FETS in the FIRE
A number of interesting new pre amplifiers were introduced in Las Vegas at the Winter Consumer Electronics Show. At last, there is a production model of the long-anticipated John Curl preamplifier from Dennesen. Designated the Dennesen JC-80, it is an all-FET unit in a complementary push-pull Class-A topology, all d.c.-coupled and with a zero-feed back input stage. Each stage is separately regulated, with no interstage coupling capacitors. The RIAA section is passive and there is switchable R and C cartridge loading as well as sufficient gain for "straight-in" amplification for most moving-coil cartridges. All signal switching is accomplished by hermetically sealed gold-on-gold relays. One especially useful feature, found on few preamps, is a switch for absolute phase-of particular importance with PCM processors and CD (DAD) players, which usually have a 180° phase reversal. John Curl has chosen to use high precision potentiometers, of the sliding fader type used in studio mixing consoles, as level controls. The JC-80 is claimed to have an extremely wide open-loop bandwidth and to be "virtually un-slewable." Price is expected to be about $3,500. John Curl is noted for his design of the Mark Levinson JC-2 preamp and his pioneering work with Matti Otala on TIM (transient intermodulation distortion).
He is a man of remarkable talents, and I can hardly wait for some hands-on experience with the JC-80.
Another FET preamplifier is the Nova CPA-100 which, quite coincidentally, has an absolute phase switch-as does the Dennesen JC-80. (Start of a trend?) This $1,600 unit features a high phono overload (300 mV rms at 1 kHz) and an open-loop bandwidth exceeding 200 kHz for each amplifier stage.
The large power supply uses a toroidal transformer, and each of the eight amplifiers in the unit has an independent wide-band regulator. The TIM is said to be virtually unmeasurable, and SMPTE and harmonic distortion are claimed to be under 0.01% at 1 V output. An optional battery-powered head amplifier is available for $300.
Still another FET preamp is the Acoustat Trans Nova, though it was introduced last summer. Its main de sign feature is a new type of RIAA phono stage which Acoustat calls "Achromatic," as it is "neither active nor passive" but "combines the advantages of both." The firm says that with this new arrangement virtually all later stage noise disappears.
Acoustat also states that with this new phono circuit, their Trans Nova preamp has more gain, less noise and more headroom than any previous preamp. They further claim that even the lowest output moving-coil cartridges can be used without any step up device. Switchable phono loading is provided, as are such amenities as two tape monitors, external processing loop, passive high filter and loudness compensation. Price is $850.
Perreaux introduced the SM-2 pre amplifier as a companion for their 2150B and 1150B amplifiers. The big feature on this unit is a phono overload of over 1 V, and it is claimed that an output of over 25 V with no measurable distortion can be achieved. Perhaps we are seeing the beginning of another trend, for the SM-2 is also claimed to handle the lowest output moving-coil cartridges "straight in," without head amps or step-up transformers. Price of the SM-2 is $990.
Lastly, Jim Fosgate of Fosgate Research has come up with a specialized preamplifier, the Model DC-301. Using Class-A circuitry throughout, with a regulated power supply, the unit uses his patented active equalizer along with National Semiconductor DNR noise reduction. The equalizer can provide boost of up to 15 dB at 20 Hz and up to 5 dB at 20 kHz. One of the few preamps to offer DNR, it can pro vide an improvement in signal-to-noise ratio of up to 14 dB. Both the equalizer and the DNR can be bypassed. Price not yet determined.
As usual with loudspeakers at any CES, "hope springs eternal" in the speaker designer's breast. They are all looking for a magic formula that will produce a high-volume, high-profit speaker. Alas, for the most part we have legions of walnut boxes, all seemingly cast from the same mold, and all sounding about the same-which is to say, not very convincing in the reproduction of music. The other side of the coin is the exotic speaker designs that appear at every CES. They usually share the common attributes of imposing size and weight and stratospheric price tags. Some try to abrogate the laws of physics. There are those, how ever, that represent good design based on solid scientific rationale, and some of these speakers can be mighty impressive transducers.
A case in point is the VMPS Wide Range Ribbon speaker system. The brainchild of Brian Cheney, the clever chap who owns VMPS, this is some thing of a breakthrough in ribbon speaker technology. Ribbons have al ways been highly regarded for their ultra-fast transient response and low distortion. They are equally well-known for their lack of durability and poor power handling. The result up to now has been a minimal use of ribbons in speakers, except in some tweeter applications.
Essentially, Brian has taken a 130-inch-long, 5/16-inch-wide, flat aluminum-alloy ribbon and bonded it to a gossamer--like polyester backing film, less than a third of a millimeter thick.
