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Fender DR build.. Reverb BUZZ Gremlin.

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  • #1

    Fender DR build.. Reverb BUZZ Gremlin.

    Chaps,

    I have a DR RI new build. Original fender populated boards & rev xfmr fender/ PT & choke hammond, OT Mojo. Orig DR chassis.. so effectively an orig DRRI with upgraded-if-you-will xfmrs, simple as that.

    This is perplexing. A -very- LOUD reverb hum/ loudest Ive ever heard (I cant turn rev up to 11- its so loud) increacing with reverb knob. Reverb works ok behind the noise.

    New reverb tank. Correct one.
    New rev xfmr. Correct one, fender part.
    New reverb leads. Tried another set, better shielded. No change.
    Cleaned all contacts, pinched connections a tad for a tighter dead-cert fit. No change.

    It worked fine only a few days ago nothing moved or different at all.. so why suddenly its appeared is a mystery. It 'sounds' simply like a "pg 1 didnt plug the ground in dummy! error". But all is in correctly. Wiring to tube socket checked, wiring into boards checked.

    I did have a feedback issue once past dial '5', so I moved pan around (& now ok back where it started, in the head?!) & that gone now at least.

    Any help- as always appreciated. Thanks SC.
    Tags: None
  • #2
    Try unplugging the cable from the input RCA jack on the amp and turn up the reverb a bit. Hum still there?
    "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

    • #3
      Originally posted by Chuck H View Post
      Try unplugging the cable from the input RCA jack on the amp and turn up the reverb a bit. Hum still there?
      Hi ChuckH. Yup- still there exactly same.

      Comment

      • #4
        Pull the Reverb tube, V4.

        If the noise goes away (as it should), then there is an issue on the return side of the circuit.

        I would check that R33 (220K) is firmly attached to ground.

        65_deluxe_reverb_Rvb Circuit.pdf

        Comment

        • #5
          Just to be clear... The cable was unplugged from the amp, not just the pan end with the cable still dangling from the amp.?.

          If the cable was not connected to the amp and the hum is still present that eliminates:

          the pan
          the cable
          the reverb transformer
          all the reverb driver circuitry

          So the problem is in the recovery stage (V4A) and is almost certainly a bad ground connection or a grossly noisy tube. If another tube has been tried, the normal channel is working correctly, the hum is analogous to the reverb level setting and the reverb is operational with the exception that it hums this eliminates

          the tube
          the cathode ground for V4A (C16/R30)
          the ground on the level control pot (R31)

          This leaves only the ground connection for the sleeve of the RCA jack on the amp connected to V4A grid, which I suspect is shared with the ground for the V4A grid load (R28).

          Regardless of whether you've crimped/tightened connections or how many times you've inspected wiring, this is the most likely area for the problem. With the cable still unplugged, touch your meter's black probe to the amp chassis touch the red probe to the sleeve of the RCA jack for the V4A grid. There should be almost zero ohms. Likewise, with the black probe still on the chassis, touch the red probe to both ends of R28. It should read 220k on one end and almost zero ohms on the other.

          If the test isn't done with the reverb cable unplugged from the V4A input jack the results will be useless.

          I'm linking the service manual again on this thread, as I did on your previous thread, in the interest of clarity so that all posters have the information and a common point of reference.

          http://www.ampwares.com/schematics/6..._Reverb_RI.pdf
          "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
            Originally posted by Jazz P Bass View Post
            Pull the Reverb tube, V4.

            If the noise goes away (as it should), then there is an issue on the return side of the circuit.

            I would check that R33 (220K) is firmly attached to ground.

            [ATTACH]33779[/ATTACH]

            Hi JazzP. Yup- pulled V4 and noise goes away. Its odd tho, as all the R's etc populated on the pcb (IE not a p-to-p home build) Id expect slim chance of any not beng bolted in ok.

            Comment

            • #7
              Originally posted by Jazz P Bass View Post
              Pull the Reverb tube, V4.

              If the noise goes away (as it should), then there is an issue on the return side of the circuit.

              I would check that R33 (220K) is firmly attached to ground.

