Adding another cabinet questions

Discussion in 'Amp Central Station' started by MHorne39, Jun 11, 2019.

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  1. MHorne39

    MHorne39 TDPRI Member

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    Hey!

    So right now I have an amp head that can switch between a 4-ohm load (50 watts), an 8-ohm load (25 watts), and a 16-ohm load (12.5 watts). I have it running a single 1x12 8-ohm cabinet. If I wanted to daisy chain an identical speaker cab to the first one (speaker out from amp>input of first cab>output of first cab> input of second cab), would I leave the Ohm Load switch at 8-ohms? Please explain it to me like I'm 5, electrical things scare me and I just want to make nice sounds I can try to provide any additional information as needed. Thanks again!
     
  2. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    Usually, the sockets on the rear of cabs are paralleled, so your head --> first cab = 8 Ohms, add the second cab and the load becomes 4 Ohms, so switch to 4 Ohms for best results.

    You can confirm this by plugging both speaker cables into the first cab and measuring the resistance tip to tip. If it's paralleled, the resistance will be negligible, while tip to sleeve will be around 6.5 Ohms ( impedance and resistance aren't quite the same thing, don't worry about your 8 Ohm cab reading six-ish Ohms, it's normal )
     
  3. MHorne39

    MHorne39 TDPRI Member

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    So I could run a speaker cable from my head to my first cab, and them another speaker cable from my first cab into my second cab and it'd be fine? Even with parallel inputs?
     
  4. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    Yup.

    Prove it to yourself with a meter.
     
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  5. Torren61

    Torren61 Tele-Afflicted

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    Plus, a decent amp can go 100% mismatch in impedance. You can have a head that takes 8 Ohms load and you can use 4, 8, or 16 Ohms. You can’t use 2 Ohms. A lower impedance number out of 100% mismatch will blow a fuse, fry a resistor or smoke your output transformer. 4 Ohms is 100% mismatch for an amp that wants to see 8 Ohms. 16 Ohms is 100% mismatch for the same head. If your head wants to see 16 Ohms, you can use an 8 Ohm speaker but not a 4 Ohm speaker. I’m talking about TUBE powered heads, NOT solid state heads. Different story there.

    Some will disagree and I am now wearing a flame suit, but it’s true.

    So, if you parallel two 8 Ohm speakers, you get 4 Ohms. If you put two 8 Ohm speakers in series, you get 16 Ohms. Paralleling halves and series doubles. If your head is rated for 8 Ohms and you use a 4 Ohm speaker, it’s gonna be louder than 8 Ohms and even louder still than 16 Ohms. Sometimes it sounds better if you use a different Ohm speaker.
     
  6. MHorne39

    MHorne39 TDPRI Member

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    What's the difference between parallel-ing cabs versus series-ing cabs?
     
  7. Tonetele

    Tonetele Poster Extraordinaire

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    the Omhs woill be significantly bigger.
    Series Rt=8/1+ 8/1 -16 Ohms
    Let's use 8 Ohms
    Parallel 2x8 Ohms= 1/Rt=i/8 + 1/8
    =2/8

    So if I/Rt = 2/8 we can invert : Rt= 8/2 =4 ohms.
    Wiring in parallel generally always lowers resistance and is favoured by electricians in buildings etc.
     
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  8. AJBaker

    AJBaker Friend of Leo's

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    Hang on, is this a tube amp or solid state? A solid state doesn't work like a tube amp in regards of impedence or matching.

    Can you send a picture of the back of the amp?


    To answer your question: two daisy chained 8 ohm cabs need the amp set to 4 ohm.
     
  9. MHorne39

    MHorne39 TDPRI Member

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    Thanks for keeping it simple. It's a tube pre and a solid state power amp. One of them new fangled Vox MV50 AC amps. There's nothing in the manual for either the head or the cabs except saying that the cabs are parallel inputs. Thanks again!
     

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  10. AJBaker

    AJBaker Friend of Leo's

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    Ok, a solid state amp is a different kettle of fish and has very little in common with the way you match tube amp impedance. For starters, there's no output transformer.

    I'm not quite sure what that switch is doing, but I'm guessing it's to adjust the EQ (among other things possibly...). A solid state amp doesn't need impedance matching, there is simply an impedance at which it gives maximum power. Any higher and you have less power, any lower and something will eventually blow.

    Here's an example of how my solid state PA works, and how impedance affects output:
    I have a column style speaker with a 600w amp that can drive up to four speaker units (each with a impedance of 16 ohm). Depending on how many speaker units I use, I get the following power:

    - with one 16 ohm speaker, the amp will give 150 watts of power.

    - with two 16 ohm speakers (= 8 ohm), the amp will give 300 watts of power.

    - with four 16 ohm speakers (= 4 ohm), the amp will give 600 watts of power, it's maximum.
    If I tried adding more speakers (bringing the impedance below 4 ohm), the amp will try to produce more than the maximum 600w, and will either shut down or damage itself.

    My PA has a switch where you select the number of speaker units installed, but that's purely for eq reasons.

    With a tube amp in the other hand, it's important to match the impedance as closely as possible, though you can often get away with half or double the required impedance.
     
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