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History of Vibrato

Vibrato is one of the oldest types of guitar effects and, being old, has many, many interesting tales to tell. It was invented in a time before digital shift-registers and BBD chips, the transistor and magnetic tape, when even the vacuum tube was a relatively new thing. Designers of guitar equipment had very little to work with and yet they still imagined and innovated…

Introduction

In my younger days I shunned and scorned vibrato effect pedals. Effects, such as delay, reverb, chorusing, overdrive, pretty much, any other effect, were more exciting and useful than boring, old-fashioned vibrato. But then I discovered the music of Jimi Hendrix, Robin Trower and David Gilmour. These guitarists used vibrato sparingly and artistically to add depth and movement to the sound of their guitar making it richer, more complex and deeply interesting. My thoughts on vibrato slipped into new adjustment: this effect wasn’t just useful, it was an essential tone tool!

I became a convert, and soon after began designing my own vibrato pedal, drawing inspiration from the vacuum tube vibratos found on vintage Magnatone^® and Vox^® tube amps and Hammond^® organs. But where did these manufacturers draw their inspiration from? Well, the story of electronic vibrato goes way, way back; back to the 1930s, and even further—so let’s take a look at the history of the development of electronic vibrato.

What is Vibrato?

Vibrato is a musical effect where the pitch of a sound changes subtly over a very short period of time. Its name originates from the Italian word “vibrare”, which means to vibrate or pulsate, and is typically associated with the vocal performance of opera singers. Singers use vibrato to add expression, richness and body to their vocals, and musicians also exploit the effect to add tone colouration and character to their instrument when playing.

String players, such violinists and guitars can apply vibrato by wiggling or bending strings with their fingers; and players of trombones, flute and other brass and woodwind instruments can achieve the effect by breathing technique. The vibrato of a string instrument or wind instrument really is just an imitation of a vocalist. However, it is not possible for a pianist to add vibrato, as there no mechanism exists to for the player to introduce it. The same is true of harpsichord, xylophone and most percussion instruments.

AM FM Radio — Vibrato is FM (Frequency Modulation) and tremolo is AM (Amplitude Modulation)

Vibrato is characterised by the amount of pitch variation (“extent of vibrato”) and the speed with which the pitch varies (“rate of vibrato”). Technically speaking, vibrato is frequency modulation (FM). This is not to be confused with tremolo, which is a variation in volume, a.k.a. amplitude modulation (AM). The effect if altering the musical pitch of a note cyclically is very pleasing to the ear, much more pleasing than simply altering the volume (amplitude).

“The vibrato may be defined as a condition in which the instantaneous frequency of the generated signal is caused to vary between certain frequency limits at a rate slow enough for the ear to perceive the over-all effect as a sound of constant intensity but of varying pitch.” — John M. Hanert

The pitch-changing effect of vibrato could be thought of as being analogous to cyclically altering the colour balance of a photograph. However, not all colours would be affected equally, some would be changed drastically, whilst others would hardly be affected at all and remain relatively unchanged. The overall effect would be distortion and blurring of colour information to alter the perceived mood and atmosphere of the picture. Trippy, huh? For comparison, tremolo could simply be considered as a photograph cyclically fading in and out of darkness. Conceptually, tremolo is a much more straightforward effect and, as it turned out, it was much easier to create electronically too.

So, before we go any further, just to make sure we’re all on the same page, here’s a sound clip of electronic tremolo:

And here’s a sound clip of electronic vibrato:

Faux Vibrato

In fact pitch-shifting vibrato turned out to be an extraordinarily difficult trick to pull off. The problem is this: How do you alter the frequency of an audio signal electronically? Today such a feat can be achieved with digital processing chips, or if you want to get old school, varying the speed of magnetic tape, but there was a time when such wizardry didn’t exist. What then?

Well, you do what you can. That’s what engineer and inventor Laurens Hammond did when he created the Hammond Model A electric organ in 1934.

DeArmond Tremolo Control — The first effects pedal: The *DeArmond* "Tremolo Control"

Hammond’s patent [US Patent 1,956,350] describes his new invention in great detail and a tremolo (“Tremulant”) mechanism driven by a synchronous motor. As the motor rotates it periodically presses metal contacts together shunting the audio signal to ground to create the tremolo effect.

A similar approach was used by Story & Clark in their electric piano. Their Storytone debuted at New York World’s Fair in 1939 and a year or so later retrofitted with DeArmond tremolo units underneath the keyboard. This electro-mechanical tremolo, like Hammond’s, also operated by shunting audio signal to ground. However, DeArmond’s tremolo had a small glass jar partially filled with an aqueous electrolytic fluid. A motor vibrates the jar and the fluid splashes against two metal contacts inside the jar; one of these is connected to ground and the other to the audio signal. Again we get tremolo, but not true vibrato.

