Kenwood KX-71RB Cassette Deck Review

Kenwood's KX-71RB is a moderately priced two-head cassette deck with auto-reverse, bidirectional record and playback capabilities, Dolby-B and Dolby-C noise reduction, and rapid program-search facilities. Its transport is solenoid operated and has a separate capstan for each tape direction; the capstans are belt-driven by a d.c. servomotor. A second d.c. motor is used for the tape hubs. The record/playback head, made of hard permalloy, is mounted together with the erase head on a fast-acting rotator mechanism. When the tape direction is reversed—either manually or automatically, when the tape leader runs out—the head-mounting plate of the rotator spins through 180 degrees, turning the heads around. In the normal forward direction the heads scan the stereo tracks on side one. In the reverse direction the inverted heads scan the stereo tracks for side two. In this way both sides of a cassette can be recorded or played without manually turning over the cassette itself.

Cassettes are inserted into a typical cassette well. Its large, clear door affords ample label visibility, but the lack of interior illumination makes it somewhat difficult to see how much tape remains on the side in use. The door is easily removable for head cleaning and demagnetizing.

Unlike most cassette decks, which require both the record and play buttons to be pressed simultaneously in order to start recording, the KX-71RB begins to record as soon as its copper-colored rec/arm button is pushed. If this button is pressed a second time, however, the record-mute function is activated, and four seconds later the deck stops in the pause mode. Other pushbutton controls in the transport section can be used to locate the blank spaces between selections (blank search) or to play the first few seconds of each successive selection until the desired one is found (index scan).

Two columns of seven LED’s are used as peak-reading record-level indicators. Calibrated from —20 to +6 dB, with the Dolby marking at + 3 dB, the LED’s are orange below 0 dB and red for 0 dB and above. Record levels are set with the very large knob on the right of the front panel together with the small channel-balance knob. The tape counter is the conventional three-digit mechanical type. The remaining front-panel switches turn the noise-reduction systems on and off; select bias and equalization settings for ferric, CrO2, or metal tape; set the deck for oneway, one-cycle (forward and reverse), or “endless-loop” operation (which automatically shuts off after eight complete loops); and set the deck for recording or playback controlled by an external timer. There are also front-panel jacks for two microphones and for a pair of stereo headphones.

The rear panel of the KX-71RB contains only the customary line-in and line-out jacks; there is no provision for remote-control operation. The deck measures 17-1/8 inches wide, 4-1/4 inches high, and 8-1/4 inches deep, and it weighs about 10-1/2 lbs. Price: $320.

Laboratory Measurements

We measured playback frequency response in both directions and with both ferric (120-microsecond, or μs) and Cr02/metal (70-μs) tapes with BASF IEC-standard calibrated test cassettes. With both equalizations the response did not vary between the two directions by more than 0.5 dB, so we averaged the results to obtain the curves shown in the graph. With both tape types the response was extremely flat and smooth from the lower limit of the test tapes, 31.5 Hz, up to 14,000 Hz, after which it rolled off to approximately —5 dB at 18,000 Hz.

Kenwood did not supply information about which tapes we should use for testing the KX-71RB. After trying a number of different brands (most of which, as we expected, gave very similar performance), we settled on the three shown in the graph: Maxell XLI-S (ferric), TDK SA (high-bias, Cr02-equivalent), and TDK MA (metal). The superior high-frequency headroom of the metal-tape formulation is clearly evident in the 0-dB-level response curves. At the — 20-dB recorded level all three tapes showed a dropoff above 15,000 Hz (the — 3-dB point was between 16,000 and 17,000 Hz), which is clearly the designed maximum frequency of the deck. The new Scotch XS I (ferric) formulation gave flatter high-frequency response ( + 3.5 dB at 14,000 Hz) than the Maxell XLI-S we selected, but the latter had a better signal-to-noise ratio (S/N). At the low-frequency end, the —3-dB point was between 30 and 35 Hz, which is commendable in a deck of this price. The Dolby-system tracked within ± 1 dB.

In attempting to measure the S/N for each of the three tape types, we encountered a situation on which we have had occasion to comment before: the IEC reference level of 250 nanowebers/meter (which, though relatively high, is still below the level that produces 3 per cent third-harmonic distortion with a properly biased deck and today’s tapes) was a full 6 dB above the indicated “0-dB” level of the KX-71RB. As a result, using the 0-dB indications on the deck to set a maximum record level (which is what they are supposed to be for) will produce tapes that are underrecorded by at least 6 dB. This is practically the same as giving up the additional noise reduction provided by Dolby-C and simply recording with Dolby-B at a proper level. We can only point out again to Japanese manufacturers that 125 nWb/m is not the proper place to set the 0-dB (“maximum”) point on their record-level indicators and advise owners of the KX-71RB that, since + 6 dB is the highest level the machine can display, they should try letting signal peaks hit the very top of the scale.

At Kenwood’s indicated 0-dB level, the third-harmonic distortion of a 315-Hz test tone measured 0.35 per cent (Maxell XLI-S, ferric), 0.2 per cent (TDK SA, high-bias), and 0.25 per cent (TDK MA, metal). To reach the 3 per cent distortion point for these same tapes required raising the level to +8.6, + 7.4, and +8.4 dB, respectively—all above the maximum on the indicator scales. Referred to the 3 per cent distortion point, unweighted S/N’s with no noise reduction measured 54.6, 53.5, and 52.5 dB for Maxell XLI-S, TDK SA, and TDK MA, respectively. With Dolby-B and IEC A-weighting these figures improved to 68, 66.7 and 64.9 dB, and using Dolby-C raised them to 73.6, 73.3, and 72 dB.

With our Teac MTT-111 test tape, the wrms wow-and-flutter of the KX-71RB measured 0.052 per cent in the forward direction and 0.037 per cent in reverse. On the stricter DIN standard the forward and reverse figures were 0.075 and 0.059 per cent, respectively, which is typical for a single-capstan deck in this price class. The speed accuracy was only moderate: 0.76 per cent fast in forward and 0.86 per cent fast in reverse. High-speed winding times were a little over 2 minutes for a C-90 cassette and just over 80 seconds for a C-60. A line input level of 61 millivolts (0.061 volt) was required to reach an indicated 0-dB record level, at which point the line output measured 220 mV. At the microphone jacks a 0-dB record level required a 0.5-mV input level; the microphone inputs began to overload with signal levels in excess of 50 mV, a typical 40-dB range.

Comment

We listened to the KX-71RB with both prerecorded and dubbed cassettes, and we found that it did a creditable playback job. It cannot and is not intended to compete with our high-performance reference deck in terms of sparklingly clear high-frequency response. On the other hand, with the vast majority of prerecorded cassettes, if you left the room with one deck running and returned with the other running instead, you’d probably not notice that a substitution had been made. Our response to dubs of a variety of musical materials was essentially similar.

We do have some criticisms to make of the deck’s human engineering. In part because of the dual use to which the record button is put, you cannot quickly shift from one direction to the other while recording. Holding down the record button and hitting the tape-reverse control won’t work; the 4-second record mute is initiated, and then the machine stops and ignores the direction change. To change directions manually while recording requires a four-step control sequence: stop, play (in the other direction), stop, and record. This seems overly cumbersome and time-consuming. Also, the deck cannot perform “punch-in” recording, in which you enter the record mode while the deck is playing. Few new machines today lack this capability, which helps make “seamless” dubs.

These idiosyncrasies apart, the KX-71 RB does provide good bidirectional re-cord-playback performance, playback auto-reverse, useful scan and search features, and Dolby-C noise reduction, all at a price many will find attractive.

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