Help...another question on ohms and watts

Discussion in 'Amp Tech Center' started by tweeet, Mar 1, 2020.

  1. tweeet

    tweeet Tele-Holic

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    I'm currently using a Roland JC 22 into a 2x10 cab with Eminence GA10 sc64's in with a 12 string electric...Byrds Beatles etc clean tones only. This set up isn't quite doing it for me...I was in love with the JC but now the love has gone ! I love the sound of a tube amp so I'm in the process of deciding what !
    I've tried reading up on watts and ohms but I just can't get it. The Eminence speakers are 20w and 8ohms. The amps I'm looking at are Bugera T50 (50w) Bugera V22 (22w) Vox night train (15w) and Hughes and Kettner tubemeister 18 (18w). All these as you can see have different wattage and Ohms outputs at the rear. So my question is would all of these be ok or which amp if any would blow up using my speaker cab...or which amp would blow the speakers ? Thanks. T50-INFINIUM_P0B47_Rear_B.png V22HD-INFINIUM_P0B0M_Rear_B.png night train.jpg download 2.jpg
     
  2. ClashCityTele

    ClashCityTele Tele-Afflicted

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    Stick with an amp 20W or less that has an 8ohm output.
    Your safest bet is the Vox. The H&K at a push.
    Forget the rest.
     
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  3. thankyouguitar

    thankyouguitar Tele-Meister

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    If each speaker is 8 Ohms, and you have two speakers, the total resistance will either be 4 Ohms when wired in parallel or 16 Ohms when wired in series. The amp you select should have either of those options in order to use your speaker cabinet. Also, it is not too difficult to re-wire speakers in series for parallel and vice versa.

    As for wattage, there are many theories on this that can perhaps be better provided by another user. I myself prefer to double the RMS wattage of the amplifier I'm using but I am not just going for Byrds clean tones....

    *edited to fix typo
     
    Last edited: Mar 1, 2020
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  4. scottser

    scottser Friend of Leo's

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    Can you show us a picture of the inside of your cab? Or do you know what the cab's impedance is?
    At a guess it'll be probably be either 8 or 16ohms and most heads will have those output options.
    Your cab should be rated at twice the wattage of your amp, so if you have 40watts worth of speakers then a 20watt amp is plenty for the cab.
     
  5. tweeet

    tweeet Tele-Holic

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    Two speakers are 8ohms each 20w
     
  6. Dacious

    Dacious Poster Extraordinaire

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    If you have two 8ohm speakers connected in parallel you have 4 ohms - connect to 4ohm outlet. Connected serial, 16 ohms. Connect to 16 ohm jack.

    The power handling adds - so the two SC64s will handle 40 watts connected either way. The tone may change wired serial vs parallel, because wiring serial for a larger value impedance engages a larger mass of wiring in the output transformer secondary. Try it both ways. You may prefer one over the other.

    The output transformer is actually correctly termed an impedance-matching transformer. It is only there to match thousands of kohm of resistance between the plates of the power tubes to 4, 8, 16 ohms at the speaker terminals so the whole power section of the amplifier 'sees' the correct operating characteristics.

    Because it's transmitting power in the form of AC volts/watts there's heat involved. So running the impedances mismatched will probably cause there to be more heat than designed for. It may shorten output transformer and tube life by minutes, hours, days, weeks or years but shorten life it will.
     
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  7. Dacious

    Dacious Poster Extraordinaire

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    PS - I'm not surprised you found the SC64s to not enhance the Roland. They are deliberately flavoured to sound like 60s US speakers for low wattage tube amps - low wattage, tight voicecoil gap with smaller magnet and paper voicecoil former. With the Roland you're looking crystalline clears for the chorus effect. Legends are probably a better choice as they're more open and neutral sounding.
     
    Last edited: Mar 1, 2020
  8. tweeet

    tweeet Tele-Holic

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    alas too late..these are what I've got
     
  9. thankyouguitar

    thankyouguitar Tele-Meister

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    Understood, but depending on how the speakers are wired together inside the cabinet, the total resistance of the cabinet could be either 4 or 16 Ohms. If you have a multimeter, you can determine the total resistance of the cabinet. Plug a guitar cable into the cabinet. Select the lowest band in the resistance sector of your multimeter (mine's 200 ohms). Now work with the end of the guitar cable that isn't plugged into the cabinet. Place one lead on the tip of the jack and the other on the sleeve. If it reads something less than 16 but more than 8, the speakers are wired in series and you want an amp with a 16 Ohm option. If it reads lower than 4 but more than 2, the speakers are wired in parallel and you want an amp with a 4 Ohm option.

