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Kalamazoo Bass 30 Tame?

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  • #1

    Kalamazoo Bass 30 Tame?

    Well, I'm back. I picked up a Kalamazoo Bass 30 for $75 a few months ago, that just hummed loudly. Some new filter caps & a resistor or two & it's back to work. I like the sound, it's kinda lo-fi. I also ganked the speakers (Jensen C10P ) for my 61 Concert...
    I've done some reading & I think this amp is kinda wimpy for what it is. My old 67 Reverberocket 2 was louder. The Internet seems to agree on the wimpiness. Any suggestions on getting a bit more oomf? I don't need a Super Reverb here, but I feel like it's far from living up to its potential. I don't really WANT to rewire it with a LTPI & 2 gain stages, but this thing is a wuss! I'm trying to attach the preamp schematic; lessee if it works.

    Thanks,
    Jusrin
    1 Photo
    "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
    "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
    "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -
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  • #2
    Hey there. Good to see you. And...

    For starters that input circuit is voltage dividing the signal from your instrument A LOT. You could start with rewiring just the input to be more like a typical guitar amp.
    "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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    • #3
      In case there were any questions

      Click image for larger version Name: mlfi1.png Views: 89 Size: 44.2 KB ID: 997927
      "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
      • Likes 2

      Comment

      • #4
        [QUOTE=Chuck H;n997926]In case there were any questions

        SO I can name this kind of input tomfoolery "Signal Suckers?"
        Thanks Chuck! Like I said, I don't really want to do a full preamp rewire unless necessary. It's just a weird design to me. Closer to a big Ampeg of the early 70s. I'll give it a go.

        Jusrin

        "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
        "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
        "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

        Comment

        • #5
          And, I don't have to mess with the chassis cuz this is one of those things where they put all that on the control panel with an umbilical.

          ​​​​​​JUsrin
          "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
          "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
          "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

          Comment

          • #6
            I would bump up the cathode capacitor to 25uf for more bass response.
            Last edited by Jazz P Bass; 04-21-2024, 02:15 AM.
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            • #7
              Thank you, Jaxz!

              Jusrin
              "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
              "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
              "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

              Comment

              • #8
                Well I took the time to simulate the circuit as best I could using 12ax7's and el84's. I don't have tube models for 6eu7's or 7591's. And...

                The amp is whimpy for a reason. Crossover distortion starts to present at the onset of clipping and gets worse the more you push it. Pretty sure this is happening at the amplifier stages following the cathodyne and is not due to power tube bias. It's a lousy design.

                The tone stack isn't much better. It eats a lot of gain and you'll have to have the treble control on ten any time a six string is plugged in.

                Sorry to say but I'd gut that amp. Almost any other circuit would be better. If you ever decide to do that I'll bring the cheese.
                "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
                • Likes 1

                Comment

                • #9
                  Hey Justin! I just came up with what I think is a pretty clever mod you can do to take that amp into real guitar amp territory with almost no work. I ran simulations and the results look great. It changes the cathodyne to a gain stage and turns the gain stages following the cathodyne into a LTP PI. Optional snip in the schematic increases higher treble if the amp sounds muffled at all but I can't say if it will cause instability.

                  Click image for larger version Name: kalamazoo30schem.png Views: 70 Size: 250.1 KB ID: 997982
                  "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
                  • Likes 1

                  Comment

                  • #10
                    Also... I just looked at an actual Kalamazoo schematic for that amp and it looks to me that the input circuit is wired correctly for hi/lo jacks. There were some other small differences too but I know there were many designs with in that model. I only see the incorrect wiring indicated on the later copied schematics. I can't say what's in your amp but it's probably already correct.
                    "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
                    • Likes 1

                    Comment

                    • #11
                      Is that 0.0047uF cap off the Loudness pot wiper in the schematic the right value or is that a typo? That just seems super small, especially for a "bass" amp.
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                      • #12
                        It's plenty of value for that circuit and probably won't present any knee in the audible range of speaker of the era. Helmholtz would know the math and circuit parameters to calculate for this. I just know some of this rote.
                        Last edited by Chuck H; 04-21-2024, 07:53 PM.
                        "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
                          Hey Chuck & Glebert,

                          I haven't looked into the control panel too much, I just know this thing was all original when I got it. The schematic was inside the back psnel, unfortunately mice had gotten to it as the amp lived in the garage for about 20 years.

                          This one is the columnar 2x10", resembling a Gibson Thor cosmetically. I've seen a few "horizontal" examples too.

                          What I'm gonna do is try the smallest changes first, & then go for the more radical stuff. But ultimately, I just wanna hock it for $250-300 ASAP cuz I'm eyeing a Rivera-era Concert to go with my 75.

                          Keep on making suggestions, though I work full time now so there's usually only one day a week I can get to this stuff. I mean, if it's not nice enough to go to the beach.

                          Jusrin
                          "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
                          "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
                          "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

                          Comment

                          • #14
                            Well I just looked up the innards for those amps and AAAAARGHH!!! They're all PTP on little terminal strips. This makes interpreting the circuit from a schematic a real pain. I'm trying to find a good gut shot image so I can make the mod simpler. As in red arrows and "snip here", "jumper here", etc. Still working on 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
                            • Likes 1

                            Comment

                            • #15
                              Chuck, I can follow it okay. I'm used to true PTP messes cuz that's pretty much how I build. I'm also familiar with the layout after having spent nearly 2 years on a Gibson Thor, trying to kill a hum that turned out to be a hell of a noisy PT. I've already redone the power supply & put the fuse & switch on the actual chassis. I just don't trust that plastic connectors with my safety...

                              I'll see if I can get you a clear gut shot tonight, AND of the front panel.

                              Jusrin
                              "Wow it's red! That doesn't look like the standard Marshall red. It's more like hooker lipstick/clown nose/poodle pecker red." - Chuck H. -
                              "Of course that means playing **LOUD** , best but useless solution to modern sissy snowflake players." - J.M. Fahey -
                              "All I ever managed to do with that amp was... kill small rodents within a 50 yard radius of my practice building." - Tone Meister -

                              Comment

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