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Why do combos clip?

Discussion in 'Amps and Cabs [BG]' started by rabid_granny, Nov 29, 2002.


  1. I was looking at the specs for the Fender Bassman 400 and I noticed that it has indicators for clip LED's for the pre-amp and power amp.

    Why should a combo amp clip? It sounds like the designers screwed up by putting the incorrect speaker in the amp, right?

    Also, why does this amp have two clip indicators?
     
  2. TRU

    TRU

    Apr 12, 2002
    Northern Europe
    Any amp will clip if you're driving it too hard. Putting a "correct" speaker to the amp has nothing to do with it. You can overload the preamp by using too much input gain or the power amp by having the master volume up beyond the power amp's capacity. So there are two clip indicators to help you prevent both types of overloading/clipping.
     
  3. Would it be possible to overload the pre-amp using a passive bass?

    Also, why would a combo use a power amp that can't run at maximum volume?

    Also also, what is the difference between the volume knob and the master volume knob? My friends can't explain that to me.
     
  4. TRU

    TRU

    Apr 12, 2002
    Northern Europe
    Yes.


    Also, why would a combo use a power amp that can't run at maximum volume?


    Good question. That's the way they are. The manufacturers are not interested in matching the maximum output with the speaker. Maybe because buyers are not interested either.


    Also also, what is the difference between the volume knob and the master volume knob? My friends can't explain that to me.


    Your signal chain:
    Bass -> preamp input (gain control) -> eq, effects, etc. -> power amp (master volume) -> speaker

    So gain control (or volume) matches the output of your bass to be suitable for the electronics in preamp (eq, compression...) and master volume adjusts the power amp gain. You should use the master volume to make your combo louder or quieter.

    If you want to know more about amps, read the amp FAQ: http://www.talkbass.com/ampfaq/
     
  5. dumeril7

    dumeril7

    Oct 21, 2002
    Austin, TX
    Several answers....

    You have to remember that the amp designers can't take into account every possible factor in designing an amp. Theoretically, you can overload a preamp with a passive bass if its pickups have enough output. Or better yet, if the player sticks a preamp or distortion pedal between the bass and amp. Amp designers worth their salt try to engineer as much headroom as possible into a preamp, but you never know what some knucklehead is going to plug into an amp. ;-)

    As for why a combo amp might use a power amp that can't run at max volume: Well, think about a car. You can floor the accelerator on a car, but if you do it for long enough, the engine is going to have problems because you're simply making it work too hard.

    Typically the "volume knob" controls the amount of preamp gain, and the master volume controls the amount of signal sent to the power amp. In practice, you set the volume/preamp knob to as high as possible before clipping, and then use the master to set your desired volume. A variation on that approach is to use the volume/preamp to set the level of overdrive and the master to set the volume.


    D7:)
     
  6. I see now...thanks for the answers.

    As for the Amp Faq, I had been waiting for a while for that to come out. Unfortunately, I haven't had time to crack it open just yet.