In-line mike preamp

Archived from groups: rec.audio.pro (More info?)

What the world needs is a cheap, battery operated stereo mike preamp
with fixed gain that will goose up a condenser mike to line levels.
The unit I'm imagining would run from a pair of AA batteries, have a
1/8" TRS stereo jack for the input, and a cable with the same type
plug on the other end. It would have "plug-in power" for low-priced
mikes and a gain that could be changed internally to suit the
particular mike. It would be priced somewhere between $50 and $100.

If it already exists, would someone please direct me to it.

Thanks,

Norm Strong
14 answers Last reply
More about line mike preamp
  1. Archived from groups: rec.audio.pro (More info?)

    normanstrong wrote:
    > What the world needs is a cheap, battery operated stereo mike preamp
    > with fixed gain that will goose up a condenser mike to line levels.

    Fixed gain would not work for many situations depending on the levels involved.


    > The unit I'm imagining would run from a pair of AA batteries

    That's going to limit your output level and lower your S/N unless you use a DC-DC converter to drive the opamp (not likely at that price.)


    > 1/8" TRS stereo jack for the input, and a cable with the same type
    > plug on the other end. It would have "plug-in power" for low-priced
    > mikes and a gain that could be changed internally to suit the
    > particular mike. It would be priced somewhere between $50 and $100.

    <http://www.soundprofessionals.com/cgi-bin/gold/item/SP-PREAMP> but the price is higher than you want. They did have some closeouts of an earlier version awhile back.
  2. Archived from groups: rec.audio.pro (More info?)

    > What the world needs is a cheap, battery operated stereo mike preamp
    > with fixed gain that will goose up a condenser mike to line levels.
    > The unit I'm imagining would run from a pair of AA batteries, have a
    > 1/8" TRS stereo jack for the input, and a cable with the same type
    > plug on the other end. It would have "plug-in power" for low-priced
    > mikes and a gain that could be changed internally to suit the
    > particular mike. It would be priced somewhere between $50 and $100.
    >
    > If it already exists, would someone please direct me to it.

    Radio Shack Boosteroo, designed for boosting headphone levels, replace male
    input plug with female jack and use it backwards.

    For better results in that price range, buy two used DOD mosfet preamp
    pedals at around $25-30 each, hack the guts to fit into an appropriate
    smaller case and provide suitable voltage to the mics, it can all run off
    one 9V battery, preferably lithium. It'll sound as good as the preamps
    you'd find in a typical Behringer/Mackie caliber board.
  3. Archived from groups: rec.audio.pro (More info?)

    Sugarite wrote:
    >>What the world needs is a cheap, battery operated stereo mike preamp
    >>with fixed gain that will goose up a condenser mike to line levels.
    >>The unit I'm imagining would run from a pair of AA batteries, have a
    >>1/8" TRS stereo jack for the input, and a cable with the same type
    >>plug on the other end. It would have "plug-in power" for low-priced
    >>mikes and a gain that could be changed internally to suit the
    >>particular mike. It would be priced somewhere between $50 and $100.
    >>
    >>If it already exists, would someone please direct me to it.
    >
    >
    > Radio Shack Boosteroo, designed for boosting headphone levels, replace male
    > input plug with female jack and use it backwards.
    >
    > For better results in that price range, buy two used DOD mosfet preamp
    > pedals at around $25-30 each, hack the guts to fit into an appropriate
    > smaller case and provide suitable voltage to the mics, it can all run off
    > one 9V battery, preferably lithium. It'll sound as good as the preamps
    > you'd find in a typical Behringer/Mackie caliber board.

    What is the gain and the noise EIN for each of these options?


    Bob
    --

    "Things should be described as simply as possible, but no
    simpler."

    A. Einstein
  4. Archived from groups: rec.audio.pro (More info?)

    On 14/11/2004 22:44:32, "Sugarite" wrote:

    >Radio Shack Boosteroo,

    You're just sick...

    That thing doesn't even qualify as a headphone amp.

    --
    m.
  5. Archived from groups: rec.audio.pro (More info?)

    On 12/11/2004 18:27:12, "normanstrong" wrote:
    >What the world needs is a cheap, battery operated stereo mike preamp
    >with fixed gain that will goose up a condenser mike to line levels.

    >It would be priced somewhere between $50 and $100.

