Harman Kardon TD4600 Cassette Deck Review

The Harman Kardon TD4600 is one of the first cassette decks to incorporate the highly sophisticated new Dolby S noise-reduction system in addition to the more familiar Dolby B and Dolby C systems and Dolby HX Pro headroom extension. Other features include memory rewind and replay, intro scan, and remote control.

Since the Dolby S circuitry has not yet been reduced to a single VLSI (very large-scale integrated-circuit) chip, its inclusion imposes a significant premium in manufacturing cost. The Dolby electronics in the TD4600 occupies its own 9-1/2 x 7-1/4-inch circuit board, which holds no fewer than six large IC chips and a myriad of resistors and capacitors. Harman Kardon has compensated by economizing elsewhere in the $699 TD4800, using a combination record/play head instead of the separate recording and playback heads typical of most other decks in this price class and a single-capstan tape transport rather than a dual-capstan one. (These high-end features are included in the company’s other Dolby S deck, the TD4800, but together with duplicate Dolby circuitry for off-the-tape monitoring during recording, they drive up the price to about $500 above that of the TD4600.)

The TD4600’s cassette well contains sensors that detect the tape type in use and automatically set the bias and equalization for average ferric, chrome (or chrome-equivalent), or metal tapes. The well cover is easily removable for routine head cleaning. A four-digit fluorescent tape counter indicates elapsed time only (not time remaining) in fast-wind as well as record and play modes.

Recording levels are indicated on a twelve-segment-per-channel fluorescent display that is calibrated from — 35 to +8 dB. Sensibly, the 0-dB marking coincides with the double-D logo signifying Dolby level. The display is supplemented with & meter weighting switch designed to simplify setting recording levels by providing a “target” of + 3 dB for the loudest passages, compensated according to the tape type and the high-frequency content of the music.

Recorders equipped with Dolby S must, as a license condition, provide user-adjustable bias and tape-sensitivity controls to accommodate the normal variations of tape formulations within the same type. Such calibrations are relatively straightforward on a three-head deck, since you can monitor the output off the tape as you make the adjustments. On a two-head machine, such as the TD4600, the procedure is more complicated. Repeated record-and-replay trials, using two pushbutton tone generators and the level display, are needed to set the bias and the left- and right-channel tape-sensitivity controls for optimum performance. Fortunately, the center-de-tented positions of these controls proved adequate for the center-line TDK AD (ferric), SA (chrome-equivalent), and MA (metal) cassettes we normally use for testing.

A conveniently large knob with separate clutched sections for the left and right channels is used to set recording levels. A smaller knob simultaneously controls the output level at the front-panel headphone jacks and at the rear terminals. A switchable multiplex filter is included for use (if needed) when recording stereo FM broadcasts. No provision is made, however, for timer-controlled operation.

The Harman Kardon TD4600 measures 17-3/8 inches wide, 5 inches high, and 12-5/8 inches deep, and it weighs 14-1/2 pounds. Price: $699.

Lab Tests

The TD4600’s calibrated playback response, measured with our BASF IEC-standard 120-microsecond (ferric) and 70-microsecond (chrome) test tapes, was excellent from the bass through the low treble, with a slight rolloff at the very highest frequencies (probably because of the gap losses characteristic of most combination record/play heads).

Record-playback response at the customary -20-dB input level held within 2 dB up through 16,000 Hz with the ferric and chrome-type tapes and to 18,000 Hz with the metal tape. At 0-dB recording level, the Dolby HX Pro circuitry helped maintain the high-frequency response of all three formulations. Because Dolby S, like Dolby C, reduces the recording equalization’s treble boost when the signal contains high-level high frequencies, it also extends the effective treble capacity of the tape, as is shown in the additional trace for TDK MA in the accompanying graph.

Midrange total harmonic distortion (THD) reached 3 percent at an indicated level of +5 dB for the ferric and metal tapes and at +3 dB for the chrome-type formulation. Referred to these levels, the figures for signal-to-noise ratio (S/N) given in the box at left are very good, though not outstanding. You may find it surprising that the S/N’s with Dolby S are not much better than those with Dolby C noise reduction. The reason is that most of the additional noise reduction Dolby S provides is at low frequencies, which the standard weighting curves tend to de-emphasize. The audible benefits of Dolby S are greater than a simple comparison with the Dolby C numbers might suggest.

Measured with our usual flutter test tapes, the TD4600 registered 0.035 percent weighted RMS (WRMS) and 0.075 peak-weighted. On an overall record-playback basis, wow-and-flutter rose to 0.042 percent WRMS and 0.110 percent peak-weighted. Although these figures are within specification for the TD4600, they are somewhat above average for a deck in this price class. Along with the relatively slow fast-winding times, they undoubtedly reflect the limitations of the single-capstan transport mechanism used to keep the TD4600’s price within bounds.

Input sensitivity was normal, and the available output was higher than most of today’s decks can achieve, which is welcome news to everyone who has a CD player in his system. Dolby tracking error was remarkably low, measuring only +1.2, -0.9 dB for Dolby B, ±0.7dB for Dolby C, and ±0.6 dB for Dolby S.

Comments

Overall, the TD4600 was quite easy to use. The only significant exception was the rather complex procedure required for optimizing bias and sensitivity, but that is inevitable in a two-head deck. The rounded switch buttons were a pleasure, and the solenoid action of the transport had a positive feel. The deck did make somewhat more noise than most when switching modes or fast winding, and the dark color of the plastic covering the unilluminated cassette well makes it impossible to see the tape inside, but these are minor points.

We found the TD4600 pleasant to listen to, with wide frequency response and low noise on both prerecorded and homemade tapes. The stepwise decreases in hiss as we switched from no noise reduction to Dolby B to Dolby C were, as usual, obvious, and going on to Dolby S eliminated some of the low-frequency “garbage” that often passes unnoticed until it is magically stripped away. With normal listening materials and levels, however, the improvement when we shifted between tapes recorded with Dolby C and Dolby S, though worthwhile, was not startling. The tapes using both systems had good frequency response and adequate, if slightly narrowed, stereo imaging. Neither, however, had quite the ringing purity of tone (in solo-piano notes, for example) of the original compact disc.

On the other hand, Dolby Labs says that S-type noise reduction is more robust than C-type—less finicky about deck alignment (always something of a sore point with Dolby C) and therefore more transportable and better suited to mass duplication of prerecorded cassettes. And its performance is unequivocally superior to that of Dolby B. Without question, if the analog cassette has a long-term future in the high-fidelity world, Dolby S is a key to its continuing success, and if you want to hear it for yourself you should surely give the Harman Kardon TD4600 a listen.

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