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Eminent 310 String Synthesizer

The world's first commercially available string synthesizer, the Eminent 310, came from an unlikely source, a Dutch home organ manufacturer. It was further advanced through an even more unlikely partnership, with the legendary American synth makers ARP...

In our February Retrozone article, we featured the story of Ken Freeman, the pioneering keyboard designer who was instrumental in creating and bringing to market early polyphonic string synthesizers, for the many players keen to find a way of affordably producing orchestral-style timbres. However, Freeman wasn't the only one chasing this goal back in the 1970s, and this month we're going to take a look back at another participant in the race.

Eminent 310 String Synthesizer

In 1972, the same year that Freeman demonstrated Prototype #3 of what would eventually become his String Symphonizer, at the Frankfurt Musikmesse, the world's first actual string synthesizer appeared. Utilising quite a different approach to generate its ensemble effect, it was the grandfather of almost all string synths. Yet, despite its importance, it went almost completely unnoticed. This is because it wasn't a 'pro' keyboard at all. Manufactured by the Dutch company Eminent, it was a home organ: the Eminent 310 Unique.

The Eminent 310s

Eminent had been founded in 1923 as a small, family-owned shop that sold organs and harmoniums, but in the 1950s and 1960s it experienced tremendous growth, eventually employing over 400 staff. In 1969, the owners decided to start building their own organs under the Eminent and Solina brands, and the 310 was one of these.

As home organs go, the 310 Unique was a very attractive example of the species, with a 42-note upper manual (C-F) and a 44-note lower manual (F-C). The organ tabs provided conventional organ voicing, with traditional stops ranging from 16' to 4' on the upper manual. Likewise, the lower manual (8' and 4') and pedal stops (16' and 8') stops were traditional, while a selection of accented 'Sustain' stops could be directed to both the upper and lower manuals to generate a more percussive type of sound.

The conventional organ-like Timbre, Vibrato and Reverberation sliders of the Eminent 310 Unique.The conventional organ-like Timbre, Vibrato and Reverberation sliders of the Eminent 310 Unique.To the right of the lower manual there were four sliders: three of these controlled Timbre (a mild low-pass EQ); a fixed-rate Vibrato; and Reverberation, which was supplied by an internal spring reverb tank. The fourth balanced the volumes of the upper and lower manuals. However, that was where the conventional organ technology ended. The other three control panels made the 310 very special indeed.

To the right of the upper manual, there was a panel called Strings Ensemble, featuring eight buttons and a slider. Defeating all the organ tabs and pressing the 8' button on the upper manual produced a deep, lush string ensemble sound. The 4' button produced a thinner version an octave above. Of course, you could use these in unison, but the envelope of the sound was still rather organ-like so there was also a button marked 'SUST'. This duplicated the 8' Ensemble tone but with a polyphonic (ie. every note independent of all the others) extended release. Select all three together, start playing, and... wow!

It's hard to imagine the impact that this sound must have made in 1972, but it was far from the end of the story. Using the upper 8' and/or 4' Ensemble settings defeated the conventional organ tabs for the upper manual, but you could use the sustained strings with the traditional organ stops as you pleased. But what about the fourth button for the upper manual? This passed the so-called 'principal' organ stops through the Ensemble circuit, meaning that you could combine your choice of 16', 8' and 4' organ stops, turn them into a mighty ensemble and still add the SUST string Ensemble sound if you wished.

The 8', 4' and SUST buttons on the lower manual offered the same facilities, but instead of passing the standard organ stops through the Ensemble, the fourth button passed the pedal sounds through it. The range of possibilities suggested by this architecture were mind-boggling; the 310 was not only the first but perhaps the most powerful string synthesizer ever to be released. But wait (he said in his best advertising voice), there's more...

The Strings Ensemble panel, which gave access to the ground-breaking "deep, lush" Eminent String Ensemble sound.The Strings Ensemble panel, which gave access to the ground-breaking "deep, lush" Eminent String Ensemble sound.To the left of the lower manual, there was a control panel called Orbitone. The two switches marked On/Off and Chorus/Tremolo tell you what this was for, but the functions of the four buttons were less obvious. To cut a long description short, the Orbitone module was a gentle two-speed chorus that allowed you to select which of four sections — the upper principals and solos, the lower principals, the tibias and the sustains — were treated, and which were not. So, for example, you could mix the strings, 'Ensembled' principals and 'straight' tibias on the upper manual, with strings and chorused principals on the lower, while playing the polyphonic bass pedals without modulation... or any other combination. In addition, the EQ didn't affect the strings, so you could make the organ component of the sound more or less strident without changing the Ensemble sounds, then add delayed vibrato, make the principals percussive, add sustain to the pedals, and more. The sounds generated by the 310 were stunning.

