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Copying Op Amps to Make Mic Amps

Discussion in 'Electronic Design' started by D from BC, Mar 17, 2007.

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  1. ehsjr

    ehsjr Guest

    It is interesting, but why it's called it "mic" amps
    is confusing. It seemes to be about comparing the size
    of organs. :)

    Ed
     
  2. Eeyore

    Eeyore Guest

    Nice work if you can find it.

    Graham
     
  3. John  Larkin

    John Larkin Guest

    The other problem with audio has to do with business culture. In every
    industry, there are superstars and roadies. Doctors and nurses,
    researchers and assistants, athletes and trainers. In big-science type
    businesses, like scientific instruments and national labs, or pharma,
    the PhD scientists are the stars and the engineers are the roadies. In
    the recording biz, the stars are the performers and the producers, and
    the audio people mostly get noticed when there's hum on the mikes. I
    prefer to work in a business where the tekkies are the stars.

    John
     
  4. Phil Allison

    Phil Allison Guest

    "tempus fugit"
    "Phil Allison"

    ** Have I got news for YOU !!!!

    Condenser mics have * pre-amps* inside them !!!!!!!!!

    Almost always, the noise level coming OUT of these internal per-amps is way
    MORE than the input noise level of typical mic-pres in mixing consoles and
    elsewhere.

    There is no noise benefit in using a low noise pre-amp UNLESS it is being
    used with a dynamic mic.

    This is what the EIN figures always refer to a 150 ohm or 200 ohm source
    impedance - ie a DYNAMIC mic !!

    It all goes RIGHT OUT THE WINDOW when a condenser mic is used.




    ........ Phil
     
  5. Phil Allison

    Phil Allison Guest

    "Eeysore"

    ** No I was not.


    ** The damn mic generates its own background noise, way about that suggested
    by its impedance.




    ....... Phil
     
  6. Phil Allison

    Phil Allison Guest

    "Eeysore"

    ** But these alleged "improvements" are not of the audible kind.



    ....... Phil
     
  7. Phil Allison

    Phil Allison Guest

    "John Larkin"

    ** I only know one business like that.




    ........ Phil
     
  8. Phil Allison

    Phil Allison Guest

    "John Larkin"

    ** The mic-pre is a multi purpose circuit

    Works with all dynamic mics, all condenser mics ( FET, tube, true condenser
    or electret ) plus gadgets called "active DIs".

    Most accept balanced audio lines too.

    Very versatile.



    ........ Phil
     
  9. Eeyore

    Eeyore Guest

    Being active of course it would do.

    Graham
     
  10. Eeyore

    Eeyore Guest

    Since when isn't noise audible ?

    Graham
     
  11. Phil Allison

    Phil Allison Guest

    "Eeysore"

    ** Usual lack of sane answer noted.

    Just another one of Stevenson's idiotic straw men instead.




    ........ Phil
     
  12. John Fields

    John Fields Guest

     
  13. John Fields

    John Fields Guest

     
  14. Phil Allison

    Phil Allison Guest

    "John Fields"


    ** Oh - that is a cruel pun.




    ....... Phil
     
  15. cledus

    cledus Guest


    Why is distortion not specified on the data sheet? Is the distortion
    good for this part? Or has a tradeoff been made?

    -c
     
  16. Jim Thompson

    Jim Thompson Guest

    In a multi-channel sonar chip I designed...

    Process = PolarFAB BiCMOS... high beta and high fT NPN's AND PNP's
    plus 0.8um feature-size CMOS

    ...Jim Thompson
     
  17. Eeyore

    Eeyore Guest

    How much do they effectively cost ?

    Graham
     
  18. Phil Allison

    Phil Allison Guest

    "cledus"


    ** THD is rarely specified in op-amp data.

    There are too many variables affecting THD to make one figure meaningful or
    even one graph.

    These include frequency, stage gain, output level, output load condition and
    topology ( inverting or non inverting).

    See this site for a more info on the topic.

    http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm


    ........ Phil
     
  19. Eeyore

    Eeyore Guest

    That does make it more difficult but it's not unknown to see it specified e.g.
    NJM2068

    Total Harmonic Distortion THD AV=20dB,VO=5V,RL=2kohms, f=1kHz 0.001%

    Graham
     
  20. Phil Allison

    Phil Allison Guest

    "John Larkin"
    "Phil Allison"

    ** Shame how that figure is not typical.

    For the non inverting mode, with 600 ohms load, gain of 1000 ( as used in a
    mic pre-amp ), frequency 20 kHz - the THD figure rises by 1000 times to
    a mediocre 0.1%.



    ....... Phil
     
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