The Leslie Rotating Speaker

It was radio repairman Don Leslie who took the first steps towards creating artificial vibrato in the late 1930s. Leslie was a keen amateur musician and proud owner of a Hammond Model A electric organ, a rare and precious piece hardware at the time. He liked his Hammond but found it lacked the full, dimensional sound of a real pipe organ. He got to thinking if there might be some way to breathe life into that flat, sterile sound.

Well, the beginnings of an idea came to him, whilst out in his front yard, a flatbed pickup truck sped past his house. Mounted on the truck was one of those big old horn speakers broadcasting an advertisement for a political candidate. Leslie noticed how the pitch of the sound from the speaker changed as the truck drove by. What he was observing, or to be more exact hearing, was a phenomenon described as the “Doppler-effect“.

The Doppler-Effect

Discovered by Austrian mathematician and physicist Christian Doppler (1803-1853) in the early nineteenth century, the Doppler-effect is the apparent variation in pitch that a stationary listener hears from a moving sound source. The key word here is “apparent”. What it means is: the pitch of the sound being broadcast by the horn speaker does not change, but it’s perceived pitch does. How does such witchcraft work?

Well, as the pickup truck speeds towards Don Leslie, each sound wave emanates from a point nearer him than the previous one; the arrival time between sound waves is therefore decreased, so the perceived pitch of the sound is higher. Conversely, as the truck passes past him and down the road, each sound wave emanates from a point further away than the previous one; the arrival time between the sound waves is increased, so the perceived pitch of the sound is lower.

So, the pitch of a sound can be altered artificially, well, at least in principle. The trick is to keep the sound source moving relative to the listener, which, in the case of his Hammond organ, means keeping the loudspeaker moving. But how can this be realised practically, as a working piece of apparatus? Well, Leslie’s first thoughts were to exploit a slow-turning baffle in close proximity to the speaker to alter the direction of the sound.

His first rotating speaker was a primitive Heath Robinson lash-up, essentially a modified phonograph record player, where the phonograph’s metal horn was mounted on top of the turntable with a small radio speaker installed inside. As the turntable revolved, the speaker spun around creating the Doppler-effect. Further experimentation revealed that a faster speed produced a pleasing tremolo too, which sounded richer and more full-bodied than the electronic Tremulant effect on the Hammond organ.

Donald Leslie Patent 2,622,693 "Apparatus For Imposing Vibrato On Sound"

Leslie continued refining his invention and in 1940, after many months of development, he released the model 30A Vibratone [US Patent 2,489,653].

The first Vibratone was a formidable and imposing mahogany veneered wooden cabinet, roughly the size of a “Kelvinator” fridge. The cabinet housed a powerful 35W monophonic push-pull amplifier based on four 6L6 vacuum tubes; an 800Hz 16Ω passive crossover; large motors to drive a rotating treble horn and a rotating reflector baffle located beneath a 15″ bass speaker.

The rotating speaker elements directed sound out the sides and back of the cabinet, which then reflected off nearby walls and surfaces. The listener hears this combination of primary and reflected sound as a moving audio field. In practice, the loudness of the sound also appears to vary and it is this combination of frequency (vibrato) and amplitude (tremolo) modulation that give Leslie Speakers their characteristic sound. Adding a second cabinet further enhances the effect. Even when the audio source (organ) is mono, the rotating speaker elements and reflected sound create a realistic stereo effect.

Scanned Transmission Line Vibrato

Leslie had devised a marvelous apparatus capable of imposing vibrato on sound; however his rotating speaker system was mechanical and this made it very bulky, to say the least. An electronic apparatus might be more compact and easily portable, but at the time it was not at all obvious how electronic vibrato could be achieved. What was needed was some kind of medium to capture the audio signal, so it could be manipulated, that is, slowed down or sped it up to create pitch-shifting vibrato. Magnetic tape hadn’t been invented, and even primitive wire recorders weren’t readily available. Electronic vibrato seemed an impossibility with 1930s technology… to the average electronics engineer.

It was going to take a genius to crack the problem. Enter John M. Hanert. Hanert certainly was not your average engineer. He held over 60 patents to his name and was head of research at the Hammond Organ Inc in Chicago; he was the brain behind the Hammond B-3 “tone-wheel” organ and inventor of the Hammond “Novachord“, an electronic synthesiser created decades before Robert Moog even conceived of such a thing; and Hanert possessed the imagination and intellect to overcome the severe technological limitations of his day to make electronic vibrato a reality.

Hanert’s idea was to employ an electrical “transmission line” as a medium to create the vibrato effect [US Patent 2,382,413]. A transmission line is just fancy terminology engineers use to describe long cables used for radio frequency or speech transmission, for instance a telephone line. Like a guitar cable, a transmission line is not a perfect conductor of electrical signals. What Hanert did was to exploit its imperfection, more specifically, its non-ideal electrical properties, in a new and novel way.

