Every guitarist (and keyboard player) knows the swirling sounds of the legendary Leslie speaker. The Rotosphere, which authentically recreates the Leslie vibe in stompbox format, is possibly the most fabled of the Hughes & Kettner TubeTools pedals, and it’s been a mainstay on the boards of such guitar luminaries as Jeff Beck, Joe Bonamassa, Warren Haynes and even Arctic Monkeys frontman Alex Turner, among others. Here we give you the story of the Leslie’s success, and how the Rotosphere took things to a new level for guitarists, with an excerpt from our official company history, Into The Blue: A Brief History Of The Technology Of Tone.

When the moon is in the Seventh House

And Jupiter aligns with Mars

Then peace will guide the planets

And love will steer the stars

This is the dawning of the Age of Aquarius

The Age of Aquarius

Aquarius! Aquarius!

And so on.

They keep giving Nobel Prizes to physicists, yet the great question of the universe has already been asked by that R&B genius Billy Preston: “Will it go around in circles?”

The answer is, apparently, yes. All things elementary want to revolve.

Electrons orbit atomic nuclei, planets orbit their sun, satellites orbit whatever celestial body in the neighborhood exerts the greatest gravitational force.

Well, we never thought we’d get to wheel this old chestnut out again! But truth, if needed, that everything guitar-related does indeed orbit something greater than itself.

But, as far as we know, no two orbits are identical (someone let us know if that’s not true in the comments down below please!).

The trajectories of protons, planets and other orbital protagonists usually vary wildly in speed, distance and angle of inclination.

Let’s go round again

Don’t worry, this gear blog is not about to morph into an examination of Heisenberg’s uncertainty principle.

Instead, we’re going to explore how a device combines the same sort of chaos and revolution to serve up a swirling smorgasbord of satisfying sound for guitarists and keyboardists. (The latter usually go unmentioned in this space, but as much as it pains us to say it, they do come in handy sometimes.)

The origins of the Leslie speaker

A rotary loudspeaker-and-amplifier system developed by one Don Leslie in the 1940s first went by the name of Vibratone.

Taking on its inventor’s moniker, the Leslie cabinet soon became the go-to sound-sculpting tool in the arsenal of many a Hammond organist.

The Doppler Effect caused by the rotation of the loudspeakers, paired with the surround sound of reflections bouncing off all the walls, created an enveloping sonic image that seemed to come from everywhere. It’s also the foundation for an unbeatable party costume:

But, clothing-based woes aside, that immersive audio experience was its ticket to success.

Oscillations, modulations, and tone and volume fluctuations conjured an irresistible cloud of sound that continues to charm and delight those of us who like that sort of thing.

Join us on a journey Into The Blue

Perhaps inspired by the budding psychedelia genre, more and more guitarists discovered this effect later in the 1960s.

To put it in the patois of the day, that sound was “heavy, man”! And, crucially, it could not be properly reproduced by any other means.

Now we’re going to delve into Into The Blue – our official history tome – to tell you a little more about why the effect is so special, and just how much work it took to distill the tone of a genuine Leslie cabinet into a compact floor pedal – the Rotosphere!

This is it: the legendary Hughes & Kettner Tube Rotosphere pedal.

SRV and Gilmour – the first Leslie superstars

“Since the 1960s, various guitarists had borrowed a typical keyboard effect to conjure an effervescent sound that swirled like a cyclone and bubbled like witch’s brew.

In particular, two iconic guitarists – Stevie Ray Vaughan and David Gilmour – had made waves with their use of a Leslie.

The late Texan bluesman liked to kick it in towards the end of a solo to send the finale swirling into the stratosphere, while Pink Floyd’s guitarist used it to summon evocative soundscapes.

The two styles were worlds apart, but had in common that the effect could only be achieved with an original Leslie (or some other rotating speaker).

How to achieve those heavyweight Leslie tones?

That idiosyncratic tone was not easily generated.

To achieve it, a louvered drum called a rotor is mounted on the bottom of the cabinet. It then revolves in front of the Leslie’s speaker, while a top-mounted horn also spins, both driven by a motor and amp.

All this paraphernalia is heavy, cumbersome and a living hell for any roadie or tech.

An original weighs about 100 kg (that’s 220 lbs.!) and perhaps nobody will be surprised to learn that it also costs a pretty penny.

Yes, that’s how big and cumbersome an original Leslie cabinet is! Pictured here are Rotosphere creators (left) Thomas Blug and (right) H&K’s genius head designer, Bernd Schneider.

