Announcement

Collapse
No announcement yet.

Blackface Pro Reverb Mid control

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

  • Blackface Pro Reverb Mid control

    Customer has a Pro Reverb that he says is a bit too midrange for him. He wants a mid control. All the mid control mods I am seeing are to add mids, usually by adding a 25K pot in series with the 6.8K resistor in the tone stack, so with the pot down full it is stock, and turning it up adds mids. But I want to go the other way. Would replacing that fixed resistor with a 10K pot do the trick?

    https://cdn.shopify.com/s/files/1/23...97210715640943
    It's weird, because it WAS working fine.....

  • #2
    Absolutely
    Its worth checking that the 6k8 mid resistor value hasn’t drifted a bit high.
    Or that the 47nF mid cap drifted low etc.
    Last edited by pdf64; 08-06-2020, 08:23 PM.
    My band:- http://www.youtube.com/user/RedwingBand

    Comment


    • #3
      Just replace the 6.8k with a 10k pot. He can control the mids the way he wants then.

      Comment


      • #4
        A 10KA pot would be even better

        Comment


        • #5
          Originally posted by Randall View Post
          All the mid control mods I am seeing are to add mids, usually by adding a 25K pot in series with the 6.8K resistor in the tone stack, so with the pot
          down full it is stock, and turning it up adds mids.
          Passive controls remove frequencies, not add them - unless you're looking at active circuits.
          Jack Briggs

          sigpic
          www.briggsguitars.com

          forum.briggsguitars.com

          Comment


          • #6
            There is no general reason (apart from circuit restrictions) why a modification to an existing passive filter should not allow to boost frequencies.

            Increasing the mid resistance in the tone stack increases the (available) overall gain at mid frequencies. I'd call that a boost. You may call it less attenuation.
            - Own Opinions Only -

            Comment


            • #7
              Originally posted by booj View Post
              Just replace the 6.8k with a 10k pot. He can control the mids the way he wants then.
              Still best to check for drift in the 6.8k fixed resistor and the value of the mid cap. That may indicate an actual repair is appropriate. Modding to solve problems rather than diagnosing them can often lead to confusion later.
              "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

              "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

              Comment


              • #8
                Originally posted by jack briggs View Post

                Passive controls remove frequencies, not add them - unless you're looking at active circuits.
                What Helmholtz said. The mod discussed actually does add mids. At least with respect to the stock circuit. But as a concession to what you wrote I will note that it add mids over the stock configuration by reducing signal loss through the passive tone stack.
                "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

                "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                Comment


                • #9
                  Originally posted by Chuck H View Post

                  ... by reducing signal loss through the passive tone stack.
                  If you use Duncan's Tone Stack Calculator, you will see that it actually doesn't.

                  Increasing the mid resistance works like increasing the lower (shunt) part of a (frequency dependent) voltage divider.
                  - Own Opinions Only -

                  Comment


                  • #10
                    Using Duncan TSC I used the Fender tone stack. I set the mid control full and plugged in a value of 6.8k. That is the green trace. Then I changed the mid value to 31.8k. That is the orange trace.

                    Click image for larger version

Name:	ictlsl1.PNG
Views:	61
Size:	20.7 KB
ID:	911246
                    "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

                    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                    Comment


                    • #11
                      Originally posted by Chuck H View Post
                      Using Duncan TSC I used the Fender tone stack. I set the mid control full and plugged in a value of 6.8k. That is the green trace. Then I changed the mid value to 31.8k. That is the orange trace.

                      Click image for larger version  Name:	ictlsl1.PNG Views:	0 Size:	20.7 KB ID:	911246
                      Sorry, I misread your post above being irritated by the term "concession". In fact, increasing the mid resistance reduces insertion loss at all frequencies. This means a total boost.
                      Last edited by Helmholtz; 08-16-2020, 07:07 PM.
                      - Own Opinions Only -

                      Comment


                      • #12
                        If you're the only person I irritate with my choice of words today I'll be surprised
                        "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

                        "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                        Comment


                        • #13
                          Originally posted by Randall View Post
                          Customer has a Pro Reverb that he says is a bit too midrange for him. He wants a mid control. All the mid control mods I am seeing are to add mids, usually by adding a 25K pot in series with the 6.8K resistor in the tone stack, so with the pot down full it is stock, and turning it up adds mids. But I want to go the other way. Would replacing that fixed resistor with a 10K pot do the trick?
                          Somehow I missed this 10 days ago. Either that or I thought gaz had the good answer, and I still do. Fender's mid control in the classic mid 60's & 70's amps that have it (Twin Reverb, Bassman 100 & 135, Showman, Dual Showman etc), is exactly that, a 10K pot wired as a rheostat aka variable resistor. As you dial it down from 7 towards 1, you develop a bigger "ditch" in the midrange. I found it handy for use on bass guitar when a friendly chap lent me his 100W Bassman head in the mid 70's - I got the sound I wanted by dipping that mid control all the way.

                          Chuck, hows about a graph of the mid pot set all the way down to zero ohms compared to stock 6K8 resistor? TIA!

                          Some guitarists, especially blues players ask me for a mid control that only adds mids, and doesn't cut them. And lots of mids at that. A 25K or even 50K mid pot with the stock 6K8 resistor in series makes 'em happy. I have to warn them, when you have the mids cranked up a lot, your treble & bass pots won't do much anymore. Note Mesa/Boogie's boost circuit in their original Mk I amps switched a 47K resistor in series with the mid pot, effectively bypassing the lossy tone control circuit entirely. Some players loved it, others complained " it sounds honky, and my tone controls don't do anything" whilst in the boost mode. Well, that's why. Then the next iteration of amps from Mesa and their competitors notably Sundown had separate channels with an extra gain stage for the boost plus tone controls for each. That's how progress is made. Mesa's business thrived while Sundown withered on the vine, such is life.

                          Enjoy. Every. Sandwich.

                          Comment


                          • #14
                            Originally posted by Chuck H View Post
                            If you're the only person I irritate with my choice of words today I'll be surprised
                            Well, there's my new tag line.
                            -tb

                            "If you're the only person I irritate with my choice of words today I'll be surprised" Chuck H.

                            Comment


                            • #15
                              Click image for larger version

Name:	maz1.PNG
Views:	52
Size:	23.3 KB
ID:	911285
                              "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

                              "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                              Comment

                              antalya escort
                              kartal escort
                              sex vidio
                              Working...
                              X