The Official Marshall Studio Classic Thread Sc20

Discussion in 'Marshall Amps' started by scozz, Jan 26, 2019.

  1. frankyfal

    frankyfal Well-Known Member

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    I haven't been here in a while. My GAS issues really re-surfaced with the Origin line. Good to read all the info and see the usual posters. When I read about this new line I had to come back. I am torn about which one to buy. The JCM800 demo really cleaned up well, almost plexi. I am unsure about the headroom at that lower gain stage though. The plexi had that tone I try so hard to squeeze out of all my gear though. I guess pushing the plexi with my OFA or a Timmy is an option at bar volume, but the JCM800, if some what loud enough with just a little dirt would allow me to just ride my vol pot. Ill wait on reviews and demos here.
     
  2. Fender

    Fender Active Member

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    given the complexity and the numer of components on the PA side, not sure that's the only thing done... on traditionnal 2204, there are more components on the preamp side than on the PA side, this is largely the opposing way there...
     
  3. pedecamp

    pedecamp Well-Known Member

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    Interesting, I never heard that, I thought if an amp was wired for a tube type that was it! So I can put a pair 6550's in it if I want?
     
  4. Fender

    Fender Active Member

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  5. pedecamp

    pedecamp Well-Known Member

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    That's cool, I just never heard that before.
     
  6. pedecamp

    pedecamp Well-Known Member

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    I had to have my 2204 rewired to swap from 6550 to EL34, I don't know the science behind it but I wouldn't think I could swap tubes around unless they were direct drop in like you mentioned - EL34, 6CA7 KT77.
     
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  7. pedecamp

    pedecamp Well-Known Member

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    I don't know man, I'm still skeptical. Auto bias is an automatic task, changing tube types to me is something totally different. I'd have to hear or read something from Marshall before I tried swapping tube types that weren't direct drop ins.
     
  8. Fender

    Fender Active Member

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    because a 2204 is fixed bias not cathode bias
     
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  9. Fender

    Fender Active Member

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    maybe wait for direct comparisons to verify if the PA is really the same as the mini-jub, but in the case of the latter, it comes from one of the designer of the amp himself : http://www.marshallforum.com/threads/marshall-mini-jubilee-2525h-review.90343/page-2#post-1528021 (santiall was an amp designer at Marshall at the time)
     
  10. johan.b

    johan.b Well-Known Member

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    Going by the pics. Individual 5w 150 Ohm cathode resistors on power tubes, so cathode biased.
    stand by switch selects different windings from transformer. It's power scaling, not triode/pentode
    J
     
  11. Fender

    Fender Active Member

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    PA and preamp use different windings instead of dropping down from a unique B+ , then ?
     
  12. pedecamp

    pedecamp Well-Known Member

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    Right, I'm trying to wrap my brain around this, whats the difference between dropping a different tube in and manually biasing vs dropping that same different tube in and the amp auto biasing, I would think none. But at the same time I had to have my amp rewired to switch tubes types. I'm gonna need some more background on this to understand it.
     
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  13. Fender

    Fender Active Member

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    well cathode bias is sometimes referred as self bias cause it naturally gives stability in voltage/current flowing to the cathode
    Yet some say (and they're "right") that each type of tube need its resistance to get the point of stability right.
    And I'd say it's kind of true when running at full tube capability. But in this kind of low voltage PA, the margin gets high as even with the "EL34" resistance needed, isn't likely to run a 6L6 that hot or a 6V6 that cold (the risk is higher at 50W yet some manufacturers still claim to accept 6L6 AND EL34 with no resistor switch needed, they simply put a intermediary value which allows to run "quite good" any of those two tubes...)
    There's still much debat about bias, but I would say there's no such thing as a "precise bias" and I defy anyone to be able to recognize by ear a 10% (or even 20%) bias difference in a double blind test. Bias is just important to not burn a tube or not run it too cold where it gets audibly bad, but the margin of "sounds good, make no difference" is large
     
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  14. MaskingApathy

    MaskingApathy Active Member

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    I would be interested in hearing KT88s in this amp. Would be fun to try all the different tubes and see which I like best.
     
  15. marshallmellowed

    marshallmellowed Well-Known Member

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    Marshall uses the term "Power Reduction", in reference to these amps. They've not made any references to "Power Scaling" (that I've seen). "Power Scaling" is typically variable, and not limited to 2 modes (Hi/Lo).
     
    Last edited: Jan 29, 2019
  16. scozz

    scozz Well-Known Member

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    :lol: :thumb: Yup, I know what you mean!
     
  17. marshallmellowed

    marshallmellowed Well-Known Member

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    I've not seen any schematics of these amps, but according to Marshall, the "Power Reduction" is "Pentode/Triode". Maybe Steve is incorrect (mentioned just after 1:30)...

     
    Last edited: Jan 29, 2019
  18. Fender

    Fender Active Member

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    Saw this too, but steve is quite unreliable when it comes to technical details it seems (DI conpensated or not ? he said the contrary to the user manual) whereas Santiago has designed the basis of this power amp (even if they could have changed it since he left)
     
  19. johan.b

    johan.b Well-Known Member

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    I heard it too, but look at the pics. Clearly two different windings on switch, not going to the tubes but to rectifier.. also, it looks like the di. Is fed from an opamps with filters around it.. I'd say emulated, but who knows..
    J
     
  20. marshallmellowed

    marshallmellowed Well-Known Member

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    You should probably contact Marshall. Let them know that their spokesman is "quite unreliable", and that they need to add "Power Scaling" to the list of features for their studio amps. Good luck.
     

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