Nakamichi RX-505 Cassette Deck Review

The Nakamichi products have long been IX known for embodying unique solutions to subtle design problems few other manufacturers are willing even to face. The Nakamichi RX-505 is the latest example of the company’s penchant for the unique. Besides incorporating completely separate recording and playback heads, a closed-loop dual-capstan drive, and both Dolby-B and Dolby-C noise-reduction systems, the RX-505 is a unidirectional auto-reverse cassette deck.

That last phrase may seem like a contradiction in terms, for other auto-reverse decks move the tape bidirectionally, first in one direction, then in the other. Playing the flip side of a cassette on a conventional unidirectional deck requires manually taking the cassette out of the deck, turning it over, and loading it into the machine again. What the RX-505 does, essentially, is to automate that manual process. When its eject/load button is pressed, an assembly inside the deck slides forward by a little more than 2 inches, revealing a holder or carrier into which the cassette is inserted with the tape openings upward. When the button is pressed again, the assembly is drawn into the machine, where spring-loaded arms snap into place to ensure that the cassette is properly seated.

When the end of the side is reached during recording or playback, or when the user presses the reverse button, the assembly pops out again, the cassette and its holder spin around 180 degrees, thus turning the tape over, and the assembly nips back into the deck, ready to go. This unique auto-reverse procedure is remarkably quiet, and it takes only about 1-1/2 seconds. For unloading, the assembly emerges once more to proffer the cassette, always with the side first inserted facing out, rather like a perfect butler delivering a letter on a tray.

There are serious reasons behind this approach to implementing the auto-re-verse function. Maintaining consistent frequency response at 20,000 Hz at the cassette tape speed of 1-7/8 ips (a Nakamichi hallmark) requires maintaining extraordinarily precise azimuth alignment. (Perfect azimuth alignment occurs when the tape head’s magnetic gap is absolutely perpendicular to the edge of the tape.) With any cassette deck, an azimuth error of only one-sixth of one degree (ten minutes of arc) will produce a loss of 10.25 dB at 20,000 Hz.

Many factors—the perpendicularity of the capstan(s), the manufacturing tolerances for the rollers and tape guides in the cassette shell, and the accuracy of the tape slitting, to name a few—affect the exact tape path, and hence the azimuth angle, in a cassette system. Unless the deck has an auto-correcting azimuth-alignment system (such as that of the Nakamichi Dragon), the tape heads must be permanently aligned so as to balance these factors. In general, if this balance is satisfactory when playing a tape in the forward direction, it will remain satisfactory when the cassette is turned over.

According to Nakamichi’s investigations, however, this balance is not preserved when a cassette tape is driven backwards. (In the typical auto-reverse deck, for example, an entirely different capstan is used for the reverse direction.) The amount of additional azimuth error produced by conventional bidirectional operation can be small enough to be tolerable on decks not aiming at flat response to 20,000 Hz (or above). But Nakamichi was aiming for such response.

The system of unidirectional auto-reverse also enables the RX-505 to use discrete recording and playback heads, each with its own azimuth adjustments. This permits each head to be designed for its specific function and enables direct comparison between the input signal and its recorded result. A standard bidirectional deck, in which the heads are rotated, must use either a single combined record-playback head or one in which separate recording and playback head elements are contained in a common case. In Nakamichi’s view, this compromises performance. In the RX-505, the recording and playback heads are made of Crystalloy and have gap widths of 3.5 and 0.6 micrometers, respectively. Etched slots along the top and bottom edges of the head faces, where the tape edges pass, prevent development of a wear groove and contribute to the rated 10,000-hour head life. A pressure-pad lifter on the playback head (another Nakamichi exclusive) eliminates the modulation noise that can be created by a cassette’s integral pressure pad.

The transport of the Nakamichi RX-505 uses four motors. The dual capstans are belt-driven in a closed-loop configuration by a d.c. servomotor controlled by a PLL (phase-locked loop) circuit; they have slightly different diameters and masses to prevent resonances and to provide the differential tension to hold the tape against the heads. A second d.c. motor is used to turn the supply and take-up reel hubs, and a third operates the cassette-well assembly. The fourth motor replaces the solenoids normally used to activate the tape heads, pinch-roller, and hub brakes, ensuring quieter and gentler operation and making it possible to include a two-speed cueing facility.

