Ad Widget

Collapse

Announcement

Collapse
No announcement yet.

Marshall Preamp

Collapse
X
Collapse
 
  • Page of 1
  • Filter
  • Time
  • Show
Clear All
new posts
Previous template Next
  • #1

    Marshall Preamp

    My buddy is having an issue with his JMP-1 preamp.

    The clean patches are nice and loud, but the OD1/OD2 patches are about 60% lower in volume.

    I took a peek under the lid and this thing looks very complicated. To me at least...

    I swapped out the 2 tubes.

    Anyone have any experience with this model?
    Are there any easy checks i can do to locate the signal loss without a scope?

    schematic:

    http://www.drtube.com/schematics/mar...jmp1-61-04.pdf
    Tags: None
  • #2
    How is the unit being used?
    MiDI Out?
    Master Out?
    Speaker Emulator?


    If using the Emulated Out each bank is set by software at Key #8.

    http://www.marshallamps.com/download...MP_1%20Hbk.pdf

    Comment

    • #3
      yeah, no doubt some patch setting. I'd check the tubes if not, as the clean settings would use fewer tube stages so if one used only by the disto settings is bad or someone put a lower gain tube like a U7 in there that could do it. But i'd wager a patch setting.

      I had a JMP1 long ago. I gigged with it about 6 months but i couldn't get past the lack of dynamics when using seperates. Pre and power amps gotta share the same PSU IMO or it feels sterile. For total shredders i guess it wouldn't matter as much.

      Comment

      • #4
        not a patch setting--we adjusted everything possible.

        using either the left or right 1/4" main out

        not a tube, i swapped them with 2 others---its something in the preamp thats lost a ton of level---it has plenty of overdrive, just no volume on the 2 dirty channels.

        Comment

        • #5
          If it sounds right, but just has lower output, it must have something to do with the finals. Which may be a secondary silicootie thing in that box. Probably in fact. Nothing to do with tubes or their circuits at all.
          "Take two placebos, works twice as well." Enzo

          "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

          "If you're not interested in opinions and the experience of others, why even start a thread?
          You can't just expect consent." Helmholtz

          Comment

          • #6
            Have you tried factory resetting the unit (Hold down OD1 and Clean1 while powering up the unit)? You could simply have some corrupt data. Also, check and/or replace the battery. Many times corrupt data is caused by a low/dead battery.

            Edit: Do know that a factory reset might fix it, but it will restore the unit to factory settings. All user data will be lost.
            Last edited by The Dude; 12-31-2013, 05:06 AM.
            "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

            Comment

            • #7
              tried the factory reset.

              battery is good at 3.1v

              no change

              Comment

              • #8
                Have you tried the Speaker Emulation Out?

                Effects out?

                Simply to see if there is a difference.

                Comment

                • #9
                  Originally posted by Jazz P Bass View Post
                  Have you tried the Speaker Emulation Out?

                  Effects out?

                  Simply to see if there is a difference.
                  yes---no difference

                  Comment

                  Previous template Next
                  Working...
                  X