Behind The Scenes (Sept. 1977)

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The 1977 Summer Consumer Electronic Show in Chicago marked the eleventh anniversary of this annual event. It also nicely coincided with the Edison Centennial, celebrating 100 years of recorded sound, and the 30th anniversary of commercial television, as well as Audio's 30th. Obviously, the CES had a lot going for it this year, and to put icing on the cake, Chicago obliged us with some highly unusual delightfully cool weather, albeit with some rain, and thunderstorms too.

Probably heartened by the surprising success of the winter CES in January and the apparently ongoing improvement in the general business climate, despite inflationary pressures, the mood of the 45,000 plus attending was very upbeat, buoyant, and determinedly optimistic. All first day attendance records were quickly broken as huge crowds surged into the vastness of McCormick Place, and for the first time, in addition to the main floor, both sub-floors were needed to cope with the great number of exhibitors. Across the street, McCormick Inn was reserved for the exclusive use of audio exhibitors.

There were mixed reactions to this facility. Most people liked the idea of so many audio exhibits in one location handy to McCormick Place ... but there were many complaints about the small size of the demonstration suites at the Inn, its poor soundproofing and ventilation, and above all, the exasperating slowness of the elevator service, which led to long waiting lines in the lobby and on the exhibit floors. The audio industry has become so large that it still was necessary to visit enclaves of audio manufacturers who were in most of the major Chicago hotels, and the taxicabs were generously enriched by our excursions to the various inns.

One thing is certain about the CES. No matter how energetic or conscientious one is, it is just plain impossible to see everything, even when you know where specific demonstration suites are located, to say nothing of interesting exhibits you only learn about when the show is over. Needless to say, there were many interesting new products, with various trends being reflected in what was offered.

Receivers It was evident that the receiver power race which has dominated the industry for the past several years is still very much with us. To wit: Marantz became the new champion with its Model 2500, rated at 250 watts per channel into 8 ohms, and for those who own 4 ohm speakers, a rather staggering 330 watts per channel. Features on this receiver include a built-in oscilloscope for tuning indication, signal strength, multipath rejection, stereo separation and other signal indications, and a claimed signal-to-noise ratio of 50 dB with only 25 microvolts of signal. What Marantz terms a "turbo-flow heat dissipation system" with "pin fin" heat sink design is said to keep this receiver cool, and as a result, the unit is not of the size and weight usually associated with this much power. All this can be yours for a mere $1495.00. Hitachi has its SR2004 Receiver rated at 200 watts into 8 ohms, but with its Class G amplifier circuitry it is claimed to be capable of 400 watts per channel within rated distortion on transient peaks.

The circuit is somewhat analogous to the "current dumping" scheme of Quad amplifiers in that most signal information is handled within the 200 watt power rating of the unit, but when high level transients are encountered, the circuit sort of "shifts" its electronic gears and goes into the higher power mode. The efficiency of the Class G circuit is said to result in less heat for such a high power output, and thus means less heat sinking and lower weight. The other high-powered receivers at the show have maintained their status quo, with Rotel at 180 watts per channel into 8 ohms, Technics at 165 watts per channel and Kenwood and Pioneer both at 160 watts per channel. With those companies who did not choose to compete in the horsepower race, their receivers reflected technical refinements. Thus the units from Sansui and Sherwood, for example, featured improved sensitivity, better stereo separation, better and more flexible tone controls, phono preamp sections with less noise and distortion, and more accurate RIAA circuits.

When will the horsepower race reach a point of diminishing returns? The end is apparently not yet in sight, with rumors of several 300 watt per channel units in the offing! The size and weight of these brutes can be the limiting factor, but consider the fact that Sony, for example, could conceivably incorporate its Class D switching amplifier into a receiver, which because of its efficiency, put out 350 watts per channel, and still be relatively compact and lightweight.

