RUN A FULL STACK WITH A TOTAL LOAD OF 4 OHMS WITH A AMP THAT HAS 8 OHM AS A LIMIT

Discussion in 'Cabinets & Speakers' started by Exotic, Dec 10, 2019.

  1. Exotic

    Exotic Active Member

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    ok i would like to run a full stack using 2 marshall 4x12 cabinets with speaker configuration that is not original ,but both cabs are wired correctly and both cabs have 4 8 ohm speakers in them so a total of 4 ohms load ,but my jcm 900 only has 8 and 16 ohm options . what to do ? i am aware of cab lynk ,but i don't know what config my cabs are? series? parallell? series-parallell? they have the same wiring as marshall 4x12's that use that 4,8,16 ,mono ,stereo switch .

    also i can run like that easy with my marshall jcm 800 2 cabs 8 ohms each for a 4 ohm load and the amp has that covered ,but ,imagine if i pull 2 tubes for a 50 watt amp the impedence gets cut in half? so how?
    IMG_1801 (Phone).JPG IMG_1807 (Phone).JPG IMG_1810 (Phone).JPG IMG_1967 (Phone).JPG IMG_1975 (Phone).JPG IMG_13.JPG
     
  2. Jon C

    Jon C Well-Known Member

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    Don’t
     
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  3. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    either:

    wire both cab's series (32 ohm) & run them parallel (16 ohm)

    or, get yourself a series splitter box, that will run both cab's series at 16 ohm (8x2=16)
     
  4. Michael Roe

    Michael Roe Well-Known Member

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    Take the amp to a qualified tech. From my understanding, the "4" you see in (parenthesis) at the impedance selector means that there is actually a 4 ohm tap on your output transformer that can be utilized if wired up by a tech.
     
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  5. Adieu

    Adieu Well-Known Member

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    Or you can mod one of your cabs for series daisy chaining
     
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  6. scott-colorado2016

    scott-colorado2016 Active Member

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    I did this with a pair of cabs. The both had 8 ohm speakers in them, I added a second jack to each. The first cab had a standard parallel jack added, the second cab I added a series jack to it. So when the amp was connected to the second cab alone (or the first cab alone) it was 8 ohms, but if I plugged in the first cab into the series jack on the second cab, then second into the amp, it was 16 ohms. I used a stereo/switching cliff jack for the series jack if I remember correctly. Was pretty easy to do. I drew it out on paper first, been a long time, so I don't have my drawing anymore, but I could redraw and post this weekend if you'd need.
     
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  7. scott-colorado2016

    scott-colorado2016 Active Member

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    The cablink is not asking you how the individual speakers or amp are wired, it showing you how the jacks on the box are connected and how you want them to connect to the amp. For your setup, each of your cabs (based on the info you've given) is 8 ohms each, right? To hook them up to your current amp (with only 8 and 16 ohm outputs) you would use the series jack to the amp and plug each cab into the speaker a and speaker b, for a total load of 16 ohms to your amp.

    **Edit** Ignore the diagrams on the Radial Engineering web site, they are wrong!
     
    Last edited: Dec 11, 2019
  8. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    you would have to somehow have the wiring scheme like this.


    series.jpg

    Not sure how you could wire a single jack inside 1 of the cab's...
     
  9. scott-colorado2016

    scott-colorado2016 Active Member

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    Not a single jack, two jacks on one cab. The one I did, I added a second switching jack that when another cab was plugged in to it, the second cab was in series with the first, when nothing was plugged in it completed the circuit normally.
     
  10. Exotic

    Exotic Active Member

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    how many watts is a jbl d120f?
    just like u can measure the ohms of a speaker with a dmm ,can u also measure the watts of a speaker somehow?
     
  11. Gutch220

    Gutch220 Well-Known Member

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    Get a Weber Z-matcher. you'll use it for the rest of your life, and it's the same price as if you got a tech to hook up your 4ohm tap.
     
  12. South Park

    South Park Well-Known Member

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    Now if you hook up those cabs right and the ohms match is right it works. Or the ohms is a mismatch and the amp is KFC. So what’s it going to be
     
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  13. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    1. Set the meter for ohms.
    Measure each speaker individually with the ohm meter. (when the speaker is unhooked from the rest of the speakers)
    Report the results of all 4 individual speakers.
    Then we can come up with a plan to wire the speakers inside the cabinet.

