Behind The Scenes (Jan. 1978)

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In New York, there is a snap in the air, and the autumnal colors have come. Even without these harbingers of Fall, I know the season is upon us by the number of press releases and invitations to press conferences to preview new audio equipment. The Audio Engineering Society reminds me I am due at the 58th convention at the Waldorf, November 4-7. No sooner do we catch our breath, when we check into Terry Rogers' "New York Hi-Fi Stereo Music Show" at the Statler Hilton, running from November 10th through the 13th. There has been much controversy about the value of "hotel hi-fi shows" to audio manufacturers.

Be that as it may, the show appears to be "sold out." Since this is the first hi-fi show in New York in over four years, interest among the audiophiles is sure to be high, and the audio companies are going to tempt them with a plethora of new products.

You may recall that I visited Studer/Revox in Zurich during July of 1976, and Willi Studer gave me a "look see" at some new developments, with intimations of other products to come.

Thus, when I. recently received an invitation to a Revox press conference, I felt sure I would be shown a new generation of Revox audio components. Not only did they show the new B77 tape recorder I expected, but the B760, a new quartz-controlled digital FM tuner; the B750, a 60 watt/channel @ 4 ohm integrated amplifier, and, totally unexpected from Revox, a very sophisticated, quartz-controlled, direct-drive turntable with a tangential-tracking tonearm!

------(image coming soon) Revox B77 tape recorder

Revox Roundup

The B77 is a new tape recorder, but it is not the successor to the A77, which stays in the line. It does however retain many of the features of the A77, such as the die-cast chassis, the outside-rotor supply and take-up motors, and the servo-controlled, direct-drive capstan motor. New on the B77 is full electronic logic control of tape motion. There are no levers or relays and any of the drive modes can be entered directly without going through the Stop mode. There are new record and playback electronics, with the bias oscillator putting out 150 kHz.

Revox is particularly proud of the 24 dB headroom on the B77 in both record and playback, which puts it right up with the professional recorders in this respect. Revox also makes a point of their frequency response of 30 Hz-20 kHz,±3 dB @ 7.5 ips, noting that their 0 dB point is at 1 kHz, thus their worst case droop at the upper and lower frequency extremes is only 3 dB. Revox makes much of the fact that their heads, made in their own plant, do not exhibit the low frequency head-bump excursions, which are a design anomaly present even in some of the best professional heads. A very strong claim is made for the wear characteristics of the B77 magnetic heads, stating that head life cannot be surpassed by any recorder currently on the market. The B77 employs new VU meters, considerably larger than the meters on the A77, and they are fitted with long scales and LED overmodulation indicators. To the right of the head assembly, the B77 sports a new splicing block with built-in shears. New muting circuits are used which prevents source/tape monitor switching transients from affecting the recorded signal. Electrically, the B77 claims a S/N ratio of 66 dB @ 7.5 ips, half-track "A" weighted, and total harmonic distortion of 1 percent for the record/play cycle. The B77 will be available with quarter or half-track head configuration with tape speeds of 3.75 and 7.5 ips. No doubt, a high-speed (7.5/15 ips) version will ultimately be available, as was the case with the A77. The suggested price of the B77 is $1195.00. With a recorder in this price and quality range, there will be some who question the use of microphones with unbalanced lines and input impedances 600 ohms and up.

However, with most high-quality mikes having impedances of 50-150 ohms, this shouldn't be much of a problem.

Another point of controversy is that bias and equalization facilities are not available on the front panel nor does the playback potentiometer control the VU meter movement, making the use of alignment tapes difficult. With any new tape recorder there is bound to be some nit-picking. All in all though, the B77 seems to have a lot going for it, and with Willi Studer's well-founded reputation for high quality, it should prove to be a fine performing tape recorder. Time and testing will tell!

Revox, like many other audio companies these days, evidently wants to have a full line of components to offer audiophiles. Their B760 digital FM tuner is a very sophisticated unit, utilizing frequency synthesizer tuning controlled from a quartz reference crystal. There are 15 pushbuttons which can activate a CMOS memory and store the frequencies of 15 stations. Tuning is as simple as pressing a button, and the number of the station, and the station frequency is digitally displayed. A 68.18 nS digital FM demodulator is a feature, and the unit has very wide bandwidth and linearity, plus very low distortion. A Dolby card can be plugged into the tuner for decoding of Dolby FM broadcasts.

The B750 integrated amplifier puts out 60 watts/channel into 4 ohms, with THD less than 0.1 percent up to full output. A fully complementary push-pull output stage is featured for each channel, and Revox makes the eyebrow-raising claim that the amplifier has no transient intermodulation distortion! A unique feature is that the two amplifier sections can be separated by switching for separate use or for coupling to an external equalizer.

Surprise of the Revox press conference was the B790 turntable, a direct-drive turntable with servo electronics phase locked to a quartz reference. Nice, but nothing too unusual there. Ah, but the arm is another matter. After a record is placed on the turntable, an arm cradle assembly is swung into position and an ultra-short arm, less than 2 inches in length, tangentially tracks the record.

