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Brownface tone control question

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  • Brownface tone control question

    I've been playing around with an old Masco amp, changing cap/resistor values to make it more suitable for guitar. It has 2 knobs Bass and Treble controls and I'd like to keep these but change the circuit. As is, the Bass control seems to be working off of the NFB and the cathode bias of the phase inverter?

    I'm hoping to roll off some bass and maybe get a bit more brightness. I definitely want to keep a bass and treble control so I think I'm gonna give the Brownface circuit a go. I'm missing the 250P capacitor, but I have a 500P or a 100P laying around. Could I use a 500P or a 100P cap to get more brightness here? I see the Brownface circuit calls for 250K pots. Would there be any difference in using the 500K pots that are already in there?

    Thanks!

    Brownface Tone Stack
    http://www.hereforever.org/6G5.gif

    Modified amp schematic
    http://www.hereforever.org/cm8.jpg

    Original amp schematic
    http://www.hereforever.org/cm8.jpg

  • #2
    The 250p cap is a treble cap. Increasing it will let more highs through. The easiest way would be to put the 100p cap in parallel, which will make it 350p.

    Changing the pot values will change everything - it won't sound right for guitar.

    Your best bet is to stick with stock values, or play with the tone stack calculator
    http://www.duncanamps.com/tsc/index.html
    See the birth of a 2-watt tube guitar amp - the "Dyno Tweed"
    http://www.naturdoctor.com/Chapters/Amps/DynoTweed.html

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    • #3
      I don't think the Brownface tone control is in the tone stack calculator unfortunately

      Comment


      • #4
        That's a really odd amplifier circuit!

        Comment


        • #5
          Oops. the original is at http://www.hereforever.org/cm8orig.jpg

          Whats so odd about it? As modified it's similar to a Fender deluxe, but I agree that the original circuit is wacky!

          Comment


          • #6
            As shown in the schematic, the fuse is on the wrong side of the line.

            Comment


            • #7
              There is no fuse. I had to put one in

              Comment


              • #8
                Originally posted by PRNDL View Post
                The 250p cap is a treble cap. Increasing it will let more highs through. The easiest way would be to put the 100p cap in parallel, which will make it 350p.

                Changing the pot values will change everything - it won't sound right for guitar.

                Your best bet is to stick with stock values, or play with the tone stack calculator
                http://www.duncanamps.com/tsc/index.html

                I'm sorry PRNDL, but that's wrong. Caps in parallel add up! and in series you have f1Xf2 / (f1+ f2)

                so 500X100 = 50000 / 600 =83.33 IIRC

                http://www.aikenamps.com/AddingComponents.htm

                Comment


                • #9
                  I saw that there was no fuse. My question was wether the one you going to install was like it was drawn on the schematic or the correct way, on the hot side of the line.

                  Comment


                  • #10
                    Oh! My mistake, yes thanks for the tip I hadn't noticed my mistake there. haven't added it yet but duly noted

                    Comment


                    • #11
                      "odd", because I've never seen an amp wired that way. For instance, the unusual bass level control, and the way they voltage diviede one of the PI plate signals.

                      However, I don't actually know that much about the various amps out there, at least by specifics.

                      Comment


                      • #12
                        Originally posted by Earl View Post
                        "odd", because I've never seen an amp wired that way. For instance, the unusual bass level control, and the way they voltage diviede one of the PI plate signals.

                        However, I don't actually know that much about the various amps out there, at least by specifics.
                        Actually it is a very commonly used tone stack... in the past and even today.
                        If you look closely and spin the bottom around the common leads, the Brown tone stack is almost exactly like an AC30 Top Boost, AC50 and AC100 tone stack except that VOX uses 1M pots, 22nF cap and a 47pF treble cap!
                        Attached Files
                        Bruce

                        Mission Amps
                        Denver, CO. 80022
                        www.missionamps.com
                        303-955-2412

                        Comment


                        • #13
                          Interesting note about the Brownface tone stack, Bruce. I haven't played around with Vox controls yet but I was thinking I might look into that. I ended up going with the classic Bass, Treble, Mid Fender circuit subsituting a resistor for the Mid control and playing with values in the Tone stack calculator until I got something usable with the 500K pots. It sounds awesome now but I was surprised by how much gain is lost in the tone control

                          I think previous poster was referring to the Masco's tone controls. I agree that the bass control is pretty weird going off of the NFB. It seemed to have more of an effect over the Crystal input on the original circuit, maybe because the coupling capacitors on the Magnetic input having an already pretty bassy sound.

                          Comment


                          • #14
                            Originally posted by hearforever View Post
                            Interesting note about the Brownface tone stack, Bruce. I haven't played around with Vox controls yet but I was thinking I might look into that. I ended up going with the classic Bass, Treble, Mid Fender circuit subsituting a resistor for the Mid control and playing with values in the Tone stack calculator until I got something usable with the 500K pots. It sounds awesome now but I was surprised by how much gain is lost in the tone control

                            I think previous poster was referring to the Masco's tone controls. I agree that the bass control is pretty weird going off of the NFB. It seemed to have more of an effect over the Crystal input on the original circuit, maybe because the coupling capacitors on the Magnetic input having an already pretty bassy sound.
                            Ah... I thought the "unusual" comments were with respect to the Brown face tone controls... which by the way... who's idea was it first? Vox Fender

                            Also, over the years I have come to the realization that good players, who favor the Fender TMB vs VOX TB and the Marshall TMB... really don't care for the other's tone stack that much, especially if you are not a VOX tone lover. And, when installed in the same place in a high gain metal amp using a cathode follower driven TMB , the metal head guys really dislike the Fender TMB .
                            Last edited by Bruce / Mission Amps; 04-06-2008, 06:06 PM. Reason: added comment
                            Bruce

                            Mission Amps
                            Denver, CO. 80022
                            www.missionamps.com
                            303-955-2412

                            Comment


                            • #15
                              Yeah, I was refering to the other things going on in that particular amp. Passive EQ's are .....well......passive EQ's .. :-)

                              I agree about the Vox vs. Fender/Marshall deal. At least in my case, never did like that Vox "sound". I've bin using Fenders since '62. I guess you just get used to that sound.

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