    2. The (4) ohm marking on the amplifier refers to a tap on the output transformer that is used for combo amps.
    The (4) ohm tap is used for combo amp versions, and is not used for head versions.
    However,
    The 4 ohm tap "can" be hooked up inside the amplifier by a qualified person.

    3. IN THE HEAD VERSION, ONLY THE 8 AND 16 OHM TAPS ARE HOOKED UP.
    But this can be changed to the 4 ohm, by a qualified person.

    A. Measure the speakers FIRST with an ohm meter. Report your readings of all speakers.
    B. Rewire the cabinet if needed, according to your measurements. (we will walk you through wiring)
    C. Do not operate the amp, until everything has been measured and verified FIRST.
    D. Do not guess or assume anything. Measure everything and write down the results.
     
  14. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    The z matcher cuts the power in half to match an 8 ohm amp to a 4 ohm speaker.
    This is an auto-former.
    However by re-wiring speakers this type of matching is normally not needed or required.
     
  15. Gutch220

    Gutch220 Well-Known Member

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    The people at Weber told me this wasn't the case, and that it doesn't cut power.
    If you want, email them and ask them specifically what you're saying.
     
  16. Jethro Rocker

    Jethro Rocker Well-Known Member Premium Member

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    A couple of things stand out to me.
    1. Is that cable coming from the amp a speaker wire? Because it looks rather thick and possibly like a shielded guitar cord. I could be wrong.

    2. The speakers in the first cab are certainly mismatched speakers. They may well be 8 ohms each but the sensitivity may vary quite greatly, especially with the big old looking unlabeled one. Might have troubles hearing some of those lower sensitivity speakers with the others.
     
  17. RLW59

    RLW59 Well-Known Member

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    Exotic has done a dozen + threads in all the forum subsections cross-referencing the speakers, the JCM800, and now the JCM900.

    He'll start a thread about modding the 800 for more gain, or running one of the amps on 2 tubes instead of 4, then throw in tidbits about the speakers. You kind of need to read them all, because the same questions, observations, and suggestions are being raised over and over again by people who don't know from any one thread alone that a lot of this stuff has been covered already.

    There are so many threads, Amp Mad Scientist forgot that he gave lots of good advice about the speakers back when Exotic was loading them in the cab. They're all marked 8 ohms, and the JBLs' polarity are correct.

    There was some confusion about DMM readings. But eventually the conclusion was reached that all the speakers are indeed 8 ohms as marked. Each cab is series/parallel for 8 ohm total impedance.
     
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  18. RLW59

    RLW59 Well-Known Member

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    1. I buy speaker cables with thicker covers than my guitar cables intentionally. Lamp cord is fine, but I like thick rubber covering for cables that are at risk of getting squashed under cabinets, or wheels rolled over them.

    I've never done abusive things to speaker cables, but I've seen others do it. So just in case.

    Plus I think fat cables look cool.

    (And in other threads Exotic has said he understands to use speaker cables for speakers.)

    2. JBLs + Greenbacks is both an EVH and Duane Allman thing. Yes the JBLs are louder, but the dirt from the Greenbacks is audible and rounds out/warms up the predominant JBL tone.

    I really like mixing JBL/EVM/Altec/CV with Greenback types. My main rig is two open back 112s with a CV PS12 (last version of the ER123) and a G1265. (The CVs are a little less efficient and a little dirtier than JBLs, but still a little louder and a lot cleaner than G1265s.)
     
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  19. Jethro Rocker

    Jethro Rocker Well-Known Member Premium Member

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    Cool. Good to know! Wasn't sure where he stood on speaker wire vs shielded.
     
  20. Exotic

    Exotic Active Member

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    YEAH THAT'S RIGHT ,thanks u guys i have learned alot on here ,right now my jcm 900 is running fine and safe with the jbl + greenback cab ,i guess the cab is 80 watts? and the amp is 50 watts ,so that's safe ? i won't worry about using a full stack at the moment because i can do that with my jcm 800 if i ever get it back . and the 4 speakers sound pretty good together ,although i'm not getting as much distortion as i would like ,makes me think the tubes might be going ,just got the damned thing ,how am i supposed to know if it's time for a retube? i do have 2 speaker cables ,thanks for checking .the switch for ohms on the jcm 900 only has 2 positions ,so if it was wired by a tech for 4 ohms ,what 2 choices would be available ?
    to have all 3(4,8,16) like the jcm 800 u would need a new switch right?
     

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