > > > "Op-amps are generic term for a generic device that has a differential
    > > > input of nearly infinite gain. The circuits using them rarely depend

    > on
    > > > a specific type. Use any basic circuit and any good op-amp."
    > > >
    > > > Kevin -
    > > >
    > > > I'd be interested in what quirks in particular you experienced with

    > the
    > > > 741. While it's true that the 741 has been around for awhile (I think it

    > was
    > > > a follow up of the 709), it is still made because it is such a good,
    > > > reliable general purpose device. While I wouldn't use it for precision
    > > > instrumentation, it is admirably suited for the purpose intended in
    > > > Chrisvasi's original post. I think you would be amazed at how much

    > military
    > > > and Fortune 500 equipment the 741 wound up being designed around. Would

    > I
    > > > use it today for non critical applications? You betcha!

    > >
    > > The LM324 quad and the LM358 dual op amps are cheaper, more compact,
    > > just as crummy and work as single supply op amps. Using a 741 is pure
    > > lazyness.
    > >
    > > The guys who design for the military had an excuse - it takes a long
    > > time to qualify an integrated circuit for high reliability military
    > > applications, and their choice of op amps used to be limited.
    > >
    > > Fortune 500 equipment represents a different problem, not unlike high
    > > end audio, where the customer wants something idiosyncratic to
    > > indicate their unique capacity to throw money down the drain, and that
    > > market is too small to pay for good design - whence loads of 741's.
    > >
    > > ------
    > > Bill Sloman, Nijmegen

    >
    > Bill -
    >
    > Laziness is not exactly how I would characterize it. I think hermetic
    > sealing and reliability may have just had a little something to do with it
    > :)


    For military applications, and the occasional harsh industrial
    environment, but even there, using the 741 is generally a cop-out.
    These days there are always better amplifiers for any specific job.

    ------
    Bill Sloman, Nijmegen
     
    Bill Sloman, Sep 3, 2003
    #10
  11. Chisvasi Sebastian

    Zak Guest

    Robert Monsen wrote:

    > Although the OP doesn't specify his needs very clearly, its clear that he is
    > working with audio. Are most run of the mill opamps fast enough to handle
    > high audio without distortion?


    Well, the LM324 for example isn't.


    Thomas
     
    Zak, Sep 3, 2003
    #11
  12. In article <>,
    Kevin McMurtrie <> wrote:

    > In article <3f5537d4$>,
    > "Allen Bong" <> wrote:
    >
    > > This site is cool! I really enjoy it. Thanks
    > >
    > > Allen
    > >
    > > "Baphomet" <> wrote in message
    > > news:...
    > > > try this single op amp circuit
    > > > http://www.uoguelph.ca/~antoon/gadgets/741/741.html
    > > >
    > > >
    > > > "Chisvasi Sebastian" <> wrote in message
    > > > news:...
    > > > > Hello, i need a easy to build signal amplifier (i'm a begginer), not a
    > > > > complex one, my problem is that the input signal is below a millivolt
    > > > > and i need to raise it to at least a copple of volts (tenths of volts
    > > > > will be perfect) anyway the output signal is going to the mic jack of
    > > > > my soundcard (because i intend to use it like an osciloscope).
    > > > >
    > > > > Thanks ...
    > > >
    > > >

    > >
    > >

    >
    > I'd avoid the 741 op-amp. It's an ancient op-amp with quirks that can
    > be frustrating unless you know how its internals work. Radio Shack
    > sells a dual JFET input op-amp that's good enough for most uses. Some
    > fancy op-amps are specially made for audio use (low distortion open loop
    > gain).
    >
    > Op-amps are generic term for a generic device that has a differential
    > input of nearly infinite gain. The circuits using them rarely depend on
    > a specific type. Use any basic circuit and any good op-amp.


    Opps. I was thinking of another op-amp. The 741 probably isn't so bad.
     
    Kevin McMurtrie, Sep 3, 2003
    #12
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