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  • Need more bass thump from Champ

    My BF Champ has a 4.7uf cap alongside that 1500K resistor going to the first preamp tube. Can't remember why that value since this amp has been moddded a lot. If I go back to the standard 25uf will the amp have more bottom? It's in a cab with a 12" G12H so the speaker is not the issue. The amp sounds good in general but lacks low end thump.

    Or should I look at the tone stack for changes? Right now it consists of: .02, .02, 500pf and a 100K slope resistor.

  • #2
    The words "Bass Thump" and "Champ" are not to be pronounced in the same phrase.
    Besides, it's a basically flat amp, with no great equalization to speak of, just raw tube sound.
    You have already done the second best: hook it into a better speaker.
    Even better?: hook it to a 4x12".
    That's the maximum "acoustic" bass it will provide.
    Any "electronic" bass increase will only turn it into mud.
    Just my two cents.
    Juan Manuel Fahey

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    • #3
      I should have been more descriptive about the amp. It has a larger Heyboer PT and a larger multi-tap OT--I use the 8 ohm tap. I usually run it with an EL34/GZ34 tube combo, though it can take 6V6 and 6L6 too. So it's not really your garden variety Champ. Based on this I would think it can achieve more bottom expression if tuned properly. I'm not a tech however, just a guitar player. I do solder pretty well though.

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      • #4
        If I go back to the standard 25uf will the amp have more bottom?
        Is that the 25uf that would go in the first stage? If so it sould give more bass then. Also sounds like the tone stack has been altered. A blackface champ has a 250pf, .1, and .047 going down vertically looking at the scat.

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        • #5
          You're correct the tone stack was altered to give a more Marshall tone. I'm wondering though if changing the bass cap back to .047 or maybe .033 would give it more low end oomph.

          Thanks for your help.

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          • #6
            It may either give more bass or shift the frequency response or both

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            • #7
              Originally posted by J M Fahey View Post
              The words "Bass Thump" and "Champ" are not to be pronounced in the same phrase.
              Besides, it's a basically flat amp, with no great equalization to speak of, just raw tube sound.
              You have already done the second best: hook it into a better speaker.
              Even better?: hook it to a 4x12".
              That's the maximum "acoustic" bass it will provide.
              Any "electronic" bass increase will only turn it into mud.
              Just my two cents.
              +1.

              Garden-variety Champ or not, the amp as it is is NOT a thumper, and the "Marshallization" of the preamp to roll-off lows actually makes it sound better and louder through the internal speaker by narrowing the power bandwidth, as well as quelling some IM distortion from excessive lows. You'll need a closed-back cab to get some "thump" from that amp.
              John R. Frondelli
              dBm Pro Audio Services, New York, NY

              "Mediocre is the new 'Good' "

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              • #8
                +2

                If the OD your achieving is from the overall amp at max power and not from some preamp or pedal the amp is already producing all the bass it can. The only way to get more is with a bassier cab/speaker OR to reduce other frequencies relative to the bass that's there. The latter will usually cause a loss of gain and definition in the tone. Increasing bass in the preamp will only have the effect making the tone more flabby. Not more bassy.

                Chuck
                "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

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                • #9
                  Upgrade your output transformer to a healthy Hammond SE style, and change the cap into the driver to a .0056. Less mud into the output stage, and the better iron should wake it up !

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                  • #10
                    I can get behind this. What I said before still applies, and there is only so much one can expect from a 3 to 4 watt single ended amp, but...

                    I did get some proprietary OT's from Heyboer that did for me exactly what Andy describes. If the OT is generously able to reproduce whatever bass the amp is making you CAN expect an improvement. My only concession is that there isn't much to start with on a small single ended amp.

                    I met Andy at the 2009 winter NAMM show. Dweezil Zappa was chewing his ear so he didn't have much time for me His amps sound good and he hit on something I should have mentioned. You should give it a try.

                    Chuck
                    "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

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                    • #11
                      +1. The biggest bass thump you'll ever get from a Champ is when it hits the bottom of the Dumpster.

                      Seriously though. They're nice amps but they're not thundering monsters of rock.
                      "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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                      • #12
                        Originally posted by Chuck H View Post
                        I can get behind this. What I said before still applies, and there is only so much one can expect from a 3 to 4 watt single ended amp, but...

                        I did get some proprietary OT's from Heyboer that did for me exactly what Andy describes. If the OT is generously able to reproduce whatever bass the amp is making you CAN expect an improvement. My only concession is that there isn't much to start with on a small single ended amp.

                        I met Andy at the 2009 winter NAMM show. Dweezil Zappa was chewing his ear so he didn't have much time for me His amps sound good and he hit on something I should have mentioned. You should give it a try.

                        Chuck
                        Even the Weber WSE-15 (which is a Chinese clone of the Hammond 125E) is a substantial improvement over the stock output. Those outputs are way too tiny for real music. They look like the outputs from tube table radios of the day !

                        Yes, you cannot get "more than 5 lbs of $hit in a 5 lbs bag". Watts are watts, but you can wring more apparent projection and punch from frequency contouring (low end especially) and a heftier output. Maybe a little more supply capacitance. Heck, get silly and add a choke too .

                        Sorry we couldn't chat at NAMM. Maybe another time. DZ is good people.

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                        • #13
                          What Kinda spkr is in it? different amp but a ragin cajun really bumped up the bottom and sensitivity in my super champ... Leo

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                          • #14
                            How big is your main B+ filter, go to 100uf if it is less than this.

                            SS rectifier?

                            A 100uf cathode bypass cap (100v rating) at the power tube should help tighten the low end...ideally convert to fixed bias.

                            A KT66 power tube has some rolled off high end compared to most 6L6/EL34 & may give the impression of being bassier, maybe try one, or if the PT will take the extra heater current, a KT88.

                            Everything Chuck, Andy & Steve says still stands, but these suggestions may help improve your current situation.

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                            • #15
                              Increasing the amount of negative feedback (Heresy! Ban him!) might tighten things up and give the illusion of deeper bass. I haven't tried it, so watch out for instability if you do.

                              Getting those guts into a larger cab with a bigger speaker would be my first step though.

                              - Scott

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