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MarkBass clipping in low volumes

Discussion in 'Amps and Cabs [BG]' started by Agito, May 17, 2010.

  1. Agito


    Jun 27, 2009
    I have something really annoying with my CMD151P
    I use a passive bass and it clips in about 35% of the volume and Gain, they usually the same, is anyone familiar with this? Why does it clip like insanely even when I play softly?

    Should I ignore that? What can be the damage?
    This is really making me thing about selling my CMD151P and getting an Ampeg or something like that :scowl:

    BTW, how can you measure loudness in amplifiers? I know wattage is not really important, what is important?
  2. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    You should experiment with the volume and gain knobs to see where the clipping is occurring. If the input stage is clipping, the gain knob will fix that. If the output stage is clipping, the volume knob will fix that.

    Also, are you talking about seeing a clip light, or hearing clipping noise?
  3. If it's a clipping noise rather than the clip light flickering, it could be something as simple as a bad cable. When my fave instrument cable started crapping out on me, I would get an intermittent horrible clipping sound that I thought was a damaged speaker until i changed cables.
  4. Agito


    Jun 27, 2009
    what do you mean by input stage and output stage?
    And I need to turn both down and then try each one separately to see where is the limit?
  5. Correct. Remember, the gain control (the volume control on the left of the amp) is there strictly to control and optimize the level going into your amp based on the output of your instrument. So, the first thing to do is turn the master volume down (the control on the far right) to a very low volume (so you don't hurt your ears), and then play your open E string as loud as you would ever play it. Turn the input gain on the amp up until the clip light comes on, then back it off about 10%.

    This will result in the optimized input signal to the amp (i.e., the hottest input level before clipping, resulting in the best signal to noise ratio).

    Now, use the master volume to actually control how loud your amp gets. There is no indicator light or whatever at the post stage of the Markbass amps. It isn't really necessary, since there is power amp limiting that keeps the amp from distorting (it will just stop getting louder eventually, and gently compress).

    A small, single, 8ohm 115 will only get so loud. If you need more volume, you most likely need an additional cab.
  6. Agito


    Jun 27, 2009
    I seriously didn't know that, that's great, I'll play with the Gain control and then pump out the volume!

    I feel earth shaking :evil:

    Anyhow, I have another question, how can you measure loudness? And I mean more like what's louder to the ear, by cab sizes, tweeters etc.
  7. bongomania

    bongomania Gold Supporting Member Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    Loudness is totally subjective. There are devices for measuring loudness, but they are just as flawed as any human ear. The only valid meter for loudness is what people hear.

    Just to explain input/output stages, an amplifier is not just one black box that sound comes out of. An amp is a chain of different devices that work together. So for example the gain knob on the amp controls a device that governs gain; then it sends its signal on to (for example) the EQ section, and the EQ is its own independent device that processes the signal. Then it sends the signal on to the next device inside the amp.

    At any stage, the signal level may get too "hot" (amplitude too high) for that stage, and you get clipping. So when you hear clipping, try adjusting each of the stages, to see if lowering the level at that stage stops the clipping.

    Imagine a big water tank, with an input valve (for water coming in) and an output valve (for water pouring out). If the tank overflows, then you have to adjust the input and output valves until you get just the amount of water you want pouring out of the tank, but with no overflow.
  8. Of course, there are DB meters you can buy. However, I think what you are asking is what makes one rig louder than another. The biggest part of the equation (IMO) is the speaker. Speaker SPL (i.e., how loud per watt) is key, since a low SPL cab can take a LOT of watts to pump out the volume. A low SPL cab is typically one that is tuned very low... lots of deep bass, which takes a lot of power.

    The other key driver of volume is the size of box and number of speakers. A 112 will rarely get as loud as a 210, no matter how many watts. A 210 will rarely get as loud as a 212, and a 212 will rarely outperform a 410 (assuming the designs are roughly the same), etc., etc.

    Finally, both wattage and the voicing of the amp are key. An amp that has a huge low end (i.e., the internal hi pass filter set to allow the amp to reproduce very deep bass... which sucks a lot of power) will not sound as 'loud' as another amp of equal wattage that is tuned to be more mid punchy.

    So, the simplest way to get louder is to add nother speaker cab. This results in more wattage, since the impedance goes down, and also adds the additional drivers, and results in the magic of 'coupling', which results in a sort of synergistic effect that results in two boxes to be MUCH louder, fuller, deeper than a single one (more than you would expect).

    From your previous thread, the one thing that will happen for sure if you clip that input section and push the amp and cab beyond what it was designed to do... the tweeter will go by-by!
  9. Agito


    Jun 27, 2009
    Weak weak tweeters, but I still need these :(
    Anyhow, I learned a lot, thank you very much!