The mind boggles! As you are no doubt aware, as receivers have become more powerful, more complex, bigger, and heavier, the market for separates has grown apace. Of course, the idea of a separate preamplifier, power amplifier, tuner (and these days, equalizer) is as old as high fidelity itself, and in my book the new emphasis on so-called separates is merely an index to the ever-increasing number of audio consumers who have become audiophiles. I don't think there is any question that separates afford more flexibility, technical sophistication, and exalted levels of quality than is likely to be incorporated into any receiver. For those with the wherewithal to indulge themselves in separate components that are at the fine cutting edge of the art, the sky is the limit. Nuff said?

Tuners

Sherwood's $2000.00 Micro/CPU 100 FM tuner is finally in production and can probably rank as one of the most sophisticated audio components extant. Using micro-processor technology, it achieves state of the art levels of performance in nearly every FM parameter. For those who like to indulge in "one upmanship," how about a tuner where you can punch a button and come up with not only a LED readout of a station's frequency, but its call letters as well! There is a growing trend to so-called "slim-line" components with low physical profiles. Lux has what they call the LRS series and they have a frequency synthesizing digital tuner (as well as companion preamp, amplifier and graphic equalizer) with very fine specifications. As usual with this company's products, they are cosmetically attractive and beautifully finished.

Technics calls their low profile components the "Flat Series," and it comprises an FM/AM tuner, preamp, amplifier, equalizer and metering unit.

The tuner features flat group delay filters and is said to be capable of reproducing square waves.

In more conventional format, Sansui was showing their new TU-717 FM/AM tuner which features selectable i.f. bandwidth for lower distortion, 0.09 percent in stereo is claimed. Still more remarkable is their claim of a S/N ratio of 77 dB in stereo.

Yamaha was showing its well regarded CT-7000 FM tuner, which has extremely low stereo distortion. There were many other tuners in various price ranges from the likes of Pioneer, Kenwood, Marantz, Onkyo, in which even the modestly priced units had levels of performance undreamed of just a few years ago. A good many of the tuners (and a lot of receivers) featured Dolby B FM decoding circuits with the 25 microsecond de -emphasis built in, and as Dolby FM broadcasting grows, this will be an ever more appreciated facility.

Amps

Moving on now to preamplifiers, power amplifiers and integrated amplifiers, I must confess to a personal idiosyncrasy, in that I have never had much regard for integrated amps.

However, there is no doubt of their growing popularity, especially when coupled with some of the jazzy new tuners now available. These integrated amps are no slouches when it comes to power. Marantz has a new Model 1260DC integrated amp which is rated at 130 watts per channel into 8 ohms, with no more than 0.03 percent THD. Pioneer's SA9900 integrated amp puts out 110 watts per channel, while Kenwood has their Model 600 with 130 watts per channel.

There are other 100 plus watt units from Lux, Hitachi, Rotel, and Sansui.

Irrespective of power output, more attention is being paid to extended frequency bandwidth, minimum phase shift, very low distortion, and RIAA equalization held to a tolerance of ±0.2 dB, in several of the new integrated amplifiers, notably the Marantz 1260DC listed above, and Sansui's 85 watt per channel AU -717, which boasts of response from d.c. to 200 kHz, +0.0 dB, -3.0 dB, with THD rated at 0.025 percent. Clearly, many integrated amplifiers have achieved levels of performance, that not too long ago were the exclusive province of very fancy and expensive power amplifiers.

