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What causes clipping?

Discussion in 'Amps and Cabs [BG]' started by chutsk10, Jun 13, 2007.


  1. Just a quick question, what causes clipping at the poweramp stage... is it too hot on an input signal or is it due to tryign to push the amp too hard?
     
  2. ChenNuts44

    ChenNuts44

    Nov 18, 2001
    Davenport, IA
    To answer your question, it's too hot an input signal. It's also, in a sense, when you "push the amp".

    A power amp is usually a gain stage set to X dB of gain. Ideally a signal of Y dB driving the power amp will result in absolute maximum power. Real audio signals aren't at a constant level. In order for the signal to never clip, it has to be at or below a level of Y dB. However, since most of the time the signal will never reach Y dB, there's extra power being wasted. In order for the power amp to reach full efficiency, the levels will need to be at the point where the majority of the signal is at Y dB while it occasionally goes beyond (transients), clipping the power amp.

    If you try to "push the amp", you're running past the point where most of the time the signal is Y dB and drive the power amp into clipping. You're trying to get more signal out of your amp than it's capable of producing, thus the clipping.

    Hopefully that makes sense. It's been a long night tonight, but if this isn't clear enough I can illustrate with plots when my mind is a bit more "clear". :)
     
  3. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Both, as they amount to the same thing. Once you reach the limit of the amps output capability any additional input doesn't give additional linear output across the full spectrum. Additional output is gained in the harmonics only, and when this harmonically 'enriched' waveform is viewed on an oscilloscope the top of the wave appears to be clipped off, thus the name.
     
  4. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Yes, both.

    All a power amplifier does is to take a small signal voltage and output a larger voltage that is exactly like it except for the voltage. Any difference is called distortion.

    The amplifier has a power supply, which is X volts, say 80 volts for a reasonable sized amp. It also has a "gain", which is the amount the output voltage is larger than the input. If that gain is 40, the output is 40V for an input of 1V, for instance.

    OK, so the amplifier receives a signal of 1V peak. it puts out 40V peak, and all is well. (1V x 40 = 40V)

    If it gets a signal input of 2V, it puts out 80V, and all is still well, but that is its limit. (2V x 40 =80V)

    If you give it a input of 3V, now there is a problem. The output voltage SHOULD be 120V, but there is only 80V available.

    So what happens is that the output voltage goes up as the input signal increases, UNTIL the output gets to the 80V. That happens at 2V input.

    As long as the input signal is larger than the 2V, the output doesn't change at all, it remains "stuck" at 80V. When the input comes back down below 2V, the output again 'follows" the input.

    That time when the output is 'stuck" at maximum is called "clipping", because it is as if someone "clipped off" the output with scissors.

    Obviously, whatever the signal was doing during the time the output is 'clipped" is totally lost. The distortion is essentially 100% for that time.

    So giving the amp too much input signal is the same as "pushing it too hard".
     
    Thuston Howell likes this.
  5. Maybe i worded my question incorrectly, by "pushing it too hard" I meant cranking the gain knobs on the power amp itself and not increasing the input level.
     
  6. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    The result is the same, but if you crank the levels on the pre you can introduce clipping in the pre as well as in the power amp.
     
  7. Thunder Pulse

    Thunder Pulse

    May 12, 2007
    That kind of distortion is a concept that a lot of people have a problem with who are new to this stuff. As soon as the word 'distortion' gets used they're thinking guitar distortion, rock & roll, 'clipping' distortion, but what was meant was "a distortion of the truth."
     
  8. slapagroov

    slapagroov

    Apr 24, 2007
    Fort Myers, FL
    Thanks for asking that question; I was wondering something along the same line.

    Can an old pre amp tube cause clipping as well? I have an Eden wt 800 and the clip lights are flashing at moderate volumes, but it should be capable of more. I set the gain correctly and the master volume is only at 11:00. That's loud, but it should be able to get louder without clipping, right?
     
  9. Emprov

    Emprov

    Mar 19, 2003
    Here's another question: does the cab have anything to do with the point at which the amp will clip? I'm talking about say, 2 8ohm cabs designed differently. My brain tells me that it shouldn't but it seems like my head clips a bit more quickly when it's hooked up to one cab than it does hooked up to another.
     
  10. Bryan316

    Bryan316 Inactive

    Dec 20, 2006
    Detroit
    Wait... any amp is capable of more, depending on what that amp is driving. What are your speaker cabs, and what ohm loads are they?

    Also, how are you running the 800? Stereo? Dual-mono? Bridged? Crossover used or off?
     
