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  • Originally posted by Helmholtz View Post
    Yes but frequency-dependent. It allows reducing NFB at higher frequencies and thus acts as an active treble control.
    I believe he already understood that aspect. Mark (I think that's his name ) catches onto this stuff easily and a lot faster than I think is typical. I do like that you point out the specifics though because it makes these threads more informative for more viewers. Since I idealize this forum as an information resource I think it's a good thing.
    "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

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    • Since I idealize this forum as an information resource I think it's a good thing.
      Same with me.
      - Own Opinions Only -

      Comment


      • Originally posted by Chuck H View Post
        I believe he already understood that aspect. Mark (I think that's his name ) catches onto this stuff easily and a lot faster than I think is typical. I do like that you point out the specifics though because it makes these threads more informative for more viewers. Since I idealize this forum as an information resource I think it's a good thing.
        Nah, I never use my name on the internet. But I was in a band with a guy called Marc Davis, and I figured Dark Mavis would be a cool name for a character in an urban legend. Once I got all the grounds moved, I'll give the amp a quick try, to see if that has somehow cured the problem - I already recorded a demo of the original problem, so I'll be sure to include that - then I guess it's on to measuring the stuff I never got round to measuring.
        I think I also need to double check the shematic I drew. Right now it's a combination of the schematic I got with the amp, and what's actually in the amp. There may still be discrepancies. For example: That 47k resistor to ground right after the effects loop, isn't in the amp. Though, I might have missed it if it's on the Jack socket. It's the first place I'd look right now, but I've slept since.
        What other stuff should I measure? I don't recall if I measured any voltages on the power tubes, and I know I never measured any currents, cus I assumed I'd have to break a connection to do that...or maybe do math. Both of which I'll need a rainy day for.

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        • There's also that 47k resistor to ground, that exists on the original schematic,
          V5 grid needs a ground reference under all circumstances, so a resistor to ground makes sense. Not all effects provide such DC path to ground.
          - Own Opinions Only -

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          • Originally posted by Helmholtz View Post
            V5 grid needs a ground reference under all circumstances, so a resistor to ground makes sense. Not all effects provide such DC path to ground.
            This^^^^^^^^^^^^^^^^^^^^^^^^^^

            Though you mentioned that resistor before I hadn't looked into it. I'm surprised at the 47k value though. On the return jack for the effects loop recovery you typically want a somewhat higher impedance. When the loop is not in use (and assuming the switching jack is working correctly) that 47k would be parallel to a 6.8k and the reverb circuit load. But if you were to plug a cord into the return jack and leave it unterminated or if it's plugged into a device without a reference to 0VDC the recovery triode could actually become damaged. I'd hang a 1M resistor there rather than a 47k. Really. I think it's schematic error or Dan was off his meds that day.

            And can I call you Mark anyway
            "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


            • There seems to be an awful lot of people confidently saying that the things that other people are confidently saying, are incorrect.
              I think someone achieves a successful design, and assume that must be the right way. Reality is there are many "right" ways.
              Education is what you're left with after you have forgotten what you have learned.

              Comment


              • Originally posted by Chuck H View Post
                This^^^^^^^^^^^^^^^^^^^^^^^^^^

                Though you mentioned that resistor before I hadn't looked into it. I'm surprised at the 47k value though. On the return jack for the effects loop recovery you typically want a somewhat higher impedance. When the loop is not in use (and assuming the switching jack is working correctly) that 47k would be parallel to a 6.8k and the reverb circuit load. But if you were to plug a cord into the return jack and leave it unterminated or if it's plugged into a device without a reference to 0VDC the recovery triode could actually become damaged. I'd hang a 1M resistor there rather than a 47k. Really. I think it's schematic error or Dan was off his meds that day.

                And can I call you Mark anyway
                I'll check again. Maybe I didn't check on the jack itself, since I was trying to determine which of the star grounds everything was connected to.
                Ah. Yeah, it was on the jack.
                Yeah, y'all can can me whatever you want

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                • Originally posted by Dark Mavis View Post
                  Yeah, y'all can can me whatever you want
                  just don't call him late for dinner........


                  nosaj
                  soldering stuff that's broken, breaking stuff that works, Yeah!

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                  • Quick question: Since I'm limited to using those little solder tags for grounds, and space is limited, I'm thinking of just bolting down 2 or 3 of them and connecting them together with a ring of wire that can act like a mini circular bus bar. It will give me the room I need to connect all the grounds, and will minimize the number of mechanical contacts acting as electrical contacts. But...is there any reason not to do this? I never see it done else where, but I can't think of a single reason not to, except...maybe ground loops? But they'd be tiny. Smaller than the holes drilled in the chassis anyways for the tube sockets. It just seems like too simple a solution, to not have a downside. Or maybe I can cram enough tags onto one bolt, if I keep them flat and let them overlap. I'm just thinking of if I have to go back in there and desolder or resolder a wire.

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                    • All practical considerations. And the method you propose isn't a problem. The short length and low resistance of that piece of bus wire will be inconsequential. You don't need a ring or a closed loop for any reason (and that actually DOES make a ground loop, but such a short path that it wouldn't manifest). You could just have a three inch piece of buss wire from each ground point off of one tag. When you're done soldering you just bend it over out of the way. But I like your idea of having several tags on one bolt too. If you turn them in a spiral and can tag a little solder between them to avoid so many possible oxide points. It might make for a neater appearance. But either way will work. And I've seen the inside of that thing so I don't think you're trying to make it look fancy now.
                      "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


                      • Originally posted by Dark Mavis View Post
                        Quick question: Since I'm limited to using those little solder tags for grounds, and space is limited, I'm thinking of just bolting down 2 or 3 of them and connecting them together with a ring of wire that can act like a mini circular bus bar.
                        I used to use these. Stack two together and you have a 10 point star. They can be bent up a little to clear the chassis or use a nut as a spacer.

                        Click image for larger version

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                        • Originally posted by Dave H View Post
                          I used to use these. Stack two together and you have a 10 point star. They can be bent up a little to clear the chassis or use a nut as a spacer.

                          [ATTACH=CONFIG]56642[/ATTACH]
                          I was looking for something like that on Ebay, but didn't know what to call it. I might make something similar. I wanna do it tomorrow so I can't order anything. I could just cut something out of sheet steel and tin it, I guess.

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                          • Actually...COULD the grounding be the cause of the issue I described? Filter caps supplying the first preamp tubes are grounded at the same point as those providing the plates of the output tubes, and the B+ to the output trans primary. Could that cause a situation where, above a certain volume, there's a kind of feedback, where some of the signal at the output part of the amp, finds its way back into the earlier stages, and the amp runs away? And might that manifest as just higher than expected hum at lower volumes? I don't know much about this stuff, but that kinda feels like something that could happen

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                            • Improper grounding has been known to cause instability. Or, maybe more accurate, correcting improper grounding has been observed to cure instability. Not exactly the same thing I guess because it's always possible that something other than grounding is inadvertently corrected in the process. But that's just my experience. Others here do have more conviction about it.
                              "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


                              • Originally posted by Chuck H View Post
                                Improper grounding has been known to cause instability. Or, maybe more accurate, correcting improper grounding has been observed to cure instability. Not exactly the same thing I guess because it's always possible that something other than grounding is inadvertently corrected in the process. But that's just my experience. Others here do have more conviction about it.
                                Well, I'll find out tomorrow. Either way, I'll post a video, cus I've recorded a demo of the problem. If the problem persists, it's back to diagnosing. After that, I got a 1978 Orange that's basically just a pile of parts

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