Monday, April 27, 2009
ROLAND JAZZ CHORUS:ANATOMY OF A CLASSIC - 1984 REVIEW
In any endeavor, even artistic or scientific endeavors, the common-place and the mediocre exist beside the original and the classic.
This also includes the arena of amplifier design, where a few participants impart on their work the distinguished stamp of classic—that seemingly elusive combination of originality, popularity, and longevity.
The Roland Jazz Chorus series amplifiers, particularly the JC-120, have earned the designation of classic.
Introduced in 1977, the JC-120 was the first in a series of amplifiers that has continued to evolve in response to the demands of the musicians that have used it.
The new Jazz Chorus amps, the JC-77 and JC-120H, are proof of this continued improvement.
Adrian Belew, Robert Fripp, Andy Summers, Steve Kahn, AI Di Meola, Tommy Tedesco, Lee Ritenour, Bob Seger, Jeff Baxter, Elliott Easton, and Ric Ocasek; these musicians, though their styles vary, share the fact that a Roland JC amp is one of their music making tools.
At Roland, we know the musicians listed above are probably nice guys. We're sure they write their mothers regularly and don't kick their dogs. But frankly, when it comes to amplifiers, these guys are TOUGH.
They demand outstanding performance, unique features, and day-to-day depend-ability.
The JC's performance begins with its sound.
It was designed to deliver the kind of audio performance normally associated with high fidelity amps.
Right from the inputthe JC delivers more "headroom" than other instrument amps.
This headroom lets the JC handle signals from single and dual coil guitar pickups as well as the much hotter signals from synthesizers and other keyboards.
Roland engineers spent a great deal of time investigating the properties of the guitar's magnetic pickups, and how they affected pre-amp, equalization and power amps. These studies led to the development of intearated circuits (ICs) that allow the true character of the vibrating string to pass through the system without alteration of harmonic content or color.
To date, the JC amps have the widest bandwidth and cleanest sound around.
Why ICs, when all the amp classics up until the JC had been "tube" amps ?
During the development stages of the JC, Roland engineers realized that the era of the vacuum tube amp would soon be drawing to a close.
Not that tube amps were considered outdated in sound quality, but because so few component manufacturers were making tubes of any quantity or quality.
Most of these companies could no longer invest their time manpower or money to make vacuum tubes when their main accounts, television and stereo makers, were switching to "solid state" components.
This realistic appraisal has proven out as most amp models available today are either solid state or very expensive versions of early tube amps.
Roland set out early on to make the first classic of the integrated circuit era.
After input headroom is supplied, other elements of the pre-amp design must be considered.
The special passive equalization controls, echoing the concern for headroom, are designed to allow subtle and effective changes to be made in the High, Mid, and Low frequencies without losing the original harmonic quality of the vibrating string.
The new JC-77 and JC-120H have a further refinement.
They use a four band equalizer section that adds a Hi-Treble control.
One of the most popular features of the tube amp classics results from an imperfection in their original designs.
Tube pre-amps produce a unique form of distortion, particularly when combined with tube power amps. When pre-amps are overdriven, they will tend to over-drive power amps.
The product of all this distorting and overdriving is the screaming guitar solos of the six-ties and seventies complete with that other beast-or-burdens, feedback.
Again opting for originality, Roland engineers created a new kind of distortion circuit. The original JCs had a distortion system that began to change the waveform of the input signal into the shape of a square wave.
As the intensity of the effect was increased the original waveform begins to look more and more like the perfect square wave.
This system is called Variable Feedback Distortion and produces a much more mellow effect than the difficult to control tube amp distortion. This circuit has also been refined through the years.
The distortion circuit of the JC-77, JC-120H, and JC-120 amps made after November 1984 have greater intensity in their square wave effect and deliver a higher level of gain. This new circuit produces an effect similar to the popular BOSS Heavy Metal Pedal.
A distortion circuit that delivers, flexible equalization, and audiophile input specs; the engineers were on a roll.
What's next? Stereo Chorus. In 1977, the chorus effect was a relatively new idea and the stereo chorus was only available as a BOSS effect costing about $200.
The engineers put the stereo chorus into the first JC amp, thus the name Jazz Chorus.
To make the effect truely stereo and truely spectacular youwould have to use two speaker cabinets and phase the chorus between them. "Wait a minute!" Someone said. "Let's put the chorus in the pre-amp and use two separate power amps, pulsing the signal between them." So you have the unique JC amp system: a mono pre-amp, stereo power amp, a speaker for each power amp.
The Chorus and Vibrato in the JC amps have a spectacular feeling of motion as the sound pulses from speaker to speaker.
JC-77 and JC-120H have further refined the Chorus by adding a Manual Mode that allows the user to adjust Rate and Depth.
We've already mentioned the unique power amp configuration of the orginal JC-120.
The JC-120 has two amps each providing 60 watts RMS of power to 12 inch speakers. On the surface the JC-120 is a standard 2 X 12 120 watt guitar amplifier. Beneath that surface it is something special.
The new JC-77 and JC-120H have the same basic configuration as the original JC-120.
The JC-77 has two 40 watt power amps feeding two ten inch speakers. The JC-120H is a head-only amp that lets the user assign its two 60 watt power amps to speaker combinations of their choice.
"Esoteric designs are fine," said our mother-writers, "But my amp has to perform every day." After eight years on the market, less than one percent of all the JC-120s made
have been in the shop for service. ICs are much less prone to damage than vacuum tubes, but the JC amps also have high impact corner and edge protectors.
The control panel is recessed to prevent accidental damage to the knobs. The amplifier itself resides in an all steel chassis.
Every step necessary to make the JC a tough and dependable per-former has been taken. 99% of all the JCs made have never seen the inside of a service center and that means the engineers were successful again.
In the JC-77 and the JC-120H we have two new versions of a classic design that offers outstanding clarity of sound, unique features, and dependability.
We're sure the JC-77 and JC-120H will experience tremendous popularity. Afterall, their older brother has been getting ovations from some tough audiences for years.
From Roland USERS GROUP magazine 1984