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Cascading gain stages?

Discussion in 'Amp Central Station' started by Brick, Jul 11, 2007.

  1. Brick

    Brick Tele-Holic

    Age:
    65
    818
    Mar 22, 2003
    San Jose
    OK, I'm planning my next build and am thinking of building Dave Hunter's ("The Guitar Amp Handbook") two stroke amp as presented in his book. Class A running parellel with some interesting switching to change the bias resistor values so as to enable the running of a few different tube combos. I was thinking of adding a gain stage for giggles, but really, how different is this from running a clean boost, aside from being tube powered. Has anyone built this amp?
     
  2. 11 Gauge

    11 Gauge Poster Extraordinaire

    Mar 21, 2003
    Near BWI Int'l
    To me, cascading gain stages will always be the most difficult thing to tweak.

    I've found that with most modern 'high gain' amps that there are simply too many gain stages. It makes it nearly impossible to get a good tone because everything is clipping so heavily.

    To me, the best tube amp grind I have ever heard has come from old Marshalls and HiWatts, and they have only 2 or 3 gain stages. I've also been playing around with TrainWreck - styled preamps, and they get whopping gain from just 3 gain stages.

    IMO, the only real advantage to an add'l stage is that you get a chance to vary the harmonic content a bit, by biasing the tube differently, jumping the input or output impedance up or down, switching to a different value coupling cap. But even then, I've heard great results with fairly analagous gain stages as well.

    I'd say that if it is your first build, keep the preamp tubes down to 2. As for the power amp section, I'd go with class AB and cathode biasing if it is a first build. I've yet to find a real advantage to going class A. Most amps claiming to be so, aren't, BTW.

    Keep it simple, and have fun. If it needs more gonzo, you can probably scrounge up a bit here and there by tweaking the circuit.
     
  3. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

    Mar 12, 2005
    Fullerton, CA


    Cascaded gainstage can be a bit tricky when it comes to getting a great overdriven tone... mainly because everyone has specific tastes when it comes to overdrive.

    I actually really dig Master Volume controls most of the time (which probably puts me in a "hair metal" category here on TDPRI hehehe)... a close second place is often a low watt amp dimed. Depending on the circuit, having a cascaded gainstage switched in or out can be good as well... but it depends on taste and the circuit.. hell, sometimes I really dig massive powered amps dimed into attenuators, or even some amps with OD pedals up front.





    Another advantage depends on the amp's circuit and power output. For instance, after much thought, my 25-30 watt 5D8 tweed Twin build is on the bench again - for a cascaded gainstage. Partially due to the convenience of an extra half of a triode sitting around unused, and also because the amp sounds great dimed, but not filthy enough for some uses... in this case a MV aint what I'm aiming for... just a little kick in the pre for those certain sounds.





    Class A is great for building a single power tubed 5 watt amp... Class A, cathode biased amps are very inefficient and can get you very low wattage/power to crank... multiple power tubes in parallel Class A? Thats different.

    I'm with 11 Gauge here.

    The fewer tubes to wire, the better for beginners. Also, the fewer gainstages for a first build, the better... otherwise, noise becomes a troublesome issue... shielded wire, keeping grounds seperate, etc.

    Keep your first build as either a true single ended Class A with ONE power tube, or Class AB if you're going to have a second power tube anyway (instead of Class A in parallel).

    Then again, I'm all for building exactly what you want right off the bat as well - just be prepared to troubleshoot (which can be very demoralizing)
     
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  5. Brick

    Brick Tele-Holic

    Age:
    65
    818
    Mar 22, 2003
    San Jose
    This is my third build

    First- Tweed Champ

    Second- Conversion from Hi Fi to 5E3

    Third? Dave Hunter's design. Why? Basicaly a tweed front end with a class A parellel output tube section. Why? So I could run dual 6v6s for 8 watts, one 6v6 for 4 watts, one 6L6 for 8 watts, one EL34 for 9 watts, or a 6K6GT for 3 watts.
    Also 3 way switch for manipulating first stage bias resistor/bypass cap values.

    I'm into low watt amps these days and being able to tube swap looks like it could be a lot of fun.

    I could build this in most any small tweed style chassis.


    Amp has only one 12ax7, two 6V6 (in it's basic design configuration) and a rectifyer tube.

    Also uses a OT tapped for multiple impedences.

    I'm also addicted.
     
  6. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

    Mar 12, 2005
    Fullerton, CA


    My mistake - I thought this was a first build.

    In that case, your points on parallel make perfect sense now... pulling tubes, changing impedance, and plugging away at different power levels - I like that idea :)

    As far as how different it would be than running a clean boost... I'm actually not too sure.

    I'd like to know how this build turns out though!
     
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