Advances in Technology, Revisited
I've been playing my guitar through a modeler - and nothing but a modeler - for four months now. I've had no desire to go back to my tube amps; the modeler sounds great. I am holding on to my tube amps, at least for a while. Tube amps are, after all, the benchmark of great guitar tone. But I'm beginning to wonder whether the benefits of a tube amp aren't outweighed by its disadvantages.
I won't belabor the benefits of a tube amp: the dynamic response to a player's touch makes the amp an extension of the instrument. Indeed, many guitarists believe that a great amp is more important than a great guitar. But let's take a step back and examine the so-called "great" guitar amp with a more critical ear. Are all tube amps "great"? No. In fact there are some that are, for various reasons ranging from poor maintenance to poor design, pretty darned bad sounding. Personal taste has to figure into that assessment, of course. The point is, though, that any particular tube amp is not going to be a "great" amp from every player's perspective. If you're a tube amp enthusiast, chance are that you've gone through a number of tube amps to find one or two that really satisfy you. That's to be expected. You've probably noticed that your playing has adapted a bit as you've converged upon your ideal amp. That's also normal. A good amp is an extension of your instrument; your technique adapts to get the most out of the instrument.
A great tube amp, though, tends to be a finicky beast. The magic of a good tube amp is in the synergy of all its component pieces working together in ways that are not readily predictable. This is why we say that an amp has a "sweet spot". You have to push it hard enough so that the components start interacting with your guitar tone, the environment and each other in interesting ways. There's a sense of being "on the edge of control", where small changes in playing technique are rewarded by dramatic changes in the sound. Part of the challenge - and the joy - of playing a great tube amp is finding that edge and dancing along it. The problem is that the edge isn't always in the same place. You may always be able to find it, but you're going to work for it. If the line voltage or the humidity is higher or lower than usual, the amp will behave differently due to changes in the performance of the circuitry and speakers, respectively. Component values drift over time. Tubes wear. Speakers change due to break-in (and late in their life span, degradation of materials). These gradual changes are easier for the player to track on a day-to-day basis, but more insidious over the long term because the sound and behavior of the rig changes and you tend to adapt to gradual change without noticing that anything is different.
With the exception of the negative feedback loop around the output stage in certain designs, a tube guitar amp runs entirely "open loop". This means that almost every component contributes something to the way the signal is transformed by the amplifier. Small changes in component values or behaviors can have observable (even if not fully predictable) effects upon the sound of the amp. Again, this is part of the charm...
By way of contrast, an amplifier designed using "closed loop" principles has a much more precise relationship between the input and output signal, determined by certain mathematical relationships between key components. The feedback loops are designed to normalize the behavior of the amplifier despite changes in things like the line voltage, component tolerances and tube age. This yields greater predictability in the behavior of the amp over its life span at the expense of suppressing all the wonderful little unpredictable "nuances" that one gets from an open loop design.
It's the simplicity of tube circuitry that gives tube amps their magic. Tubes really are very simple devices. I understood how a vacuum tube operated at the age of six, and was building my own tube circuits by the age of ten or twelve years. It's genuinely difficult to put together an audio amplifier that doesn't work, once you comprehend the technology and the requisite assembly skills. There's a lot of discussion among tube aficionados about the "mojo" of certain designs or designers. If you want mojo, buy yourself some inexpensive totem (a rabbit's foot, perhaps) and don't worry about all the points debated by self-professed experts. The truth is that the overall sound and behavior of a tube amp is determined primarily by its design and to a lesser extent by a few key components. All the other stuff is so far "down in the noise" that you'd be hard-pressed to identify a particular designer's or builder's amplifier by sound or feel in a blind test. Frankly, even for the details which have observable and repeatable effect upon the behavior of an amplifier, the end result is a matter of taste. In the end, it's your musical vision and skills that are important.
There are some tube amps that sound great. And some that don't... Let's be realistic: the presence of tubes does not guarantee a great-sounding amp. And even the great-sounding tube amps have their downsides. Tubes have a limited useful life. I'd argue that a lot of tube-amp owners replace tubes far too often. Even so, tubes develop unmusical noises due to materials impurities and mechanical defects, and these tubes must be replaced. Tube amps have a lot of iron in their transformers and chokes, which makes them more difficult to lift. And then there are the issues related to open-loop design and variations in components and operating conditions. None of these are fatal flaws, of course. Guitarists have played through tube amps for over sixty years and - the free market willing - will probably continue their love affair with tubes for at least another few decades.
