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Three simple mods I did to my tweed Champ that made a huge difference:

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  • Three simple mods I did to my tweed Champ that made a huge difference:

    Here the basic schematic of a tweed 5E1 Champ. (the one with a choke)
    It's a great base for a lot of modding. The general thought with tweed Champs is that they are a "one-trick pony" Dial it up to 12 (the only way they sound good) and play. No cleans to be had worth mentioning. Ironic because that wasn't what Leo was after. Is it possible to get more tones out of this design without a lot of money?






    I should mention that besides these 3 mods I replaced the speaker with a 10" Weber. The mods still work with the 8" but a 10" gives you more range. Less boxy which enhances the tone further.

    Mod #1 Look at the inputs. Both of them have that same 68K resistor. What's the point in that? The guitar sounds exactly the same through both of them. I want more gain and brightness out of input #1. I'll swap out that 68K resistor for 20K. This allows the signal from the pickup to hit that preamp tube harder. Less resistance means less attenuation of the trebles at lower volumes too. Try other resistors and see what you like. If you reduce it too much you might get too much distortion at lower volumes. Leave the 68K on 2 to keep the original circuit there for the purists.



    Mod #2. When you turn down the volume on a Champ, things get muddy. My answer was to put a treble bypass cap across the volume pot. A value around .022 uF (more or less try different ones) works great here. You can even install a little toggle switch to engage or disengage the cap from across the volume pot to toggle between the mod and "stock Champ circuit"



    Mod #3. An old trick that some modders like is to do is to eliminate the negative feedback 22K resistor that comes off the speaker here:


    Some people disconnect the wire entirely. Others change the value. Leo Fender put it there to tame all the distortion. He was trying to make a cleaner amp. But we might WANT distortion. I decided to replace this resistor with a 10K resistor in series with a 500K audio taper pot. This allows me to dial in lots of different values including the original value. This mod increases treble and acts like a gain control. Works great with the other mods.

    Not only do these mods increase versatility and volume, they actually make a simple signal path even less restrictive. For the cost of a resistor, a cap and
    a 500K pot you can open up a world of improvement without sacrificing the amps original tones.
    "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen

  • #2
    I dont own this amp but I find this interesting and educational.

    I have been wanting to get into the 'tech' side of amps lately.
    Good transactions with: JonathanD, NixerX, sdhupelia, jtizel666, The suicider, dbonanzam, phatgirl, Xenoanthropus, Sixtonoize, 98 les paul

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    • #3
      I'm really an amateur but I'm starting to discover that swapping out a small capacitor or resistor in my amps can often have as much of effect on your tone as expensive speaker, pickup or tube swaps. It's diverted my attention away from that stuff over the past year. It's like you can get a whole new amp without spending money. It's also saved some of my unused gear from getting sold off.
      "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen

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      • #4
        I guess I should UPDATE this thread with a 4th mod I discovered:



        This section is the preamp gain section. Coming off the cathode (which is the at bottom of the 12AX7 tube symbol on the schematic) you see a 1500 (1.5K)resistor in parallel with a 25v 25uF capacitor to ground. These are the cathode resistor and cathode bypass cap. I'm not exact on this but I believe the resistor functions to set the bias of the tube and the cap functions to increase gain and bass at the expense of some distortion.

        Now if you look at a later version of the Fender Champ (the 5F1 version) this little capacitor isn't there. Why not?

        Some people feel it was just Fender cutting corners. Others believe it had to do with the first Champs having a 6" speaker and needing more bass. When they went to 8" the designers eliminated the cap because they didn't need to push for more bass and gain. To further confuse matters, a huge number of Champs built in the late 50's and early 60's that are supposedly the later 5F1 version STILL HAVE THIS CAP, even though the schematic shows it missing.

        At any rate I decided to reduce the value if not eliminate this cap entirely.

