A Question.

Discussion in 'Amps and Cabs [BG]' started by foolfighter24, Aug 23, 2001.

  1. foolfighter24

    foolfighter24 Guest

    Apr 22, 2000
    Can I use the Direct line out(XLR) on the back of my amp to connect to a bass cab? And, more importantly, does it matter what OHMS i match up? Sorry if this is confusing, but I am confused if I can do this so that it is ok with the speakers and such. Thank you!
  2. JimM

    JimM Guest

    Jan 13, 2000
    Northern California
    Until someone more knowledgeable answers,let me just say,no,the power needed to drive a speaker is many many times stronger than the signal from your DI.also,the DI has three connectors,I think,but a speaker takes a two connector cable.And NOT an instrument cable,they can't handle the wattage needed by the speaker.

    The ohm load of the speaker must not be less than the amp's minimum rating,which is usually four ohms,but it can be eight or two ohms.If the amp is rated four ohms,you can run two eight ohm cabs,or one 4 ohm cab,but not two four ohm cabs,that would be a total of two ohms.The lower the ohm total of the cabs,the more energy comes from the head and thus the more heat.most amps can't handle the heat of less than four.

    The reason two eight ohm cabs equals one four ohm cab is that ohms are a measure of resistance or impedence.Ohms aren't a power to be measured,but rather they resist,or impede power in a measurable way.

    If your amp is solid state and rated at a four ohm minimum,you can drive a four or eight ohm cabinet with no trouble.But if it's a tube amp,the speaker(s) must be matched to the head exactly.Some tube amps have a switch so you can use either four or eight,some have multiple speaker output
    jacks that allow you to match the speaker's impedence that way.

    I don't know why you want to use to DI for a speaker,maybe the spkr jack is messed up? I know it won't work however.

    Man,I hope that made sense.trying to put it on paper is a challenge.If you are used to using an ohmmeter (I use one everyday)it makes sense.
  3. Matthias


    May 30, 2000
    Vienna, Austria
    The direct line out (DI out) porovides an unamplified signal, either completely unaffected (Pre EQ) or including EQ settings and effects (Post EQ). You use this output if you want to run your signal to a mixer (for PA or recording).
    Cabs always need an amplified signal (as long as they do not have an internal amp)

  4. foolfighter24

    foolfighter24 Guest

    Apr 22, 2000
    Ok, thanks guys. I was just wondering if you used the DI so you didn't have to match OHMS with the combo and cab. So I won't try that now....

    But you say with a SS amp at 4 OHMS, I can hook up a cab running at 8 OHMS to the the Speaker Jack, and it will be ok for the original combo amp, correct? Thanks again!:cool:
  5. IF the speaker(s) in your original combo constitute an 8 ohm load or higher, then yes, because the total load resulting when you add an external 8 ohm speaker would not be lower than 4 ohms. IF the combo's speakers are already giving the amp a 4 ohm load, then no, because a 4 ohm load in parallel with an 8 ohm load yields a 2.67 ohm load, which would be too low for an amp rated for use with a minimum 4 ohm load.
  6. CS


    Dec 11, 1999
    If your amp has a minimum load of 4 ohms NO.
    The safest way is to use two 8 ohm cabs.

    I sure someone can explain this better. But I thought the short version before you try it would save you some problems.

    PS Richard Lindsey-thanks
  7. foolfighter24

    foolfighter24 Guest

    Apr 22, 2000
    Ok, here is what my little Manual says:

    It says it runs at 100 watts RMS@ 1% THD 4 ohms, 120 VAC.

    and also says of the speaker jack-

    USe this Jack to connect to an extension speaker cabinet. This jack is wired in series with the internal speaker.

    So it wouldn't be in "parellel" with my speaker, but in a series. Does this change anything?

    and finally, of the Balanced Line Out:

    Use this XLR type connector to send a balanced preamp signal to a house mixing board, recording console, or an external amplifier.
    Does this change anything?
  8. If the jack is in series (less common than parallel but not unknown), yes, that changes something, it means that impedance goes up instead of down when you add speakers. Thus, if you have an 8 ohm internal speaker and you add an 8 ohm external one *in series*, you get a total load of 16 ohms. This means you are unlikely to end up with a load that's too low for your amp, but the downside is that as total impedance goes up, the power your amp delivers will actually go down. Which seems kinda pointless.

    To figure out what the load on your amp is gonna be, you still have to find out what the impedance of the internal speaker(s) is. Does the manual give that, or is it anywhere on the back of the amp?

    Regarding the line out, no, what you stated here doesn't change anything from what's already mentioned. You still can't drive a speaker with it.
  9. You're quite welcome. Just remind me ... what are you thanking me for?:)
  10. Luis Fabara

    Luis Fabara

    Aug 13, 2000
    Ecuador (South America)
    Audio Pro - Ecuador
    I dont buy that "Series" wiring..
    but If it is.. then It must be a CRATE AMP.

    Crate is one of the very few manufacturers that are so stupid to do so.
  11. foolfighter24

    foolfighter24 Guest

    Apr 22, 2000

    It is a Crate amp. So, the ohms rating is at 4 ohms and I add an 8 ohm cab, how does that math work? Is it just adding the two ohm numbers? Cause if thats the case, thats kinda high ohms isn't it? That would be close to defeating the purpose, right?
  12. EString

    EString Guest

    Nov 20, 2000
    Los Altos, CA
    Equation for total resistance in a parallel wiring circuit:

    (1/Resistance A) + (1/Resistance B) = 1/Total Resistance.

    4 ohm in parallel with 4 ohm = 2 ohm total
    8 ohm in parallel with 8 ohm = 4 ohm total
    4 ohm in parallel with 8 ohm = 2 2/3 ohm total
  13. Matthias


    May 30, 2000
    Vienna, Austria
    And in the case of series wiring you just have to add impedances, so that would add up to 12Ohms.