Bias and playback equalization for ferric, CrO2-type, and metal tape formulations are selected with pushbuttons, and a user-adjustable bias fine-tune control is included. Although there are no built-in test facilities for bias adjustment, the three-head design permits bias tuning by ear (using low-level FM interstation hiss as a test source, for example) with at least some assurance of success. Recording levels are set by separate left- and right-channel controls and are indicated on a peak-reading LED display that has ten segments per channel. The display is calibrated from — 40 to +10 dB; while not marked as such, 0 dB was set at the Dolby-calibration level. Tape position is indicated by a conventional four-digit electronic counter.

In addition to its auto-reverse operation, the Nakamichi RX-505 includes a number of unusual automatic features. During playback, for example, if the skip switch is turned on and a blank section longer than 30 seconds is encountered, the cassette goes into fast forward to the end of the tape. If the reverse mode switch is also on, playback will then continue from the other side. During recording, if the auto rec pause switch is on and no signal is recorded for 45 seconds, the tape is rewound the equivalent of 30 seconds and the deck goes into record-pause mode. If the auto fade switch is on during recording, the deck detects the imminent end of a side some 20 seconds before the tape leader is reached and performs a smooth 2-second fadeout. The fadeout point is determined by measuring the hub speed differential. During auto-reverse recording, this same function then fades back up for the second side. Buttons are also provided for a slow (2-second) or rapid (1-second) manual fade down or up if desired during recording. The transport-function buttons may be pushed in any order without destructive consequences, and “punch-in” recording (beginning to record directly during playback, without stopping first) is also possible.

Additional front-panel controls are provided for selecting Dolby-B, Dolby-C, or no noise reduction, playback or source monitoring, insertion of an FM-multiplex filter and/or an infrasonic rumble filter, operation from an external timer, program-seek cueing (using the blank spaces between selections to count ahead or backwards), and memory rewind to stop or play. There is an output-level control that affects the signal level both at the rear terminals and at the front-panel headphone jack.

The rear panel of the RX-505 contains the usual line-in and line-out jacks as well as a DIN-type connector for use with a remote control. There are no microphone inputs. Overall, the RX-505 measures 17-3/4 inches wide, 5-3/4 inches high, and 11-5/8 inches deep, and it weighs about 22 pounds. Price: $1,090.

Laboratory Measurements

We tested the playback response of the Nakamichi RX-505 with BASFs IEC-standard ferric and CrO2 calibrated tapes and found it to be within +2.5, —1 dB throughout the tapes’ 31.5- to 18,000-Hz range. Two things about the curves shown in the graph are noteworthy. First, the very low bass end does not have the typical peaks and valleys (often amounting to several decibels each way) that we usually en- counter. Second, there is a slight rise (1.5 dB for ferric, 2.5 dB for chrome) at the highest frequencies, which is typical of what we have found with other top-quality decks. Protests that the IEC tapes themselves are “hot” at the extreme high end have been received from several sources, and we’re beginning to believe the concerned manufacturers.

Our sample of the RX-505 was supplied with the three Nakamichi tapes used for its setup, namely, EX-II (ferric), SX (chrome-equivalent), and ZX (metal), and we used these tapes for our evaluation. Magnetically, their behavior is essentially identical to that of Maxell UD XL-I, TDK SA, and TDK MA, which are typical premium formulations. The bias fine-tune control on the RX-505 was capable of altering the 20,000-Hz response by +2, —1 dB in the metal position and + 6.5, —4 dB in the ferric and high-bias positions, a range that encompasses nearly every top tape brand we know about.