But now there's competition from a completely different technology. Back in the early `90s (or thereabouts) some entrepreneurs asked the question: "Can we use digital signal processing (DSP) to emulate the behavior of a tube amplifier?" In the early days, the answer from tube-amp users was, "No, you really can't do that." And they were right at the time. Early DSP models were overly simplistic; they made unwarranted assumptions about the actual behavior of tube amps. As the years went on subsequent revisions and generations of DSP amp modelers implemented more complex behaviors, narrowing the gap between the modeler and the "real thing". I'm almost certain that the latest generation of modelers does not accurately emulate a tube amp. In fact there are behaviors that I doubt will ever be modeled either because they're too subtle or because modeler users would prefer a certain degree of long-term predictability in their guitar tones.
The question then becomes, "what do modelers bring to the table?"
The first and most obvious answer is that a modeler offers predictability. DSP is deterministic. A particular signal will elicit the same response whether the line voltage is 105 or 115 or 125. (A DSP is, after all, a computer and computers regulate their internal power supplies despite variations in the line voltage.) The response will be the same whether you're playing in an inadequately heated garage on a winter's eve or a festival stage in the blistering summer sun. (So long as the temperatures remain "safe" for the gear, the same numbers get processed to create the same results.) Perhaps most important of all, the response will be the same five years from now as it is today. (The result of a calculation doesn't change as the computer itself gets older.) A modeler's predictability will not allow for the "pleasant surprises" that we sometimes get from tube amps as conditions change. On the other hand, the "good sound" that I dial in on my modeler today will not slowly mutate over time. It's sound exactly the same every time I need it. I can even replace the hardware and - so long as I've saved my patch - get the exact same sound with the new hardware. Try doing that with two different instances of the same model of tube amp.
The second thing that modelers bring to the table is portability. The lower bound on a modeler's size and weight tends to be determined by its controls and (in the case of a combo amp) speaker cabinet. Modern digital electronics is very small and lightweight compared to the kind of vacuum-tube electronics found in guitar amplifiers.
The third positive attribute of modelers is their scalability, in a sonic sense. Whereas a tube guitar amp must be operated in it's "sweet spot" to sound its best (at volumes which are increasingly incompatible with modern-day small live-performance venues), a modeler can - with some basic volume-dependent EQ adjustments - sound just as good at any volume, from quiet intimate club to outdoor festival. This scalability happens because the tone generation (which happens in the DSP) is decoupled from amplification. Sound-reinforcement amplification is clean and transparent, not adding any of its own coloration. For purposes of amplifying a modeler, one power amp is as good as the next so long as they all offer sufficient power. Likewise, sound-reinforcement speakers (unlike guitar amp speakers) are expected to be neutral-sounding. Also, sound-reinforcement speakers tend to be far less susceptible (by design) than guitar speakers are to the effects of humidity.
The only downsides of modelers are the limited choice and the relative complexity, as compared to tube guitar amps. Regardless of the labels on the amp model control, every brand of modeler has its own sonic signature. You may or may not like that signature. Given that there are only a handful of brands and that each manufacturer spins multiple products from the same DSP code base (products are differentiated by packaging and feature set, with the larger more complex devices commanding higher prices), you really only have a few "sounds" from which to choose. The situation is exacerbated by the relative difficulty in coming up to speed on any given product. To go beyond the preset patches (which invariably won't agree with your personal tastes) you have to invest at least a couple of hours in learning the architecture and programming of each modeler that you'd like to audition. That investment in time is enough to scare off many potential modeler users, given that one can walk up to any tube amp and know in a few minutes whether a good sound can be had.
For me, the benefits of a modeler are clear and compelling. I get the sounds I need from a package that's compact, lightweight and easily replaceable. Furthermore, I can play through any full-range flat-response amplification system, which makes it much easier for me to tailor the gear to the venue (or to simply use the venue's amplification). I have to admit that it took me a while to find a modeler that worked for me. On the other hand, it took me a long time to find a tube amp that worked for me, too.