Amp clipping and the signal chain...

Discussion in 'Amps and Cabs [BG]' started by GeorgiaHonk, Feb 10, 2005.

  1. ...I've been using my basses straight in to my amp head (Peavey 450 Max) and have occasionally had to get fairly loud in order to be heard. Sometimes the volume is up to the point where the clipping indicator stays lit for longer than my comfort zone allows. Last night at practice, I placed my SABDDI into my signal chain right before the amp's input and used that all night. The result was an incredible increase in loudness without once even approaching clipping. I'm an effects moron, so please explain to me why this happened. An effect can increase volume and not cause clipping? I had to back off of my bass' volume knob by about 50% to get the volume to mix with the rest of the band. Could there be something wrong with the Peavey's preamp?
  2. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Does the clip light indicate clipping in the output of the head or in the preamp circuitry?
  3. Petebass


    Dec 22, 2002
    QLD Australia
    I'd say that most hass heads indicate clipping at the input stage and most power amps at the output stage. See the problem?
  4. Actually, I don't. At least, not yet. Anyone?
  5. If you are talking about the DDT limiter in Peavey amps, then it is signalling the poweramp clipping.

    Doesn't the Sansamp boost low mid and perhaps add some compression? It's trying to emulate a big tube amp being driven hard and this is what happens.
  6. Petebass


    Dec 22, 2002
    QLD Australia
    The problem is that it creates all this confusion over what the clip light does. In a perfect world the industry would standardise it so all clip lights do the same thing.

    I guess in theory it makes more sense to make the clip light turn on when you clip the output stage, and that's what most power amps do. But from what you've said, I'm almost certain your clip light comes on when you overdrive the input.
  7. Okay, but why does my bass straight into the amp's input cause the light to come on, when my bass into a pedal and then into the amp's input NOT cause it to light? Especially confusing to me when the volume using the pedal is much louder than without, but still no clipping.

    It seems to me that if overloading the input were the problem, the pedal's additoinal gain would drive the input into clipping whereas the bass' straight signal would not. When, in fact, the opposite is what I'm observing.

  8. Petebass


    Dec 22, 2002
    QLD Australia
    I'm just wondering if it's technically possible incorporate compression or limiting into the signal post amplification? I'm thinking of the PA's I've seen where such devices are usually incorporated somewhere between the mixing desk and the power amp.

    I see where you're coming from Big Benner, but I'd also argue that my sansamp is more likely to scoop out mids than add them. Of course it all depends on the settings.......

    Anyhow, here's the way I interpreted it. Without your sansamp, your signal was weak enough that you had to boost the pre-amp a bit to get it stronger. In doing so, the clip light was comming on. At this point the power amp section may or may not have been working to it's full capacity. In effect your preamp was acting a bit like a distortion or overdrive pedal, clipping the signal prior to amplification, then sending that clipped signal to the power amp section. As you know, you can run distortion pedals full tilt, even at very quiet volume, because turning down the amp doesn't reduce the amount of squareness in the input signal. I could be wrong, but I believe a similar this is happening inside your amp head.

    By adding the samsamp, the input signal was initially stronger, so there is no need to boost it at the pre-amp of your amp head. So it can take the signal provided and transfer it to the poweramp unaltered and unrestricted. So the poweramp sees more signal and you're therefore louder.

    I'm only guessing though. Please step in and correct me if I'm out to lunch.
  9. boogiebass


    Aug 16, 2000
    Are you actually hearing clipping or just worrying about the light? If you're not hearing the amp start to clip, I think Big Benner has hit the nail on the head: that light indicates limiting is on, NOT that it's driven into clipping. I don't see any indication in the product literature that your amp even has a clipping indicator!!!??? :eyebrow:
  10. I too am only guessing but Pete Bass I think you might have the right idea.

    Just for fun, GeorgiaHonk, can you tell us your settings (example: pregain 12o'clock, bass 1o'clock).

    Passive input on the amp with your Fender Standard Precision, right?

    And I'm assuming that when you say "the clipping indicator stays lit" you are talking about the orange DDT light?

  11. What Petebass wrote makes sense to me, too. Sorry if I seem so dense on some of this stuff.

    As for amp settings, from memory, I have the contour on 0, the bass is cut by about 6dB, the mids (around 250) are boosted by 3dB, and the treble is flat. Preamp is set near 1:00, and the MV is at 11:00.

    And actually I experienced this using my active Traben. Tone controls on the bass were all set flat.

    And yeah, I was referring to the DDT indicator light.

    Thanks for the input so far folks-----very enlightening, as always.
  12. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    the ddt light indicates a limiter coming on right before the poweramp stage. those DDT amps don't really let you clip the poweramp, they just squash the heck out of your signal.