Preamps

Preamplifiers. They come in all sizes, shapes, and price ranges, and currently they seem to enjoy the status of a "glamour" component. A great deal of research is being conducted on preamps, and many new designs are on the market. Preamps are the special joy of the most avant-garde audiophiles, and the more exotic the design and specifications, the better. These people feel that various preamps have a profound influence on the quality of sound they get from their stereo systems. Preamps are reviewed and endlessly discussed in the "underground" audiophile magazines, and their sonic qualities described in such terms as "hard and grainy," "gritty," "sweet and open," "transparent," "good depth perspective," "high definition," "ambience suppression," etc. Whatever your reaction to this colorful terminology, and the fact that it does neither quantify nor qualify the particular technical virtue or anomaly which stimulated such responses, there is little doubt that many people do indeed perceive audible differences between various preamps, even when the technical specifications of the pre amps are nearly identical. Over the past few years there has been an intensive effort to correlate objective measurement techniques with subjective listening responses to pre amps. There have been some moderate degrees of success in this respect ... in particular, the work of W. Marshall Leach of Georgia Tech, and the joint venture of Otala and Leoninen of Finland and John Curl in this country on the phenomenon of transient intermodulation distortion has been quite revealing. It is thought by many people that even a very tiny percentage of TIM can make a preamp have an unpleasant sound. Many designers of preamps now feel that the standard steady-state harmonic and intermodulation distortion measurements which have been used for years have little or no relevance to the dynamic aspects and complex waveforms of music. Unfortunately, there is presently no fully recognized standard of measurement for transient intermodulation distortion. Be that as it may, a number of people claim to have proprietary methods of measuring TIM, and this has influenced the design of their preamps. If one can make a generalization in this matter, those who subscribe to the idea and importance of TIM want a circuit that will give them an "ultra -fast" preamp, where transient signals are not distorted by "time delay" or "time smear" as it is sometimes called. Of course, there is a great deal more to designing a preamp, but this emphasis on TIM would seem to be entirely justified in the light of present experimental evidence. Needless to say, different engineers have different ideas, and the preamps shown at the CES reflected this diversity.

By far the most radical departure from conventional preamp design was Crown International's DL -400 Stereo Control System. This consists of a switching module, power module, and phono stage module. The switching module has eight high level inputs which are digitally selectable via pushbuttons with LED indicators.

There is a unique Volume/Balance control, which is pushbutton controlled and digitally stepped in 0.5 dB increments (129 positions in all). These controls have a dynamic range of 63.5 dB, and an LED display shows gain in dB above minimum level.

Channels can be independently adjusted or ganged over the full range, with a tracking accuracy of 0.2 dB. The tone controls cover bass, midrange and treble, with adjustable turnover frequencies, and are stepped type providing ±15 dB of boost and cut. A cancel switch is available which will remove the tone controls from the circuit for true flat response. There are rumble and scratch filters, also with cancel switch, a stepped 31 position "Panorama" control for adjustment of stereo image, and inputs and outputs with switching controls for external signal processors such as equalizers and noise reduction units.

Well, that is all very nice, but get this people ... input selection, power Off and On, mute, volume, and balance can all be remotely controlled! The power module of the DL-400 has seven switched and one unswitched a.c. outlets, and can handle up to 50 amps.

It furnishes d.c. supplies to the switching and phono modules. The DL-400 phono module is designed to be mounted at the turntable to reduce the length of low voltage r.f. sensitive cable. A switch provides RIAA equalization or flat response for use with a microphone. There is a 30 to 50 dB adjustable input gain, and 47 or 100 kilohm input impedances which are switch selectable. Phono input of up to 330 mV is monitored by an LED overload indicator. A moving coil phono module will be optional. Finally, the DL-400 is designed to accept an upcoming Microprocessor Control for the application of computer control techniques. Clearly, the DL -400 breaks new ground, and I like the concept that allows considerable signal processing, or thorough defeat switches, no processing at all. You may remember that over a year ago predicted that remote control of pre amp facilities would be forthcoming, and now Crown has taken the first step. The projected price of the DL 400 is $1495.00. Another interesting preamp seen at the CES was the Model 520 Stereo Preamplifier made by Analog Engineering Associates of Silver Spring, Maryland. Of modular construction, the unit is built to very high standards, using such parts as printed circuit boards of Military or NASA specifications. All interconnecting pins, as well as phono input jacks are 24k gold-plated. Resistors are all 1.0 percent tolerance, capacitors are solid tantalum, mica, or metallized poly carbonate. Control potentiometers are Allen Bradley Tight-Trac units.

