What is the job of a power amp?

Discussion in 'AV Receivers & Amplifiers' started by Yards, Dec 25, 2004.

  1. Yards

    Yards
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    What should a power amp do to your sound?
    Simple question I know, but a simple answer is required!
     
  2. eviljohn2

    eviljohn2
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    Reasonably simple. A little bit of amplifier theory will tell you that to generate a signal that a speaker can use from a source (such as a CD player) you need to be able to change the volume and amplify the signal to a level that will be able to drive the speaker.

    A little bit of theory will demonstrate that the best way to do this is to use a low noise first amplifier stage (the preamp) and a more beefy power amplifier stage (the power amplifier). The theory will demonstrate that the noise level of the power amplifier in such a system is far less relevant.

    Essentially, the preamp does the signal processing whilst the power amp will amplify the signal level to a suitable power for the chosen speakers.

    I hope that helps (it confused me) but Merry Christmas anyway :hiya:
     
  3. Reiner

    Reiner
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    The short answer: the power amp should do nothing to your sound, i.e. it should remain neutral and merely amplify what comes in.
     
  4. Poolsharkie69

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    Ok to make it even more confusing...how do you know when u need to buy a pre amp? I have been toying with the idea. My set up is in my signature.
     
  5. eviljohn2

    eviljohn2
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    Your integrated Yamaha amp combines the 2, (hence it being called "integrated").

    A seperate pre-amp would be used with seperate power amps.
     
  6. Poolsharkie69

    Poolsharkie69
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    Ok...for a dumb guy like me that woudl mean no I don't need one then.
     
  7. Tejstar

    Tejstar
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    A pre-amp is also known as a processor.
     
  8. Mylo

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    Not right :lesson:

    A pre amp is the control part of an amplifier, it takes the inputs and feeds them to the power amplifier.
     
  9. Tejstar

    Tejstar
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    :oops: I was always under the impression that some people refer to the pre-amp as the precessor. You learn something every day!
     
  10. eviljohn2

    eviljohn2
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    The term processor is more appropriate for AV equipment. The digital signal is "processed", then fed to a "preamp" stage (usually within the processor) and then sent to a seperate "power amp" stage. Of course you can also "process" analogue signals by adding DSP's to them or similar.

    Integrated amps combine all 3 stages so everyone has them, even the most basic micro stereo system will have a preamp and power amp stage. :)
     
  11. Stuart Wright

    Stuart Wright
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    That's the problem - a little knowledge can be worse than none at all. Specially if it's given with an air of authority.
    I'm glad there are plenty of experts around here to correct mistakes.
     
  12. eviljohn2

    eviljohn2
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    It's a big problem, and the mags have a lot to answer for in this respect IMO.

    It does help emphasise the benefits of these (and other) forums though. Knowledgable people have as much time as necessary to explain things to the interested. :)
     
  13. Tejstar

    Tejstar
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    So am I right in saying that pre-amps are more common with stereo equipment?

    And is it possible within AV equipment to get separate processor, pre-amp and power-amp? As far as I knew, I thought within the home cinema route you'd normally go for processor and power amp if you weren't taking the integrated route?
     
  14. eviljohn2

    eviljohn2
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    Seperate preamps are more common in the stereo arena. I've certainly never come across a 5-channel preamp!

    The "processor" you mention will contain both a processing stage (where all the DSPs, bass management etc are implemented) and a preamp stage.

    It's mainly nomenclature but your signal will be processed in the digital realm (ie. DD, DTS, DPL , bass management etc). Then it will be sent to the preamp stage (usually as analogue) where the signal will be amplified to a level usable by a power amp. This preamp stage will have a very low noise level. Then, the preamplified signal is sent to a power amp stage which boosts the gain to a level which can drive speakers. Seperating the preamp and power amp (rather than just having a big beefy preamp) is to reduce noise in the final output signal.

    The important thing to remember is that the part of your system with the volume control is the preamp stage. The part that's rated at "80Watts per channel" for example is the power amp stage. The bit that does any digital processing of the sound is the processor. As I've mentioned, an integrated stereo amplifier will combine a preamp and a power amp in the same box. An integrated AV amplifier will combine all 3 stages within the same box. An AV processor will combine the processing and the preamp in the same box.

    I hope that makes some sense :suicide:
     
  15. Tejstar

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    Very well explained John - thanks for taking the time to explain it to me :)
     
  16. eviljohn2

    eviljohn2
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    Glad to help, there's quite a lot more to it when considering the noise implications but that covers the basics of what does what.

    It's the same principle as CD players combine a transport and a DAC in one convenient package. If you don't understand what the words mean though it gets a bit complicated. :)
     

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