How does a jtm 45 work?

Discussion in 'Amp Central Station' started by Bikerider20, Sep 27, 2021.

  1. Bikerider20

    Bikerider20 TDPRI Member

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    So I’ve been looking at Marshall amps, I’m a fender amp guy I love the cleans of the twin and the deluxe and the super but I’ve been hearing Marshall clean tones and they sound really rich and lush and I was wondering what the presence knob does on the amp and what is the difference between the two 1 channel and the two 2 channel inputs and volume knobs? I know that Marshall’s can use kt66 tubes and el84 tubes and 6550 tubes and was wondering how they are different tonal wise and is it attainable to get fenderish cleans by using the eq?
     
  2. loopfinding

    loopfinding Friend of Leo's

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    Just off the top of my head...

    -the preamp stages are voiced a little differently with bypassed freqs

    -the tonestack is like a tweed bassman, less of a mid scoop than a BF and higher center freq for bass, cathode follower to drive it without a recovery stage, and later in the chain (right before the PI).

    -the presence is just a filter on the negative feedback, like in most amps.

    -one channel has a bright cap on it to bypass some treble frequencies at the mixing stage. the two inputs are the same as fender (hi/lo), plugging into one halves the series resistance before hitting the grid of the first stage, so hitting it harder.

    -Celestions are way more mid forward than jensens, plus a closed back cab on a Marshall usually.

    IMO they sound less “open”/more focused and are more snarly and spiky when driven. I don’t think the tubes matter all that much vs the overall architecture + cab config. A tweed bassman sounds pretty damn close. And probably almost indistinguishable through a closed back celestion 4x12. There is some mysticism about the OTs on some years IIRC.
     
    Last edited: Sep 27, 2021
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  3. Bikerider20

    Bikerider20 TDPRI Member

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    In your opinion what blackface amp is very open sounding that does Hendrix well that’s the sound I’m going for
     
  4. loopfinding

    loopfinding Friend of Leo's

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    a tweed bassman is a little more american sounding on the count of the cab/speaker config than a Marshall...but not BF cleans. I think Hendrix used the blonde showman in the electric ladyland era somewhat. if you want the BF fender clean but still want to get your Hendrix on, a tubescreamer or Marshall in a box and a fuzz face will get you most of the way sound wise with the AB763 types (deluxe, twin, super, etc). Maybe you want to throw celestions in it too. I think faking the Marshall drive is easier on a BF than faking a BF clean on a Marshall.
     
    Last edited: Sep 27, 2021
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  5. Bikerider20

    Bikerider20 TDPRI Member

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    Well since the twin is my dream amp I’ll save towards one and I’m getting a fuzz face for Christmas so I’ll buy a ts808 for Christmas, but if you recommend a 6L6 BF amp that takes pedals better and breaks up at decent volumes I’m all ears
     
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  6. Bikerider20

    Bikerider20 TDPRI Member

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    Meant fuzz face for my birthday
     
  7. '64 Tele

    '64 Tele Tele-Afflicted

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    Twin is gonna be loud and clean. You will peel paint off the walls before it breaks up.
    JTM 45 is going to be closer to Tweed Bassman than any other Fender amps.
    A friend has a JTM 45 that I've played quite a bit with his SRV Strat.
    Marshall cleans are very nice....4 hole with channels jumped is how this Marshall amp comes alive.
     
    Last edited: Sep 27, 2021
  8. jball85

    jball85 TDPRI Member

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    Yes, you can get Fenderish top notch cleans from a 45, no problemo. However, I don't care to use my telecaster with my 45 too much due to the feedback. If you have noiseless pups, then it's not a problem. The JTM will slay with a Strat or LP. Cleans with a Strat are something to behold.

    The presence knob is kind of like another treble control.
     
  9. loopfinding

    loopfinding Friend of Leo's

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    The pro is sort of like a half power twin w/ a fixed mid. If you can dig 10s or a 15 you can also try the super or the vibroverb for the SRV-ish thing.

    But not having the BF clean is not the end of the world. The Marshall clean can be nice. Just a different thing.

    Obviously further away from a fender than a jtm45, but here at 4min:

     
    Last edited: Sep 27, 2021
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  10. arlum

    arlum Tele-Afflicted Platinum Supporter

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    In my opinion Marshall took the mid level breakup of the Fender Bassman and bumped up the gain to push the controllable breakup into "crunch". I'm not a fan of the original KT66 versions but have found certain tonal qualities of the later EL34 versions that truly separated Marshall from Fender tone. It's obvious that the tones of Jimi Hendrix could never have been created with a Fender amp. A huge part of the British invasion depended on this new Marshall tonality. That said ....... The British Invasion tone also included Orange amps, combined with a Marshall, to create the tone of "Free's "All Right Now" and Hiwatt on it's own to create the tones of The Who. 50 years later ...... I'm not a fan of EL34's. I prefer the Fender 6L6GCs, 6V6's or Vox amp type EL84's. EL84s are my all time favorite for the output section of a tube amp.
     