I’m sure guitarists will be familiar with “tone-sucking“, the loss of high frequency that occurs, when using certain types of instrument cables. Tone-sucking is caused by the capacitance of the insulation surrounding the inner core of the cable. The capacitance shunts higher frequencies to ground, effectively creating a low-pass filter. The longer the cable, the greater its capacitance becomes, and the greater the loss of high frequency content.

But there’s more to it than that, a lot more. The capacitance, and inductance, of a cable also alter the phase relationship of different frequencies within a signal during transmission. This phase change, a.k.a. “phase distortion”, distorts the shape of the signal’s waveform. Phase distortion, like “clipping distortion” can seriously degrade the fidelity of a signal to mangle its shape in quite bizarre, and unexpected, ways.

Phase delay distortion imposed severe limitations on the speed at which data could be transmitted over long distance telegraph lines, until inventor Michael Idvorsky Pupin figured out what was happening to cause it. Pupin went on to develop “loading coils” [US Patent 519,346] to correct and minimise phase distortion in a transmission line, and this enabled faster data transmission.

“Every electrical circuit behaves, in consequence of its self-inductance and capacity toward a periodically varying electromotive force, just as a heavy elastic body, in consequence of its inertia and elasticity, behaves toward a periodically varying disturbance.”—Michael Idvorsky Pupin

Pupin understood that, unlike resistors, which limit the flow of electrical current, capacitors and inductors are “reactive”, that is, they don’t just limit current flow, they push back against it. This is because they’re converting one form of energy to another: capacitors store energy in an electric field; and inductors store energy in a magnetic field. This energy conversion is not instantaneous, it takes time for the fields to build and collapse. I’m aware this is beginning to sound very much like a school physics lesson, but stay with me on this a little longer; it will be worth it!

Think of reactance as a kind electrical sluggishness—a common analogy is to equate electrical reactance with physical mass: the heavier an object is, the more effort required to get it moving. Imagine a steam train getting underway; it takes a lot of energy to get up to full speed. What’s actually happening is that potential energy, from burning wood or coal, is being converted in kinetic energy. Once the train attains a constant speed, it’s kinetic energy is no longer increasing and wood only needs to be burnt to overcome wind resistance and the frictional losses of the railway tracks.

Now, staying with the physical world, rather than the electrical, let’s expand on Pupin’s idea of a “periodically varying disturbance” in an “elastic body”. Think of a speaker cone moving back and forth. As it does so it causes the air to stretch and contract like an elastic band. This results in regions of high and low density; that’s what sound is: pressure variations propagating through the air. Technically, the air is the transmission medium for sound. When the air is maximally stretched or contracted (compressed) it’s stationary and only has potential energy; and when it’s halfway between these two extremes, it’s moving at greatest velocity and all its energy kinetic. In an oscillating system like this, a clock pendulum, or a guitar string there’s an ongoing exchange or conversion between potential and kinetic energy.

An electrical transmission line is analogous to air. Both are transmission mediums and both possess this sluggishness and elasticity when transmitting waves, whether as electricity or sound. And it’s this sluggishness and elasticity that results in a phase delay. And it’s this phase delay that Hanert exploited to create his vibrato. This is an early example of audio “signal processing“

What Hanert did was create an “artificial” transmission line made up from a network of inductors and capacitors. Think of it as being a simulation of the worst cable imaginable, a cable with a huge amount of reactance and sluggishness, to maximise phase delay at audio frequencies. This was the exact opposite of what Pupin was trying to achieve with his inductive loading coils, which he added to minimise phase delay.

Hanert’s vibrato scanned “tap” points along the artificial transmission line using a single-pole 16-throw air-dielectric capacitor switch driven by a motor. The switch is wired to scan tap points along the entire line twice—up and then back down, for each scanner rotation—at seven cycles a second (7Hz). As the line is scanned, phase is progressively added-to and then subtracted-from the signal; the continuously changing phase generates the vibrato effect. The output of the scanner is then fed into the grid of a vacuum tube in order to maintain the proper load impedance.

Hanret’s vibrato was compact enough to fit inside an electric organ, and was installed many of Lauren Hammond’s organs, such as the B-3. A nice additional feature was the ability to mix the scanner output with the dry signal to create a “chorus” effect. The phase and frequency differences between the dry and scanner output signals create the illusion that a second, slightly de-tuned instrument is being played at the same time. This, a highly desirable effect and is precisely the same principle on which modern transistorised analogue phaser and vibe effects pedals operate on. Hanret’s transmission line and scanner vibrato laid down foundations for things to come.

Diagram of scanned transmission line vibrato [from *Hammond* B-3 organ manual].

The Wurlitzer Vibrato

Although considerably more compact than a Leslie rotating speaker cabinet, Hanert’s vibrato is still a relatively large apparatus. And, it’s not purely electronic: scanning vibrato is an electro-mechanical hybrid made up of numerous complex intricate moving parts, which have to be specially fabricated. Manufacture was undoubtedly time consuming, and expensive. However, Hanert had proved that the phase delay in an electrical transmission line could be exploited to alter the perceived pitch of an audio signal, clearly pointing the way to a truly all-electronic vibrato.