The 310 Unique wasn't the only Eminent model to offer these facilities. The traditionally cased (and somewhat uglier) Eminent 310 Theatre included everything found on the 310 Unique, but added a primitive rhythm unit. This offered eight preset rhythms, but allowed you to combine any number simultaneously. A huge variety of combination rhythms was available, but if you can find a way to make Waltz/Samba/Slow Rock/Cha-Cha a viable basis for a track, you're a better man than I.

Finally, the 310 offered a signal input although, to correct what you may have read elsewhere, this bypassed the Ensemble and Orbitone generators. It also offered a three-channel output socket, so you could create a wonderful, warm stereo field of chorus and Ensemble, not just using its multiple internal speakers, but on recordings too.

The Technology

Unlike the Freeman String Symphonizer, the 310 had a single master oscillator. The output from this was divided down into the frequencies needed for the top octave, and then divided repeatedly to generate the various footages. The secret to its ensemble sound therefore lay in the adoption of the new bucket-brigade devices (BBDs) that had recently appeared, rather than using multiple banks of oscillators and applying differing speeds and depths of pitch modulation to these.

The Orbitone panel allowed selected sounds to be treated with a gentle but effective Chorus or Tremolo effect.The Orbitone panel allowed selected sounds to be treated with a gentle but effective Chorus or Tremolo effect.The 310 took the input from its single audio source, and passed it through no fewer than six modulated delay lines. Three of these comprised the string Ensemble circuitry and three comprised the Orbitone section. In both cases, the outputs from the three delay lines were connected individually to the three output channels but, apart from modulation depth and speed, the main difference between the two effects was that the Ensemble circuits were cross-connected, to create a wider and more swirly effect. Interestingly, one of the technological deficiencies of these BBDs had a beneficial side effect. The frequency range of the early devices was no more than about 6kHz, so the top end of any sound passed through them was attenuated. As a result, the 310 lacked the high-frequency edginess of the Freeman, so it sounded warmer in comparison. Many players liked this.

As you might imagine, few people in 1972 recognised the 310 as the pioneering instrument that it was. And, let's be honest, a home organ the size and weight of a Mellotron Model 300 was never going to appear in the keyboard rigs of the rich and famous. Nevertheless, a trawl through the equipment lists of the mid-'70s reveals that a handful of artists investigated its potential. The most famous use of a 310 was by Jean-Michel Jarre on his albums Oxygene and Equinox. Just select the SUST strings and an 8' organ tab with chorus on, and you can't help but play Equinox Part 1. It's iconic, and no string synth has ever sounded better.

The Eminent Solina

If Eminent had stopped there, the 310s would have been little more than footnotes in the history of rock & roll keyboards and we would have been robbed of one of the most revered of all vintage keyboards but, fortunately, financial pressures persuaded them to develop a new-fangled portable keyboard thingy suitable for a rock band. Using a modified Ensemble system in which the sound generator was passed through three delay lines, each modulated out of phase with respect to the others by a pair of LFOs, the Solina String Ensemble appeared in 1974.

The 310 Eminent 'Theatre' variant certainly looked the part...The 310 Eminent 'Theatre' variant certainly looked the part...Based around a 49-note keyboard, the Solina weighed in at a hefty 49lbs, yet produced just six sounds: Viola, Violin, Trumpet, Horn, Contra-Bass and Cello. Of these, the Contra-Bass and Cello were monophonic voices that encompassed the bottom 20 notes, whereas the others could be played across the keyboard and used in any combination, thus offering 15 timbres in total. The Solina's only other controls were the global Crescendo and Sustain Length sliders that controlled the attack and release rates of the single envelope generator. Later dubbed 'paraphonic', this architecture had significant shortcomings, because it was unable to articulate notes correctly if others were already — or still — held. Nevertheless, a single envelope was better than none.

