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preamp vs. amp?

Discussion in 'Electronic Basics' started by jack, Oct 18, 2003.

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  1. jack

    jack Guest

    As a newcomer to electronics and teaching myself along the way, I 've
    come to a obviously simple question that does not seem to be answered
    in any of my books. What determines whether an amplifier setup I've
    made should be called a pre amp or just amp,in other words ,what type
    of voltage or current inputs would a preamp handle versus an
    amplifier.? Does a preamp assume a certain signal to noise ratio that
    an amplifier design would not? What's the dividing line? Thanks for
    any help. Jk
     
  2. There is no dividing line, just accepted practise. A 1kW amp might be
    considered a pre-amp, if it was driving a 100KW transmitter.

    Typically a pre-amp refers to low output current, and small input
    signals. An output of a pre-amp, might be a small or a large signal,
    i.e. from mv to several volts. Its all a bit arbitrary really.

    Pre-amp, is also somewhat of a redundant term. Just sticking to amp on
    its own is all that's really required.

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  3. That would be called an exciter or buffer amp. I assume the OP was
    referring to audio amplifiers, and not RF amps. But even RF preamps
    are for very low level signals in a receiver's front end.
    But industry standards are a line level of 0 dBm which is 1 mW into
    600 ohms. One could assume that anything that amplifies line levels
    (for instance a power amp) is an amplifier, and anything that
    amplifies very low level signals, and equalizes them, is a preamp.

    But HiFi nuts have a box they call the preamplifier, which is really a
    combination of things. It's a preamp for a phono cartridge and
    microphone, and a switch to choose what program source to listen to.
    Another requirement for a preamp is to have low noise to amplify very
    low level signals.
    --
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    ###Got a Question about ELECTRONICS? Check HERE First:###
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  4. Dana

    Dana Guest

    Can I ask what led to that assumption. I would assume he was talking about
    RF as I deal mostly in RF circuits, and the audio circuits on the radio's I
    maintain are all built on one IC.
    I would have an RF preamp in almost every radio to incerease the incoming
    signal.

    But even RF preamps
    Yep. And easily overloaded if not careful during design.
     
  5. I would usually refer that term to a completely different field.
    Ho hummm . Its all arbitrary. Anyway, a buffer is *typically* a unity
    gain urrent amplifier, not an voltage amplifier.

    I assume the OP was
    I didn't assume anything, other then the name.
    This isn't relevant. The term pre-amp doesn't assume audio industry
    standards at all.
    And also that anything that does this as just an "amplifier" as well. It
    doesn't require the "pre" bit at all.
    Not at all. There is no assumption of low noise.

    I personally feel the term pre-amp a bit redundant. It doesn't serve
    mush purpose. Other than the convention in the above mention pre-amp
    hi-fi unit, it is probably better to dispense with the term.

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  6. On the radios (no apostrophe needed) that I maintained, called RADARs,
    a half megawatt exciter drove a 5 megawatt output magnetron (actually
    an amplitron).
    [snip]

    --
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    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  7. Buffer amps are used in RF equipment to prevent the modulated stage(s)
    from loading the xtal osc, and may (and usually do) have both current
    and voltage gain, because they're transformer coupled.
    Maybe I should've said 'requirement for an audio preamp..' above.
    That would've clarified it. But either way, it's quite obvious that
    any preamp that amplifies low level signals is going to have low
    noise; if it doesn't, it's going into the repair shop! ASAP!
    Yeah, mush is what you get if your preamp is not working right!
    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  8. There is no real dividing line. Basically, if a relatively low signal is
    amplified in multiple stages, the first one is the preamp. Sometimes
    however, especially when dealing with low-power amplifiers, the whole thing
    is in one chip where it does not really make sense to call a part a preamp
    unless you are talking of the internal design of the chip. In audio
    equipment, microphone signals are usually preamplified before being fed to a
    common amplifier with a switch and multiple inputs. So are signals from
    cassette player heads and phono cartridges (Thx, Mr. Watson). In radio
    technology, a preamp often amplifies low antenna signals before a tuner
    picks the needed one (usually the tuner comes with an internal preamp, so no
    external device is needed). If you want to listen to AM radio stations that
    are very far off so the signals are too low for your receiver to handle, the
    device used to 'bring them nearer' is very likely to be called an antenna
    preamp. In general, a preamp is a device that amplifies a signal to a level
    less than the one finally required, so one or more additional amplification
    stages are used to complete the operation. There is however no need for the
    word 'preamp', it is quite reasonable and much simpler to call every device
    that makes a signal 'stronger' an amp.

