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How can a pre-amp clip?

Discussion in 'Amps and Cabs [BG]' started by Sanctum, Jun 5, 2002.


  1. mmmkay, i though clipping had to do with the poweramp. so how can a pre-amp clip if its hooked to a poweramp that you know is providing ample power to the cabs? I thought clipping had to do with the pre-amp having to "hold back" signal if the poweramp couldnt drive the given cabs.

    OR, am I just an idiot on this matter? does clipping have to do with input signal?

    cheers

    Greg
     
  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    Because either the input stage or any preamp section is overdriven, meaning that the input signal or the signal from the previous gain stage within the preamp is too hot for the next one.
     
  3. lneal

    lneal

    Apr 12, 2002
    Lee County, Alabama
    Any amplifying device (tube or transistor) will clip if driven too hard. Doesn't matter which stage its used in. Clipping means that the device is "chopping" the peaks of the signal off because it can no longer respond to the input signal; in other words its maximum limit has been reached.

    No, DiN you're not an idiot, just another victim of equipment manufacturers using specs and jargon to sell rather than inform.
     
  4. jokerjkny

    jokerjkny

    Jan 19, 2002
    NY / NJ / PA
    actually, preamp clipping happens often. My Stewart is especially sensitive to my Demeter preamp. i have to adjust the internal trimmer, cause it slams the poor stew so hard. usually, if you've got a "gain" knob, you can control that over-clip. remember this is different from amp clipping ala bass distortion which sounds heavenly. :)
     
  5. chucko58

    chucko58

    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    It's really easy to clip a solid-state preamp, if the designer wasn't careful about gain staging. When I hot-rodded my Carvin Pro Bass 15 preamp, I actually reduced the input stage gain quite a bit to raise its clipping point.

    A passive bass pickup can easily put out a 4 V peak-to-peak signal; an 18V active bass can go as high as 16 V P-P. It takes some thought to design a preamp that can handle those signals and still provide enough gain for low output pickups.
     
  6. I agree.

    It's not that difficult to overdrive any electronic system if one tries hard enough:eek: Not that it's always deliberate, mind you, but it's not that difficult.

    As chucko58 said, there's plenty of output from a bass. And there's loads of gain available from various stages of a preamp. There'll almost certainly be straight gain, then there's frequency selective gain from tone controls. The gains multiply up so it's not difficult to get some signals amplified (say) 100 times, and more.

    For example, for a complete small setup, 100 Watts across 8 Ohms (approx) = 80 Volts P to P (approx = 28 V RMS). Taking Chuck's figure of 4 Volts P to P, you'd only need to amplify that 4 V PP by x20 to get the 80 V PP.

    But you've got much more gain than that available in the preamp. And the power amp alone could easily have a (fixed gain) of x30!

    It's really easy to clip the preamp, the poweramp and both together.

    John