Celestion G12-75 + Jmp 2203 Help

Discussion in 'The Squawk Box' started by 74Evan, Nov 9, 2017.

  1. 74Evan

    74Evan Senior Member

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    My rig consists of a 1980 JMP 2203 and Marshall 1960B cab. Guitar is a 1974 Gibson Les Paul loaded with Bill Lawrence L500 pickups. I've come to notice that when I play with the amp cranked (master volume 9, pre-amp volume 8) it sounds amazing but when the master volume is under 4 it sounds very shrill with a harsh top end. Is this a result of 75 watt celestions? I like how they sound at loud volumes. A lot of bottom end and very tight. However low volumes it just sounds shrill and weak. I've heard videos on YouTube where people only have their master volume at 1 or 2 and preamp 10 , and it sounds much better than my amp with the same settings. I've been thinking about trying out the 25 watt Greenbacks or maybe trying an X pattern of the greenbacks with the 75 watt speakers, but I don't want to loose that tight clean sound the g12-75's give me and the bottom end which I really like. Any suggestions? Maybe I should try changing my settings when I play at lower volumes and roll back the mids and the treble? I like bright tones with a lot of midrange but also want it to have a tight bottom end without the shrill highs.
     
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  2. mmd

    mmd Senior Member

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    In my experience, the G12-75 likes to be HAMMERED. I have always had the same issue you are describing - beautiful when my amp is cranking, shrill and harsh at lower volumes. My fix? Change settings when playing quiet, or use a different cab.
     
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  3. RAG7890

    RAG7890 Premium Member

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    Bogner's Uber Cab is great..........X pattern with V30's & G12-75's.

    :cheers2:
     
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  4. Ginger Beer

    Ginger Beer Senior Member

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    I have an 80 jmp 2203 as well. While the g12-75’s are not my favorite for this amp, changing the speakers is not going to solve your problem.
    I tamed my bright end by performing a simple operation on the amp...I clipped one leg of the bright cap. Snipping one leg made the amp’s treble control functional instead of having to shut it all the way off.
    You can read all about the 2203 “brite cap mod” or clip on the internet but this 5 minute reversible mod was the best thing I ever did. The treble is controlled now and the amp just sounds more ballsy, far less fizzy, at low volumes
     
  5. Ginger Beer

    Ginger Beer Senior Member

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    I’ll add that I would change your speakers only after you hear what your amp “can” sound like. After that, I would suggest some type of greenback variant if your looking for a more “classic” sound. I settled on some G12-30h myself.

    Also..the mod is not difficult at all. Screwdriver and a set of wire snips is all you need but, they’re are leathal voltages inside your amp so take it to a tech if you hsve any doubts at all. I can’t imagine them charging much as it literally takes 5 minutes.
     
  6. C_Becker

    C_Becker Dat Gibson smell Premium Member

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    This. Using my Marshall JCM800KK, the G12-T75s alone sounded harsh and shrill to me, too much top end.

    Swapped out two of them for V30s, et voilá - perfect sound
     
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  7. Big John

    Big John tastes like chicken V.I.P. Member

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    I've always felt that 2203's/2204's sounded the best with greenbacks or blackbacks. As for the 75's, I put them in the same catagory as the G12-M70...that would be the "Sell them quick" catagory.
     
  8. Mr Insane

    Mr Insane Senior Member

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    I have the 1960a with those speakers, no complaints against them at all.
     
  9. EndGame00

    EndGame00 Senior Member

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    Greenback + G12T75 is actually great combination for older Marshall amps.... I actually prefer this combo than Greenback/V30....
     
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  10. rogue3

    rogue3 Senior Member

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    Nice rig!

    I have an early 80's JCM2203.Very similiar circuits.Mine does not have what you describe.(ears not-with-standing ;) )

    I can't comment on your speakers,except to say if those 75 cones are well broken in,the treble spike is reduced.I have played them many times,but currently play my 2203 through a 1982 lead cab loaded with original vintage G1280's.They are a warmer speaker without annoying treble spike,but very tight fat bottom end...with authority.More oomph than the 75's.That is traditional for 1982 cabs from the beginning,afaik.

    As for the 2203. They are traditionally loaded with Dagnall transformers,and, ime lack the harsh top end that Drake loaded 2204's of the early to mid 80's had. I have modified my early 80's 2204 with great results in taming shrill..but from day one,i have not needed to touch my 2203,in any way.It sounds perfect,to these ears.

    Is it the Dagnalls in my 2203? Is it the speakers? idk, but ...but...in the case of my 2203 ,there is one more thing. Reviewing the chassis and circuit when i bought it,it had a small modification...the bright cap on the preamp volume was removed.

    This is easily done, you don't even have to remove it entirely,just snip one leg on the cap,bend back a little to ensure no contact, & leave it in place. If you don't like the results, put the leg back in place,a little dab of solder and back to stock. I have also played with the values and composition of the bright caps on those jcm's.that can also bring that high end down, while keeping the tightness a band pass cap in this application gives, if you play with the preamp volume at values less than 10(i do typically play with preamp at 4)

    Note that when the preamp volume is maxed out,the cap no longer impacts on the circuit. So if you have this problem with the preamp maxed out,this won't solve the issue,look elsewhere.

    I believe i used a silver mica in my 2204 on the preamp volume, because sometimes removing the cap entirely can make the amp too muddy.But with my 2203, and no preamp cap, the sound is golden! Let your ears decide.good luck...a great amp,one of the best!

    edit: oops,i just read ginger beer...what he said.:D
     
    Last edited: Nov 13, 2017 at 6:05 PM
  11. EndGame00

    EndGame00 Senior Member

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    A very few players have used this mix before:

    Classic Lead 80 and G12T-75 or Vintage30...a buddy of mine has this pair-up on his 4x12 with a Hiwatt DR103 (instead of Fane speakers) - talk about ice cream headache brightness...
     
  12. Duane_the_tub

    Duane_the_tub Senior Member

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    +1

    Toss a V-30 into there, sounds like it would add exactly what you are looking for.
     

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