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  11. Phrygian77

    Phrygian77 Friend of Leo's Gold Supporter

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    The 5F6A is unique (edit: and the 5F8A), so you can't really lump it in with the other Fender tweed amps. It may have more mids than a blackface, especially with the mid control up, but it's still mid scooped.

    The main difference is the preamp architecture. Some of the overdrive comes from the preamp. A blackface amp is pretty much all power amp overdrive because none of the preamp gain stages really clip much.

    There were changes to the circuit that nearly all real 5F6As have (not included in the schematic or layout) that were not copied in the JTM45.

    The JTM45 also has more preamp gain (12AX7 vs 12AY7) and twice the NFB, so that encourages more clipping from the preamp.
     
    Last edited: Sep 27, 2021
  12. Timbresmith1

    Timbresmith1 Tele-Afflicted

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    If you can go somewhere and play a jtm type, do it. I like the Marshall clean, breakup and distortion sounds WAAAY better than the bf Fender amps. I’ve owned Bf champ, Deluxe,Princeton, Pro, Super and Twin. All were good, but the Marshall makes me smile every damn time.
     
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  13. Paul G.

    Paul G. Friend of Leo's

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    Since most of you never saw Hendrix live, I'm assuming you want to emulate his tone from recordings. Ha, joke's on you -- lots of Fenders in his recordings. Your best bet is to get an amp you like and spend your time working to get what sounds right to your ears. Also, practice, practice, practice -- a lot of his tone came from his technique and great R&B comping.
     
  14. ce24

    ce24 Poster Extraordinaire

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    TRAYNOR YBA1....JTM45/BASSMAN. 45 WATTS of TONE! PXL_20210924_163902193.jpg
     
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  15. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    To expand on what @loopfinding wrote in post #2...
    Each channel uses one half of V1. The anode of V1b is pin6 for input one, the bright channel. The anode of V1a is pin1 for input two, the normal channel.

    The bright channel has a bright cap on the volume pot and another cap bypassing the 270K mixing resistor. At lower volume settings the bright cap will let more highs through. At high volume settings the bright cap will not have much effect. Channel one will still be brighter than the normal channel because of the bypass cap on the 270K mixing resistor.

    For both channels, when plugged into the lower jack, the 1M input resistor is bypassed. The 68K resistors form a voltage divider. Half of the signal voltage is bled to ground. The signal is down about 6dB compared to the upper jack. One of the 68K resistors acts as the grid leak resistor.
    For both channels, when plugged into the upper jack, the 68K resistors are in parallel and act as a 34K grid stopper. The 1M input resistor is not bypassed, and it acts as a grid leak resistor.

    The volume pots are configured as variable voltage dividers. They attenuate the gain of each channel to the next stage.
     
    Last edited: Sep 28, 2021
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  16. Bikerider20

    Bikerider20 TDPRI Member

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    Any idea what fenders he was using in the studio?
     
  17. El Marin

    El Marin Friend of Leo's

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    Try a Marshall Origin 50

    They are Bassmans, JTM45 on the cheap.

    Actually I had a Bassman 59 LTD that I sold for a Origin50, really
     
  18. Mad Kiwi

    Mad Kiwi Friend of Leo's

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    Do you know what model Orange was paired with his Marshal amp for the All Right Now tone?

    I have been trying to get close on my L6 Helix and it's always missing something, that's a very interesting sound, to me at least.

    I could/will try and run a dual amp path to replicate a bit better. Having a clue as to what Orange amp would help considerably :)
     
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  19. Paul G.

    Paul G. Friend of Leo's

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    Definitely a Silverface Twin Reverb. Eddie Kramer says there was also a Blonde Showman. The recordings done at Electric Ladyland were reported to be mostly the Twin.
     
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  20. Wally

    Wally Telefied Ad Free Member

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    +1 on knowing what Hendrix sound one wants. He performed live with Dual Showmans in 1968. Here is a wild version of Purple Haze from that time….Dual Showman…
    Hendrix was Hendrix no matter what amp he plugged into, but I can hear a BF/SF Fender sound here….and it works.
     
    Last edited: Sep 28, 2021
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