Jcm800 2205 Muddy Tone

Discussion in 'Marshall Amps' started by Joe Hamilton, Jan 18, 2019.

  1. Joe Hamilton

    Joe Hamilton New Member

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    OK- I have a pristine '82 JCM800 2205 head that looks like it was bought and stored in a closet. It has a few issues that I'm trying to learn more about and decide if I should persue resolving them.

    Here's my rig setup: 2205 head run through a 1960 Vintage cab, 1999 Gibson LP Classic 1960 reissue. No pedals other than a tuner and noise gate run into the front. An MXR EQ, MXR Phase 90 and Caitlinbread Ecorec run through the effects loop. All my pedals run off of isolated power and I use Mogami cables.

    Here are the issues:

    1) It sounds real muddy in the boost channel. I mean flubbery like a cold bowl of oatmeal. The normal channel cranked breaks up pretty good but, c'mon, I didn't buy it to run that channel. It should be hair raising crunchy in the boost channel. Also, when switching between the normal and boost channel there is no volume change. it just sounds worse.

    2) In overall volume it's really not that loud for a 50 watt amp run into a 4x12. I have the exact same head in a combo ('86 4212) and it just SCREAMS and sounds exaclty like it should. It buries this poor 2205 in volume (and sadly tone too). This thing should be loud enough for Rob Halford to hear it 2000 miles away, right?

    Here are my 2205 settings (from L to R):
    MASTER
    Presence 8
    Vol 9
    Reverb 2

    BOOST
    Bass 3
    Mid 8
    Treb 9
    Vol 9.5
    Gain 10

    NORMAL
    Bass 7
    Treb 8
    Vol 8

    I've messed with the EQ settings to no avail. I also don't want to run OD, boost, etc pedals into the amp as a band aid, I want this thing to melt faces like it should. Any thoughts on how to get the 2205 to sound like the screamer it's supposed to?
     
    Last edited: Jan 18, 2019
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  2. Ufoscorpion

    Ufoscorpion Well-Known Member

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    What sort of valves has it got in it , I've found jj's and groove tubes to make an amp sound really dull .
     
  3. Jethro Rocker

    Jethro Rocker Well-Known Member

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    Yes maybe it needs new valves. Bias set too cold? Try some new pre tubes and power tubes.
     
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  4. mikebinthesky

    mikebinthesky Member

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    I would lean towards tubes-especially if that LP has the 496r 500t pups-treble cranked-should be extra sharp and crispy
     
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  5. thunderstruck507

    thunderstruck507 Well-Known Member

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    I would start by pulling a preamp tube from your combo (or just buy one for $10) and try it in the other amp one position at a time and see if it changes. That should be cake to do.

    If it's not that it might be time for power tubes and a bias job or it could be something more serious.

    At the volume levels you posted it should be deafening.
     
  6. Gunner64

    Gunner64 Well-Known Member Premium Member

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    I had an issue with my 87 2205 where the volume on the boost channel was weak, as well as low distortion. I read somewhere that the solder connections where the pots are connected to the pcb are prone to break. I don't know exactly which pot was the culprit ( Although I suspect the gain pot) as I reflowed all the pot to board connections and the amp works perfect now. Idk if this is the problem with yours but that was my experience with mine..and if it has been sitting its a good idea to clean the pots, jacks and tube sockets as well. That thing should indeed rip your head off at those settings.
     
  7. marshallmellowed

    marshallmellowed Well-Known Member

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    "cold bowl of oatmeal", that's funny. It could be any number of things. Are any of the round capacitors bulging on top? Do you get the same results with nothing in the FX loop, or with only a patch cable in the loop? Something as simple as an oxidized jack can cause low volume and lack of detail. Check the simple things first, then venture on to tubes/replacement. My 2 cents.
     
    Last edited: Jan 18, 2019
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  8. Adieu

    Adieu Well-Known Member

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    Are all the tubes glowing evenly? Any idea what the bias is set to?

    Is the cleaner channel turned up high still properly loud, or does it also top out?

