Gain: what do it are?

Discussion in 'Amps and Cabs' started by smolder, Jul 4, 2008.

  1. smolder

    smolder Gold Supporting Member

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    Apparently I am not thinking of gain right. What is the definition? How does it differ/relate to overdrive and distortion? I have looked in the books and online and can not find a decent definition.

    I think I understand in the context of gain stages in the pre amp and output curcuits of the amp it is the process of fattening the signal.

    I mentioned in a thread that it seemed like my Mini Z had a lot of gain - and was told that it this amp does not have a lot of gain. What I meant was it rolls over quickly (like at 9 o'clock)... to get the slur, crunch and dirt sound at a pretty low volume.

    Thoughts? Clarification so I don't speak out of the wrong end (no guarantee here btw) ...and thanks in advance.
     
  2. dwoovre

    dwoovre Member

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    Gain is simply the ratio of the output signal of an amplifier to the input signal. A gain of 10 means that a 1V peak-to-peak signal going in will have a 10V peak-to-peak signal going out. When an amplifier stage doesn't have the ability to put out a full 10V, for example, the wave form gets 'clipped off' at the available supply voltage level. For example, a basic 9V pedal can not put out a signal more than 9V peak-to-peak, because there is simply no higher voltage supply available. Distortion is caused when an amplifier tries to put out a signal at a higher voltage than its supply can achieve. Putting a signal through multiple gain stages, with each hitting the clipping point, is the basic recipe for overdrive/distortion/fuzz, or whatever you want to call it. Tubes do this 'clipping' in a nice gradual way, whereas transistors do it pretty suddenly, which is why they tend to sound different.

    People use the term 'gain' to refer to the amount of distortion in an amplifier, but that is sort of a misnomer. It is true that dialing up a lot of gain on an amplifier stage can produce distortion, but only if it is designed for that, and you give it large enough input signal to cause the amplified output signal peaks to be greater than the available supply voltage.

    Someone saying that your amp does not have a lot of gain is probably referring to the relatively few number of gain stages involved. A 'high gain' amplifier will usually have four (or more) gain stages in the preamplifier, whereas I would venture a random guess that your Mini only has two or three. This limits the amount of saturation that can be achieved, even if the stages that are in the amp are designed to distort nicely at low volume.
     
  3. smolder

    smolder Gold Supporting Member

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    Very cool - thank you very much.

    Soo, one follow up question. As I switch from my strat with single coils, to humbucker, and then to the guitar with P90's, I seem to punch the amp harder. A boost pedal seems like it does even more of the same. Are these also gain stages?
     
  4. Flux

    Flux Member

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    Think of your electric guitar rig as a device that creates an audio signal that passes through a series of gain stages to produce a louder guitar sound. All the way along the chain are components that amplify the signal - including the pick-ups, tubes and speakers. Each gain stage can add distortion, which may be a good or bad thing. Either way, attention should be paid to whether gain stages are pushing or pulling on your audio signal, because it does affect the quality of the sound. When the gain stages hand off the audio signal to each other with no mis-match it's referred to as 'unity gain'.
     
  5. smolder

    smolder Gold Supporting Member

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    Thanks Flux (and dwoovre). All good stuff... and the sort of thing I am sure my father told me (electrical engineer and moonlight tube circuit repair guy in the day) but I was too thick headed to listen to.
     

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