The all tube modeling amp -- pipe dream?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Mickey_C, Mar 7, 2006.

  1. Mickey_C

    Mickey_C The Original Racketeer Gold Supporting Member

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    I've been toying with this idea for a bit... somebody pinch me, and wake me up - or methinks I might try this:

    Imagine if you had an amp that had 4 of the big multi-selection multi-pole rotary indexed switches on the back (or even the front). http://www.nkkswitches.com/pdf/hs_ps_ts.pdf

    Each dial, being coupled to an amplifier stage.

    Let's say one for V1, one for V2, one for the tone stack, one for the PI, and one for the power amplifier.

    By turning these dials, you reconfigure the circuit of each stage, giving a wide range of tonal possiblities.

    I know these switches are like 100.00 per pop, but is this a pipe-dream, or can it be accomplished?

    I'd really like to take a swing at doing it. I am currently doing something similar with just the preamp stage of a JTM45 style amp... but it really begs the question if this can be more broadly applied.

    If it works, it could eventually be done with a CPU, optical isolators and relays. Then you could have the programmable truly tube tone amp.

    Fantasy or reality?


    Mickey
     
  2. slhguitar

    slhguitar Member

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    sounds like a suped-up version of the mesa road king to me....But without the rectifier circuit as a constant. I can't see why this wouldnt work....but in the beginning would be unbelievably expensive and complicated. I'm interested in hearing what other people who know more than me think about this.
     
  3. utterhack

    utterhack Member

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    http://www.zinky.com/superfly.html :)

    But yeah... I was thinking about this the other morning. In theory there's no reason you shouldn't be able to store and access any number of gain and EQ combinations, which would get you 80% of the way there.

    Not unlike the ol' Reverend "schizo" switch I guess...
     
  4. Mickey_C

    Mickey_C The Original Racketeer Gold Supporting Member

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    Bruce, is that you? Slummin' it hey?

    I did not know about the Superfly. Does it actually change the configuration of the stages? Basically redesigning the circuit itself? For instance, switching the PI from a long-tailed to cathodyne? Or a plexi input stage to a 2203 stage?

    Pretty wild stuff... you've done this already?

    WOW.

    Mickey
     
  5. Mickey_C

    Mickey_C The Original Racketeer Gold Supporting Member

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    I've now looked at the Road King and the Superfly.

    I am not sure the Superfly does this - the website doesn't really spell it out. It looks more like it has programmable front panel controls, which is a good thing, but doesn't really say it actually reconfigures the amplifier itself, into a completely different amp. For instance going from a true Marshall 2203 circuit to a true fender AB763 circuit.

    The Road King does this with the power amp section, but does not appear to do this with the preamps... however I am not really sure. Other than the fact that Randall Smith has patented this in as wide a scope as possible. Surprised? But does the Road King actually reconfigure the preamp stages? Change the type of phase inverter? Change the tone stack configuration?

    If so, then I definitely want to try one. However, I think I'm going to build my rotary dial one anyway, just for fun.

    mickey
     
  6. utterhack

    utterhack Member

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    If only! Nope, I'm a n00b, and my ID should be an accurate description for the foreseeable future.

    Apologies if I got your hopes up - the last-mile 20% that those solutions leave off is indeed the hard (and cool, and costly) part that you're looking for.
     
  7. slhguitar

    slhguitar Member

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    yeah, i think the road king only switches power tubes.....but I really dont know. I dont think it changes any preamp configuration. If you end up completing this creation of yours, let us know how it works out!
     
  8. donnyjaguar

    donnyjaguar Member

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    This is interesting. You'd end up with an amplifier that is very complicated and difficult to "drive" though. But that's not saying its a bad idea.

    I wouldn't use a multi-pole switch myself as this would be a good application for a PIC controller, perhaps with an LCD display. This would be less than the $100 for the rotary switch and could be programmed to mute the amplifier when switching modes. You can get high-voltage transistors that could be wired to bring tubes in and out of the circuit and these are cheaper than relays - not much current required for tube VAs so they won't be power types. The one exception here would be switching between pentode and triode mode where you'll definitely need to use a relay. No problem DPDT is good enough.

    I like the idea of switching between a conventional tone stack and a Baxandall circuit although this would be very complex and you may just want to use double-pots and switch the in and out. Also switching between a paraphase and williamson phase splitter would be interesting, but there'd be a big difference in gain here that you'd need to compensate for elsewhere in the circuit.

    Switching between a vacuum tube rectifier and solid state would also call for a relay.

    Another thing to consider (and I considered this for my last amp build) is switching between fixed bias and cathode bias. You could do this without a relay but it would introduce a semiconductor to your signal chain which may be considered sacrilege.

    This project is definitely do-able. You know that they say, if nobody laughs at your dream it isn't big enough.

    DJ
     
  9. mbratch

    mbratch Member

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    Sounds like, perhaps, a tube version of a Tech 21 PSA-1?
     
  10. paintguy

    paintguy Long Hair Hippy Freak Silver Supporting Member

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    What about the Randall modular stuff? Just thinking out loud.
     
  11. einstein

    einstein Member

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    line 6 should use tubes to gain a bigger market
     
  12. mbratch

    mbratch Member

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    Johnson Amplification used tubes in their amp modeling, but they're not in that business any more.
     
  13. John Phillips

    John Phillips Member

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    The simplest way would be to do it like the Road King but with more tone differences and parts - ie several completely separate preamps (not just four Mesas using the same basic structure ;)), each with their own tubes and gain/tone configuration (there aren't actually that many really different ones, so this would be possible), also possibly with switchable control networks on the same audio path (also already done, the Mesa Nomad channels 2/3 and the Fender Tone-Master are examples). Then have a couple of separate PI configurations, also each with its own tubes and parts, then several power tube sets and rectifiers. (And cabinet switching, since that's an important part of the tone.)

    OK, the whole thing will be huge and heavy... complex stuff with tubes is always going to be - have you ever seen a tube computer? ;) About the size of a house and with less processing power than a modern pocket calculator :).

    In the end it's probably just easier to use several separate amps - although there are still a few advantages to putting them all in the same box (common FX loop routing, overall volume control etc) - because to really 'model' some of the differences accurately you're even going to need different transformers etc... so basically you're just building several different amps on the same chassis. The great advantage of digital modeling is that it doesn't use any of the same physical technology, so it can just sidestep all that. (The disadvantage is that it just sounds crap :p.)
     
  14. mbratch

    mbratch Member

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    Here's what the options seem to be shaping up to be so far (in order of decreasing complexity and decreasing flexibility OR tube-ness):

    1) John's shown the path to nirvana for a tube-based amp modeler. In essence, you really end up with at least entire pre-amp circuits in a switchable array of some kind. In part because a significant contributor to the sound of an amp is the topology of the pre-amp circuit (e.g., they have their tone stacks in different places/stages for one thing). Maybe the best thing you could do, besides having separate amps, is to have an array of complete pre-amps switchable through an array of complete power amps/cabs.

    2) The next most practical approach is what paintguy pointed out: what Randall has done with their modular amps. It works fairly well, except probably more limited in terms of the variety of amp tones you'll get as compared to #1. But you still get real tube sound/tone.

    3) Take the SansAmp PSA-1 approach, perhaps using tubes instead of FETs. Similar pros/cons as #2 I think, but perhaps easier to use.

    4) Do what Johnson Amp and Vox have done and use digital modeling with a tube or two added to enhance the sound to be more tube-like. This gets back to greater flexibility (more amps sounds) but much less tube-ness in tone/sound since now you're in the digital amp modeling with the tubes relegated to an assistant position.
     

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