In 1953 electronic vibrato made its first appearance in the Wurlitzer Model 44 organ electrostatic reed organ. There are no motors, speakers, transmission line of complicated electro-mechanical switches in Wurlitzer’s elegant design; the vibrato effect is created solely by minute, invisible electrons. At the heart of the electronic circuitry is a triode “Cathodyne” phase-splitter and passive phase-shift network made up of capacitors and resistors.

The audio signal enters this circuit and is split into two signals that are 180° out of phase with each other. These signals are fed into the grids of two more triode tubes that operate as switches, alternately routing the out of phase signal to the output. Switching is occurring at 6Hz and viola! We have vibrato. A more thorough explanation of Wurlitzer’s vibrato can be found in the January 1955 edition of Radio Electronics (pp. 128-134).

“A phase change can be detected as a frequency change as long as the phase is continuing to change.”—Richard H. Dorf

Just to be clear, the vibrato systems installed in Wurlitzer, and Hammond, organs both work on the Doppler principle, where advancing phase creates a perceived pitch change. This technique is commonly used in phase-modulated R.F. transmitters to generate frequency modulation, and is almost certainly where Wurlitzer drew their inspiration from for their circuitry. Unlike, Hammond (Hanert), Wurlitzer did not file a patent for their vibrato concept, which meant they left the door wide open for electronic hobbyists and audio equipment manufacturers to utilise their work for their own ends… and they did.

The Universal Vibrato — A phase modulator circuit which can be used with guitars, organs, pianos, etc., to produce a realistic vibrato effect.

Guitar Amp Vibrato

Wurlitzer’s vibrato and variants featured in several electronics magazines, for instance Richard H. Dorf‘s article published in the April 1954 edition of Radio & Television News (pp. 52-93) in the early 1950s. A modified version of the circuit eventually found its way into Vox Amplification’s AC-30 guitar amps in 1958. On the control panel of the Vox AC-30TB (Top Boost) was a switch, which shorted one side of the phase-shifter outputs to ground, transforming the circuit into sweet sounding tremolo. The vibrato could be switched on/off remotely using a footswitch—a very cool feature, considering most guitar amps at the time only possessed tremolo.

Vox weren’t the only manufacturer bold enough to incorporate true vibrato into their amplifier range. At about the same time the Vox AC-30TB burst onto the scene, Magna Electronics (Magnatone) launched their Custom 200 series guitar amps. The new Magnatone amplifiers were were jam-packed with vacuum tubes, looking like a miniature, scaled-down glass bottle factory inside. The additional real estate required—tubes, resistors, capacitors, wiring and chassis space—to implement vibrato meant the Custom 200 series amps were more expensive than other guitar amps of the time. It wasn’t just the higher component count that added to the cost, it was the complexity of the assembly process and test procedures—remember, all the electronic assembly work had to be done by hand, which took time, and time is money. Magnatone amps did not come cheap. For instance, in 1964 they released a beautiful combo that featured true stereo vibrato—the Magnatone Custom M14. The stereo vibrato circuitry required three dedicated tubes and eight varistors to work, making the M14 one of the most complex and costly guitar amplifiers ever made.

The vibrato is achieved using a cathodyne phase-splitter circuit and “varistor” (voltage dependent resistor) circuit developed by Don Bonham in 1954 [US Patent 3,146,292]. As the resistance of the varistor changes with applied voltage, the in-phase (0°) and phase-inverted (180°) outputs are mixed in varying proportion to create a varying phase-delay (shown in the animation below). Dorf exploited a similar concept in his Schober “Thyratone” electronic organ kits, but instead he utilised a center-tapped audio inter-stage transformer to split the signal into two phases [US Patent 2,835,814]. His minimalist vibrato circuit also features in the March 1957 edition of Radio Electronics (pp. 57-59).

Cathodyne phase-shifter animation — ϕ₁ = 0° (signal is in phase); ϕ₂ = 180° (signal is phase inverted)

The numerous vibrato patents would make difficult navigating for electrical equipment manufacturers. Perhaps because of this, and costs incurred by it’s complexity, the majority of guitar amp makers steered well clear of vibrato; it was easier to equip amps with tremolo. For instance, the control panel of Fender’s “Deluxe Reverb” and “Twin Reverb” amplifiers are labelled with the word “vibrato”, even though they possess plain old tremolo. Fender even advertise their amplifiers as having vibrato and give them names, like the “Vibrasonic” and the “Vibrolux”. But it wasn’t always that way.