    Really, you can get so deep with the stuff but only if you think it's fun. Here are a few wikipedia pages I refer back to from time to time:

    https://en.wikipedia.org/wiki/Series_and_parallel_circuits#Series_circuits
    https://en.wikipedia.org/wiki/Series_and_parallel_circuits#Parallel_circuits
    https://en.wikipedia.org/wiki/Nominal_impedance

    *edited because I forgot some words hah.
     
    Last edited: Mar 1, 2020
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  10. tah1962

    tah1962 Friend of Leo's

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    This is another option.

    upload_2020-3-1_17-8-17.jpeg
     
  11. tweeet

    tweeet Tele-Holic

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    interesting .....so with this the two Bugera's come back into the mix ??
     
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  12. tah1962

    tah1962 Friend of Leo's

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    No, just the 22 watt. The Z Matcher allows you to mix ohm loads. Example; 8 ohm tap out of your amp to the 2 GAsc64’s. Wired in parallel would be a 4 ohm load, wired in series would be a 16 ohm load. Set the IN of the Z Matcher to 8, and the OUT to 4 or 16 depending on how your cabinet is wired. This will save your output transformer from getting too hot running mismatched ohm loads.

    With the two GAsc64’s, your cabinet will only be able to handle 40 watts. You wouldn’t want to run a 40 watt cabinet with a 50 watt head. As others have said, a 20-22 watt head would be the max for your current speakers. You could safely run all the other amps you listed, except the Bugera 50 watt head.
     
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  13. tweeet

    tweeet Tele-Holic

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    Thanks for all the input...I'm a lot clearer on what's occurring now...finally this has come into the mix...sounds great on youtube..got lots of options on it...so ...who knows !! unnamed.jpg download3.jpg
     
  14. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    You're still missing the critical piece of information that has been mentioned - the impedance of the cabinet. Until you know how the speakers are wired, we're only making guesses.
     
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  15. tah1962

    tah1962 Friend of Leo's

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    This should give the OP a clear understanding of parallel and series wiring.

    @tweeet , just watch this video then look in your cabinet and it should become obvious if your speakers are wired in parallel or series.

    Just remember the formula;

    Parallel halves the load 2 8 ohm speakers = 4 ohms
    Series doubles the load 2 8 ohm speakers = 16 ohms

     
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  16. scottser

    scottser Friend of Leo's

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    OP - look at how your speakers are wired up.
    follow the cable from the cab's jack input. one lead will go to +, the other to - on one of the speakers.
    follow the lead from the + tab on the speaker. if it goes to + on the other speaker then it's wired in parallel and the load of the cab will be 4ohms.
    if the lead from the + tab goes to the - tab on the other speaker then it's wired in series and the load of the cab will be 16 ohms.
     
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  17. tweeet

    tweeet Tele-Holic

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    I've reconnected the JC speakers to it's original config as I'm selling it now...but I wired ( I can hear screams already for you tech guys ) each JC speaker wire + and - to a separate jack...speaker cable to separate jack inputs on the cab....and inside the cab separate + and - wires to each speaker...I would post pics but all my gear is now in the loft until the next gig ( the wife hates my gear being around the house !)....hope the diagram helps....this is why I asked about ohms and watts :):) thumbnail (3).jpg
     
  18. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Ah - it's stereo output. So 8ohms each side. You have it hooked up fine then.
     
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  19. tweeet

    tweeet Tele-Holic

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    At least I got it right then...no harm done
     
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  20. 1300 E Valencia

    1300 E Valencia Friend of Leo's

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    Sure, the stereo Roland JC-22 is hooked up correctly: one 8 ohm speaker to the right output, one 8 ohm speaker to the left output.
    Unless the new amp is also stereo, the two speakers will be wired either parallel (4 ohms) or series (16 ohms). The new amp needs to have a 4 ohm speaker out, or a 16 ohm speaker out, or two 8 ohm speaker outs.
     
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