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Silly Bass to Amp Impedence Question???

Discussion in 'Amps and Cabs [BG]' started by jokerjkny, Aug 25, 2004.

  1. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL

    so, i thought had the impedence thing figured out, but when it comes to bass to amp impedence, kinda took things for granted, since its not quite as life/death as amp to cab impedence, so...

    my sadowsky onboard active puts out a boat load of output, but i dont wanna hurt or slam the front end of my amps too hard, e.g. my Acoustic Image Focus.

    so, explain to me what i should look out for, and how i can tell if the input of the Focus can properly handle the push of my Sadowsky.

    here are their respective websites with stats:

    Sadowsky active onboard specs

    Acoustic Image Focus specs
  2. brianrost

    brianrost Gold Supporting Member

    Apr 26, 2000
    Boston, Taxachusetts
    First off, impedances do not need to be carefully matched at the input to an amp. In general you want the input impedance to be quite high, the higher it is the less loading of passive pickups. If you use an active bass (or pedals with buffering in your chain) the input impedance of the amp almost doesn't matter. As long as the input impedance of the amp is higher than the impedance of the bass output you're all set. If the input impedance is LOWER you can get signal loss and also loss of low end.

    Input impedance of amps typically ranges from about 20K ohms up to 10M ohms, though amps with impedances above 1M are rare. Most that do have super high impedances are designed for upright bass, because the piezo pickups used for URB are very high impedance devices. Very high input impedances require careful design because they are more susceptible to picking up noise.

    OK, on to the specific units you mentioned. The impedances (1K ohm out driving 1M ohm in) will work fine. What is missing from the specs is info on the LEVELS that the preamp can deliver and the sensitivity of the amp (i.e. how much input signal to generate full power output). The worst that can happen is that with severe EQ boosts on the preamp you might overload the amp input, so just turn down the volume at the preamp until the sound cleans up.
  3. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL
    thx bri,

    yea, i'm more concerned about how to tell if i'm gonna overdrive the input of the amp, cause my Sadowsky has MUCHO output.

    but thx again.
  4. Petebass


    Dec 22, 2002
    QLD Australia
    The difference in output between a strong bass and a weak one in probably within 1 or 2 volts tops. Once it's amplified, the voltage increases many times over, so suddenly things like impedance start to matter.

    I don't worry too much about signals that are before the amlification stage. They're not strong enough to do any real damage. At worst your input might distort if the signal is too hot. Just turn the input gain down to match.
  5. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Yep. That's the short answer. If your amp starts to sound funny, your bass is too loud and you should turn down the volume. My MTD-535 is very hot, and has an incredible dynamic range. The signal peaks can be ten times the average level (I actually measured it on a scope). Those peaks will drive even an excellent amp like a WW Ultra into a sonic frenzy that sounds like screaming banshees. In those situations where the signal "peaks" are extreme, a judicious amount of compression or limiting might help. In situations where the "average" signal level is too high, the only solution is to turn down the volume control.