  11. Bryan316

    Bryan316 Inactive

    Dec 20, 2006
    Detroit


    Sorta-kinda, yes. The amp can only do so much work. It's X work into Y load in ohms at Z current in amperes. If the load is different, the same work is done but at a different current.

    If you have less of a load, you can pass more current. That work is more efficiently utilized, because that larger current turns into more wattage and more air pushed. This is why an amp will be louder with a 4-ohm load than with an 8-ohm load. 4 ohms doesn't restrict the flow of current as much as an 8-ohm load. So instead of X work meeting resistance to current flow and being quieter, that amp can open up and get you louder.


    So to answer your question, your power amp will clip at the same amount of input signal, but at different audible volume levels coming from your speakers. If you look at the master volume knob, it should blink at the same setting. But if you listen to the amp, it'll clip sooner in relation to actual volume and decibels of sound produced at those same master knob settings. You'll just hear clipping at lower levels.
     
  12. slapagroov

    slapagroov

    Apr 24, 2007
    Fort Myers, FL
    The 800 clips at higher volumes when I run it bridged and stereo. I don't have the crossover on. When bridged, I use an 800 watt, 8 ohm 410. I also use a GS 112 for smaller gigs. I notice it clipping more when I try to crank it while using one of the 400 watt sides, but happens when I use it bridged as well. Obviously I don't crank the volume too much when using the 112. I don't hear anything bad coming out, just see the lights coming on.
    Thanks
     
  13. Bryan316

    Bryan316 Inactive

    Dec 20, 2006
    Detroit
    Hmm... now, you're seeing the LED light blink representing the clipping, or you're hearing the clipping? Cuz you also gotta hear the difference between power amp clipping distortion, and speaker cone farting distortion. Different sounds, both bad.
     
  14. Vanceman

    Vanceman

    Feb 14, 2007
    So. Cal.
    I'd like to get some feedback to something I tried after reading a discussing about clipping and AC versus DC current. I have no formal electronics education, but I do know how to solder.

    My old Yamaha PB1 preamp is causing the power amp to clip when set at anything above 4 on the volume, as indicated by the red light on the power amp and the distorted sound. I bought a Sansamp RBI to replace it.

    After reading said discussion, I used a multimeter to check the output of both the PB1 and RBI. Both preamps measured around 13-14 volts maximum when measuring AC current, and acted similarly as the volume knob was turned. Big difference when measuring DC voltage. The RBI never exceeded .5 volts, even at full output, but the PB1 jumped to around 3.5 volts as the volume went past 4, eventually ending up around 10-12 volts DC at full output.

    Is the DC current the cause of the clipping? There must be a problem with the PB1, which sucks, because I love how fat the tone is.
     
  15. slapagroov

    slapagroov

    Apr 24, 2007
    Fort Myers, FL
    I'm really not hearing any clipping at all. I just happened to notice the LED 'clip' light coming on when I dig in at loud volumes. That's why I was wondering if it was an old tube that needed to be replaced. It's definitely not the speaker. I know that sound (unfortunately) :(
     
  16. rockstarbassist

    rockstarbassist Inactive

    Apr 30, 2002
    The Woodlands, TX
    Endorsing Artist: HCAF
    What bass are you using?
    Does the A version have the -12db pad?
    I HAVE to use this when my Moduli are plugged in. Will drive the snot outta that amp if not.
     
  17. slapagroov

    slapagroov

    Apr 24, 2007
    Fort Myers, FL
    I have a Q6 that is really hot, but I set the gain like everyone says. Turn down the volume, etc. and make sure it isn't clipping. It has also done it with my VJ that is passive - I know that's not too hot. Does running an 8 omh cab make it more likely to clip?
     
  18. rockstarbassist

    rockstarbassist Inactive

    Apr 30, 2002
    The Woodlands, TX
    Endorsing Artist: HCAF
    Not sure. I run my 800B on one channel into a 4 ohm Whappo Jr. I have the -12 pad on, Gain around 1:00, Presence off, and adjust a little bit of the Bass and Low EQ's to taste. I haven't even come close (that I can tell) to clipping. With these settings my Master hasn't gone past 12:00.
     
  19. slapagroov

    slapagroov

    Apr 24, 2007
    Fort Myers, FL
    Cool. Thanks for the input. I ordered a new preamp tube. I don't know if it's ever been changed. I've only owned the head for a year or so, but it's an older one. Hopefully it's that simple.
     
  20. rockstarbassist

    rockstarbassist Inactive

    Apr 30, 2002
    The Woodlands, TX
    Endorsing Artist: HCAF
    Check it out and then report.

    Allegedly, our A and B models are supposed to be the ones "that work"! ;)
     
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
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