Effectively, this put the effect out of most guitarists’ reach, unless they stumbled across one on the off-chance in a studio.

Switchable motor speeds and a foot brake

It might have been maddening from a practical standpoint, but the Leslie was redeemed by its tone.

The motor has two switchable speeds – slow and fast – and one of the best aspects of this effect is that the speakers’ rotational speed can be adjusted on the fly using its brake circuit.

If you ride the brake hard, the speakers come to a standstill.

The positional relationship between the speaker and horn is ever-changing, creating a sense of movement and a sound that is constantly in flux, which is partly what makes the effect so fresh and compelling.

However, it also makes it hard to emulate with an electronic circuit, especially given that the rotational speeds of the woofer and horn are not the same.

To replicate that chaotic – if not entirely random – maelstrom of sound was a task to make most engineers quake.

The Doppler Effect

The effect’s different speeds stir yet another delicious flavor into the pot.

The Doppler Effect, whereby pitch is varied according to the speed at which the sound source moves towards and away from the listener, is responsible for the lion’s share of this sonic voodoo.

The constant to and fro between natural chorusing and tremolo causes a wild warbling, burbling sound that was thought at the time to be inimitable.

The late, great Jon Lord – of Deep Purple and many, many other classic rock mainstays – was a fervent Rotosphere fanatic.

What made it even harder for would-be simulations is that the best-sounding Leslies owed their appeal to their speaker rotation units’ worn drive belts: a certain amount of slippage added another welcome element of random chaos.

Recreating the Leslie in pedal form

Naturally, then, the intrepid H&K R&D team wanted to have their own bash at a Leslie-type effect.

The main challenge facing them was to quantify all these myriad properties, render them with a device no larger than the original’s foot control, and ultimately create an electronic effect indistinguishable from the original for keyboardists who had grown up with this sound.

From the outset, it seemed like a herculean task, and so it proved: the team would take an intensive year of analyzing sounds, developing circuits, writing algorithms and A/Bing results before this magic could be distilled into the layout of a compact PCB.

Enter the Rotosphere

At last, the deed was done, and the team proudly introduced the Tube Rotosphere.

The name of this spellbinding little box was a portmanteau of ‘rotary’ (a nod to the original’s revolving speaker), and ‘sphere’ (the bubble of celestial sound it enveloped you in), prefixed by the ‘tube’ that shaped its overtones.

Finally, a standalone pedal had been created that took guitarists and keyboardists on the same psychedelic magic carpet ride as the original Leslie.

These days, the Rotosphere is becoming increasingly rare, and therefore extremely collectible, with prices for models in top working condition (and with power supply!) seemingly going higher by the month.

Since then, the Tube Rotosphere has become the go-to solution when producers and tone freaks worldwide want that spin-cycle sound without the hassle of chasing down the original behemoth.

It’s fair to say that no other device of a similar nature has captured this effect in such style.

Witness the glowing endorsement of Deep Purple’s Hammond maestro Jon Lord: a cherished friend of the company, who was a loyal devotee of the device until his passing on July 16, 2012.”

The show must go on

Fascination with the Rotosphere and the Leslie effect continues to this day.

With the advent of digital technology, something like that Leslie sound can be had in many effects and pedals, sometimes in impressive quality, for a scant few increments of your local currency.

Every guitarist who likes to indulge in a little chorus or flanger from time to time really should explore the Leslie effect. Try it; you may join the ranks of those of us who love it.

If you see one, buy it!

Sadly, the fully analog Hughes & Kettner Rotosphere is no longer made for a lack of components that are indispensable to its analog circuitry.

So, if you come across a second-hand Rotosphere somewhere, just bite the bullet and go for it!

You’ll be the proud owner of a bona fide classic pedal.

Guitar gods like Jeff Beck, Joe Bonamassa, Warren Haynes, Doyle Bramhall II, Pearl Jam’s Mike McCready, and Arctic Monkeys’ Alex Turner – as well as the aforementioned Jon Lord – have all got great use out of the Rotosphere over the years, and we’d wager that they’d second our opinions there!

Preowned prices can get pretty high these days, but perhaps your stars will align when the moon is in the seventh house and the universe will send an affordable Rotosphere your way.

More information on Into The Blue is here.

First published: August 02 2019. Most recent update: August 05 2019.

Into The Blue is the official written history of Hughes & Kettner, written by one of Blog Of Tone’s very own contributors!