              [ATTACH]33779[/ATTACH]
              Ah. I was still posting when you jumped in. Now we have two links to the schem. I don't suspect R33 ground though. It seems to me that if the hum is analogous to the reverb level setting that the problem is behind the reverb pot in the signal chain. Even without the R33 ground there should still be sufficient loading for the V4B grid through the reverb pot. Which must be grounded properly because the reverb is adjusting correctly.
              "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

              • #8
                ChuckH- yes the rca input under the amp was pulled. Noise remains.

                Ok Im reading your post #5 again.

                Comment

                • #9
                  Originally posted by Chuck H View Post
                  Just to be clear... The cable was unplugged from the amp, not just the pan end with the cable still dangling from the amp.?.

                  If the cable was not connected to the amp and the hum is still present that eliminates:

                  the pan
                  the cable
                  the reverb transformer
                  all the reverb driver circuitry

                  So the problem is in the recovery stage (V4A) and is almost certainly a bad ground connection or a grossly noisy tube. If another tube has been tried, the normal channel is working correctly, the hum is analogous to the reverb level setting and the reverb is operational with the exception that it hums this eliminates

                  the tube
                  the cathode ground for V4A (C16/R30)
                  the ground on the level control pot (R31)

                  This leaves only the ground connection for the sleeve of the RCA jack on the amp connected to V4A grid, which I suspect is shared with the ground for the V4A grid load (R28).

                  Regardless of whether you've crimped/tightened connections or how many times you've inspected wiring, this is the most likely area for the problem. With the cable still unplugged, touch your meter's black probe to the amp chassis touch the red probe to the sleeve of the RCA jack for the V4A grid. There should be almost zero ohms. Likewise, with the black probe still on the chassis, touch the red probe to both ends of R28. It should read 220k on one end and almost zero ohms on the other.

                  If the test isn't done with the reverb cable unplugged from the V4A input jack the results will be useless.

                  I'm linking the service manual again on this thread, as I did on your previous thread, in the interest of clarity so that all posters have the information and a common point of reference.

                  http://www.ampwares.com/schematics/6..._Reverb_RI.pdf
                  Amp out again, whilst not powered up..

                  I read normal ~1.5r continuity between amp's rev rca input socket & chassis gnd (rev pan plugs are pulled).

                  I read normal ~1.5r continuity between R28 & gnd.
                  I read 220k from R28 other end & gnd.

                  Comment

                  • #10
                    Have you tried a different tube in V4?
                    "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

                    • #11
                      Dont have another 12AT7 you see or would have.

                      Im using a 12ax7 for the PI too (IE if normally had a 12AT7 there I could have swapped) as read this is ok/ saved me buy another tube you see as had a few generic types spare.

                      Comment

                      • #12
                        V4 is supposed to be a 12ax7. V3 (driver) is a 12at7. Pi doesn't matter so much and not at all WRT this problem.

                        Pull V1 and stick it in the V4 socket. The normal channel won't work and the vibrato channel will have a tad more gain but it will tell you right away if the V4 you have now is noisy.
                        "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

                        • #13
                          Originally posted by Chuck H View Post
                          V4 is supposed to be a 12ax7. V3 (driver) is a 12at7. Pi doesn't matter so much and not at all WRT this problem.

                          Pull V1 and stick it in the V4 socket. The normal channel won't work and the vibrato channel will have a tad more gain but it will tell you right away if the V4 you have now is noisy.
                          Ah yes of course- as indeed I have in there. Ok good I will swap the V4 12ax7 (jj ecc83s) out for a generic cr*p 12ax7. I have a 12AY7 in V1 you see, tho like most dont use normal much.

                          Comment

                          • #14
                            Chuck-

                            is there any way of ID'ing 12ax7 size tubes if the writing rubbed off? Ive no idea whatI have here, to swap into V4. Its right size and a usual make-monkey, but has 2 horizontal plates twds top of tube and one twds lower part of it.. normally I see 12ax7 types have just two plates one twds top, one twds lower part of tube.

                            Comment

                            • #15
                              Originally posted by Sea Chief View Post
                              Chuck-

                              is there any way of ID'ing 12ax7 size tubes if the writing rubbed off? Ive no idea whatI have here, to swap into V4. Its right size and a usual make-monkey, but has 2 horizontal plates twds top of tube and one twds lower part of it.. normally I see 12ax7 types have just two plates one twds top, one twds lower part of tube.
                              Why not getting a set of preamp tubes, try them in your amp to rule out bad tubes.
                              In this forum everyone is entitled to my opinion.

                              Comment

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