        My input resistor mod, volume pot bypass, and negative feedback resistor pot mods all functioned to increase gain some anyway, and I could probably afford to lose this cap to sacrifice gain for clarity. Moreover I have a 10" speaker now and the bass isn't hurting any from that. Since there are Champs out there with the cap totally missing it's not like I have to worry about the amp blowing up over this at any rate.

        Long story short I ended up replacing the cap with a 4uF 25V cap. I eliminated the cap entirely and also tried a 3uf 50V cap, but the 4uF worked best. The overdrive smoothed out a lot with more compression and sustain. These are things I would equate with MORE gain and not less, but what I think is happening is that the frequency response shifted a touch higher which worked better with the speaker and other mods. Best way I can decribe it is a little less bass, a little more mid hump, especially overdriven...and a smoother overdrive.

        I noticed with this recent mod that more guitars I play through it sound great.
        I had thought about making this a "swithchable" mod like the other mods, but the sound is so good I don't think I'd ever use the amp with the bypass cap engaged. I have read about some amp modders making the cap a switchable "boost" switch with a 40% increase in gain claim. Personally I think it's more of a sound shaping mod that an all-out gain boost.

        If you have a Champ and want to find this cap (if your Champ version has it)
        It's usually located at the end of the board with a 1.5K resistor running in parallel with it.
        "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen

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        • #5
          Cool mods!

          I may try the NFB mod on my Vibro Champ.

          All Champ/VChamp owners should check the amp's bias. Both my Vibro Champ & the Champ head I built passed WAY too much current through the 6V6 stock. I nearly doubled the cathode resistor & changed the 25/25 bypass cap to a 25/50. Both now pass 26-28 ma & sound much better, particularly when overdriven (smoother, sweeter).
          ____________________________________________
          The Homebrews!http://home.bellsouth.net/p/PWP-rupertamp

          "The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair." -Douglas Adams, Hitchhiker's Guide to the Galaxy

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          • #6
            I'd considered experimenting with the cathode resistor and cap of the power tube but it sounds really nice the way it is right now. I hate to mess with it.
            I've never actually checked voltages with these mods either.

            I might consider swapping out the treble bypass cap over the volume pot to a slightly lower value (.01uf? .006uF?) to maybe see if I can squeeze a touch more brightness out of the amp at low volumes...but other than that I think I'm done. Maybe I'll do a Youtube demo of the mods.
            "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen

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            • #7
              Hi,
              The input #1 has a 34k resistor and the #2 68k resistor. No need to change it.

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              • #8
                Originally posted by guitarcapo View Post
                Mod #1 Look at the inputs. Both of them have that same 68K resistor. What's the point in that? The guitar sounds exactly the same through both of them. I want more gain and brightness out of input #1. I'll swap out that 68K resistor for 20K. This allows the signal from the pickup to hit that preamp tube harder. Less resistance means less attenuation of the trebles at lower volumes too. Try other resistors and see what you like. If you reduce it too much you might get too much distortion at lower volumes. Leave the 68K on 2 to keep the original circuit there for the purists.

                Originally posted by berl View Post
                Hi,
                The input #1 has a 34k resistor and the #2 68k resistor. No need to change it.
                berl is correct

                both inputs #1 and #2 use switching jacks - plugging into #1 removes the shunt from across the 1Meg resistor and, with nothing plugged into #2, the two 68k resistors are in parallel resulting in an effective resistance of 34k.

                plugging into #2 disconnects the parallel resistance and, with nothing plugged into #2, one end of the second 68k resistor is tied to ground creating a voltage divider circuit that results in half the output voltage of the guitar going to the control grid of the first tube.

                this is not to say that replacing one of the 68k resistors will not increase the effective gain of input #1 - it will also decrease the gain of input #2 by changing the ratio of the voltage divider.



                Last edited by onelife; 05-01-2017, 10:29 PM.
                As a human being, you come with the whole range of inner possibilities
                from the deepest hell to the highest states.

                It is up to you which one you choose to explore
                .

