Ohms... just a simple yes or no.

Discussion in 'Marshall Amps' started by JCMRobbo, Jul 9, 2020.

  1. mickeydg5

    mickeydg5 Well-Known Member

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    Is there a vaccine for this mono you speak of?

    Wait, there is no vaccine for that shit!
     
  2. RLW59

    RLW59 Well-Known Member

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    After you get a meter you should check all your speaker cables. And verify that all your speakers are in phase. Remove the push-on speaker connections and solder the wires to the speakers. Upgrade to thicker speaker wire while you're at it (though AMS used to say you should switch to thinner wire in the cab because it sounds better). And... and...

    Yeah, ask for a simple answer and every one of us is going to add more little things until it's overwhelmingly complicated.

    Simply... Verify that your 212 with two 16 ohm speakers is actually 8 ohms total (will probably read an ohm or two lower/higher on your meter) and then set your amp to 8 ohms with the 212.

    Verify that your 1960's 16 ohm setting is actually 16 ohms (+/- a couple of ohms) and set your amp to 16 ohms when you use the 1960.
     
  3. Chris-in-LA

    Chris-in-LA Well-Known Member

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    That member just re-emerged today to berate someone else in that same thread.
     
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  4. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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    yeah, it's called stereo... :)...
     
  5. neikeel

    neikeel Well-Known Member

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    I confess to being a ‘bear of little brain’ and keep things simple. I only have 16ohm cabs and 16ohm attenuators i keep my amps that have selectors on 16ohm options (yes even the window ones! But they are tight and secure).
    I converted my ‘modern’ Marshall 4x12 to mono by removing the stereo switch and putting in the witches hat socket to avoid tears.
    Still need to have the discipline/routine of head-Attenuator-cab-power in - signal in sequence before switching on.
     
  6. mickeydg5

    mickeydg5 Well-Known Member

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    Stereo Vaccine, good band name if done stereoed. :D

    On another note, most who contract mono probably stay in their rooms listening to the stereo for weeks.
     
    Last edited: Jul 10, 2020
  7. 67mike

    67mike Well-Known Member

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    You can run the amp into a higher ohm rated speaker....ie 16 ohm speaker with 8 ohm amp setting......BUT NEVER EVER run an amp into a lower ohm setting....ie do not run an amp set at 8 ohms into a 4 ohm speaker.

    I do this all the time with different amps.

    Mesa Boogie also says the above is true in their manuals.
     
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  8. JCMRobbo

    JCMRobbo New Member

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    At rehearsal it started melting like burning and then one of the 4 valves started turning blue (which isn’t too bad) anyway every time I chugged it flashed blue and then started buzzing and then went all different colours so decided to turn it off before it actually blew the valve.

    dirty.
     
  9. Jethro Rocker

    Jethro Rocker Well-Known Member Silver Supporting Member

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    Ah so you blew a valve. Nothjng to do with speaker set up then.
     
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  10. JBA

    JBA Well-Known Member

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    Now here is what you should have done:
    Next time record the jam session. When flashes occur, crank it up louder and keep playing until the amps explodes into fire.... finish the song regardless of how crazy it gets. Unplug the amp and put the burning amp out with a beer after you take a swig. Post on YouTube, go viral, and take that money to buy any new amp you want. Probably a good career booster too.
    And I’m an electronics guy..
     
    Last edited: Jul 14, 2020
  11. guitronics

    guitronics New Member

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    Make sure that you have a Speaker cable,and not an instrument cable on your connection between the head and the speaker...use the ohms range on your VOM to test your speaker cord for shorts and opens.

    You do this for opens" tip to tip shows 0,or close to zero ohms...(on the lowest scale),and sleeve to sleeve the same".

    For shorts " Tip to sleeve shows infinite ohms". These are the "good cable" readings.

    You can tell if it's a speaker cable if it's marked on the cable jacket "speaker"...otherwise (if it isn't marked) open one end and see if it is shielded...if it is,you will have an instrument cable.

    You can tell if it is shielded by looking at the sleeve wire....if it is a bunch of wires,it's shielded (for instrument inputs)...if both wires are single conductor,it is a non shielded,speaker wire(cable)....NEVER use an instrument cable on a speaker output.
     
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  12. Dogs of Doom

    Dogs of Doom Moderator Staff Member

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  13. Lt.Dan

    Lt.Dan New Member

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    Think of it this way. A piece of copper wire in a straight line will have some resistance to current flow. If it's 2 ft long it'll have very little, if it's a mile long it'll have more, ohms that is. A single coil pickup has about 6-7k ohms. A humbucker will have about 11-14k ohms.
    The coil in your speaker is the same. If you put a ohms meter on a 8 ohm speaker it'll read 6-7 ohms because your using dc to do the test. (the battery in the meter) Like someone mentioned earlier. But your sending a ac signal to the speaker from the pickup to the amp, to the speaker. The speaker reacts differently to different frequency's and cause a emf force back at the amp.
    So to come up with an impedance number they put all the frequency's your pickup can produce through the speaker and measure the resistance to each. Then average the those numbers to call it the impedance.
    Speakers wired in series add up. In parallel they cut in half.
     
    Last edited by a moderator: Jul 16, 2020
  14. DerekLicon

    DerekLicon Member

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    If it's the 1960a with the switch in the back switch it it MONO and plug in to the 16 ohm side.

    You can use whatever plug on the back of the head itself 4, 8, or 16----> single 16 ohm cab but it will be quieter on the 4 and 8 settings. Just dont go try running the cab on 4 ohms mono and plugging into the 16 ohm jack on the back of the amp.

    I measured the Resistance for the 1960a that I have and the ohms were dead on in every setting. Some guys have talked about the switch failing though so to be safe just measure it.
     
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  15. JBA

    JBA Well-Known Member

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    Ok, ok, I did go a bit to far with the wasting a beer part. :D
     
  16. El Gringo

    El Gringo Well-Known Member

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    Bright and early this morning this topic is making my head hurt .
     
  17. MarshallDog

    MarshallDog Well-Known Member Gold Supporting Member

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    Resistance (ohms) is used when applied to DC circuits and Impedance is used when applied to AC circuits. An AC circuit is a sine wave which is always changing so a true impedance value has the resistance and the angle associated with the changing sine wave, blah, blah, blah!

    Anyway, here is a good read about these two resistance terms and you can see how it relates to a speaker seeing as a speaker has a magnet with a coil wrapped around it.

    https://www.physlink.com/education/askexperts/ae517.cfm

    I went to college for Electrical Engineering and this was one of the tougher concepts for me to grasp. I dont use it anymore in my daily job so I have become rusty with it.

    Enjoy and have fun!
     

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