The arm is servo controlled, with a geared servo motor guiding the tone arm cradle across the record. Two photo diodes on the end of the arm receive infra-red light from an LED through a slot in the arm. Any canting of the arm from perpendicularity causes an asymmetrical amount of light at the diodes, the servo pre-amplifier detects this, and appropriate correction is made. Lowering and lifting of the arm is via electro-magnetic control. An Ortofon VMS20E phono cartridge is supplied with the unit, and while it is not a special type, changing of the cartridge is supposed to be a factory matter. I don't know whether you are "locked" into the Ortofon cartridge. It is a fine cartridge, but if someone prefers another brand, this may pose problems. In any case, this a unique, "hands off" turntable that provides optimum tangential tracking.

Price is supposed to be "around $700.00."


Technics SE-A1 amplifier (image coming soon)

Technics Triumph Hard on the heels of the Revox conference, Technics held a press conference and introduced some new components that really had us all agog. How about a 350-watt-per channel, class -- A d.c. stereo power amplifier! This is the rating of their SE-Al unit which is claimed to have no more than 0.003 percent THD from 20 Hz to 20 kHz. At 1 kHz, they state the THD is unmeasurable on the best test equipment. All this is accomplished by what Technics calls "class-A plus" operation. In their explanation, a class-A amplifier, of about two watts power, has its power supply ground potential floated, while a high voltage, synchronized with the amplitude of the audio signal, is applied from an independent power supply amplifier.

The output of the "class-A plus" is connected directly to the speaker terminals in push-pull operation, thereby eliminating switching and crossover distortion. To do all this, a total of eight separate power supply stages have been incorporated, four for each channel, in this bi-monophonic constructed amplifier. Four electrolytic capacitors of 100,000 µF each have been coupled to the class-A amplifier, and another four capacitors of 22,000 µF each are connected to the power supply amplifier. Both left and right channels also include high capacity, low d.c. resistance toroidal transformers. All coupling capacitors have been eliminated from the signal path, including the negative feedback loop. The problem of d.c. drift, common to all d.c. coupled amplifiers, was solved with an active, thermal servo control amplifier, independent from the signal path. With this new circuitry, in spite of the huge 350-watt/channel output, the amplifier is not overly large, although it weighs 112 lbs. and does not get hot enough to require a cooling fan. This is, of course, in marked contrast to most class-A amplifiers. Frequency response of the SE-Al from d.c. to 200 kHz is +0,-1 dB; S/N ratio, IHF "A" weighted, is 120 dB, and the unit has a slew rate of 70 volts per microsecond. The amplifier has two special +10 to-50 dB, rapid response, peak-reading power meters, with switches for 4-, 6-, 8and 16-ohm readings. It has four sets of speaker terminals with four independent level controls. Input terminals are gold-plated. Obviously, a class-A amplifier of this power breaks new grounds and is most likely the prototype for a whole new family of class-A amplifiers. It is incontestably the tops in one category ... price. Are you ready, fellas? ... $4000.00! As a companion unit to the SE-Al amplifier, Technics introduced their SU-A2 d.c. control amplifier, which combines the functions of a preamplifier and parametric equalizer. Class-A amplifier operation is employed in all stages of the SU-A2 and is claimed to completely eliminate all switching and crossover distortion. There is a separate phono input for moving-coil cartridges with a S/N of 80 dB @ 100 µV. The phono input for moving Technics SU-A2 magnet cartridges is said to have the astonishing S/N ratio of 107 dB for 10 mV! The MM input signal is claimed to have less than 0.003 percent THD from 20 Hz to 20 kHz. As in the power amplifier, all coupling capacitors in the signal path have been eliminated. The equalizer circuit is completely d.c.

The d.c. drift is again under control of thermal servo circuits. The preamplifier has fade-in/fade-out, touch-type switches which eliminate crosstalk signal leakage and shock noise by utilizing reed relays for optimum switching. This unit has "whistles and bells" galore ... a built-in oscillator which produces sine waves, square waves, pink noise, and warble tone signals, plus a universal frequency equalizer. There are special meters for peak and average modes, and peak hold as well. All input and output terminals are gold-plated ... I could go on and on, but you get the idea! Another $4000.00 will mate this pre amp control unit with that nice 350 watt amplifier. Can't you just see this $8000.00 pair showing up as "his and her" baubles in the Neiman-Marcus Christmas catalog?

AES Prelude

The 58th AES convention at the Waldorf is shaping up as one of the biggest ever. In fact, new areas of the hotel are being used for the first time.

As I have pointed out before, the AES is becoming a mini hi-fi show, with this year over 30 companies presenting sound demonstrations, necessitating a move to the 10th floor. The trend to digital recording may well begin at this convention, with a number of systems finally available for commercial use.

The showing of a digitally-encoded audio disc with laser read-out, a la the Philips/MCA videodisc, by Teac at the Tokyo Audio Fair, may give added impetus to the idea of digital recording.

As usual, I will bring you a complete report on the audio products making news at the AES convention.

(Source: Audio magazine, Jan. 1978; Bert Whyte)

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