Imagine, if you will, an all-tube guitar amp that’s completely programmable. That would give you as a guitarist the best of both worlds: pure tube tones and smart control features – like the option to save and recall all your favorite sounds (up to 128 of them, in fact!), including your gain and EQ settings as well as more standard stuff like FX. Can it really be done? Happily, the answer is yes, and the technology that lets it be so is called Smart Rotary Controls. But first, we’re going to talk about the joys of beer (trust us, the two things are linked!)…

Smart what? I don’t know about you, but I can use all the extra smarts technology can provide.

Speaking of intelligence, according to a recent University of Illinois study, drinking beer may make people smarter – especially in creative problem solving.

They should have spared themselves the trouble and asked guitar players. Rehearsing and gigging is thirsty work, so we’ve always been aware of beer’s IQ-boosting benefits.

Blog of Beer

While we’re on the subject of malt liquor: ever heard of the Reinheitsgebot, or German Beer Purity Law? No?

Let me explain. This commandment, which dates back to the days before the New World’s discovery, still lays down the law for today’s Teutonic brewing guild.

It’s strict – no other ingredients but hops, malt and water may be used to brew that scrumptious barley juice. Yeast, a natural fermentation accelerator, was grudgingly added to the modern list.

This is what the old Reinheitsgebot documents looked like. And no, we have no idea what the arrow is pointing too, but we’re sure it’s proper exciting stuff! (Picture by Burkhard Mücke, used under the Creative Commons Attribution-Share Alike 4.0 International license.)

Chemical additives, flavorings, preservatives and even stabilizers (Viagra for the foam) are still taboo.

Brewing impure beer was a capital crime in the Middle Ages. Violations were punishable by death, or worse yet, confiscation.

In any event, this law has ensured that German beer has remained a pure, natural product for many centuries.

Cars, Birkenstock sandals, gummi bears and supermodels

It may seem old-fashioned, but experts agree that the Reinheitsgebot is one, if not the, main reason why beer is Germany’s most popular export alongside cars, Birkenstock sandals, gummi bears and supermodels.

Sydney, New York, Rio, Tokyo – parched punters around the globe reach for a German beer when the going gets thirsty.

Munich’s Oktoberfest, that sacred shrine of suds, is paradise for all those sanctified millions who worship at the altar of ale.

The history of German beer and the Reinheitsgebot is a perennial success story, the roots of which predate the Renaissance, humanist ideals and even towering accomplishments such as Twitter.

From this, we learn that sometimes it pays to cling to dearly held values.

From pure beer to pure guitar tone

Which brings us back to the topic of this blog: there is a similar proven Purity Principle that applies to guitars, tube amps and tone in general.

Of course, this stick-to-what-works mindset is derided by the camp that embraces disruption and change as the only catalysts for innovation.

Call it knee-jerk conservatism, fanatical purism, or a conviction informed by applied physics, but for most tube amp aficionados, dropping digital components into the signal path of a tube circuit is practically sacrilege.

Many guitarists still insist on all-analogue, all-tube amps, even though digital technology has come on in leaps and bounds over the last few years. This, by the way, is the AS 64, the first amp Hughes & Kettner ever built way back in the 1980s.

Even if the impact is inaudible to most, players can feel it and gauges can measure it. The fact is that AD/DA converters (that is, analog to digital converters) introduce some latency and limit the dynamic range.

Is the best tone always analog?

Connoisseurs of fine tone insist that the analog flow of electrons between the guitar and speakers must not be interrupted even if the signal is digitized later in a computer or mixer.

The Faith Militant, bless their hidebound hearts, rail loudly against the impurity of digital FX in the main signal path.

Every sensory experience leads me to believe that there is some truth to their orthodox dogma.

The Hughes & Kettner engineers evidently agree, given the way they map signals in amps with on-board effects: wet signals always travel in a parallel circuit and even modulation effects are blended in with the dry, tube-driven signal.

But exactly how that works is another story…

Improving a classic

There are vestiges of the Seeker in even the most traditional-minded guitarist, and the Seeker in me had me wondering if blind adherence to the Purity Principle comes at the steep cost of stagnation.

Is there not a way to advance the art without trampling tradition?

Sharper minds than mine thought there ought to be, and so they set out to put digital capabilities to good use to control a tube amp’s workings without compromising that oh-so-sacred analog signal path.