    Dimitrij
     
  9. The word preamp has been traditionally used to indicate a low level,
    low noise amplifier. There is a need for a word that differentiates a
    low level, low noise amplifier from a regular amplifier, and the word
    preamp is a suitable choice.

    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  10. I simple don't agree with this low noise tradition assertion at all. For
    starters, "low noise" itself doesn't really mean much. In fact, the term
    "a low noise pre-amp" is often used, which implies that there are low
    noise and noisy preamps.

    Kevin Aylward

    http://www.anasoft.co.uk
    SuperSpice, a very affordable Mixed-Mode
    Windows Simulator with Schematic Capture,
    Waveform Display, FFT's and Filter Design.
     
  11. I haven't really thought about consistency, but one reason there are
    "preamps" is because someone has put an amplifier in a separate box
    and it's output is supposed to feed something else.

    In other words, the name is applied because of it's standalone nature.

    So you've got an old shortwave receiver that could use better sensitivity.
    You build or buy a preamp, to put between the antenna and the receiver.

    Or, you've got an audio power amplifier that doesn't have anything but
    a volume control. You build or buy a separate box that has a phone
    preamp, source selector switches, and tone controls. This would be a preamp.

    That doesn't quite explain "phono preamps" in stereo receivers, or
    for that matter why the low level stages in said stereo receiver might
    be referred to as the "preamp" stages. I would suggest that perhaps
    it's because of the external box definition. Maybe in those early days
    of hi-fi, the low level stages were always a separate box (or weren't called
    preamps in the early days) and when they were integrated into the main
    amplifier or receiver, the name stuck to define the area.

    Michael
     
  12. Lord Garth

    Lord Garth Guest

    I recall a preamp to be primarily a voltage amp while a power amp is a
    current amp. This is however a huge generalization, use at your own risk.
     
  13. Fred Abse

    Fred Abse Guest

    IME, there are noisy preamps and noisier preamps ;-(
     
  14. Rich Grise

    Rich Grise Guest

    It comes from the fact that in the olden days, all the mics and
    crystal/ceramic phono cartridges and tuners had a high-impedance,
    high-level output (which standard has evolved into 1VRMS into
    high-impedance); when some pundit came up with low-impedance
    (with concomitant lower induced-noise pickup - look it up ;-) )
    magnetic phono cartridges and dynamic mics, they needed to
    amplify those pesky millivolt signals up to something easier
    to work with. Designing an amp with a 3 dB noise figure (for
    example) is a HECK of a lot easier when your signal is 1VRMS
    than when it's in the sub-millivolt range. Ergo, you concentrate
    your harder design efforts on the more sensitive parts.

    And you can use the same tone control for all of them, and
    sometimes switch in fixed precomp/decomp ("equalization")
    curves.

    But it turns out that elfa needed a crossover network, after
    all; and hopefully I've been some assistance in that department.

    :)

    Cheers!
    Rich
     
  15. Michael

    Michael Guest

    Shit!!, I hope you had a fancy lead codpiece.
     
  16. Not needed, unless you are incapable of doing proper work. Only an
    idiot would work on high power microwave equipment when it is in an
    unsafe condition. Only a total fool would fire it up with any loose,
    missing, or damaged waveguide, and a dummy load or antenna. On the other
    hand, if you do fire it up under those dangerous conditions, you deserve
    what you get.
     
  17. Jim Large

    Jim Large Guest

    What? An apostrophe i's alway's needed. If there
    werent any apostrophe's, wed never know when a word
    wa's about to end with an 's.

    -- Jim L.
     
  18. LOLPIMP! ;-)
     
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