Overall construction is anodized aluminum. Phono and high level inputs are pushbutton selectable, as are tape monitor, high and low filters, and mode. Specially configured bass and treble controls, and loudness controls are provided. This is a fairly straightforward design with a minimum of frills. Here is a case where the designers are acutely aware of TIM, and a situation in which they have their proprietary method of measuring TIM. According to the company, they are actually able to use music for their dynamic measurements signal, and after manipulation it is fed into their own computer for analysis. The pre amp has impressive specs, not the least of which is in the phono section, where they claim a "total transient error" of 0.004 percent, 20 Hz to 20 kHz, measured under actual dynamic conditions. Price is less than $600.00. The company also manufactures two pre-preamps for moving -coil phono cartridges, the deluxe Model 515 featuring variable gain to match MC outputs and variable frequency compensation to compensate for the rising high end of some MC cartridges. The price has not been announced.

The Rappaport PRE -1 stereo pre amp was shown at the CES, and is another modular construction unit, that already has earned a following among audiophiles. Here again, the emphasis is on a simple unit with a minimum of signal conditioning to achieve low distortion.

RAM Audio Systems were showing their new RAM200 preamp. The unit features direct input for moving -coil cartridges, wide bandwidth, high slew rate, and all output circuits are Class A complimentary bipolar transistors.

Level attenuator is a 36 position gold-plated switch, with metal film resistors. There is a dual LED output level indicator with 46 dB dynamic range.

Phono inputs have adjustable resistive and capacitive loading. All inputs feed into FETs for low noise.

Price

$1000. David Hafler made audio history with his original Dynaco preamp kit.

Having long since divested himself of his interests in Dynaco, and more recently Ortofon, he has formed his own David Hafler Co. in Philadelphia.

Now he is once again offering a pre amp kit (it will be available wired as well), the Model DH -101. This is another basically simple unit, with a volume and balance control, bass and treble controls, and pushbutton selectable phono, tuner, tape, aux, etc. The difference that makes this kit remarkable is that for an anticipated price of $200, this unit has been designed with close attention to TIM distortion. So much so that they have published scope photos of the square wave and pulse response through the phono section of the preamp (using, of course, an inverse RIAA equalizing network) and the input and output traces are impressively symmetrical. I should also note that they use the September 1976 revised RIAA equalization specification, and this unit is ±0.5 dB from 2 Hz to 20 kHz. It will be interesting to hear what this preamp sounds like.

Harman Kardon was showing their new $550.00 Citation 17 preamp. Now this unit was designed with close adherence to the ideas on TIM distortion expressed in the Otala/Curl paper. Thus, they have opted for the use of minimum negative feedback, fast square wave rise -time, fast slew rate, and other means to achieve very low TIM. The Otala/Curl paper is not a blueprint or circuit diagram, but its ideas can be translated into engineering applications, and I certainly want to listen to a preamp designed around these principles.

Power Amps

Power amplifiers are dear to the heart of every rabid audiophile. The remarks I made concerning preamplifiers in respect to transient inter modulation distortion are equally applicable to power amplifiers with, of course, proper modifications in consideration of the vastly greater output of these amplifiers. Amplifiers have their own special problems too. The class they operate in and the output wattage can affect their thermal stability ... some need more heat -sinking of the output devices than others ... some amps need forced air cooling as well. Protection circuitry against shorts can be a problem, especially since some of them have an audible effect on the signal. Many amplifiers are sensitive to varying types of load, and with some units if the load impedance falls below 4 ohms you see some catastrophic failures. All of this doesn't faze amplifier designers ... hope springs eternal with them, and new amplifiers appear almost as often as loudspeakers. At the CES, power amplifiers were all over the place, but here is a selection of those we saw that appeared to have some special qualities.

