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A Question About Ohms (JVM210H & 1960A)

Discussion in 'Cabinets & Speakers' started by colchar, Jul 3, 2021.

  1. colchar

    colchar Well-Known Member

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    As many of you know, I recently picked up a used JVM210H and a Marshall 1936 cab. Since I just knew I'd go to a 4x12 at some point, I decided that there was no time like the present and scooped a 1960A that is in great condition for $500 (Canadian). I will be exchanging the 1936 for it later today.

    I am normally a combo guy and never have to worry about ohms or inputs, so I need some help.

    My understanding is that I can plug the JVM into the 1960 using either the 16ohm or the 4ohm connection on the amp. Is that correct? If so, does it make any difference which I choose (ie. does the choice affect the sound in some way)?

    If that isn't correct, which should I use - 16ohm or 4ohm?

    The cab won't arrive until later in the week so I've got time to learn before I'll have to connect them.

    Thanks in advance.
     
  2. fitz288

    fitz288 Well-Known Yinzer Silver Supporting Member

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    I could be wrong (happens often), but IIRC, the audible difference between 4ohm and 16ohm settings is not noticeable, and more of an option on the cab to accommodate different amps.
    If the JVM210H can do either, you can hook up the cab either way also.
     
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  3. Dillon Keough

    Dillon Keough New Member

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    I’d definitely recommend hooking up the JVM210H from its 16 ohm jack to the mono 16 ohm jack in the cab.
     
  4. RLW59

    RLW59 Well-Known Member

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    There are three common opinions.

    1) Doesn't matter.

    2) 16 ohms uses all the coils on the transformer so it gives the best tone.

    3) For the same output power, 4 ohms pushes more current at lower voltage (Ohm's Law), and speakers are primarily driven by current, so 4 ohms gives tighter and stronger bass response.

    #2 was proposed by Gerald Weber in a very influential early book about how tube guitar amps work. So it's widely believed, even though there's no real theory or evidence to support it.

    #3 is based on electrical fact -- transformers work by changing the voltage/current ratio and speakers respond to current. Under ideal conditions, if you listen very carefully, you may hear it.

    #1 is based on most people's real world experiences. Most people never notice a difference. And of the people who notice a difference, most of them decide it's too insignificant to matter.
    ---------------------------
    But you might as well try both ways.

    Just be very sure that you understand the 1960's switching jackplate, because the way you plug into the cab determines which amp output you use.
    ----------------------------
    People often point out that the 1960 switching jackplate is prone to malfunction and that you should hardwire it for whichever impedance you prefer.

    But I get the impression it's a new cab with warranty, so you might as well experiment with it during the warranty period.

    When I get a new cab I always use a multimeter to check the resistance before I connect it to an amp. When I had a Genz-Benz with a switching jackplate I checked it every once in a while just to make sure nothing went wonky.
     
  5. pedecamp

    pedecamp Well-Known Member

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    Match your ohms, if its a 16 ohm cab which I believe it is, plug it into the amps 16 ohm input.
     
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  6. RLW59

    RLW59 Well-Known Member

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    1960 has a switching jackplate. Mono 4 ohms or mono 16 ohms, or stereo 8 ohms each side.

    Way back when, the 1960 started out with a single 16 ohm jack. And maybe some reissue models still do. But all modern standard 1960's have switching jackplates.
     
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  7. colchar

    colchar Well-Known Member

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    Really informative, thanks.

    It is used, but is in excellent condition. Despite being used, it comes with a warranty.
     
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  8. colchar

    colchar Well-Known Member

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  9. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    Yeah I would pick 16 too. That way you could add another speaker if necessary.
    No biggie. Just match it and go.
     
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  10. pedecamp

    pedecamp Well-Known Member

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    Last edited: Jul 4, 2021
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  11. RLW59

    RLW59 Well-Known Member

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    I hate to be argumentative, but if you only have one cab and plan to leave it stock, you might as well try both 4 and 16 ohm to see if it makes any difference to your ears. It doesn't stress the amp in any way.

    The 1960 switching jackplate fails in many different ways. Even if you always use the 16 ohm setting it can malfunction and give the wrong impedance. So you're not really safer using just the 16 ohm input. (Possible that using the 4 ohm jack occasionally will help keep the switching contacts clean and reduce the chance of failure.)
    -------------------------
    If I was going to hardwire it for a single impedance I'd choose 16 ohms for the flexibility of being able to add a second cab.

    (Unless I actually heard a difference and preferred 4 ohms. Then I'd wire it for 4 ohms, and if I ever wanted to add another cab I'd spend 10 minutes rewiring it to 16.)
    -------------------------------
    Most 1960 switching jackplates work perfectly forever. Marshall wouldn't use them on flagship cabs if all or most of them failed.

    Marshall sells more switching cabs than anyone else. It's likely that other companies designs have similar failure rates but we don't hear about them because there aren't a lot of other cabs out there.

    For me, there's zero need for mono/stereo and I've never really needed 4 ohms (I don't notice a tone/response difference between 4 and 16). So I prefer hardwired with virtually zero chance of failure.

    But again, most people leave their 1960's stock and never have problems. And if you leave it stock you might as well experiment with the extra features. Both your amp and cab can accommodate 4 or 16 ohms. It's simple and free to try both options, and it won't hurt the amp or cab in any way.

    I hope that in a couple of weeks after you've thoroughly compared both options, you'll bump this thread back up and tell us your conclusions.
     
  12. colchar

    colchar Well-Known Member

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    Thanks.

    And I will give it a bump to let you know what I think.
     