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                • #9
                  After the resurrection of this old thread I figured I'd post the values over the years I ended up with for this amp...It's pretty far removed from the Champ design at this point but sounds fantastic.

                  "I don't want to be immortalized through my work. I want to be immortalized by not dying." Woody Allen

                  Comment


                  • #10
                    I didn't realize it was an old thread.

                    Thanks for the update - I noticed you removed the negative feedback completely.
                    As a human being, you come with the whole range of inner possibilities
                    from the deepest hell to the highest states.

                    It is up to you which one you choose to explore
                    .

                    Comment


                    • #11
                      I know a majority of guitarist prefer tube over solid state BUT!! Has anyone played through any decent solid state amps?
                      I recently picked up a fairly old Yamaha G100 amp head.Other than pots being scratchy everything worked very well. I feel I got a steal for this amp head (120.00 cash) and then a friend calls me saying he had found some speakers big huge ones ended up he only had 1 left. I bought this 15" Lansing (Altec Lansing that is) vintage woofer for...................... .... 35.00!!!!!!!!!! went on-line and foud 2 being sold on e-bay for ..................................ready? 800.00 and a pair for 1,500. I had no cabinet so I built a fairly quick cab not expecting much but was very pleased with my dirt pedals into this head's clean side. Pretty cool.
                      So......anyone have some experience with a decent solid state amp combo or otherwise? I'm curious as to what you used and ran into the amp. Pedal wise guitar and amp make.
                      The distortion in the Yamaha is weak, no bite at all. So what Im really getting at is if anyone has any mods or ideas I could use to make this already good sounding amp into a better one.

                      Comment


                      • WRGKMC
                        WRGKMC commented
                        Editing a comment
                        You're better off using pedals to get what you need from the amp. SS amps usually have integrated circuits and PCB boards which make them difficult to mod, plus you're dealing with low DC voltages on components that have narrow tolerances.

                        When you tweak the voltages of solid state devices there's practically no margin between the component under performing and overheating. Mods therefor have to center around the entire circuit design for circuit, not just tweaking small things here and expecting big results like you can with a simple tube amp.

                        What it winds up being, is taking circuits and components and complete redesigns which is not only expensive but high tech also. If you could get the schematic into a CAD program used for designing circuits and key in all the different parameters of the components, then make one small change it affects things globally. Changes in the preamp affects the current being used and signal strength being applied to the next stage. You have to vary all the other components down the chain to protect components from being damaged and by the time you get done there's no guarantee the amp will sound any better then it did to begin with.

                        In summary, its a matter of tweak ability vs cost. You can spend a few dollars and get big changes from a tube amp. SS its high tech and expensive to modify. Engineers who design SS amps are already picking the best components for the cost and running them at optimum voltages. There really isn't much change that can be made on many SS amps.

                        There are a few things you can do like changing power caps when they are getting old to be sure the DC voltage is clean, making sure Pots and jacks are clean but that's just normal maintenance, not modification. The rule of thumb is, when you buy a SS amp you're stuck with its build. If you don't like the way it sounds you sell it and buy something else. You benefit from the fact the amp is usually half the price of a tube amp of similar wattage.

                        I do suggest you get some lubricating contact cleaner designed for cleaning pots and give them a cleaning to get rid of you scratchy sound problem. Pots are usually good for a couple of cleaning before they need replacement. Replacements are often more expensive to have done then the amp is worth and that's if you can even find the right pots by the time they are needing to be replaces.

                        Also Altecs are wonderful speakers. I have a pair of 12's I got in 67 with my Bassman amp and I owned a pair of 15's which I first used in my Altec A7 cabs and later in my Ampeg B52 Bass cab and ran them with a V4B bass head for years playing bass. Wish I still had them. They were my favorite speakers for tone. You can buy them for way less then $800 each. I keep an eye on them all the time and the going rate for the 15's is in the $200 range on EBay












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