The Threshold Corp. of Sacramento, Calif. were showing two of the most interesting amplifiers I've seen in a long time. Both operate in class A. Now you have to understand that "class A" has become another of those magic "cult" terms for audiophiles. It is very "in" right now, and can assure you that the midnight oil is burning in the labs of many manufacturers trying to come up with some class A amplifiers to take advantage of his situation. Briefly, the advantages of class A operation are that the out put transistors are always "turned on" and can respond instantaneously to an input signal. In class AB and B amplifiers, it takes a finite amount of time for the transistors to "turn-on" and "turn-off" in each cycle, and this causes what is termed crossover distortion, which is characterized by high order harmonics, which are generally offensive to the ear. Thus a class A amplifier does not have any crossover distortion. Class A operation achieves smooth power transfer characteristics, because the transistors are continuously operating in their most linear region. There is a more desirable distribution of distortion harmonics, and these are primarily 2nd and 3rd order harmonics, which can be reduced with minimum negative feedback. The inherent linearity of class A operation means that transient intermodulation distortion is greatly reduced. Class A certainly is desirable, but ... it is grossly inefficient and high output power is difficult to achieve, and since the amplifier is always "on," and constant bias is required even at idling, so horrendous amounts of heat are produced. Thus, class A amplifiers are usually of limited power output, and require very extensive heat -sinking and cooling facilities. The Threshold engineers have come up with a unique patented circuit to solve these problems. This is a dynamic biasing circuit, and I quote from their literature ..."the circuit senses the internal bias needs continuously and instantaneously adjusts the idle current to the levels required to maintain constant class A operation of all output transistors .... This allows the Threshold 400A amplifier to idle at one fourth the power of an equivalently rated conventional class A design." Threshold's first class A amplifier is a 200 watt per channel into 8 ohms unit, with large power output meters, and forced air cooling. Price is $2175.00. At CES, the Threshold people told me that this amplifier is gradually being phased out of production. I saw a prototype of its replacement. It is a larger unit, with massive heat sinks since it is convection cooled, but it is rated at the same 200 watts per channel. Their newest class A amplifier is the 400A, which has an output of 100 watts per channel into 8 ohms. A rack mount unit, it has LED displays for peak versus average output level readings for each channel. TIM distortion side bands are rated at 80 dB below a 10 watt output signal consisting of a 1.5 kHz square wave mixed with a -20 dB 80 kHz sine wave. This test presumably is basically the same as the Otala/Curl "square/sine" test given in their AES paper. Rise time is listed as 750 nanoseconds, and slew rate is 50 volts per microsecond. A spectacular amplifier, it is expected to sell for $1395.00. Mark Levinson now has his class A mono amplifier in production. The unit is rated at 25 watts at 8 ohms, 50 watts at 4 ohms, and 100 watts at 2 ohms. The amplifier weighs in at 45 lbs. and is also smaller (19 in. wide x 21 in. deep x 8.5 in. high) than the prototype shown last year. The unit has extensive heat sinking. The amplifier is said to use low amounts of feedback and this coupled with a high slew rate of 100 volts per microsecond should result in very low values of TIM. Because of high current output, it is claimed to be more powerful than some 100 watt amplifiers, when driving a speaker under dynamic conditions. Price is estimated at $1600.00. Crown International was showing a companion amplifier to the DL-400 preamp previously discussed. Model D-440 has an output of 221 watts per channel into 8 ohms, and 400 watts per channel into 4 ohms. THD is rated at 0.05 percent, 20 Hz to 50 kHz.

Cooling is by a two-speed fan. There is an LED indicator system for various functions, including "overload" to indicate clipping or slew -rate distortion... or in Crown's words, "sometimes referred to as TIM." No price information at present.

I have been talking about preamplifiers and amplifiers designed around some of the ideas in the Otala/Curl AES paper. Well, how about an amplifier designed by John Curl himself? John has evidently designed an amplifier for a group know as Symmetry Audiophile Systems in San Francisco. These people had a hotel suite and John Curl was there, showing a new electronic crossover he had designed. Unfortunately, the amplifier, designated the JCA-1 was not on hand, but I have spec sheets which are real eye-openers ... the unit is rated at 150 watts per channel into 8 ohms, has only 26 dB of feedback, a staggering 250 volt per microsecond slew rate, and "unmeasurable" TIM. The JCA-1 uses a V-FET front end and what John calls "four quadrant symmetry bridged outputs." The suggested price is $1100.00, and I sure would like to get my hands on these amps! There was so much new equipment at the CES, that I'll have to continue this report next month.

(Source: Audio magazine, Sept. 1977; Bert Whyte)

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