Some Mods for Marshall Class 5

Discussion in 'The Squawk Box' started by Lyle Caldwell, Jan 18, 2011.

  1. tweedman2001

    tweedman2001 Senior Member

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  2. jshakes

    jshakes Junior Member

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    Thanks.
    My other question was how to wire the bass switch.
    If I understand correctly, The switch and the 1M resistor are in parallel to one another and the cap goes to ground. How does this work? I guess when the switch is open the resistance is high enough that none of the signal goes there?

    Iron Broadsword, how much of an improvement was the cap and the tonestack change? Also has anyone turned R13 to 100k

    Am I right to say that this would work as intended for the gain switch? The idea being if the switch is open the signal will go through 230k and if it is closed it will only go through 100k? I am new to electronics theory.

    Thanks!

    https://drive.google.com/file/d/0By8Gmjh4RArzaUpYeG05T1pYT0k/view?usp=sharing
     
  3. Iron Broadsword

    Iron Broadsword Senior Member

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    I did most of the mods all at once, and when I fired it up it wasn't dramatic like a different amp, but it really just fixed the voice of the amp. I could hear right away all the individual improvements, like the gain frequency making the bass cleaner, and the tone stack giving the amp more hunk in the mids and real nice and gritty highs like the plexi's of olde.

    I definitely recommend doing it all though. I actually went and modded my other class 5 the same way except I skipped the two switches and just hardwired the more highs / less lows. It's useful to have on a switch, but I don't need two like that. Anyways, now I gig both amps in a Y formation and just use my guitar volume to get all my tones. With the extra highs in the amp and proper 50s wiring, you can get all the loud cleans you need. Tone heaven, baby!
     
  4. jshakes

    jshakes Junior Member

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    Thank you. Last question is can anyone explain to me how to wire the switch. The switch diagram doesnt help me unfortunately. And is my diagram correct?
    I am confused as to why the parts list has an ON-ON switch not an ON-OFF one
     
  5. tweedman2001

    tweedman2001 Senior Member

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    This is the one that you need. In one position it goes thru the 1 meg resistor and the other position it bypasses it. Need a three pole On-On for the center contact. An On-Off would simply open the circuit. (Hopefully I explained that ok. Christmas Cheer ya know) :D

    I've rethought this after jshakes query. See below
     

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  6. jshakes

    jshakes Junior Member

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    Merry Christmas. Enjoy time with the family!


    Thank you so much. That diagram helps a lot. So If I understand correctly, the term "ON-ON"
    means the middle is always connected to either the left or the right? Negative is facing ground right?

    Why use an ON-ON switch if one side isnt used at all?

    To clarify both the cap and resistor are connected to the center terminal and this system is parallel to R18? I am sorry for all the questions but I hope to understand the theory a little before I open it up.

    The treble switch makes more sense than the bass one to me, because the bass one has an unused terminal.
    R18 still connects to ground separately right, and so should the new capacitor?

    If I wanted to make a gain switch then, using a different value for R13
    Could I do

    Middle - R13
    Left Wire to rest of circuit
    Right wire to 120k resistor to rest of circuit?
     
  7. tweedman2001

    tweedman2001 Senior Member

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    Ok my brain hurts too much. Back to the eggnog! Merry Christmas! :dude:
     
  8. Iron Broadsword

    Iron Broadsword Senior Member

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    If I remember right, ON-OFF grounds it out when in the off position, which is functionally very different than just not connecting the wires.
     
  9. tweedman2001

    tweedman2001 Senior Member

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    That would be true but the way the switch is wired it effectively puts the 1M in or out of the circuit. It's not totally disconnecting the circuit. I believe it would work with an On-Off switch as wired.
     

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  10. jshakes

    jshakes Junior Member

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    Thank you so much, I finished the mods it sounds amazing. However I rotated my OT 90* and the amp still hums loudly. Any tips. It is clearly in the background, but it is there with no guitar, same as before the mods, and that makes me hesitant to record with this otherwise kick ass amp


    I think I get the bass switch now. The Cap is always in, but the resistor switches in and out. When the resistor is in, the resistance is so high the essentially no current goes to the cap, basically bypassing it. Whereas when the resistor is out the cap does its thing
     
  11. gouna

    gouna Member

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    Hello

    I installed the ClassicTone OT, and I added an 8 ohm output ext speaker on my combo.

    So, If I plug my 2x12 cab in the 8 ohm output, the sound comes out of the internal speaker, but not of the cab.
    No problems with the stock 16 ohms output.

    If I unplug the internal speaker, the output 8 ohms work.

    Do you know where does the problem?

    [​IMG]

    [​IMG]

    [​IMG]

    Thank you.
     