Before Leo Fender sold his company to CBS in 1965, he was building amps with vibrato in them, although this was more by accident than by design. According to a patent he filed in 1959 [US Patent 2,973,681] he was actually trying to create a pure tremolo, to minimise the Doppler effect, not create it. He’d come up with an ingenious, and quite extraordinary, modulation circuit that split the audio signal into low frequency (LF) and high frequency (HF) bands using passive low pass and high pass filters. The two separate frequency bands are amplitude modulated such that when the LF band is at maximum amplitude, the HF band is at a minimum, and vice-versa. This creates a beautiful, undulating tremolo; but how is it vibrato?

Fender tremolo concept — Leo Fender's tremolo concept described in US Patent 2,973,681.

Well, passive, and active, analogue electronic filters don’t only affect the amplitude of a signal, they also affect its phase too. You can’t escape it—it’s physics. Leo’s tremolo circuit is predominantly an amplitude modulator, but there’s also some subtle, unintended phase blurring going on as well.

Vibrasonic Amp — If it's called "Vibrasonic" and labelled clearly with "VIBRATO", it's got vibrato on it; right?

So Fender amplifiers do have true vibrato, well they did up until 1963. Between 1959 and 1963 Fender manufactured a range of gorgeous guitar amplifiers—the “Bandmaster” 6G7, “Vibrasonic” 5G13, “Super” 6G4, “Concert” 6G12, “Twin” 6G8 and “Showman” 6G1—finished in brown Tolex, brown front panels and deep brown phenolic “Dakaware” knobs, the so-called “Brownface” era. All these amps featured Leo’s unique tremolo circuitry, which was colourfully described in Fender’s adverts and sales literature as, “Harmonic Vibrato”. As it turns out, this is an extraordinarily accurate description of what his tremolo actually does: Leo’s tremolo lightly plays with the phase relationship of the harmonic content within the guitar signal so that it swirls and eddies like ripples on a stream. It’s nothing more than an ephemeral shimmer, unlike Doppler detuning, where pitch-shifting is much deeper and more severe.

After ’63 Fender began making changes to the tube circuitry in an effort to cut production costs. They stripped out the 3-tube harmonic vibrato circuit and replaced it with a much simpler tremolo based on a neon bulb and photocell. And they also changed the appearance of their amps so they had black front panels and black Tolex, the “Blackface” era. But they didn’t alter the description on the control panels though, it was still labelled as “VIBRATO”. Creative marketing at work no doubt—vibrato was a cool effect and the association could only be good for sales.

I’m convinced that Leo drew some of his inspiration from thinking about how the audio crossover in a Leslie splits low and high frequencies to feed them to the bass speaker and treble horn. In a way, his harmonic vibrato is a better approximation of a rotating speaker than any of the other phase-shift vibrato circuits described—there’s very little amplitude modulation with Hanert’s, Dorf’s and Bonham’s vibrato circuits. Leo’s harmonic vibrato is undoubtedly primitive, but it at least attempts to mimic the cyclically changing amplitude differences of the spinning treble horn and bass baffle. Now, if someone were to modify it to add a phase-modulator to the HF band, we’d have the beginnings of an interesting vacuum tube analogue Leslie emulator.

Comparison of Fender and Dorf vibratos — Comparison of *Fender* and *Dorf* vibrato responses [animation courtesy of Brett Riggs].

Console Organ Vibrato

Whilst guitar amp makers were still struggling to get their heads around the difference between vibrato and tremolo, organ manufacturers were exploring new, mind-bending phasing possibilities. Dorf had abandoned his transformer based phase-splitter design in favour of a 2-stage cathodyne and varistor vibrato circuit. Each cathodyne stage imparts up to 180° of phase-shift, so two stages give a total of 360°, generating a much “deeper” vibrato than just a single stage. He used this circuit in the Schober “Consolette” and larger “Concert” electronic organ kits, which were advertised in magazines such as Radio Electronics, Popular Electronics and Popular Mechanics from 1960 onwards.

Not to be outdone, Hammond added 3-stage cathodyne phase-shifting vibrato to their Model L-100 console organ, capable of almost 540° phase-shift [US Patent 3,258,519]. The vibrato was a completely self-contained module (part no. AO-41) housing the three 12AU7 phase-splitters and a low frequency sine-wave oscillator. Rather than varistors, Hammond’s vibrato used “saturable reactors” to adjust the phase mix. A saturable reactor is essentially a variable inductance, where the magnetic flux density within the core can be altered by applying a direct electric current to the core’s primary control winding. As magnetic flux within the core changes, the inductance changes, and so does the signal flowing in its secondary winding.

Hammond AO-41 3-stage vibrato module — *Hammond* AO-41 3-stage vibrato module.

Hammond took the development of their multi-stage phase-shifter circuitry even further, and in 1964 filed a patent [US Patent 3,325,581] for an organ celeste and chorus system. This wonderfully complex electro-mechanical apparatus consisted of several cathodyne phase-shift stages and a scanning disk. The scanning disk was made of transparent Plexiglas on which were inscribed several tracks for waveforms. Photocells and bulbs were arranged on either side of the disk. As the disk rotated the light falling on the photocells varied in a pseudo-random manner causing randomised phase shifts. Sadly, this marvellous machine never became a reality, although there are elements of pseudo-random waveform synthesis embodied in the Effectrode “Phaseomatic” vacuum tube phaser.

