NAD 6340 Cassette Deck Review

The moderately priced NAD Model 6340 cassette deck is a good example of why NAD equipment has become so popular. Almost defiantly plain in appearance and short on conveniences, it concentrates the buyer’s investment in just those features that most directly affect audible quality.

The unconventional Model 6340 is a two-head, single-capstan deck that incorporates not only standard Dolby B and the higher-performance Dolby C noise reduction but also both Dolby HX Pro and Dyneq treble-extension circuits. And although it lacks all memory features and even so much as a headphone jack, it contains both a playback high-frequency adjustment and a unique set of circuits designed to improve the sound of recordings made for use in the car.

The single record/playback head and most features of the solenoid-controlled transport system of the Model 6340 are unremarkable. One DC motor is used for the spooling functions, and another is belt-coupled to a flywheel that drives the single capstan. The tape counter is a three-digit mechanical type. An unlit cassette well provides no label visibility; indeed, it is difficult even to tell how much tape remains on a side without using a flashlight. The cassette well door is easily removed for routine head cleaning and demagnetizing.

The front-panel play-trim control is worthy of comment, however. A variety of causes often conspire to make tapes recorded on one machine sound dull on another. In part, this is a result of mistracking by the Dolby noise-reduction circuits. The treble boost/cut control incorporated in the NAD Model 6340 operates on the signal before it reaches the noise-reduction stages, and the shape of the control’s response curve effectively offsets the kinds of losses that cause Dolby mistracking. (While no schematic diagram was provided with our test unit, the curves produced by the play-trim control suggest that NAD has used the head itself as one element in the kind of tuned circuit used in graphic equalizers. This technique has the additional advantage of saving both the cost and noise of an additional transistor stage in the playback circuitry.)

The inclusion of both Dolby HX Pro and Dyneq also addresses the problem of treble-shy cassette performance, this time from the recording rather than the playback perspective. Dolby HX Pro operates by dynamically reducing the bias current used during recording at just the moments when very large treble signals are present, which enables the tape to store more high-frequency energy than it otherwise could. Permanently lowering the bias level would result in higher distortion and a worse signal-to-noise ratio, which is why the Dolby HX Pro circuitry operates only during periods of peak treble demand.

Dyneq takes the complementary approach, that is, it reduces the high-frequency demand. Even with Dolby HX Pro it is all too easy, especially when recording from CD’s, to drive cassette tapes beyond their treble capacity. When this happens, the high-frequency output from the tape does not simply level off; it actually declines as the demand rises. The Dyneq circuit monitors the signals flowing to the tape head and dynamically lowers the amount of record treble boost slightly when the current reaches the point where saturation would set in. Together, then, Dolby HX Pro and Dyneq might be said to address both the supply side and the demand side of cassette-sound economics.

A pushbutton, accompanied with one of the Model 6340’s few front-panel indicator lights, switches in yet another of NAD’s imaginative circuits. Called car (for compensated automobile reproduction), this circuit boosts low-level sounds by 12 dB, making them audible above the higher ambient noise level of a moving car. At the same time, it augments both the bass content (considerably) and the treble content (slightly) of these low-level sounds, giving them a fuller character. While the CAR circuit is obviously not a high-fidelity technique, the interior of an automobile moving at high speed is not the place to try to appreciate every nuance in the dynamic range of an orchestral composition, either.

Rather than restrict a recording’s frequency response to the 15-kHz limit of stereo FM broadcasts, the NAD Model 6340 has a switchable multiplex filter. It also sports a user-adjustable control designed to optimize the bias level for recording different brands of tape. Since the deck’s two-head design precludes directly comparing the source and the recorded sound, however, setting the fine-bias control accurately would require both considerable patience and external test instruments.

Three-position lever switches are used to select a noise-reduction circuit and to switch the overall bias and equalization for ferric, CrO2, or metal-particle tape. Overall record levels and channel balance are controlled with a clutched-knob. The tape levels are displayed on a pair of twelve-segment-per-channel peak-reading led displays that are calibrated from —20 to +8 dB.

Overall, the NAD Model 6340 measures 16-1/2 inches wide, 9-3/4 inches deep, and 4-3/4 inches high, and it weighs 10 pounds. Price: $398.

Lab Tests

The playback frequency response of the NAD Model 6340, measured with IEC-standard ferric and Cr02-calibrated tapes from BASF, was very flat and smooth, varying by only ± 1 dB from 31.5 to 18,000 Hz (the highest tone on the tapes), where it was down by less than 2 dB. Without extraordinary measures, this is about the best you can do in a deck with a single record/playback head.

As usual, we used our center-line samples of TDK AD (ferric), SA (chrome-equivalent), and MA (metal) to check the overall record-play-back performance of the Model 6340. At the bass end, frequency response was remarkably flat all the way down to 20 Hz (most decks give up at 50 Hz). In the high frequencies, the practical limit of the deck is just above 18,000 Hz. At the full IEC 0-dB level (250 nanowebers per meter), the contribution of the Dolby HX Pro and Dyneq circuits pushed the point at which response dropped to the — 6-dB level (half the voltage output) above 10,000 Hz for the ferric tape, above 12,000 Hz for the chrome-equivalent, and very nearly to 20,000 Hz for the metal. This level of performance is usually found only in more costly three-head decks.

The signal-to-noise ratio (S/N) also invites comparison with decks costing two and three times the price of the Model 6340. The limit we encountered here lay in the deck’s inability to take the fullest advantage of the potential of metal-particle tapes. The S/N figures for ferric, CrO2, and metal tapes were essentially identical. The metal tape should have done somewhat better, but even there the deck’s performance was very impressive.

Our wow-and-flutter measurements, though well within the manufacturer’s ratings, were far less impressive. When we tested the much more costly NAD Model 6300, the wow-and-flutter figures for its twin-capstan drive were among the lowest we had ever encountered. The Model 6340 does as well as can be expected for a singlecapstan (and thus less costly) drive. It is certainly adequate.

The tracking of the Dolby noise-reduction circuits was extremely good, and the sensitivity and output levels were unexceptionable. Fast-winding times were distinctly on the slow side, though acceptable.

Comments

In terms of its human engineering, the NAD Model 6340 made no secret of the cost-cutting measures needed to bring it to market at so modest a price. The transport solenoids clunked, getting into record mode was a cumbersome two-step process, the cassette-well door was utterly undamped, and the mechanical index counter and the level display seemed relics of older designs. These are not, however, things that will matter seriously to the music lover who is trying to get maximum performance at a minimum price.

Such a music lover will be mightily impressed by the Model 6340. Its frequency-response and imaging characteristics were superb. The signal-to-noise ratio was adequate, and when we suspected a slight softening of the attack edge on piano notes recorded using Dolby C, we found that the play-trim control brought it back to near perfection. Wow-and-flutter were not audible as such, though they contributed to the deck’s inability to make sonically perfect copies. Such perfection is not to be found in any cassette deck, however, at any price, and the NAD Model 6340 is easily among the most musical decks you can buy. And at its price, you can afford to buy it.

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