  13. Pete Farrington

    Pete Farrington Well-Known Member

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    Is that your hypothesis, personal experience, or have you got a reference for it? (The highlighted section, I’m not querying Ohm’s Law :) ).
    Whatever, even if it might be true for a single speaker (I’m doubtful), in this case it really can’t be correct.
    It’s the impedance of the cab that’s being switched, the impedance of the 4 individual speakers within it obviously remain unchanged.
    Hence for a given power input from the amp at either 4 or 16ohms, the current / voltage / power at each speaker is the same. What changes when switching is the ratio between current and voltage in the wiring between the amp and the cab.

    It may be worth noting that the voicecoils of regular guitar amp speakers are always made with 2 layers of windings. As 4ohm voicecoils require thicker wire than 8ohm voicecoils require thicker wire than 16ohm voicecoils, 16ohm voicecoils are the lightest (and so give the best high freq response). Hence 4ohm versions of the exact same speaker have a slightly worse high freq response, and so might be perceived as being bassier.
    Jensen provide full TS characteristics for each impedance variant of their speakers. These tend to align with the above info, which JM Fahey has posted on various fora / threads.
     
    Last edited: Jul 4, 2021
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  14. RLW59

    RLW59 Well-Known Member

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    Pete Farrington, I first read that idea from Mickeydg5 and because I'm somewhat simple I may have mangled the explanation of the concept and its effects. From Mickey and google, there are references that say that for the same wattage, higher current will make a speaker slightly louder, with tighter control of the cone.

    But I don't see what the number of speakers in the cab have to do with it. The output transformer sends more current/less voltage into a lower impedance load. When that current x voltage gets to the cab's input jack, it gets equally divided among the speakers (assuming all the speakers are the same impedance). The speakers don't change the current/voltage ratio, so each speaker will be seeing higher current/lower voltage compared to using the cab's 16 ohm jack.
    ----------------------------
    Personal experience -- in one of my walls of text I briefly mentioned that I've never noticed any difference.

    But to expand on that, I've had cabs of different impedances but when I compared them there were many other uncontrolled variables. Back when I had a G-Flex with a switching jackplate it never occurred to me that there might be a difference so I never tried a direct a/b.

    So I'm sort of living vicariously through colchar. He has a perfect opportunity to compare 4 vs 16 with limited variables.

    (There are theories that parallel, series/parallel, and series affect the interaction of speakers differently, so there really isn't a way to eliminate all variables.)
     
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  15. Pete Farrington

    Pete Farrington Well-Known Member

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    Ok, I’ll look into that.
    But all else being equal, something that’s lighter is easier to control than something heavier.

    No, for a given power output from the amp, each speaker within the cab will get the same power, whether the rig (ie amp and cab) is set at 4 or 16ohms.
    How could it be otherwise? ie each speaker stays at 16ohms, and the power from the amp is the same, therefore the current in each speaker must be the same.
    Of course the current flow between amp and cab will double in 4ohm mode. But each speaker will get the same current either way. ie in 4ohm mode they get 1/4 of twice the current. Whereas in 16ohm mode each get half the current.

    So for 100W input, at 16ohms that’s
    100 = i x i x 16,
    100/16 = i x i,
    therefore i = 2.5A. Each speaker gets half of of that, so 1.25A each.

    At 4ohms,
    100 = i x i x 4,
    100/4 = i x i,
    therefore i = 5A.
    Each speaker gets 1/4 of that, so 1.25A.
     
    Last edited: Jul 4, 2021
  16. RLW59

    RLW59 Well-Known Member

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    Yes, each speaker gets the same watts either way.

    But the "same watts" doesn't mean the "same volts times current". 50 watts can be 50 volts times 1 amp, or 1 volt times 50 amps, or 500 volts times 0.5 amps.

    For a transformer to send the same wattage into different impedance loads, it changes the volt/current ratio. Higher current/lower voltage into 4 ohms, lower current/higher voltage into 16 ohms. It's nowhere near as drastic as the "simple math" examples I gave, but transformers send different volt/current ratios into different total loads.

    After the transformer, no transforming gets done. Each speaker will get higher current/lower voltage or lower current/higher voltage depending on the total load the transformer sees.
    -----------------------------
    Edit: posted this before you edited to show maths that say the current at the speakers is the same.

    Like I said, I'm kind of simple and now I'm more confused than ever. Sometimes I misunderstand things I've read, and sometimes when I try to repeat things I've read I garble them.
    ---------------------------------
    Since I can't dazzle with brilliance, I can always baffle with BS:

    As I mentioned, some people repute that parallel, series/parallel, and series all sound a little different. So another reason why 4 and 16 on a 1960 might possibly sound different.
    --------------------------
    The reality is no one ever listened to Jimi or Eric and thought, "what a shame -- if they had used 8 ohm cabs so they could have used the 4 ohm output, they would have sounded so much better".

    I'm really just saying I've heard 3 different conflicting claims and if someone has the opportunity to compare different safe options, they might as well try it and find out for themselves.
     
    Last edited: Jul 4, 2021
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  17. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    I don't believe OP is playing in stadiums and I suspect all that tech stuff will be immaterial in the real world. Try each and see. He picks the one he likes if he even hears any difference at all.
    It really is that simple.
     
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  18. EL 34

    EL 34 Well-Known Member

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    Marshall's 1959HW owners manual states that 16 ohm is tighter and 4 ohm is looser. I always use 16 ohm.
     
  19. colchar

    colchar Well-Known Member

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    The best is when they are loose, but feel tight. Wait a minute. Are we still talking about amps here?
     
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