Announcement

Collapse
No announcement yet.

Volume when there should be none, when volume pot is at zero on Gibson Titan

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Volume when there should be none, when volume pot is at zero on Gibson Titan

    I’ve been trying numerous different combinations of search words but have had no luck in finding anything regarding my specific issue.



    I have a Gibson Titan Medalist amplifier with an unusual problem. The owner said that the amplifier started having volume issues, that it wasn’t as loud as it should be. The first thing that I found when checking it out was that the 2 amp slo-blo fuse needed replaced and one of the 470 ohm screen resistors had opened up, the other three were nicely in spec averaging about 467/8 ohms. The power tubes were old ones and kind of flaky so I replaced them. So after replacing these the volume came back for the most part. Channel one is behaving very strangely, when the volume knob is all the way down I hear a significant amount of guitar coming through… it sounds very warm, clean and pleasant at a volume about equal to an average conversation. But again, this is with the volume turned all the way down. When you turn the volume up it starts to get “flat” sounding just a little bit but I’m able to get it loud now. This effect was much more pronounced with the old tubes, it would get flat sounding but the volume would not increase. When the tremolo is on you do not hear any of the tremolo effect when the volume is all the way down, but again there is that nice warm clean sound that should not be there. I have swapped preamp tubes between both channels and the issue remains in channel one regardless of the tubes used. Channel two behaves pretty much normally, but you do hear just a little bit of sound with the volume knob all the way down. The phase inverter tube checked to be pretty weak on my transconductance tester so I replaced it. I’m not sure if this is much of a factor or not, but on the schematic it says that both plates on the PI tube should have the same voltage, but the voltage on one is significantly lower. The schematic says about 137 volts (if I recall correctly) and one plate is just about right on the spot but the other plate was something like 119 volts. So far I haven’t encountered any other resistors out of spec.



    At this point I’m a tad stumped and I’m hoping to save a little time by asking for a little help. Just about every other time I’ve had an issue I’ve been able to find the answer in a search, but not this time. Any help would be appreciated, thanks.

  • #2
    Old power tubes do loose their upper end when driven harder, not an issue. The repair of the power front end sounded good, concerning technical observations.

    As for the channel that does not diminish when then that potentiometer is fully clockwise would probably be be due to the that volume pot wiper not going to near zero when fully CCW with respect to lead on that pot's CCW terminal. Also make sure that that the ground wire connecting to that terminal is solid to ground with the other ground wires to chassis. Make sure that no DC voltage is present on the CW terminal of that pot as well, if there is that volume control would crackle for sure, the coupling capacitors routing that signal will be the culprit.

    Usually channels are summed together with divider resistors near the PI, if non of the above seem to work, trace out that node then disconnect one channel from that node to see if any weirdness happens

    Good Luck

    Comment


    • #3
      Does this amp have reverb? Try turning it off?

      Comment


      • #4
        Thanks for the replies. I'll report back after I've been back in the shop to work on the amp.

        This amp does not have a reverb unit.

        Comment


        • #5
          Thanks again to everyone who responded to this post months ago. I haven't done any more work on this amp since then because of my full time job demanding a lot of overtime. I also had a particularly unpleasant experience moving to a new place that left me exhausted because I was not allowed to take any time off of work to move. I'm happy that's over with


          Regarding R ski's comments:

          This problem is identical to both channels of the amplifier, and both pots sound quite clean when you increase the volume. At full CCW position you hear a rather "comfortable" level of volume... basically meaning that it is quite audible. The amp is also not as loud as it had been previously. It has been several months so I'm not sure if my previous comments regarding channel two operation normally were an incorrect observation, but the problem is definitely present in both channels. There is no unpleasant hum or buzzing either.

          So the question is: What could cause a two channel amplifier to give you a clean audible sound when the volume pot is all the way at zero... and have the exact same behavior in both channels?

          Comment


          • #6
            Crosstalk.
            Education is what you're left with after you have forgotten what you have learned.

            Comment

            Working...
            X