Inevitably, the voices sounded nothing like their names suggested. Without modulation, the 8' Viola and 4' Violin each produced a nasal pulse wave more reminiscent of the thinner 'reed' stops of a pipe organ than anything else. The 8' Cello and 16' Contra-bass offered similar timbres but had slower envelopes. The Trumpet sound was essentially the same waveform with a high-frequency component added, whereas the Horn was more muted, with a lower frequency high-frequency component (if you see what I mean).

The one thing that all of these waveforms shared was a strong harmonic spectrum, although this was somewhat truncated for the Horn sound. This meant that, like the Freeman String Symphonizer, the individual sounds were brighter and more aggressive than those of an organ. What's more, even with Ensemble off, there was a certain amount of 'beating' between the notes in a chord, which made the sound more appealing than it might otherwise have been; pipe organ-ish, while remaining rather nasal.

Of course, it was the Ensemble effect that made the instrument what it was. Described by Eminent as "three phase shifters" the triple delay lines provided (according to the company's marketing) "luscious, spacious, orchestral effects", and the Solina excelled at producing high-pitched, ethereal strings — especially when helped along by a bit of external reverb and echo.

Whatever Happened To Eminent?

Eminent spent the 1970s supplying string synths to ARP, incorporating monosynths supplied by ARP into its own string synths and organs, and, of course, selling organs. Unfortunately, the company was to become one of the casualties of the economic recession of the early 1980s. Demand for traditional home organs had collapsed, and potential customers were far more interested in a new breed of low-cost, portable keyboards manufactured by Casio, Yamaha, Technics and others. This had a huge impact on sales so, in 1982, all the existing staff were made redundant, and the company was relaunched with a smaller workforce, building a new product range and performing assembly work for other manufacturers. But even this wasn't enough and, in May 1984, Eminent shut down for a second time.

Two months later, a new company — Verkoopmaatschappij Eminent Orgels BV — was established to sell the existing stock and provide servicing and spares for existing customers. With just 20 staff, this proved to be surprisingly successful, so the owners decided to continue building organs on a small scale. Some time later, the company was renamed Eminent BV, and it still exists today, manufacturing organs with the Eminent, Johannes and Aalborn brand names.

The ARP String Ensemble

While Eminent were distilling the Solina out of the 310s, a much smaller company in Massachusetts, USA, were also experimenting with ensemble synthesis. The prototype of an 'ARP String Synthesizer' was spotted a handful of times and was well received, but it never made it into production. So the scene was set for one of the strangest marriages in the whole of synthesizer history.

When its in-house project went down the pan, ARP turned to Eminent and, while taking the Solina and rebadging it as the 'ARP Model 2100 String Ensemble SE-IV' hardly seemed to be a brilliant ploy, it worked. Well, maybe 'rebadged' is too strong a word. 'Re-stickered' would be more accurate, since ARP simply put stickers over the Solina name, except on the Perspex music stand, which still proclaimed the origins of the instrument.

Eminent found their way to the USA via legendary synth makers ARP, who rebadged the Eminent Solina as the ARP String Ensemble.Eminent found their way to the USA via legendary synth makers ARP, who rebadged the Eminent Solina as the ARP String Ensemble.ARP's advertising made much of the fact that the crescendo and sustain functions "allow you to ease in softly and swell, then die away gradually after releasing the keys. Try this on a keyboard/tapes instrument. It won't happen". They also pointed out that "The String Ensemble is a synthesizer. You can hold a chord till you drop from exhaustion. That certainly beats the eight-second limit found on other systems". Clearly, they had the Mellotron in their sights.

Nowadays, there's a huge amount of apocrypha and misinformation floating around about the Solina, largely concerning the nature of the relationship between Eminent and ARP. The confusion is exacerbated by rumours suggesting that Philip Dodds of ARP (the man who communicated with aliens by playing the ARP 2500 in Close Encounters Of The Third Kind) claimed that ARP invented the Ensemble effect, and that ARP selected Eminent to manufacture the instrument because the Dutch company had expertise in top-octave divide-down technology. I very much doubt that Dodds would have done so, because Tijmen van der Kooij, an employee of Eminent BV, patented the Ensemble effect in Dutch. Nevertheless, it's true that ARP later developed and patented re-engineered Ensemble circuits. Another area of confusion lay in the fact that some Solinas (and, for that matter, some ARP String Ensembles) lacked the Ensemble button. This led to a rumour that some versions lacked the Ensemble effect, whereas all they lacked was a button to switch it on and off.

