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Basic questions about amp

Discussion in 'Amps and Cabs [BG]' started by Skeletomania, Apr 2, 2006.


  1. Skeletomania

    Skeletomania

    Oct 25, 2005
    hong kong
    I don't know anything about amp and I wanted to ask about all these amp terminology. What is the difference between a tube amp and a solid state amp. What exactly is a power amp and a pre amp. Also, when it says 250w at 4 ohm, what does it mean?
     
  2. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
  3. Skeletomania

    Skeletomania

    Oct 25, 2005
    hong kong
    I did read the FAQ, but the FAQ by Joris is too confusing for me to understand. Do you have a simplified version with easier answers?
     
  4. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    A tube amp uses vaccum tubes as the device which allows the sound to become amplified (tube technology dates back to the 1930's or so). A solid state amplifier uses transistors or other 'solid state' devices for that job.

    They are the same except for scale. A premap takes a .1v signal from your bass and amplifies it to 1v. A power amp takes a 1v signal from a preamp and amplifies it to 50v for your speakers.


    It is referring to the impedance of the final amplifier section; the 'load' it is capable of driving. Solid state power amps burn up if asked to push power into a load that is too low (2 ohms in this case) while tube amps are just the opposite (but tube amps often have different output taps you can choose for different impedance loads). Impedance is basically 'resistance' as it refers to AC Circuits.

    250w refers to how much power, as measured in watts, the amplifier can supply at that load impedance. In the most common case (solid state) such an amp might supply 180w at 8 ohms, because an 8 ohm load will accept less current, and the amplifier is limited by how much current it can flow.

    Yes, the answers above are easier, but they are wrong in various respects. When you ask technical questions, the answers tend to be technical.
     
  5. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA
    A tube amp uses vacuum tubes in the power amplifier while a solid state amp uses solid state semi-conductor devices.

    You can have tubes in the preamp and a solid state power amp but this is NOT considered a tube amp.

    There have been amps made with a solid state preamp and a tube power amp but I believe these were mainly for guitar.

    A preamp shapes the signal (gain, bass, treble, etc) and a power amp takes that signal and amplifies it enough to power a speaker.

    Your bass plugs into the preamp and your speakers plug into the power amp. The typical signal chain looks like: Bass--->Preamp--->Power Amp--->Speaker Cab.

    In a typical head the preamp and power amp are in one unit while in a 'rack' they are separate.

    Here is a pic I made that is getting alot of use lately.

    HeadPrePower.


    At an impedance of 4 ohms, the power output will be 250 watts. If your speaker cabinet is 4 ohms the amp will put out 250w into it. If your cab is 8 ohms, the output will be less (typically 125w)

    :D

    Joe.
     

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