    This is interesting:

    http://www.felmicamps.co.uk/

    Quite a few candidates there :-)

    I believe I've also seen his products on an American site...


    --
    m.
  6. Archived from groups: rec.audio.pro (More info?)

    Usenet wrote:
    >
    > This is interesting:
    > http://www.felmicamps.co.uk/

    Very interesting. Shouldn't be all that hard to hack up an MP3 player to provide plug-in power on its line input jack...
  7. Archived from groups: rec.audio.pro (More info?)

    "Sugarite" <nobody@home.com> wrote in
    news:P9Rld.9622$hp3.1109905@read2.cgocable.net:

    It'll sound as good as the
    > preamps you'd find in a typical Behringer/Mackie caliber board.


    See, now, since those don't sound anything alike, I'm
    just gonna have to wonder, what you are talking about...
  8. Archived from groups: rec.audio.pro (More info?)

    Kurt Albershardt wrote:
    > Usenet wrote:
    >
    >>
    >> This is interesting:
    >> http://www.felmicamps.co.uk/
    >
    >
    > Very interesting. Shouldn't be all that hard to hack up an MP3 player
    > to provide plug-in power on its line input jack...

    These are very cool but it's ard to believe that they can
    power a pre from plugin power. It's only a couple of volts.
    I don't know what the serial resistance is, though. Low
    enough and it could be made to deliver levels not to far
    from FS line I guess.

    It's even harder to believe a phantom powered pre that could
    still pass on anything close to phantom levels.

    Are there any amp parts that need only a couple of volts and
    have quiescent currents of a few hundred microvolts? If so,
    are they at all quiet?


    Bob
    --

    "Things should be described as simply as possible, but no
    simpler."

    A. Einstein
  9. Archived from groups: rec.audio.pro (More info?)

    On 16/11/2004 05:52:48, Bob Cain wrote:
    >
    >
    >Kurt Albershardt wrote:
    >> Usenet wrote:
    >>
    >>>
    >>> This is interesting:
    >>> http://www.felmicamps.co.uk/


    >These are very cool but it's ard to believe that they can
    >power a pre from plugin power. It's only a couple of volts.

    >It's even harder to believe a phantom powered pre that could
    >still pass on anything close to phantom levels.
    >
    >Are there any amp parts that need only a couple of volts and
    >have quiescent currents of a few hundred microvolts? If so,
    >are they at all quiet?

    All excellent questions. Why don't you contact the guy and ask him, or
    better still, get some samples to test. Point out the potential demand
    (hehe!) and the benefit of publicity to sales.

    I reckon he knows exactly what he's doing, and some of his devices are good
    enough to be used by the BBC (who, of course, have different requirements
    to the typical punter here).

    --
    m.
  10. Archived from groups: rec.audio.pro (More info?)

    "Bob Cain" <arcane@arcanemethods.com> wrote in message
    news:cnc4ic01t41@enews4.newsguy.com
    > Kurt Albershardt wrote:
    >> Usenet wrote:
    >>
    >>>
    >>> This is interesting:
    >>> http://www.felmicamps.co.uk/
    >>
    >>
    >> Very interesting. Shouldn't be all that hard to hack up an MP3
    >> player to provide plug-in power on its line input jack...

    > These are very cool but it's ard to believe that they can
    > power a pre from plugin power.

    Good point. AFAIK plugin power is usually less than 2 volts with a fairly
    high source impedance.

    > It's only a couple of volts.

    Agreed, and its usually supplied through a series resistor on the order of
    1K or more.

    > I don't know what the serial resistance is, though.

    It's usually designed to power a electret mic capsule. Common series
    resistors for those are 1K or more.

    > Low enough and it could be made to deliver levels not to far
    > from FS line I guess.

    Through the magic of micropower, rail-to-rail op amps...

    > It's even harder to believe a phantom powered pre that could
    > still pass on anything close to phantom levels.

    Yes, but phantom power is huge in comparison. Minimum would be 12 volts, and
    there will be at least a few milliamps available. This is huge compared to
    plugin power, especially on the voltage side.

    > Are there any amp parts that need only a couple of volts and
    > have quiescent currents of a few hundred microvolts?

    Check Maxim and ST web sites. Here's an interesting article about some
    design features of such products:

    http://www.maxim-ic.com/appnotes.cfm/appnote_number/741

    Here's a the data sheet candidate device:

    http://www.st.com/stonline/books/pdf/docs/5560.pdf

    > If so, are they at all quiet?