Yet another significant difference lay in the number of sockets on the rear panel. Early Solinas had just three: low output, high output and an input for an expression (volume) pedal. Later ones added the so-called System Interface jacks (trigger and gate outputs) which, when used together with the Ensemble on/off button, provided the final trick stuffed up the instrument's sleeve. When passed through an ARP Axxe, Odyssey Mk2 or ARP 2600, the polyphonic sound produced by the String Ensemble replaced the monosynth's internal oscillators and made full use of the filter, filter envelope and amplitude envelope of the subsidiary monosynth. This paved the way for a much more flexible range of sounds. Of course, the monosynths could only respond to single triggers and provided just a single filter for all the notes played on the Ensemble, but this 'paraphonic' technique was also used (more or less successfully) on later single-filter synthesisers such as the Polymoog, the Korg Poly 800 and the Korg Delta. ARP called the Solina/Axxe combination their 'Polyphonic System' and it proved quite capable of producing brass ensembles, pipe and electric organs, and a few piano-like, clavi and other percussive sounds.

This ARP String Ensemble boasts the 'System Interface' gate and trigger outputs that allowed the string ensemble sounds to be passed to an ARP Axxe, Odyssey Mark 2 or 2600, to make use of the connected synth's filter, filter envelope and amplitude envelope.This ARP String Ensemble boasts the 'System Interface' gate and trigger outputs that allowed the string ensemble sounds to be passed to an ARP Axxe, Odyssey Mark 2 or 2600, to make use of the connected synth's filter, filter envelope and amplitude envelope.The final revision of the ARP String Ensemble can be recognised by the LEDs that tell you which timbres are active, and seven sockets on the back panel, with independent left and right channels to enhance the spatial effect of the Ensemble sound.

There were many revisions over the life of the Solina and the ARP String Ensemble, some with significant modifications to the octave-dividing circuitry and the ensemble unit, and some that used different BBD chips. But whichever revision you consider to be 'the' Solina, it could have been a commercial flop. Let's face it: it had no means to mix sounds in any proportions other than zero or 100 percent, and its envelope could choke, re-trigger or even re-introduce previously released notes. So why is it today one of the most revered of all vintage keyboards, and how does it command prices many times those of later, ostensibly better string synths? As always, the answer lies in the sound; people thought that it sounded great, and players and bands as diverse as Jon Lord, Gary Wright, Elton John, The Carpenters, Stevie Wonder, Herbie Hancock and Pink Floyd soon adopted it. For a while, it sold in bucketloads.

The Solina String Synthesizer

In 1975, ARP released a strange little monosynth called the Model 2900 Explorer I. Not quite a programmable synth, it wasn't quite a preset synth either, and was built cheaply. So, despite a couple of nice touches, it would have been doomed to obscurity were it not for the fact that it was with the Explorer I that ARP repaid Eminent for allowing them to rebadge the Solina, supplying the Dutch company with synthesizer circuit boards for inclusion in Eminent's own instruments.

This meant that some Eminent organs ended up incorporating Explorers, which must have been a strange hybrid of concepts. More importantly, the Explorer I was married with the Solina String Ensemble to create one of the rarest of all keyboard instruments, the Solina String Synthesizer. This might have been no better than having a String Ensemble and an Explorer sitting side by side, but Eminent re-engineered the Explorer circuitry so that the Ensemble's sound could pass through the synth's filter and VCA. This was what ARP's Polyphonic System offered, but combined in a single instrument. Mind you, it was a heavy beast, so it's quite possible that players would have preferred to carry two separate keyboards. Whatever the reason, the String Synthesizer was not a commercial success and only 100 were manufactured. Today, this makes them rather desirable as collectors' items, but in 1975 the String Synthesizer appeared — and then disappeared — without creating even a ripple on the collective consciousness of the keyboard-buying public.


Ken Freeman had blazed a trail with his String Synthesizer prototypes, but the Eminent 310 Unique proved to be the progenitor of almost all subsequent string machines. The Solina, revered as it is, was a mere shadow of the 310, desirable only because one person could carry it! What's more, and contradicting a common misconception, it wasn't even the first of the portable string machines; the Solina had lagged behind the first of the 'modern' string synths by many months. Indeed, by the time ARP rebadged the Solina in the United States, it was just one of a host of excellent string synths available from manufacturers such as... Ah, but that's a story for another time.