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Discussion in 'Amps and Cabs [BG]' started by ohmanohjeeze, Jul 13, 2002.

  1. ohmanohjeeze


    May 6, 2001
    tucson, az
    Okay I tried searching the forum and I also checked the FAQ, still didn't really get anything.
    So, what exactly is happening when the amp is clipping?
    is the the amp or the speakers?
    is this the same thing as peaking?
    thank you much, i've much to learn.
  2. Clipping is the amp. It can happen at any part of the signal chain - input stage, tone shaping stage (that's really all in the preamp section) or the power amp stage - the bit that drives the speaker cab.

    Here's what happens. A signal come in from the bass. It gets amplified by the preamp, either as 'straight' gain if all the tone controls are set to the flat position, or as tone shaped gain if you boost the bass, mids, or whatever. Now, the electronics are constrained by the power supply inside the cabinet: the preamp might have supply rails of plus and minus 15 Volts = 30 Volts total. Take from that about 2 volts per rail = 4 volts total because the chips can't usualy swing a signal rail to rail.

    So, you could get a (theoretically) clean signal from the preamp output of about 26 V peak to peak. Your peak to peak output from the bass could be perhaps 2 or 3 Volts if you hit the strings hard enough. If it's 2 volts then your preamp is only allowed a gain of x13 before. A gain of x13 is very small for a preamp!! You can perhaps see that with the same input voltage and a higher gain (say x20) you can still only get about 26 volts out but, and here's the important bit, the preamp still tries to drive harder. The result is that the tops of the signal are sheared off as it bumps into the power supply rails

    That's clipping. In a solid state amp it sounds harsh and horrid, in a valve amp its sounds good...:D

    The same basic reasoning applies to the power amp stage. The trouble is, here, there's a lot of power involved and it's all too easy to destroy the output devices because you take them outside their safe operating area (= expensive repair bill:eek: ). The loudspeakers don't really like being driven by a signal that approaches a square wave, either.

    Hope that helps.


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