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Thread: 8 ohm head, 4 ohm cabs

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    Walt-Dogg's Avatar
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    8 ohm head, 4 ohm cabs

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    I've got an 8 ohm bass head, and two 4 ohm cabs, is this safe to plug into? No suggestions, no questions. Just can I plug my 8 ohm bass head safely into two 4 ohm 8x10s?

    Or actually. A 4 ohm head into to 4 ohm cabs?

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    Sky Blue Lou is offline 1K Silver Member
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    No questions? Can't answer - or rather I won't answer. Depending on how the amp output jack(s) is/are wired it could be fine or fried. Depends on the amp.

    No suggestions? RTFM is out of the question I suppose. Good luck. Watch for the magic smoke.


    lou

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    suprstar's Avatar
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    NO! Cab's are typically connected in parallel when you daisy-chain several cab's. Plugging into 2 4-ohm cab's would show your amp a load of 2 ohms. That will be very bad for you amp, it's suck waaay to much current and probably fry your amp.

    What you need to do is get those 2 4-ohm cab's wired up in SERIES. 2 4-ohm cab's in series would be 8 ohms.

    OR probably easier - re-wire the speakers in each cab so each cab is 16 ohms instead. A 4-ohm 8x10 is probably all 8-ohm speakers wired as 4 sets of (2 speakers in parallel to 4 ohms). Those 4 2-speaker sets are wired series/parallel to grand total 4-ohm load. What you need to do is wire those 4 2-speaker sets in series to produce a 16-ohm cab. THEN you can daisy chain the 2 cabs in parallel to achieve the 8-ohm load load your amp wants.
    http://www.supr-star.com/ - suprstar studios

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    Farview's Avatar
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    No. You must match the cabinet load with what the amp expects to see. two 4 ohm cabinets hooked up to the head will create a 2 ohm load and low the amp up.

    If the lowest the amp can handle is 8 ohms, even one 4ohm cabinet will be bad.
    Jay Walsh
    Farview Recording and HERE!!!!

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    DrewPeterson7's Avatar
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    Quote Originally Posted by suprstar View Post
    What you need to do is get those 2 4-ohm cab's wired up in SERIES. 2 4-ohm cab's in series would be 8 ohms.

    OR probably easier - re-wire the speakers in each cab so each cab is 16 ohms instead. A 4-ohm 8x10 is probably all 8-ohm speakers wired as 4 sets of (2 speakers in parallel to 4 ohms). Those 4 2-speaker sets are wired series/parallel to grand total 4-ohm load. What you need to do is wire those 4 2-speaker sets in series to produce a 16-ohm cab. THEN you can daisy chain the 2 cabs in parallel to achieve the 8-ohm load load your amp wants.
    Remember, he wants no suggestions!
    "They can kill you, but the legalities of eating you are a little dicier." - David Foster Wallace (1962-2008)

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    Dogbreath's Avatar
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    Quote Originally Posted by DrewPeterson7 View Post
    Remember, he wants no suggestions!
    (stands in line for whistling innocently)


    digs holes.

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    there goes the thread.
    "They can kill you, but the legalities of eating you are a little dicier." - David Foster Wallace (1962-2008)

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    Quote Originally Posted by DrewPeterson7 View Post


    there goes the thread.





    hmmm...you're not the first to say that.







    digs holes.

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    Walt-Dogg's Avatar
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    Now what about a 4 ohm head and two 4 ohm cabs?

    Also, SUPERSTAR I'm NOT going to be daisy chaining.

    The only reason I said "no suggestions, no questions." is because I DO NOT want to be told "no, no, no, you wanna do it this way, by getting an amp and this cab, and rewiring this, blah blah blah..." All I have is a head and two 8x10s (which I'm assuming are 4 ohms.) I don't know how many ohms the heads at my disposal are.

    I have two 4 ohm 8x10s. What's the safest way to connect them to a head (to simplify, how many ohms does my head need to be to safely run two 8x10s in PARALLEL? SERIES? TWO OUTPUTS, TWO CABS. One output, two cabs.

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    Farview's Avatar
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    Quote Originally Posted by Walt-Dogg View Post
    Now what about a 4 ohm head and two 4 ohm cabs?
    No. When you plug two 4 ohm cabs into the head, the head will see 2 ohms. The speaker outputs on an amp are wire in parallel, so two 4 ohm cabinets will be 2 ohms, two 8 ohm cabinets witll be 4 ohms, etc...

    Quote Originally Posted by Walt-Dogg View Post
    All I have is a head and two 8x10s (which I'm assuming are 4 ohms.) I don't know how many ohms the heads at my disposal are.
    If the head is a tube head, you can't assume anything. You have to match the impedance with the head. If it is a transistor head, then you can have anything above the minimum impedance.

    Quote Originally Posted by Walt-Dogg View Post
    I have two 4 ohm 8x10s. What's the safest way to connect them to a head (to simplify, how many ohms does my head need to be to safely run two 8x10s in PARALLEL? SERIES? TWO OUTPUTS, TWO CABS. One output, two cabs.
    IF your cabinets are 4 ohms and you head can handle 2 ohms, just plug the two cabinets in and you will be fine.

    If the amp can only handle 4 ohms, you can only use one of the cabinets (assuming you are right and they are 4 ohms each).

    It doesn't matter if you run two outputs on the head to two cabinets or you just run one output to the first cab and daisy chain to the second one, it is still 2 ohms because they will still be wired in parallel either way.

    If you are talking about Ampeg 8x10 cabs, then they are 4 ohms. If you are powering them with a newer (not from the 70's) SVT, it should handle a 2 ohm load. But don't take my word for it, they did different things in different era's. They made 8 ohm 8x10 cabs so that you could run four of them off of one head. Way back, they made 8 ohm cabs so that you could run two off of the SVT from the 70's that (If I remember correctly) only went down to 4 ohms.

    If you built your own speaker cable to wire both cabinets in series, that would get you an 8 ohm load. However, if you screw it up, you will blow the amp.
    Jay Walsh
    Farview Recording and HERE!!!!

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