A new tube design?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by exodus, Feb 5, 2004.


  1. exodus

    exodus Member

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    I don't mean to open a huge can of worms here (famous last words....)

    But I was wondering-

    Do you think its possible to make a "solid state" tube? What I mean by that is- a sold state circuit, that tries to mimic tube characteristics under load, that plugs into the tube socket of your amp.

    Just curious.
     
  2. ekp

    ekp Member

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    There was a circuit that was alleged to replace a triode. Actually it was two junction FETs operating in cascode. The first one provided the gain and the second provided the high voltage capability. However, its characteristic curves were more ideal (from an engineering sense) than a pentodes. There is some sort of a junction FET that is alleged to have the operating character of vacuum triodes, but I have never worked with one.

    On the otherhand, I did a circuit that mimicks tubes but it operates at solid state voltages.

    The bottom line is that I believe that your quest can be done, but I doubt that it will be done because the volume that semiconductor houses need is huge. I asked about a special chip for my circuit and the producton requirements would satisfy the entire US guitar amplifier market.
     
  3. mbratch

    mbratch Member

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    The Tech*21*NYC SansAmp line is based upon that notion. They use FETs to attempt to mimick tube behavior. Of the solid state devices, the FET comes closest to behaving anything near how a tube behaves (or so I've been told). But it's still only approximate. The engineers at Tech*21*NYC have spent some serious time attempting to close that gap as much as possible.

    In the end, it's still not "just like a tube". ;)
     
  4. ekp

    ekp Member

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    I agree that FETs are not like tubes, the characteristic curves are completely different. But there is more to it than that. I have a patent on a tube emulator that mimmicks a 12AX7 so closely that the waveforms layover each other as you increase the level from clean to dirty. But this is not enough. There is a lot more going on in the output stage. In fact there is a lot more going in the output stage than in the preamp stages.

    So besides getting the preamp right, the output stage nees a lot of attention.

    Just to make life more interesting, the design information is not in text books because the engineering philosophy excludes overdriven and other sorts of non-linear behavior. In fact, the reasons that engineers and musicians are so far apart is that engineering philosophy won't consider what musicians hold dear.

    So I agree that manufacturers in general have not managed to make solid state sound right. However, from personal experience, I strongly disagree with the notion that it is impossible.
     
  5. mbratch

    mbratch Member

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    Keith, that was a very interesting post. I appreciate you sharing your expertise. I am not an EE, so what I know about FETs w.r.t. tube emulation is only based upon what I heard talking to another EE, and what I had read about the design philosophy at Tech*21*NYC.

    I agree that musicians and engineers are often at opposite ends. I am sort of a hybrid (computer engineer with only a little EE, and a musician), and I work with EEs. I've had some discussions with an EE here at our office about digital amp emulation, for example, and as far as he's concerned, it should be possible to design a system today that emulates it so that you can't tell the difference. I tried to define the word "mojo" for him, but it just didn't compute. ;)

    Anyway, when you say that it is not impossible to emulate the tube amp behavior with a solid state design, are you assuming the use of off-the-shelf components (ie, no investment in some kind of custom analog parts)? And, if so, is the reason why nobody does it is that it's cost prohibitive when compared to just doing a modern tube circuit design (I'm referring to product cost, not development cost)?
     
  6. ekp

    ekp Member

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    Most engineers will be quick to agree that it is possible to emulate a tube amp in a computer. The problem that they run into is that they do not know all of what constitutes a tube amp primarily because guitarists use tube amps in a way not really condoned by engineering and consequently not researched, and therefore because it is not taught in schools.

    My amps are built with off-the shelf components. They could be less expensive, but the economics of small manufacturers will not allow that.

    On the other hand, the advantages in my designes are in the freedom of optimization. Since the tube sound is not native to solid state, special circuitry has to be created to make it happen. This special circuitry is substantially independent of the amplifying functions and consequently can be optimized independently. I will definitely allow you to go places that tubes probably can not go.
     

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