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Reverb mod for Fender type circuits

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  • #1

    Reverb mod for Fender type circuits

    How about one we can actually use? If there's a reverb that players actually like it's the BF AA/AB 763 circuit. So I don't think we need a tone mod. But plugging in the foot switch can increase noise dramatically because of the low signal level/high gain nature of the circuit and hanging the grid lead out of the amp chassis. So why not work with a lower impedance circuit, the cathode?

    If you separate the shared cathodes for the reverb recovery and normal channel you could turn off the reverb recovery tube at it's cathode rather than grounding the grid. Below is the stock circuit with my proposed circuit next to it. Anyone see a problem with this?
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    "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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  • #2
    Will there be switching pops? When the switch is opened the tube will turn off and its plate voltage will quickly rise to the B+ rail.

    Edit: Another option would be to connect the switch to the CW end of the Reverb level control.
    Last edited by Dave H; 01-16-2018, 02:39 PM.

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    • #3
      Not sure if it would pop. Any AC-ish behavior in the voltage jump would sure do it though. That might explain why it hasn't come up before since anyone would want to reduce noise in the stock circuit if they could. I have a local customer with a reverb amp I built that uses the standard Fender type foot switch arrangement. He doesn't use the amp much so I may be able to get it on my bench and try this. Not sure when though.
      "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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      • #4
        You posted as I was typing the above edit.

        If the cathode switching pops try connecting the switch to the CW end of the reverb level pot. The impedance is lower there than the original switch position and it's not amplified by the gain of the recovery triode.

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        • #5
          Good call. In fact I just looked it up and that's just what Fender has done with the reissue circuits.
          "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
            It may also be possible to leave the bypass cap grounded and just switch the DC component with the cathode resistance. That way any AC-ish behavior has a better chance finding it's way out of the signal path. I think only bench testing will tell if it's an issue or not.

            Unfortunately the amp I built uses a stereo plug for the foot switch to handle the reverb and a trem circuit. So I couldn't use the shorting jack as in my circuit. I can still test the principle though.
            "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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            • #7
              Meh, I never switch the Reverb on and off with the footswitch. I set it and forget it. Any issues with that?

              Justin
              "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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              • #8
                Originally posted by Justin Thomas View Post
                Meh, I never switch the Reverb on and off with the footswitch. I set it and forget it. Any issues with that?

                Justin
                None at all. That's how most players do it. Probably because plugging in the foot switch makes the reverb 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

                • #9
                  I think for many scenarios, switching between 2 levels of reverb would be handier than on/off (which can sound weirdly dry in the off mode); as the V4 cathodes have been separated, that could be done with the recovery cathode bypass cap.
                  My band:- http://www.youtube.com/user/RedwingBand

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                  • #10
                    Will there be switching pops?
                    100% and loud also.

                    I think for many scenarios, switching between 2 levels of reverb would be handier than on/off (which can sound weirdly dry in the off mode); as the V4 cathodes have been separated, that could be done with the recovery cathode bypass cap.
                    That's how it's done in Mesa MarkIIC+. Only the cathode bypass cap is switched (grounded) which gives the reverb a level boost without pops.

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