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5F6A Bassman total custom build - super low output

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  • #91
    When do we get to hear it? Some sound samples would be great!
    "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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    • #92
      Originally posted by Tom Phillips View Post
      Tom M,
      There is a really efficient technique to extract the conductor wires from a braided shield. Rather than write a narrative trying to describe it, I found a video demonstration at https://www.youtube.com/watch?v=JW2esD1NIa8 The extraction process is shown starting at the 2:15 time mark. In the demonstration shown a pigtail wire is attached to the shield but that step is not always necessary if the shield is to be terminated close to the conductor connection in the build.
      Check it out.
      Cheers,
      Tom P
      That's a good video, Tom. But,......it's so much easier with a helping hand!

      Click image for larger version

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      "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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      • #93
        Originally posted by The Dude View Post
        [ATTACH=CONFIG]46720[/ATTACH]
        I have one. My wife bought it for me Used it twice for some tricky stuff and it was eminently helpful. It sits on the tool shelf waiting for a job. But when you need 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

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        • #94
          Welcome back Dude and Chuck, I thought you guys were mad at me or something. I will get a sound sample up soon. I want to tweak a bit more.

          I am going to re-do the feedback wire shielded, and also my leads for the "Boost" switch. Boost is a Robinette mod which is a switch on the cathode of V2A which places a 0.68uF cap in parallel with the cathode resistor. Supposed to increase the gain of the CF for earlier breakup, but really I don't notice much difference on or off. The boost wires are sensitive and are picking up hum.

          The tone bypass switch, on the contrary, leads to serious crunch. The heavy metal tone is EXCELLENT.

          Soak resistor seems to be working well, I can get crunch without blowing out the opposite wall. I think the resistor limits my ability to have clean tones at reasonable volume, so I am considering replacing it with a variable pot like this: DIY Workshop: How To Build Your Own Attenuator - The Guitar Magazine | The Guitar Magazine I don't have multiple output taps on the OT so it's 4 ohms only. Speakers are 8 combined so need 8 ohm L-Pad.

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          • #95
            Originally posted by tomgilmartin View Post
            Welcome back Dude and Chuck, I thought you guys were mad at me or something......
            Oh, not at all. Just waiting for the results of your tweaking.
            "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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            • #96
              Quickie video. Lemme know how it sounds, my crappy computer seems to have the sound going in and out.

              https://youtu.be/T3IlU4JBC6U
              Last edited by tomgilmartin; 01-25-2018, 12:34 AM.

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              • #97
                I tried to watch it, Tom. It says, "This video is unavailable."
                "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                • #98
                  Try again, I posted the link while it was still uploading.

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                  • #99
                    Originally posted by The Dude View Post
                    I tried to watch it, Tom. It says, "This video is unavailable."
                    I get that too
                    If it still won't get loud enough, it's probably broken. - Steve Conner
                    If the thing works, stop fixing it. - Enzo
                    We need more chaos in music, in art... I'm here to make it. - Justin Thomas
                    MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey

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                    • I'm a dummy. Set the video to private on YouTube. It's public now, for those who are still interested. Sorry to waste your time there.

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                      • I was hearing a sort of high pitch whistle type oscillation with the guitar. Is that the amp, or could it just be that the mic in the recording device is being overdriven with the high SPL and reacting strangely?
                        "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                        • It sounds really cool in a lot of ways. I really like the tone stack bypass tone. And the percussive qualities you mention. That's a signature of the Bassman circuit But that "sizzle" you mention... Hear the way it's there and then abruptly cuts off? That's actually a parasitic artifact. When the radiant field of whatever leads are interacting are large enough there is sizzle. When the fields shrink it cuts off. The reason it cuts off abruptly is because it's a positive feedback affect. So it's self propagating and obvious until conditions change and it's not. It's probably a reaction to the LF in the circuit. Maybe just see if adjusting the bass doesn't change the affect in any way.

                          I, personally, don't like that artifact. Yours isn't the only amp that does it. But it's usually a mild sort of crackling and not a on/off sizzle. I actually see it as a flaw that should be corrected. Unfortunately because your design is unusual and a parasitic can manifest in many ways I don't have a "Change this to that" suggestion.

                          EDIT: Also, the left/right cut in/out and similar effects on ambient EQ and volume throughout the video were seriously getting on my nerves and making it very hard to hear what was happening or even focus 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


                          • Yeah, not sure why the left/right thing was happening, I'm going to guess my son was blocking all or part of the mic with his hand while recording. He was trying to get cute zooming in and out. Maybe next one I will just put the phone on a stand. The SPL really wasn't that loud. Loud, but not ear-splitting. Or maybe I'm going deaf, LOL! Did you notice Finn being funny with his ear protectors?

                            I'm going to shield some more wires, it just takes a long time to dress them properly and do it up. Did up the neg feedback line just now.

                            I agree, that little sizzle drives me nuts too and MUST be rooted out.

                            I'll get a better video up soon, didn't have time to really do it justice. It was HD from my Galaxy S6, 344MB to upload!!

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                            • There are inevitably bugs to work out on a build, so don't get discouraged. Your experience is not singular. Actually, given the unconventional layout of that amp I'm quite surprised there aren't more bugs.
                              "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                              • Yes. That^^^^^^^^^^^^^^

                                I attribute it to Tom's engineering experience. For the most part his ideologies are solid, there just may be some things specific to the genre that escaped. My worry has been that taking this build all the way to fully functional may require a virtual tare down of the wiring.

                                Remember you mentioned that out of phase cross talk was also happening within an amp? Well... Long leads, twisted pairs bundled in gobs from one aluminum pipe to another,.. There are a lot of tiny capacitances in that amp, both positive and negative feedback interactions, that are not part of the stock 5f6a circuit. And always will be. Tuning THIS amp as it's own entity is the only option.
                                Last edited by Chuck H; 01-25-2018, 04:07 AM.
                                "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

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