Moving the tone stack

Discussion in 'Amp Tech Center' started by bossfrog, Sep 19, 2019.

  1. bossfrog

    bossfrog TDPRI Member

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    I have a Bugera V22 Infinium and I considering having the tone stack relocated. It is currently after all the the gain stages and is the last part of the preamp prior to the PI. I know the earlier in the circuit the more effect the tone controls have, generally speaking. I would like it to be placed immediately after the V1A gain stage. Has anyone else had this done? If so, were the results worthwhile? It seems to me to be the kind of thing an experienced tech can do in an hour or less.
     
  2. Wally

    Wally Telefied Ad Free Member

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    Moving that one stack also will change how the gain is built.....it will make it a different amp. Your amp is built loosely on the basis of what Marshall copied...the Fender 5F6A Bassman, albeit it perhaps with more gain stages. When Fender moved the tone stack to an earlier point in the circuit..after the first gain stage, they were looking for that change in order to moved toward a cleaner amp.
    The 2+1 format...2 gain stage followed by a tone stack...of the Bassman develops gain in those first two stages without the loss that comes in the 1+1 format that came in the 6G and Bf circuits. The difference in how the amp one stack works is due to that placement, which places the tone stack immediately following the first gain stage. Whatever one does with the tone stack in the 1+1 is amplified from that point on while the tone stack in the 2+1 acts on that signal after the preamp gain is created.
    It is interesting to note differences and perhaps to prefer one over the other. I can work with either one. In the 1+1 type of circuit, one has to be very careful when pushing volume that the tone controls are kept lower. Mesa Boogie has noted this in their MK amp manuals since the beginning of the Boogie amps. In the 2+1 and other circuits built on that, one can run the tone controls anywhere on the dial at any preamp volume setting with the signal going to pieces.
    I like Fender Super .champs, which are in ess nice a BF Princeton Reverb that has been hotrodded. It will do high gain, but in that mode one has to keep the tone controls down...especially the bass. I also like my fender Pro Sonic, which has its roots in the 5af6A Bassman world. In the clean mode, it has a 2+1 structure. In the Gain mode, it adds two gain stages for a 4+1 structure. The tones can be run anywhere on the dial in any gain setting.
    My opinion is that if you like anything about that Bugera, learn to work with it. If you don’t like what it does, get a different amp....something based in the BF Fender world. Ommv.
    Note: Jimmy Page has played those Marshall’s that are based in the 5F6A world. He runs the bass tone at ‘zero’. That is how he got that tone for those famous guitar riffs.
    If you are not happy with the reactions of the tone stack, you might consider changing the tone stack values rather than or at least before moving it. It is very likely that the values of the tone caps and the slope resistor are such that they avoid the mid scoop of the BF stacks. One could increase the value of the bass tone cap to bring more low end. increasing the size of the slope resistor will move the midrange response.
    In any case, good luck with it.
     
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  3. Bendyha

    Bendyha Friend of Leo's Silver Supporter

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    I would recommend using an equalizer in frount of the amp, (and maybe add the option of making the existing tone-stack switchable with a push/pull pot to lift it's grounding tail, taking it, quasi, out of the chain), that way you would have the best of three different worlds.
     
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  4. bftfender

    bftfender Friend of Leo's

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    i love my Bug 22
     
  5. bossfrog

    bossfrog TDPRI Member

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    Hmm... plenty to digest there. I might experiment with an EQ pedal a little. I've just never cared for them. They seem to introduce a lot of noise into the signal, at least in my experience.

    I have a friend who bought one of these a few years ago (and has since sold it) that had a ton of mods done to it. It had the slope resistor replaced with a pot. It had a switch to turn off the negative feedback circuit. It had the cathode resistor on V1B replaced with a pot. There were a few other things that I can't remember. All in all, it had 4 additional knobs and 3 additional switches. It had a huge array of tones you could get out of it, not all good. But the most extensive mod was a switch that moved the tone stack back and forth between the original position and right after V1A. You could do so much with it when switched earlier in the circuit. That's what got me thinking of doing this.
     
  6. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    //

    Temp thread Hijack.

    Every post from Wally and Bendyha is worth reading.

    //
     
  7. bossfrog

    bossfrog TDPRI Member

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    I do think I'll leave the tone stack where it is for now. I'm going to replace all the tone stack components to mirror those in the Marshall 2204 preamp. V1B seems to be where most of the distortion comes in on the drive channel. It has a cathode resistor of 5.6K, which puts it on the cool side but there is also a 220nF bypass cap on there, which might account for the slightly fizzy (but not unpleasantly so) quality of the distortion on this amp. I'm thinking of putting a 10K resistor in there and deleting the cap. The next gain stage has a 680Ω resistor. Is that warm enough on the bias to preserve the asymmetrical clipping or should that be changed to a different value as well? The goal here is to get a smoother overdrive and a more British flavor from the amp. Am I on the right track here?

    Here's a link to the schematic, BTW: https://www.tremolo.pl/Firmowe/BUGERA/Bugera V22 Full Schematic.png

    As for the idea of getting a different amp if I'm not satisfied with the overall character of the V22, where's the fun in that? ;)
     
    Last edited: Sep 20, 2019
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