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Can someone please explain clipping?

Discussion in 'Amps and Cabs [BG]' started by NoGraveConcern, Feb 24, 2004.

  1. I donut understand.

    Here's the scoop...I'm trying to run a cheap 10" speaker off my PV nitro head for practice situations. The head is rated for 180 w into 8 ohm and the 10 is an 8 ohm, 180w RMS full range driver. I set it up in a nice big ported box tuned to 42 Hz. Now I turn the preamp gain on the old nitro up to about 3 (I leave the power gain on 9) and the ddt (clipping) light comes on at low frequencies (mostly low E and below). My question is what causes this?

    a) The amp
    b) The speaker
    c) The combination of the two
    d) The alignment of the Planets in the cosmos
    e) Carrots

    Any more specific and technical confusion you can add will be greatly appreciated.
  2. this is going on completely inside the amp (no offense to the planets or the carrots).

    basically how it works is that the speaker has a certain impedance and is rated for a certain power. this is the power it can handle before bad things happen. so unless you're exceeding this rating, bad things should not be happening (though with cheap speakers, sometimes they do).

    the DDT LED on your nitrobass head, however, is an indicator that the DDT circuit has been activated, preventing the internal power amp from clipping. basically what you're doing is driving that power amp too hard. you're setting the pre-gain so high that it's over-amplifying the signal from your bass and overdriving the internal power amp of your nitrobass head.

    thus the DDT circuit is activated to prevent clipping the power amp. sonically, there isn't a huge difference between heavy DDT and actually clipping the internal power amp, but it's better for your head if you use the DDT circuit.

    the remedy for the situation is to turn down your pregain (unless you're going for the fuzzy sound). of course, if you're going for a fuzzy sound but don't want to overdrive the amp, turn down the master knob. personally, i wouldn't worry too much about activating DDT -- i don't think it sounds that bad when i'm overdriving.

  3. Thanks for the reply RCZ. I don't think that my pre-gain is all that high. DDT comes on around the 3rd dot on the dial which is about 10:00. And yes, it does start to sound dirty when the light comes on. The 15" Black Widow that I have doesn't cause the DDT light to come on nearly that early, however that is a 4 ohm cab (switched the 8ohm speaker for a 4). I guess I was wondering if maybe part of the problem is the 8 ohm load. That or carrots.

    F) 8 ohm load on a 2 ohm rated amp
    ADD) Screw carrots, let's get some donuts
  4. the 4 ohm load, allows the amp to put out more wattage(peak in the 250-300w range probably), thus it has more headroom, thus it requires a hotter signal to overdrive the preamp...hope that makes sense.
  5. The DDT light comes on when you are trying to make the power amp output a bigger signal than it is capable of doing. Since you are running an 8 ohm speaker, when you turn up the volume knobs to get a certain amount of power, you are asking it to put out more voltage than it is capable of and this is called clipping. The reason you don't see it as much with the 4 ohm cabinet is that for the same amount of power output (and volume level), the 4 ohm cabinet does not need as much output voltage from the amp, so it is not clipping. Also making things worse, the Black Widow is a good speaker and probably takes less power to put out the same volume as the cheaper 10" speaker.

  6. if the preamp is overdriving the power amp, it doesn't matter how much power it can source to a load -- it's still overdriving, regardless of how much headroom you might have when clean.

    do you use even less pregain with your 15BW, and you're trying to achieve the same SPL with the new 10" by turning up the pregain? if so, then you've run out of headroom, like SwilsonR says.

    otherwise, you could have a mismatch between the driver and the cabinet. the driver could be incapable of producing the lows the box is tuned to reproduce. that or there's something funcky about the impedance of the driver where it's drawing too much current at low frequencies.

  7. Nah, if I turn the pre up until the DDT light comes on and then unplug from the 10 and plug into the 15 I've still got room left before the DDT comes on with the 15. Obviously the 10 won't match the SPL of the 15.

    I used the Thiele-Small parameters to calculate a box size of 2.25 cu feet and a port tuned to 42 Hz. I'm sure that there are more complicated things to consider, but the thing is that it sounds realy good at moderate volume levels.

    That's the answer that makes the most sense to me. Thanks for the replies guys.

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