At the IEC O-dB level (250 nanowebers per meter, which reads as + 3 dB on the RX-505’s indicators), the high-frequency record-playback response fell off as the tapes (not the deck) reached their saturation point. Naturally, the metal tape (ZX) held on the longest, reaching 16,000 Hz before dropping to —6 dB. When we turned the Dolby-C system on, however, as most users are likely to do, response with the metal tape at the 0-dB level went all the way to 20,000 Hz before dropping to —3 dB, which would be quite remarkable performance even for an open-reel machine. Even more remarkable, however, are the frequency-response curves at the usual — 20-dB level, where response for all three tapes was within +0.5, —1 dB from below 100 Hz straight out to 20,000 Hz.

As is typical of LED recording-level indicators, “0 dB” on the RX-505 actually covers a range of values. Because the deck is designed to use the Dolby level (200 nWb/m) as its 0-dB reference point, we used the output from our Teac MTT-150A Dolby calibration tape to set our reference point. This was near the top of the range covered by the RX-505’s 0-dB indicator lights, which could be made to turn on initially at a level about 1.5 dB below Dolby level. At the 0-dB level, third-harmonic distortion of a 315-Hz test tone measured 0.38 per cent with Nakamichi EX-II (ferric), 0.64 per cent with SX (CrO2-equivalent), and 0.26 per cent with ZX (metal). Reaching 3 per cent third-harmonic distortion required increasing the recorded output level by 5.4, 4.3, and 8.9 dB, respectively. The unweighted signal-to-noise ratio (S/N), without noise reduction, measured 52.4 dB (EX-II), 55.8 dB (SX), and 59.4 dB (ZX). Dolby-B and IEC A-weighting improved the S/N figures to 67.2, 69.6, and 73 dB, respectively. A-weighted S/N’s with Dolby-C were 73.1, 76, and 78.4 dB (in the same order). All of these are state-of-the-art figures, and they could be made to look about 2 dB higher (better) by using CCIR rather than A-weighting.

Wow-and-flutter, measured with our Teac MTT-111 test tape, registered 0.03 per cent wrms and 0.064 per cent according to the stricter DIN peak-weighted measurement. The RX-505 ran 0.4 per cent fast and required a 50-mV input level for a 0-dB reading. Fast-forward and rewind times for a C-90 cassette were 75 and 70 seconds, respectively, which is very fast—faster, indeed, than many decks can manage with C-60 cassettes. Dolby tracking, checked at —20-, —30-, and — 40-dB levels, was exceptionally accurate, being generally within 0.5 dB for Dolby-B or 1 dB for Dolby-C even out to 20,000 Hz. Maximum error was + 1.5 dB in the 600- to 1,200-Hz range at —40 dB with Dolby-C.

Comment

Just superb. Our ears and our hands could only confirm in use what our measurements showed on the bench, namely, that the RX-505 is a member of that small, elite group of cassette decks that truly deserve the appellation “state of the art.” From the solidity of the sonic image to the solid feel of the controls, we were consistently delighted. The overall sound had a transparent quality to it that we simply do not ordinarily find in cassette reproduction. Mechanical motor noise was nil.

We do have a few small quibbles. On a machine of this caliber, a ten-segment record-level indicator is out of place. The scale numbers are confusing (one of them has no lighted segment, and one of the lights has no number), and the scale calibration is not outstandingly accurate. In another area, while I prefer the Nakamichi system of separate pushbuttons to set bias and playback equalization, many users may prefer automatic settings. (This is a little like preferring automatic transmission to a stick shift; the Nakamichi is geared to the sports-car personality.)

When we were making instant comparisons between source and tape, the Dolby-B system occasionally seemed to induce some slight high-frequency loss, though Dolby-C did not. Apart from possible tape saturation on passages where we would not have expected it, our measurements suggest no explanation for this. In any case, however, Dolby-C is the system that would normally be used. We did find one passage—the long, deep-bass (32-Hz) organ-pedal introduction to Also sprach Zarathustra—where at high listening levels residual hiss could be heard even with Dolby-C, but this was the exception rather than the rule, and we doubt that any other deck with Dolby-C would do better.

In short, it is hard to imagine better analog dubbing than we obtained with the RX-505. Whether auto-reverse is an important consideration in a given system or not, the RX-505 is a prescription for sonic happiness for even the most critical audiophile.

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