This is Bernd Schneider, the sharpest mind at Hughes & Kettner. He’s the (gigantic) brains behind all the H&K highlights, from the AS 64 in the mid ’80s to 2016’s GrandMeister Deluxe 40 – and Smart Rotary Controls too, of course! He also didn’t want to be photographed, which is we we stuck his on backwards here.

Whatever solution this effort would yield, it would have to leave the tone-shaping components well enough alone.

Enter Smart Rotary Controls

And now we have the Smart Rotary Control unit, an ingenious control technology that figures prominently in many latter-day Hughes & Kettner tube amps and surely has a lot to with to the success of the Switchblade, Coreblade and GrandMeister.

GrandMeister took the whole concept of digital control a step further with an iPad app and wireless access options (via the WMI-1 wireless MIDI interface).

Pristine all-tube-driven tone, adjusted, monitored and stored wirelessly via iPad (try the free App for iPad here!) – that kind of convenience born of Smart Rotary Control technology is a dream come true for working guitarists.

But, as usual, I digress…

The technology behind Smart Rotary Controls

So here’s the short of it: a Smart Rotary Control is a variable resistor with storable settings.

In physical terms, it’s a remote-controlled potentiometer that can serve to save every status and setting available in a classic tube amp. In theory, this gives you an infinite number of sounds to store and recall whenever the fancy strikes.

This has never been a big issue with simple switching functions such as changing channels, FX on/off and EQ on/off.

The relays that do this work do it very well; on top of that, they’re analog components.

GrandMeister Deluxe 40 features Smart Rotary Controls, taking what would otherwise be a four-channel tube amp up to a 128-channel tube amp!

However, continuously variable potentiometers produce many values than just 1 and 0, and they affect the signal in many ways. It’s very hard to translate each of these countless analog conditions into a digital status without snuffing out the lifeblood of the signal.

The world’s first programmable tube amp

Even so, engineers have long sought to turn up programmable guitar amplifiers. Hughes & Kettner, for example, unveiled the world’s first programmable guitar amp in the mid-1980s.

Equipped with two preamp tubes and a solid state power amp, the AS64 used VCAs (voltage-controlled amplifiers) to do the programming.

They certainly work, but not particularly well in all-tube amps because these active components adversely affect the tonal and dynamic ranges that make this type of circuit so coveted.

The invention of the pot

The controversy about who actually invented the potentiometer aside, Thomas Edison patented a design in 1872. Whoever came up with it was certainly blessed by the muses.

The analog pot was a first-rate variable resistor from its inception. People in lab coats later sought to make this pot remotely controllable, but they were more interested in achieving versatility and multi-functionality, with little thought given to audiophile concerns and how these controls would affect tube circuits.

A standard potentiometer, yesterday.

Analog amps + digital pots = not cool?

Digital potentiometers have been around for a while now, but they’re not well suited for what analog-minded players want because they compromise signals’ integrity.

This is why the brother- and sisterhood that still flies the tube-amp banner regards digital components in a tube amp’s signal flow with much the same fear and loathing that demons display for holy water.

For a time it seemed the only viable solution would be a motorized pot like those in iconic iconoclast Neil Young’s Whizzer, a device that sits on top of the amp and twists its knobs like a phantom hand.

Finding the ideal solution

It takes a while to tell those pots what to do, and they sure take their sweet time to do what they’re told, so this exotic solution made barely a blip on our collective radar and then faded as fast as you can say Pet Rocks (click the link or Google Pet Rocks to get that reference – and also to learn the state of the world of toys in 1975. And never say that Blog Of Tone never teaches you anything!).

Motorized pots are too slow, digital pots suck the tone out circuits, and VCAs tend to squash the dynamics and distort in nasty ways.

All that’s a no-go in tube amps, so a fourth way had to be found.

Enter the Smart Rotary Control… again

Does anyone in our game really need the infinitely variable control range of analog potentiometers?

And if they think they do, can they actually discern any audible difference between two closely neighboring settings?

Another blast from the Hughes & Kettner past: the AS 64.

Probably not, unless they happen to have the mighty greater wax moth’s extraordinary sense of hearing.

For the rest of us less auditory gifted, the values that are very close together can be lumped into sectors that make the control range more manageable.

If these sectors are small enough to enable smooth transitions between the individual steps, then you have a musical pot that, for practical purpose, covers much of the same ground and ‘sounds’ just like a standard analog resistor.