But, even back in the 1960s, varistors, saturable-core reactors and tubes were being superseded by new technologies. Once the transistor became commercially available, Dorf completely redesigned his kits to use transistors in place of triodes, and his vibrato circuitry changed too. By 1963 he’d replaced his varistor and cathodyne electronics with bipolar NPN junction transistor emitter-degenerated amplifiers, photocells (light dependent resistors) and filament light bulbs. The transistor had become the go-to method for creating the Doppler vibrato effect.

Hammond photo-opitcal Celeste-Chorus patent — Hammond photo-optical Celeste-Chorus patent.

The Uni-Vibe

It wasn’t long before someone got on to the idea of putting a phase-shifter circuit in a box. In 1968 Japanese company Honey did exactly that, and the “Uni-Vibe” pedal was born—well, not quite, originally they called their new creation the “Vibra Chorus“. Strictly speaking, the Vibra Chorus wasn’t a floor effects pedal and it wasn’t specifically designed for electric guitar either. According to Honey’s sales catalogue, the Vibra Chorus was intended as a console top unit to add vibrato and chorus effects to electronic musical instruments, such as electric guitars, electronic organs and microphones.

In order to diversify their product range, Honey married Mieda-san’s Vibra Chorus electronics with their “Baby Crying” FY-6 fuzz pedal, which they’d released a year earlier in 1967. The two separate circuit boards were housed together in the “Psychedelic Machine”. Despite it’s eccentric looking front panel, the Psychedelic Machine is essentially a multi-effects unit capable of combining fuzz with vibrato, chorusing or tremolo effects. Soon after, when Shin-ei took over operations in 1969, the Vibra Chorus became the Uni-Vibe. It was at this point that the Uni-Vibe was distributed through Uni-Vox and LaFayette Radio Electronics in the United States.

Honey Psychedelic Machine — *Honey* "Psychedelic Machine"—the world's first multi-effects unit.

But Honey didn’t design the electronics in the Uni-Vibe. The credit for that goes to freelance engineer Fumio Mieda. His name may be familiar to owners of KORG synthesizers. Fumio-san was involved with KORG from their very early days and has his hand in the design of their first synths—and he’s still working for them to this day, as a product engineer. Before he became freelance he was employed by Teisco, a Japanese musical instrument manufacturer, developing their “Teischord” electronic organ. And before that, he studied electronics at The University of Electro-Communications, which is where he developed an interest in electronic organs.

Hammond’s shadow loomed large over the electronic organ manufacturing world; they were undoubtedly an influence on young and up-and-coming companies trying to make their mark. Mieda-san says as much in a recent interview in February 2022 for NAMM (National Association of Music Merchants).

“Hammond was a huge company. So of course I was influenced. I thought the Hammond was a wonderful instrument”—Fumio Mieda

In the interview he goes on to describe how he began experimenting with constructing the prototype circuitry for the Uni-Vibe using coils (inductors) as the control element—the same approach Hammond took with their 3-stage AO-41 module. However, instead if using hot, high-voltage vacuum tube electronics, the young design engineer was working with the latest solid-state technology: the transistor. The transistor was cheap, small and operated from low voltage. Further, a high current transformer was not needed to power tube heaters, meaning his transistorised circuitry was more compact, lighter and ran cool.

The new silicon semiconductor devices couldn’t be bought in Tokyo’s regular high street shops though—of course not. For all things electronic, Mieda-san would take a trip to “Electric Town“. Electric Town, otherwise known as Akihabara electronics market (described in Popular Electronics May 1966, pp. 54-55), sat in the shadow of an elevated railway line. In a small area, barely an acre, were half a dozen arcades jammed together, each containing scores of little shops and stalls. Electric Town was the largest electronics and hi-fi market in Tokyo, possibly the whole of Asia. He found the transistors, and the other electronic components he needed there.

“As you get off the train at Akihabara and walk with the crowds to the market place, the din of a hundred television sets, hi-fi’s, transistor radios, and tape recorders drowns out the noise of the trains overhead.”—from Popular Electronics May 1966

Mieda-san made more changes to his circuitry, replacing the coils with photocells and a lamp, just as Dorf did a few years earlier in his Schober organ vibrato circuits. This approach was adopted by others too, for instance in the design of a three stage phase vibrato circuit that appeared in Electronics Australia magazine in March 1969. Ditching the bulky saturable reactors to replace them with photocells yielded further reductions in size, and weight, of Mieda-san’s phase-shifting machine.

"Radio Garden" was one of the first shops in Akihabara.