    If you call 9 uv/sqrt(hz) quiet. Probably good enough for use with electret
    mics.
  11. Archived from groups: rec.audio.pro (More info?)

    In article <cnc4ic01t41@enews4.newsguy.com> arcane@arcanemethods.com writes:

    > Are there any amp parts that need only a couple of volts and
    > have quiescent currents of a few hundred microvolts? If so,
    > are they at all quiet?

    Lots of fleapower parts out there, but they're designed for an
    industry where power consumption is of prime importance and audio
    quality is way down on the list. Think telephones. (OK, I know you
    meant currents of a few hundred microamps).

    The trick is to get sufficient output voltage (remember, this is a
    preAMPLIFIER) with a low supply voltage. Unless you use an output
    transformer or DC-DC converter, you won't get +28 dBu out of a unit
    powered from a 3V supply, though it's certainly possible if you have a
    48V supply. Given that those of us dreaming of a product like this are
    looking for something to boost a microphone up to line level, even
    when going into a nominal -10 dBV input that might be calibrated to
    a not very conservative +6 dBV for full scale, that's still a bit of a
    stretch for a 3V supply.


    --
    I'm really Mike Rivers (mrivers@d-and-d.com)
    However, until the spam goes away or Hell freezes over,
    lots of IP addresses are blocked from this system. If
    you e-mail me and it bounces, use your secret decoder ring
    and reach me here: double-m-eleven-double-zero at yahoo
  12. Archived from groups: rec.audio.pro (More info?)

    On Mon, 15 Nov 2004 21:52:50 -0800, Bob Cain
    <arcane@arcanemethods.com> wrote:

    >

    >These are very cool but it's ard to believe that they can
    >power a pre from plugin power. It's only a couple of volts.

    I recently had a need for a preamp to give 52db gain to a stereo
    electret mic into a Sony minidisk recorder line in. I ended up with a
    LM387 (old but quiet and I had one). I needed a stealth case so I used
    2 mini 6v batteries.

    It made me wonder what sort of chip this MD, uses to enable a single
    AA battery to drive phones to a decent level with good fidelity as
    well as spin the disk and move the head. The battery seems to last
    forever.


    Frank /~ http://newmex.com/f10
    @/
  13. Archived from groups: rec.audio.pro (More info?)

    Bob Cain <arcane@arcanemethods.com> wrote:
    >Kurt Albershardt wrote:
    >> Usenet wrote:
    >>
    >>>
    >>> This is interesting:
    >>> http://www.felmicamps.co.uk/
    >>
    >>
    >> Very interesting. Shouldn't be all that hard to hack up an MP3 player
    >> to provide plug-in power on its line input jack...
    >
    >These are very cool but it's ard to believe that they can
    >power a pre from plugin power. It's only a couple of volts.
    > I don't know what the serial resistance is, though. Low
    >enough and it could be made to deliver levels not to far
    >from FS line I guess.

    If you don't need much dynamic range, it's possible. I had to build a
    think like that for an intercom system not too long ago, and it was okay
    for voice applications.

    >It's even harder to believe a phantom powered pre that could
    >still pass on anything close to phantom levels.

    Phantom is easy! Phantom voltage is high enough that you can get a reasonable
    amount of power out of the thing.

    >Are there any amp parts that need only a couple of volts and
    >have quiescent currents of a few hundred microvolts? If so,
    >are they at all quiet?

    Lots of things will do that if you bias them real far down. They won't
    be very linear, but they'll be fine for voice stuff. I think that I used
    the classic 2N5457 switching FET since I have a box of them in my desk drawer.
    You can get pretty quiet if you select a good one.
    --scott
    --
    "C'est un Nagra. C'est suisse, et tres, tres precis."
  14. Archived from groups: rec.audio.pro (More info?)

    Hi, we make these preamps, the 3.5 Series work from plug in power. They
    use very specific components in a unique design to provide 20dB of very
    low noise gain with low distortion. They are used extensivley by
    wildlife recordists who need extra gain on the mic inputs of their
    recorders, where of course low noise is very important. The input
    impedance is 10k and the output matches the mic input of the recorder.
    Current consumption is around 280 microamps.

    If I can answer any other questions about our products please do get in
    touch.

    Nick Roast.
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