  12. gouna

    gouna Member

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    I added a switch on one of the internal speaker cables.
    If I cut the internal speaker, so my 8 ohms output ClassicTone works.

    I recommend installing the potentiometer (25k) to R28 (33k), I would make a video of his influence on the tone.
     
  13. gouna

    gouna Member

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    Hello,
    here is a very little sound recording of my class 5 with the latest mods.
    Tayden true brit and celestion G12H, guitar is vintage v52 telecaster
    The volume is full (gain reduced R13 mod).
    I play on the low power mode + attenuator -21db (I can not do more today, I will register later without an attenuator and on the 8ohms output).

    I recording with a camera, so the quality is bad.

    https://djpod.com/gouna/selection1
     
  14. Sam1911

    Sam1911 Junior Member

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    Hi all! First post and it's both a heartfelt thanks to Lyle and all who've contributed, a couple observations, and (of course!) a question.

    First off, I picked up an M-2012-06 Class 5 a couple of weeks ago and I've loved it! Our first tube amp and I all of a sudden totally "get it!" It is so different from our solid state modeling amps -- night and day!

    Second, I just performed the mods as listed in member "Tab"'s updated list back on page 13 (post 387). So far I have not added the bright or bass switches, but they're soldered up and ready to go in next time I take her apart. Everything else on that list is done -- except that I didn't add the 100K and 330K resistors at R13, R23, and R11 for more clean headroom. Figured I'd play it for a while and see what I like first.

    So far I'm SO thrilled!

    I haven't had time to read all 40 pages, so I apologize if my observations or questions are already covered.

    My observations are:
    a) that the 470pf cap across R12 and the 68pf cap in parallel with R26 were already present; and
    b) that my stock ('11 dated) JJ EL84 rings like a dead light bulb when shaken (or played...:(), so a new Tung Sol is on the way; and,
    c) One of the terminals for the indicator light was hanging onto the PCB by a thread and popped out easily. Easy fix, but I'm fortunate it was still working at all!

    Here's the question: The sound is fantastic! Really made the amp pleasant across so many tones, and the bass and treble pots both make an enormous difference. However, the mids pot doesn't seem to really do anything at all. Like it might even be hard to tell that it was being turned if I was playing a chord and someone was turning it out of my sight.

    Is that normal? I can understand that there's a lot of overlap through the tone stack and the mids are really not nearly so adjustable as the highs and lows, but should I notice more of a change or does the mids pot really have a very subtle effect?

    Thanks!
     
  15. Handley

    Handley Junior Member

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    I recently acquired a used Class 5 (C5-01) and it is in the mail. Not sure if I am more excited about the amp arriving or finally finishing all 40 pages of this thread.
     
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  16. Sam1911

    Sam1911 Junior Member

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    FIGGERED IT OUT! :)

    I pulled the main circuit board again and started checking each connection, going through the list once more. And then I got to the part about soldering a cap ... what's that? BETWEEN LK18 and LK19? Oh! :doh: So doing a quick thread search to learn why I don't HAVE an LK19, I discover that the circuit was a little altered in the later models, and I have to solder in the cap, and the bright switch, too, across the legs of the Volume pot.

    And, voila! It works like MAD! What a beast! :dude:
     
  17. Daniel-R

    Daniel-R Junior Member

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    Whaha i'm late i guess... With owning a Class 5 and wanting to mod it. Great topic do and thanks for all the info, Lyle in the first place.

    2 question remain after reading all 40 pages of great info. are there any good suggestion regarding new tubes?
    and 2 The VVR mod.... where to order the parts/build instructions / complete kit?
     
  18. Sam1911

    Sam1911 Junior Member

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    I can at least give an opinion on the first question.

    Mine appears to have come to me with the original tubes still in it and all three either rattled or were badly microphonic by this point.

    I replaced the EL84 with a Tung Sol as some reading I did said they were a bit more robust than the stock JJ tube.

    I am replacing the 12ax7s with the JJ ECC803-S version as I've read they've sound really great in the Class 5.

    I've also read that they're prone to microphonics and might not last in a combo amp, but we'll just have to see. :)
     
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  19. Daniel-R

    Daniel-R Junior Member

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    Let me know how it works for you!
     
  20. Sam1911

    Sam1911 Junior Member

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    Well, they're in and I think they sound great! I feel like I can get a bit more out of the clean, trebly end of it with these.

    I've got those two held by the silicone grommets and bracket arrangement that's standard on the later model of the amp, and hope that will help them stay alive as long as possible.

    (The EL84 has to make it without, as it gets too hot for its grommet and I had to cut the old one out of the bracket as it was melted to the glass! A bit of a daft design.)
     

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