The inner workings of a Smart Rotary Control

The Smart Rotary Control uses 256 of these sectors ranging from 0 to 255. (Unlike in bank balances and test results, zero counts.)

Every potentiometer’s control range is divided into 256 steps, which is plenty to allow for very subtle adjustments.

A dedicated analog resistor or combination of resistors is assigned to cover each of these steps.

Think of this as a railway traffic control center. You’re the dispatcher that has the power to shunt railway cars.

When you turn a Smart Rotary Control to a given resistance value, it’s like setting the switches to send a railway car down just that one track. Of course, you’re not shunting cars here and there to put together a train.

You’re directing the flow of electrons produced in a tube through an analog circuit.

By assigning precisely the resistance value that will get your sound to where you want it to go, you’re assembling a train and sending it to your musical destination.

Here it is: your non-stop train trip to tone! (Photo by Michael Linnenbach, used under the Creative Commons Attribution-Share Alike 3.0 Unported license.)

The tracks are the analog path; the switches are the digital sectors. Neither the train (your signal/tone) nor the driver (you) is aware of these phantom digital switches because they have no effect on the train’s performance or response.

Simple, really

If that’s still too abstract, here’s a more guitar-minded analogy: picture a very big guitar with 256 pickups and a 256-way selector switch. Every setting activates its assigned pickup. The Smart Rotary Control does the same thing with 256 resistance values.

This straightforward principle lets you store pure tube tone, unadulterated by any digital circuits or components.

The world’s first 128-channel tube amp

You may be thinking that that’s all well and good for a single-channel amp with storable settings, but a richly appointed, programmable multichannel amp could produce dozens of very different fundamental sounds.

You’d need an army of pots to this end. The number of gain, EQ, channel volume and FX control knobs could range up to three digits.

The Smart Rotary Control solves this problem, bringing order and clarity to what would otherwise be a complex and cluttered layout.

It lets you program up to 128 sounds with just one physical knob to control each function.

An animated Smart Rotary Control – look below for a diagram of how these controls work in comparison to a standard pot.

The front panel of an amp equipped with this technology looks just like that of any conventional tube amp. So go ahead and toss out that old rulebook that says the number of fundamental sounds can never exceed the number of channels.

The best of both worlds

What we have here is a strict division of labor: the analog circuit generates scrumptious tube-flavored tone; the management of these sounds is left to the devices of the Smart Rotary Control.

These are two completely separate worlds, and never the twain shall meet.

And it gets even better: the digital control that adjusts resistance remains passive until it is engaged to change a given parameter. In other words, it sleeps until you wake it up by nudging a knob.

The new value is stored instantaneously and – like a butler who knows all, sees all, but only appears when needed – the smart Rotary Control Unit returns to standby mode to await the next change in value.

That rules out crosstalk among digital control signals from the get-go.

The signal remains unsullied and the purity of a clean tube circuit intact. If you listen closely when adjusting these pots, you can hear them clicking softly through the various resistance values far off in the background.

Then when you let go of a Smart Rotary Control, it retreats in total silence to await your next command.

Want to get creative? Pick up a soldering iron

This neat separation between the two levels really is a ‘clean’ solution.

As it turns out, Smart Rotary Control technology was inspired by what Brits call white goods (a collective term for major household appliances such as washing machines, electric stoves, refrigerators, etc.).

The idea to adapt a domestic device’s control feature and turn it into a tone-shaping tool occurred to a Hughes & Kettner engineer while he was repairing his washer.

Was this the very washing machine that inspired our budding engineer? The answer is no. (Picture by Frank C. Müller, used under the Creative Commons Attribution-Share Alike 3.0 Unported license.)

The lesson learned here might be that home repairs can be wellsprings of inspiration. (I believe that this opportunity for innovation is best left to people who earn their living with soldering irons in hand; my wife disagrees, strongly.)

In any event, it pays to think outside the box.

Many great developments were preceded by a small step of the imagination that turned out to be a huge leap for the guitar-playing kind.

So, for those about to innovate, I salute you.

Now, where’s that beer?

First published: October 14 2016. Most recent update: October 14 2016.

P.S. For those of you who asked for it, here’s a diagram of the differing workings of a standard pot and a Smart Rotary Control. Enjoy!