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Pre and Power amp clip?

Discussion in 'Amps and Cabs [BG]' started by scubahood427, Feb 3, 2001.

  1. scubahood427


    Apr 13, 2000
    I have a fender bassman 100, and i pretty much have to turn it up to about 8 or 9 to get as much sound as my drummer. But when i do that, these two red lights come on when i play and they say preamp clip and poweramp clip. now i have no idea what this means. Does it mean im gonna blow out the amp or something?
  2. cb56


    Jul 2, 2000
    Central Illinois
    I'll be watching this thread also to see what all the tech heads have to say. I've been playing for about 20 years and never did quite understand clipping. I know that if you send too hot of a signal to your pre amp the little red light goes on and off and supposedly that's not good for your amp or speakers. But I use kind of a hard attack when I play and it seemes like the red light comes on with the attack not the sustain of the note so is that all that bad? Also my Ampeg has another light by the output stage called a limiter thatdoesn't come on much but I think the limiter is supposed to protect the speakers from all that bad clipping so maybe I shouldn't worry about it
  3. White_Knight


    Mar 19, 2000
    Ok, clipping the pre-amp means that you have the pre-amp gain set too high. In effect, since the pre-amp can't handle that strong of a signal, it's cutting off some of it's content. Sometimes you may not be able to hear this (such as when the light goes on occasionally), but when the light is on constantly, it means that you signal is being constantly clipped (which means that you're losing part of the signal's content). Pre-amp clipping isn't all that bad. Power amp clipping, however is. It means that the power-amp is putting out as much power as it can for the signal that is being sent to it. If the signal is too strong, then the power-amp will continue to try and amplifiy the signal, however it won't be able to because of how it's designed. And thus it clips. When a power amp clips, it means that DC is being sent to your speakers, which will eventually rip them apart no matter how loud you're playing. The DC signal is the equilvilant of trying to have the speaker change directions 180 degrees instantaneously - it's not possible. It would be like going down the road at 55 and then putting you're car in reverse and flooring it without slowing/stopping - something will break.

    Occasional pre-amp clipping is ok. It even reccommends in my owner's manual to turn up the gain until it's just barely clipping the attack of the note. The limiter will limit the power amp's output to a level just below clipping - this saves you're speakers.
  4. cb56


    Jul 2, 2000
    Central Illinois
    sounds like I'm doing it right then, cool
  5. NJXT


    Jan 9, 2001
    Lyon, FRANCE
    The salesman who sold me my amp told me the same, but it was a little confusing :
    Set volume to 0
    Hit the harder you can the B or E string
    And start increasing the gain until the clipping lead turns red (and last a little red) then turn the gain down a little.
    Then adjust the volume.
    Problem is : when do you know it's just a "little ok" clipping or a "stop this !" clipping ?
    Obviously when it's permanent lighten in red, it's no good, ok, but what a little clipping is ?
  6. dadodetres


    Dec 19, 2004
    actually try to think of a sound wave (sinusoyd) :


    imagine that is your sound (actually it isnt that perfect looking) . when something clips (ej your apre or power amp) it means that the signal going trough it its bigger than what it can handle (that is the headroom) and so it is cuted in the top making it lika square wave :


    no imagine that the speaker goes front and backuards respectly when the wave goes up and down passing the "zero".

    if the wave is flat at some point, tha speakers keeps at the max positing for a long time instead of being always moving.

    is some light turns once in a while, you problably wont have any problem, but if it is constantly on, it means that the wave goes form being flat at the top to being flat at the botom, and speaker goes from the fornt ti the back , as White_Knight sayd.

    was i claer? english is not my language, so maybe i sayd some words incrroclty :confused:
  7. IvanMike

    IvanMike Player Characters fear me... Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    ok here goes.

    clipping will not destroy your speakers all by its lonesome.

    a clipping poweramp will send a theoretical maximum of twice the power rating of the amp to the speakers which can damage them if the resultant wattage is above what the speakers are rated for.

    however, clipping can sound god-awfull. clipped poweramps sound worse than clipped preamps, but it's all distortion no matter how you look at it.

    unfortunately, at this point you need to look at getting a more powerful amp/more speaker cabinets. it's not fair, but the laws of physics dictate that us bas players need much larger amps than guitar players in order to "compete" volume wise with them and drummers. :meh:
  8. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Those lights are saying: "Your drummer is playing too loud." ;)

    Temporary clipping of a solid state power amp will not damage speakers. It only alters the harmonic content of the signal. It requires sustained operation at clipping to produce significant DC levels. And whether the speaker can handle this is determined entirely by the thermal power rating of the driver, which you don't have any way of knowing on a combo amp.

    On a lot of amps, the preamp clipping light turns on when you exceed a pre-set level that is below the actual clipping threshold. If that is the case, then you should want to see the preamp clipping light turn on once in a while. With the preamp, you can let your ears be the judge.
  9. Theres no clipping or limiter light on my svt II, it must be safe to turn it to the max then :p
  10. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
    A clipped AC signal

    is NOT


    Repeat ad neauseum. :rollno:

    A power amp which is sending out a significant amount of DC has an electrical problem, not a volume problem.

    Reread IvanMike's post again and again. Therein lies truth.
  11. dadodetres


    Dec 19, 2004

    but of you have a hasrd clip nearly all the time, the wave tend to act as a DC that changes polarity, right?
  12. chris4001asat


    Dec 16, 2002
    Toledo, Ohio
    Warehouse Manager : Reverend Guitars
    I just bought a BBE B-Max T pre amp. There is no clip light on it. How do you set it?
  13. After reading all the post above, I still dunno how to fix the problem. I have to the same amp as the thread starter, and I have been clipping my power amp constantly, cause I am competing with two 100 watt marshall combo and a drummer, so I have to basically crank the amp. Is that bad for the amp, would it damage the speaker, or is it fine the way it is? Can some pros answer this question. Thanks.
  14. Come on!!!!!! i need to know this real bad.
  15. DC which changes polarity is, by definition, AC. A square wave to be exact.

    However. amplifiers do not produce pure square waves when clipped, and even if they did, speakers can't reproduce them anyway.

    The big issue with clipping is heat. Here's where the DC myth comes in: A square wave does have heating power equivalent to DC, so clipping enables an amp to put more than rated power into a driver. However, the DC thing breaks down here because true DC would push the driver out to a certain position and it would not move after that (until the signal was removed). This would obviously rob the driver of cooling ability because speakers depend on movement for some of their cooling. But clipping doesn't stop the speaker movement so the cooling ability of the driver isn't affected by it, so the DC parallel isn't accurate.

    ....And no, speakers don't stop moving at the crests of clipped waveforms. The mass of the cone doesn't allow it.
  16. permagrin


    May 1, 2003
    San Pedro, CA
    Nothing a large influx of cash won't solve. The fix: more power, more speaker area. Rule of thumb powerwise for bass is 4-10x the guitar power. 200W of Marshalls, if they're driving them even moderately, is very loud - and a loud drummer, ... hope you're wearing earplugs. Bass frequencies require more power to get to the same percieved loudness. You could EQ out the lows, get the guitarists to EQ out their lows, play softer (sure!) but in reality a 100W bass amp and what, a single 15? is never gonna be able to keep up.

    And yeah, you're gonna blow out your speaker. And your eardrums.

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