Roland Jazz Chorus 120, bass mod?

Discussion in 'Amps [BG]' started by henfjel, Dec 11, 2012.


  1. henfjel

    henfjel

    Joined:
    Nov 30, 2010
    Location:
    Norway
    I was trying out this Roland JC 120 the other day, and i really liked the sound with my bass! But, of course you can't push that amp far with a bass before the speakers go apart. So my question is, could I just swap the two with a set of bass speakers or will the signal from the bass just fry the circuitry of the amp?
  2. mc_muench

    mc_muench

    Joined:
    Sep 28, 2010
    Location:
    Milwaukee, WI
    You should be good to go if you swap in bass speakers. It wasnt designed with bass frequencies in mind, but if you like how it sounds, thats what matters.
  3. gumtownbassman

    gumtownbassman Supporting Member

    Joined:
    May 7, 2007
    Location:
    New Zealand
    The JC-120 is an open back cab design, and runs 2 x 60 watt amps in stereo.
    [​IMG]
    They will need to be closed and ported separately for each speaker. Changing the drivers will also change the nice sound you are getting.
    There is also the JC-160
    [​IMG]

    or you could get a modeller like the Boss GT-100 and use a powered monitor or power amp, the GT-100 does a good JC-120 emulation.
  4. mc_muench

    mc_muench

    Joined:
    Sep 28, 2010
    Location:
    Milwaukee, WI
    I stand corrected, you will need to cover the open back. You could port it, or leave it sealed, but that will change the sound compared to the open back.
  5. RickenBoogie

    RickenBoogie

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    Jul 22, 2007
    Location:
    Dallas, TX
    Overall, not a good idea to use guitar combo's for bass- no matter what else. Just find a good bass combo.
  6. BassBrass

    BassBrass

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    Jul 6, 2009
    Location:
    Boston MA
    Great amps that should be left alone...1st time I saw one when they came out, it was a bass player using it, and for those volume needs it was gorgeous sounding. We weren't sick of chorus yet...that was just beginning. It's an awesome high & mid freq reproducer though with The groovy chorus, and you could use it in a bi-amped system. even with a combo added. There might be a way to use it as a preamp too. Pretty heavy preamp.
  7. jnewmark

    jnewmark Supporting Member

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    Aug 31, 2006
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    Stax 1966
    Disclosures:
    Play guitar.
    Roland DOES make a 120 watt bass combo..... just sayin'.
  8. LowEZ

    LowEZ Supporting Member

    Joined:
    Mar 29, 2011
    Location:
    Central NJ
    The JC-120 also came as a head but they're not as common as the combos. I used to play at a club in the 90's where the back line was a JC-120 head into two Hartke 410XL's, and it sounded surprisingly good.
  9. teemuk

    teemuk

    Joined:
    Mar 1, 2011
    Replace "Jazz Chorus" with "Studio Bass".

    There you go.

    [​IMG]
  10. HolmeBass

    HolmeBass

    Joined:
    Jan 18, 2007
    Location:
    Charlottesville, VA
    I have a JC-120 (that I will never sell, used to rent it as back line and both King Sunny Ade and Johnny Cash have played through it, and just a few months ago Vieux Farke Toure) and it does make a nice bass amp for a certain clean open sound. I would say it's only useful for recording though, you're not going to get the volume you need out of it, and modding it will probably just ruin it.
  11. jungleheat

    jungleheat

    Joined:
    Jun 19, 2011
    Location:
    DC
    Now this is a mod I can get behind. There are probably 100s of thousands of thee amps and they're all assembly line produced with lots of PCBs, etc... but they sound killer.

    Don't use a nice old vintage one (they have a switch for the vibrato/chorus as opposed to a 3 position knob on the newer ones). Use a used but newer (last 10-15 years or so) one. The cab as is might be a little small for bass use, so it might be better to build a dedicated cab for it. In which case you could stick with the 2x12 format, but build a ported cab for them to go in, and use bass speakers.

    They do sound really good for bass as is, but I worry about over-extending the guitar speakers with the open back cab. A friend of mine turned his into a head for guitar, but obviously it could be used for bass too. The amp is only stereo when the chorus/vibrato is on, but I'm not sure how they handle that in terms of the wiring, and whether they bridge for mono or what. Anyway, they are plenty loud enough for a quite a lot of playing situations, including small to moderate sized gigs.

    I was using mine the other day as a preamp, running it into the power section of my Masters TVA 30 (30w all tube guitar amp but with way overbuilt transformers, ideal for bass) and into my big Acoustic 106 2x15. Sounded pretty great actually, although it was kind of late so I didn't crank it too much.
  12. jungleheat

    jungleheat

    Joined:
    Jun 19, 2011
    Location:
    DC
    Speaking of this, I really want to mod my MusicMan 65-112RD to have tone stack based on the JC-120. I made a thread about it a while back to start doing some research and see if anyone had done anything similar, but didn't get much info. I love the overall vibe of the MM (mainly for guitar, but it's not bad for bass either and sounds pretty rad with my Rhodes), but honestly, I HATE the Fender tone stack. HATE HATE HATE it. How do they sell these things? I mean, Twin Reverbs sound pretty rad, as long as you want THAT one sound or a close variant.

    Anyway, the tone stack on the JC is one of the better ones out there, and I think it would match up with the funky SS OD of the MusicMan better than the stock tone stack. Does anyone know if it would be basically as easy as just swapping out some component values or is it a lot more involved than that? Guess when I get closer to being ready to actually get this done, I'll have to find a MM and/or JC forum to get more specific info on what to do to make it work.
  13. SirMjac28

    SirMjac28 Patiently Waiting For The Next British Invasion Gold Supporting Member

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    Aug 25, 2010
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    The Great Midwest
    Ok seriously how much do you want name your price sir :)
  14. Wally Malone

    Wally Malone

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    Mar 9, 2001
    Location:
    Boulder Creek, CA
    Disclosures:
    AFM International Representative
    My wife uses the JC120 as her main guitar amp and she also has a Roland synth set-up she uses with it. In addition she also owns one of the JC120 heads. I've also seen keyboard players using this amp.

    Wally
  15. lowphatbass

    lowphatbass **** Supporting Member

    Joined:
    Feb 25, 2005
    Location:
    west coast
    The JC-120 is what it is. Crisp and clear, well built and pretty heavy. They put out a decent amount of bottom for a 120w SS guitar amp. The size of the cabinet would probably have limitations regardless of what speakers you used or how you sealed/modified/ported the back. I'd say it's more useful for guitar or keys. I remember hearing stories about Jaco using Joni Mitchell's guitar amps, loving the mids and chorus and continually blowing speakers and really pissing her off....I could be wrong though, these were just old stories
  16. winston

    winston

    Joined:
    May 2, 2000
    Location:
    Berkeley, CA
    My brother had a JC-120 in the '80s. It sounded great with bass at low volumes especially close against a wall/corner.

    From what I hear the more recent versions don't sound the same after they ditched the speakers with the aluminum dustcovers.

    You could consider finding one of the smaller combos like the JC-50 (1x12), JC-55 (2x8), or JC-77 (2x10), just use it for top end character with your regular bass rig.

    Roland also made a bass preamp, I kinda kick myself for not buying one I found in a Chicago pawnshop in the '90s.
  17. bassmachine2112

    bassmachine2112

    Joined:
    Mar 23, 2008
    Roland made higher power combos a few years ago.
    they are very good and you can get a powered extension cab as well.
    DB 700,D-BASS 210,115 AND 115X,x is the extension

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