Ultimately, Fumio Mieda settled on a 4-stage phase-shifter topology for the Uni-Vibe. Much of the transistorised circuitry is straight out of the textbook. There are three emitter follower driven phase splitters, an emitter follower output buffer and high impedance input gain stage/phase-splitter. “Bootstrapping”, where part of the output signal is fed back to the input, so as to increase its input impedance, is used extensively throughout the circuitry. In fact, every effort is made to ensure that the input impedance of the first gain stage is high, until the designer proceeds to load it with a 22KΩ and 47KΩ series resistors to ground! The mind of a genius works in mysterious ways.

So, the combined 69KΩ input resistance is very low when compared to most tube guitar amps. The Uni-Vibe’s low impedance will suck the life out of the tone of a Fender ‘Strat’ fitted with single coil pickups, resulting in significant treble loss. Fender understood this, which is why their amps are designed with an input impedance that is over ten times higher than this at 1MΩ. Fortunately, the tone-sucking issue is easily remedied by replacing the 47KΩ resistor with a 1MΩ one, but do hang on to the original part once you’ve removed it.

Being such a low impedance device, the Uni-Vibe is more ideally suited to electronic organ, rather than electric guitar, and perhaps that was Honey’s primary market. Honey’s sales literature highlights how the Uni-Vibe can, “…add depth to the sound of a conventional electronic organ.” and that it can replicate the sound of Hammond’s pitch-shift vibrato, “Especially when used with an electronic organ, you can expect the chorus effect of a Hammond organ…”.

Mieda-san’s 4-stage phase-shifter topology extended the maximum phase-shift range to almost 720°. This is where things become deeply interesting. As you might expect, there’s an increase pitch detuning, however another phenomenon comes into play. When the “wet” phase-shifted signal is mixed with the “dry” signal in roughly a 50/50 mix we get signal cancellation at certain frequencies (as shown in the diagram below). This is due to “destructive interference“. Acoustic guitarists playing through a PA, or guitar amplifier, will be familiar with the phenomenon. When standing in certain places on the stage the guitar can feedback or howl: this is “constructive interference” at work, where sound waves from the amplifier are in phase with the sound from the guitar. Moving a short distance from this hotspot normally kills the howl: that’s “destructive interference”, where sound waves from the amplifier are out of phase with the guitar.

Phase cancellation - "dry" signal at the top, "wet" phase-shifted signal in the middle, and the two signals mixed together at the bottom.

For destructive interference to occur signals must cancel perfectly. For this to happen a waveform signal needs to be mixed with a mirror image of itself, or to put it another way, a duplicate that’s 180° out of phase (phase inverted). This can theoretically be achieved with a single phase shifter stage. But what happens when we start stacking more phase-shifters in series? Well, adding another stage adds another 180° phase shift, to put the signal back in phase again (360° total phase shift) meaning there’s no cancellation. Adding yet another stage adds another 180° phase shift, taking the signal out of phase again (540° total phase shift) so that we get cancellation again.

In practice a single phase shift stage always falls a little short of delivering the full 180° shift. Adding an additional fourth stage ensures the phase shift reaches at least 540° and that there will be two phase cancellation dips, or notches, in the frequency response. A SPICE simulation frequency analysis reveals one notch is positioned at around 50Hz and another up at 2KHz. These notches will move up and down from these frequencies as the Uni-Vibe’s Low Frequency Oscillator (LFO) cyclically varies the intensity of light hitting the four photocells to change their resistance.

Phasing & Photocells

Uni-Vibe schematic The Uni-Vibe is not a phaser, but you knew that, right? So what makes them different? The photocells? Uh-uh. The filament bulb? Nope. The phase-shift capacitors? Could be. There are plenty of phasers that use photo-optical control, but none with stagger-tuned phase-shift capacitors. In a four-stage phaser the values of these capacitors are identical, which creates two localised notches in the frequency response. In the Uni-Vibe the phase-shift capacitors are all different values, which pushes the notches further apart into the low and high frequency regions of the audio spectrum. It’s this that gives the Uni-Vibe its signature “lumpy” throb and thick, swirly character.

It is important to use the correct photocells and bulb though. Always replace a faulty photocell with one of the same specification. The important specification to note is “gamma” (sensitivity and linearity), which indicates how the photocell’s resistance changes in response to light intensity. Some photocells have a high gamma and are made for on/off control applications, such as turning a streetlamp on at night. Lower gamma photocells are designed for audio applications, such as compressors and remotely controlled potentiomenters. Note: the fact that the photocell might be encapsulated in a metal can with a glass lens has zero effect on it’s response and is not an indicator that it is suitable for use in a Uni-Vibe.

Finally, the filament bulb is not so critical—you don’t need to obtain the original 28V 40mA Hamai bulb for the Uni-Vibe to work correctly. Pretty much any 1W acorn bulb will do the job. You can even use 12V bulbs; just add a small resistor in series of, say, about 100Ω.

