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HELP, PLEZE..Loose nut behind the neck...

Discussion in 'Amps and Cabs [BG]' started by old grouch, Jan 25, 2006.


  1. old grouch

    old grouch "Old Fool? Ya don't get old, bein' no fool!"

    I bought an Ashdown Blue 180-15. I am thinking about getting an add-on cabinet, maybe a 2-10 or a 4-10. Thats the easy part. Knowledge is the trick....and I'm runnin a tad short.

    In the specs, it states that minimum output ohms for an extension cabinet is 4 ohms. Could someone look at the specs, at http://www.musiciansfriend.com/product/Bass/Amps?sku=485037, and tell me if I should get something like THIS? Its 8 ohms. Thats more than 4 ohms. Is that in line with "a minimum of 4 ohms?"

    I'm a tad in the dark here. The 180-15 has two 1/4 jacks in the back. One has the cord from the internal speaker plugged into it, the other is for an extension. It says 'external speaker minimum 4 ohms. How many ohms is this amp? Will any cabinet with more than 4 ohms work? 8? 16? What would the difference in the sound be. depending on putting a 4 or an 8 ohm cab?

    An yone with patience, and a basic knowledge of electric circuitry.......help. Gimme a twenty words or less (just kidding) tutorial on this PLEASE...

    orrrr, should I get a higher watt amp w/ 4/10's, and use the 180-15 as an external cab?
     
  2. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    8 is bigger than 4, so you are good there.

    Second, amps don't have "ohms" - it is a nonsensical figure in that context. An amp is rated to drive a MINIMUM load, and that is in ohms . .. perhaps that's what you mean here . . .

    From reading the rather sparse specs at MF, I get that the head can drive 4 ohms minimum - period, not that the external can be as low as 4 ohms. As such, I suspect that the internal speaker is an 8 ohm speaker, and as such, you can use another external 8 ohm speaker, for a total load of 4 ohms, OR disconnect the internal, and use JUST an external 4 ohm cabinet.
    (A quick look at the online manual confirms this - 4 ohms minimum TOTAL load, including the internal speaker.) However, the manual does not match your description of having two 1/4" jacks - the current units have one 1/4" and one Speakon. Do you also have a speakon? If not, then they just changed one connector, if so, then the manual that is online is incorrect for your amp . . . .

    - Tim
     
  3. cheezewiz

    cheezewiz

    Mar 27, 2002
    Ohio

    Exactly what Tim said. 4 ohm TOTAL load for this amp.
     
  4. old grouch

    old grouch "Old Fool? Ya don't get old, bein' no fool!"

    thanx....so then by minimum, the reference actually means to MATCH? ie, if its a 4 ohm load, then it would support TWO 8 ohm speakers, but not an 8 and a 16? Jeez...I gues I KNOW mt next research bit...Aren't ohms a measurement of resistance, and if so if the amp provides power to speakers with 4 ohms of resistance, it seems backwards...that 4 ohms should be divided into 2 ohms for each speaker. I will have to re-educate myself....oooorrr, I could just continue to feel rather errrr.....ddduuuhhh! (lol)
    Thanks for this and any future help.
     
  5. old grouch

    old grouch "Old Fool? Ya don't get old, bein' no fool!"

    heres the back of my amp. one (coming from internal) 1/4" jack, and one for extension.
    [​IMG]
     
  6. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    No, no match required. A minumum load of 4 ohms, however you get it . . . one eight and two sixteens, four sixteens, eight 32s, 4 32s and 2 16s, whatever. An 8 and a 16 will give a load of 5.33 ohms, which will be fine. You just can't run an 8 and a 4 - that would give 2.6 ohms, which would overload your amp.

    Just saw your picture too . . . it pretty clearly states what we have been saying - four ohm minimum load, no reference to an external cab - it's the rating for the entire amp. And yes, the new ones are different, and have a speakon instead of the second 1/4" jack.

    - Tim
     
  7. old grouch

    old grouch "Old Fool? Ya don't get old, bein' no fool!"

    what is a (simple) formula for determinng ohms value? like you said an 8 + 16 would give 5.33 ohms. how do you determine that? Thanks again for the help.
    OG
     
  8. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Ohms are a measure of resistance. and parallel resistances give a total less than either. Think if it in terms of water hoses, with a bigger hose having a lower resistance (lower ohm figure). If you use a certain size hose, things are fine, but lets say if you let it flow too fast, the pump blows up. If you use either a bigger hose from the faucet, OR two smaller hoses, you can get the same total flow, right? Same with your amp. A 4 ohm cab is the biggest "hose" you can use, and two 8 ohm "hoses" (1/2 the size of the 4) will give the same flow. If you want to do the math, resistances in parallel combine like so:

    R1*R2/R1+R1=resistance.

    So, from my prior answer to your question about an 8 and a 16, we get:

    8*16/8+16 => 128/24 = 5.33

    (If you have more than two, the formula is a bit more complicated, so I won't go into it here . . . )

    - Tim
     
  9. old grouch

    old grouch "Old Fool? Ya don't get old, bein' no fool!"

    Thanks Tim.. Its a lot of help.
     
  10. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    No problem. Not difficult stuff, but not terribly obvious either . . . .

    - Tim