    If cleans get proper loud, it should be something in the preamp's dirt channel gainstage.... could be as easy as a preamp tube that isn't used by the clean channel, you'd have to check schematics or ask somebody in the know about how the dirt channel works though... could also be bad caps or something else in the dirt channel signal path, look for bloated or charred parts if you end up opening her up

    Oh and beware of lethal voltages in big capacitors in an unplugged tube amp if you're new to this
     
  9. Matt_Krush

    Matt_Krush Well-Known Member

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    Definitely start with a complete retube.
    Preamp and power. Set bias appropriately.

    If you don't hear a difference, then it may have other issues...or it's not the amp for you.
    But you have to have a starting point for comparison.

    If it's night and day difference, you can start swapping in an older tube to fund the dud.

    Could be 1 or all.
    Worst case, you end up with new tubes.
     
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  10. Buzzard

    Buzzard Well-Known Member

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    How in the world can anyone help you here if you leave out important detals? What flavor oatmeal,? maple ,apple cinnamon etc etc.... What type? steel cut oats,instant, irish? sheesh . Seriously ,I've got an 87 2205 and it kills. I assume you know about the 3 interactive vol controls it has right?
     
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  11. Gunner64

    Gunner64 Well-Known Member Premium Member

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    Sounds like what mine did..instant..maple brown sugar oatmeal...had potential..but way too sweet and mushy..if the tubes dont solve it reflow the solder joints at the pots..seriously. it was like magic happened with mine.
     
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  12. Adieu

    Adieu Well-Known Member

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    Nah

    Rotate the preamp tubes (all one slot over if they're labelled identical, research or skip the one if one is a different) and see if the problem migrates channels or otherwise shapeshifts

    Randomly throwing new glass at a glitching tube amp is wasteful

    ...now if you HAVE a full set of matching and not-too-expensive (in case it's a tube eater) glass in another amp, then by all means, roll it thru to see if that fixes anything.
     
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  13. Jethro Rocker

    Jethro Rocker Well-Known Member

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    I'm thinking OP could do a full swap out from his combo. Should really keep a set of spares regardless.
     
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  14. Jeff Hudson

    Jeff Hudson Active Member

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    Personally I would start with cleaning all the tube sockets and input and output jacks if you suspect it was sitting unused for a while, second I would check bias and make sure that is correct. If unsure about tubes, I would replace all. I believe around 86 was when the amp was changed at factory for more gain so that could be the difference between the two.
     
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  15. BanditPanda

    BanditPanda Well-Known Member

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    Fix it. Sell it. Get a Kemper. :io::lol:
    BP
     
  16. Adieu

    Adieu Well-Known Member

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    If your truck needs spark plugs, go buy a Corolla logic???
     
  17. geddy

    geddy Active Member

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    Points to note:
    1. Significant architecture changes between early and late; my 84 4212 has a later design. MV was moved, valves repurposed etc.
    2. With Max gain, volume will not change as you crank the in volume as you're already clipping.
    3. Clean sounds louder than distorted.
    4. I think the tone stack changed between designs but you've checked that. Neither design will give you a flat eq however you set them.

    Most important thing is to only change 1 thing at a time. This is a cardinal rule in fault finding. Then use a logical step by step approach, don't jump between looking at different things. Write down the results of testing....it's easy to forget what you did. Now we're done with sucking eggs...

    Check out which version of the circuit you have.
    Turn of reverb, disconnect effects loop, turn Down presence etc. Take as much out of the equation as possible.
    Move 1 good valve between positions . Thoroughly check what's happening at each point.
    Check /clean pots. The gain channel has a dual pot (same as MV). Pots and sockets seem to have been at the root of a number of my problems
    Try going in through the effects return to check power amp, although if the clean channel is working that's prob ok.
    Come back for more wildly differing and random advice.
     
  18. BanditPanda

    BanditPanda Well-Known Member

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    Hardly a suitable analogy.!:coffee:
    B P
     
  19. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    Replace BC184 switching transistors
    Replace filter caps in switching circuit
    Replace 1N914 diodes in switching circuit
    Replace preamp tubes if necessary
    Verify footswitch / footswitch jack- the jack can go bad causing channel switch to malfunction
     
  20. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Yeah, he probably should have said, “if your truck needs spark plugs go buy a Chevy Bolt.”
     
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