The ribbon/film is bent into a side-by-side configuration and clamped non-compliantly between parallel rows of over 100 bar magnets of extremely high intensity. In this way, the ribbon cannot "flap" in response to low frequencies or high levels. The ribbon is driven uniformly over its entire surface in a push-pull manner. With over 41 square inches of radiating surface, the ribbon can handle over 300 watts rms between its crossover points of 300 Hz and 15 kHz. A "super-tweeter" ribbon 3/16-inch wide and 2 1/4 inches long carries on to 50 kHz (so your dog can share in the fun). From 300 Hz down, 8- and 12-inch polypropylene dynamic cone woofers and a bottom-firing, slot-loaded 15-inch subwoofer provide response to 22 Hz. The 6 1/2-foot-tall rib bon/bass columns are augmented with special Space Boxes flanking satellite/ subwoofer systems with integral electronic crossovers and their own drive unit designed by John Curl. The Space Boxes are meant to be placed 2 to 10 feet behind and somewhat to the sides of the main columns, and are said to provide "spectacular" front-to-back depth of sound field. There is a great deal more to these ribbon loudspeakers, but it would require pages to fully document this new technology. Sensitivity of the system is 94 dB SPL (1 W/ meter) with an awesome output of 128 dB SPL for 5% THD. The-3 dB frequency response with Space Boxes is 19 Hz to 50 kHz. Brian was going to bring these extraordinary new speakers to my home for extensive listening tests. Unfortunately, the blizzard of '83 hit New York, it took poor Brian 26 hours to get from San Francisco, and to top it all, the trucker could not deliver the pre-shipped speakers! Ah, well, we have rescheduled the whole thing for April, when the weather should be more cooperative. As you might expect in such an elaborate loudspeaker, the price has been set at $5,995 the pair, including the Space Boxes.
Another loudspeaker which elicited much favorable comment is from, of all places, Italy! Apparently the ESB ( Electroacoustic Systems Building) company occupies much the same place among loudspeaker manufacturers there as JBL does in the U.S. In any case, they appear to have very modern facilities, including a large anechoic chamber. The ESB 7/05 is their top-of-the-line loudspeaker. It stands 68 inches H x 18 1/2 inches W x 14 1/2 inches D and is actually a two-cabinet design.
The lower unit contains a 12-inch cone woofer with free air resonance of 16 Hz, a rear-mounted passive radiator and a control unit for low-, mid-, and high-frequency response contouring.
In the upper cabinet an 8-inch low mid range cone driver is mounted, along with a 2-inch upper midrange dome and a 1-inch dome tweeter. Crossover points are 500 Hz, 1.6 kHz, and 6 kHz.
The upper cabinet has a sloping front for phase alignment of the drivers. In each speaker the 8-inch cone driver and the 2- and 1-inch domes are mounted on a baffle board that is set at a certain angle along with a "reflector" panel. These mirror-image baffle/reflector panels afford what ESB calls "Distributed Spectrum Radiation" which is claimed to form such a wide and deep soundstage that good stereo imaging is not confined to the central sweet seat. Frequency response is quoted as 25 Hz to 20 kHz with the lower 3 dB point at 35 Hz. With an efficiency of 89 dB SPL (1 watt/meter), the 7/05 is said to be capable of handling 400 watts rms into 8 ohms. Obviously, this loudspeaker should have no trouble with digital program sources. A pair will cost $4,500.
After years of building full-range electrostatic loudspeakers, Acoustat has produced their first hybrid electro static/dynamic driver system, the Mod el Two/MH. Standing 6 feet tall with a width of 20 inches and a depth of 3 1/2 inches, the electrostatic portion covers the range from 100 Hz to 20 kHz.
Placed behind the electrostatic panels is the woofer enclosure, which measures 21 x 18 x 13 inches. Of sealed-box design, a 10-inch, down-firing woofer covers the range from 100 Hz down to 28 Hz. Acoustat claims a frequency response of 28 Hz to 20 kHz, ±3 dB, for their Model Two/MH. The system is said to produce sound pres sure levels of 110 dB at 18 feet in a 14 x 22 foot room on program peaks. A minimum of 60 watts is required to drive the system. Acoustat feels that since most of the frequency spectrum is covered by their electrostat elements, the major advantages of pure electrostatic speakers is retained.
They evidently expect the Two/MH to be a sales leader at $1,195 per pair.
As usual, one could fill every page in Audio with new product information from WCES, but space dictates only a survey of the highlights.
-BERT WHYTE
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(Adapted from: Audio magazine )
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