So what we have is a complex, swirling blend of low and high frequency amplitude modulation and low and high frequency phase modulation. Does this remind you of anything? The bass rotor and treble horn Leslie rotating speaker perhaps? Perhaps. Was Mieda-san attempting to replicate the effect of a rotating speaker electronically? After all, it can’t just be blind luck that those two notches just happen to fall in the low and high frequency regions of the audio spectrum. Surely it can’t be accident, is must be intent?

Well, examining the schematics for the Uni-Vibe, reveals that the capacitors in the four phase-shift stages are not all the same, as they would be in a typical phaser pedal, such as the MXR Phase 90. Each one has a different value—15nF, 220nF, 470pF & 4.7nF—suggesting the designer did indeed have intention. The 15nF and 220nF capacitors are responsible for the first phase cancellation notch at lower frequencies, and the 470pF and 4.7nF for the notch at higher frequencies. Were the capacitors closer in value, or all the same, as in a phaser pedal, the notches would be closer together. Mieda-san wanted those two notches to be further apart, to position them in the the low and high frequency regions of the audio spectrum.

Comparison of the distribution of notches in the Effectrode Tube-Vibe and Phaseomatic pedals. — Snapshot comparison of the distribution of notches in the *Effectrode* "Tube-Vibe" (black) and "Phaseomatic" (grey) pedals.

So the Uni-Vibe is an early attempt, perhaps the first serious attempt, to simulate the characteristics of a Leslie rotating speaker?—all the evidence is there; in the design, and in Honey’s earliest marketing literature. Well, apparently not. In an interview for Deeper’s View in 2018 Mieda-san states that it’s a common misconception that he was inspired by the Leslie speaker. In the interview he tells of how he drew his inspiration for the Uni-Vibe from the sound of Russian radio broadcasts fading in and out as result of atmospheric interference in the ionosphere. Fascinating… and surprising.

Many have been quick to adopt Mieda-san’s new narrative, after all, he is the designer of the Uni-Vibe. But there’s one thing that bothers me: MW radio interference sounds nothing like the lush, deep vibrato of the Uni-Vibe. In fact, Fumio Mieda’s Uni-Vibe makes a far better Leslie rotating speaker simulator than it does a radio interference simulator. And I’m not alone in thinking so:

“And, of course, I was playing my Strat, which pared so well with the Uni-Vibe; I mostly used the middle pickup. I loved the Leslie effect it gave me.”—Robin Trower

Robin Trower talking about his early days with Procol Harum in an interview ClassicRockHistory.com. Many, many guitarists fell in love with that complex, convoluted swirl of FM and AM, and delighted in the fact they didn’t have to lug a 70lb cabinet around with them to gigs. And some even installed the Uni-Vibe in their racks.

“You remember the old Univox Uni-Vibes? I had one built into a rack system. We even had the old logo embossed on the face plate.”—Phil Taylor (David Gilmour’s guitar tech)

So, although the Uni-Vibe’s creator never intended his invention to be a Leslie speaker simulator, it did get used as such, and, all things considered, it didn’t do a bad job of it either.

The Effects Pedal Age

With the advent of the transistor, and other new solid-state electronic devices, such as FETs, opamps, TTL and CMOS logic chips, there dawned a new age: The age of the effects pedal. The transistor was cheap, compact, and its low current consumption meant it was possible to house the audio signal processing electronics for phase-shifting vibrato inside a small box and power it from a PP3 battery. So, given this, what form did the first transistorised phase-shifter take?

Well, in 1971, Eventide released a budget-busting, bank-breaking, 19″ rackmount phaser, the “Instant Phaser” Model 101, priced at $575, which is about $3000 bucks in today’s money. So, not compact, and certainly not cheap. This kind of price was well beyond the means of most guitarists, however the 101 wasn’t really aimed at them. It was designed for studio use, to simulate tape “flanging” effects. In this context, the 101 is not such a bad deal; for a studio engineer experimenting with two reel-to-reel tape machines, variable speed oscillator and patch cables to create Doppler pitch-shifting and phase effects it as a real time saver.

Eventide’s Model 101 employed eight cascaded FET/opamp phase-shift sections to deliver a staggering 1440° of phase-shift—the sound was lush, to say the least. Such extreme pitch change is really too much for vibrato though, and manufacturers began drawing their lines at four sections—720° was enough to create useful phasing and vibrato that satisfied the frequency modulation needs of most musicians.

As the 70s progressed a dazzling array of phase-shift Doppler vibrato, a.k.a. “phaser”, pedals flourished and proliferated—the MXR Phase 90, Maestro PS-1 Phase Shifter, Colorsound Phazex, Electro-Harmonix Bad Stone Phase Shifter, Boss PH-1, the list goes on, and on… the growth was exponential. The numbers grew as manufacturers eagerly embraced the new solid-state technology. But not all. Some crazy pedal manufacturers stubbornly clung on to using vintage, high voltage, vacuum technology. Some even attempted to shoe-horn eight triode phase-shift sections and a tube low frequency triangle wave oscillator into a small box, but that’s another story…

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History of Vibrato