Technics RS-M234X Cassette Deck Review

The Technics RS-M234X is a two-head, single-capstan cassette deck that incorporates all three major noise-reduction systems—Dolby-B, Dolby-C, and dbx—in an attractively priced “no frills” design. Its record/playback head is made of hardened permalloy, and a single d.c. motor drives both the capstan and the reel hubs. The transport functions are activated by pushbutton mechanical linkages rather than by solenoids, but these are far easier to use than the old piano-key levers. A useful transport feature is that the fast-forward or rewind buttons may be depressed during play, permitting high-speed cue-and-review operations with an instant return to the play mode. A three-digit mechanical counter is used for the tape-position indicator, but no memory-stop or other counter-activated functions are provided.

Sensors inside the cassette well detect the tape type (shown by indicator lights) and automatically set the proper equalization and bias (the settings cannot be overridden manually). The clear window gives a good view of the cassette label, and the door is removable for head cleaning and demagnetizing. Pushbutton switches are used for record mute and to select either no noise reduction, Dolby-B, Dolby-C, or dbx. An additional pushbutton allows for the decoded playback of dbx-encoded discs. Recording level is set with a single slide control (13-1/4-inch travel), and an additional, center-de-tented slider (3/4-inch travel) is used to adjust left-right channel balance. No play-back-level control is provided. Recording and playback levels are shown on an eighteen-segment peak-reading fluorescent display, which is calibrated from —40 to + 18 dB with the Dolby-level marking at +2 dB. Front-panel phone jacks are provided for headphones and a pair of microphones.

The rear panel of the RS-M234X contains only the usual input and output jacks. Overall, the deck measures 17 inches wide, 4-1/4 inches high, and 8-3/4 inches deep, and it weighs approximately 9-3/4 lbs. Price: $220.

Laboratory Measurements

The playback frequency response of the RS-M234X was measured using BASF’s IEC standard calibrated tapes. Above 1,000 Hz was a gradual downward treble slope that reached — 5 dB at 18,000 Hz with the 70-microsec-ond equalization used for metal and high-bias tapes. The maximum loss with 120-microsecond (ferric) equalization was 3.5 dB. This degree of loss on prerecorded materials would probably go unnoticed under normal listening conditions, but it can be detected in direct comparison with a flat-response deck; it can be corrected with a slight adjustment of the amplifier’s treble control.

Our sample of the RS-M234X deck was factory-adjusted for the new-formulation Maxell XLI-S (ferric), TDK SA (high-bias), and TDK MA (metal), which we used for our own measurements. As shown in the — 20-dB record-playback frequency-response curves in the accompanying graph, Maxell XLI-S gave extremely flat response to approximately 16,000 Hz. The — 3-dB points for TDK SA and MA were at 17,000 Hz, and it is apparent from The rolloffs in both the —20- and 0-dB MA curves that our sample of the deck was either slightly misequalized, overbiased, or suffering from head saturation with the metal tape. Because the Maxell XLI-S tape is new on the market, we also checked the overall frequency response with a number of other ferric tapes. TDK AD-X—which, like XLI-S, normally has a slightly rising high end— gave flat response, but most premium-qual-ity ferries (for instance, 3M’s new XS-I and Maxell’s own UD) showed slight high-end losses similar to that shown for the metal MA. In any event, however, when any of the three noise-reduction systems was used a built-in FM-multiplex filter was automatically inserted into the circuit, essentially eliminating all response above 16,000 Hz. At the low end, the — 3-dB frequency was a relatively high 45 Hz, and response below that dropped severely. At least in part this appears to be deliberate (perhaps to minimize picking up low-frequency rumble), for the response of the amplifier section alone fell to -12 dB at 20 Hz.

The 0-dB level indicated on the RS-M234X’s peak-reading display was 4 dB lower than the IEC 0-dB reference level (250 nWb/m). Distortion at the deck’s 0-dB level was very low: 0.38 per cent with Maxell XLI-S, 0.4 per cent with TDK SA, and 0.34 per cent with TDK MA. Correspondingly, the overload margins before reaching the 3 per cent third-harmonic distortion point used for measuring signal-to-noise ratio (S/N) were somewhat high: 10.2, 6.4 and 8.5 dB, respectively. Based on the output for 3 per cent distortion, the unweighted S/N’s (with no noise reduction) for the three tapes were 55.2 dB (Maxell XLI-S), 56 dB (TDK SA), and 55 dB (TDK MA). With IEC A-weighting and Dolby-B the S/N figures improved to 69.2, 68.2, and 67.6 dB, respectively, and Dolby-C raised them to 74.7, 74.2, and 74.3 dB, which is very impressive indeed. These signal-to-noise ratios will only be reached in actual recording, however, if you allow signal peaks to go well above the deck’s 0-dB marking. The RS-M234X owner’s manual suggests maximum levels ranging from +4 to +8 dB, depending on the tape type and noise-reduction system used, and our measured overload margins basically agree with these recommendations.

The dbx noise-reduction system (unlike either form of Dolby) is a 2:1 compressor-expander. This means that if the input signal has a dynamic range of 90 dB, the dbx-encoded signal recorded on the tape will be compressed to 45 dB, which any good deck can handle. In playback, the encoded signal is expanded by 2:1, thus restoring the original 90-dB range. Measuring the signal-to-noise ratio of a tape deck with dbx is not always easy, however, because the compression/expansion prevents the customary 3 per cent distortion level on the tape from being reached. Instead, amplifier clipping within the RS-M234X became evident at tape-plus-expander playback levels in excess of +17.5 dB (which were actually above the +18-dB indication on the deck’s own display). At this very high output level all three tapes had an A-weighted S/N of approximately 94.5 dB. To achieve that high a figure, however, requires using an input level well above what the owner’s manual and the red line on the deck’s display (+12 dB) recommend. But to avoid treblesaturation losses, we would suggest not going much beyond the IEC 0-dB level ( + 4 dB on the RS-M234X’s display) when using the dbx system in the deck.

Wow-and-flutter, measured using our Teac MT-111 test tape, was 0.045 per cent wrms and 0.08 per cent DIN peak-weighted. Both figures are about average for a deck in this price class. The tape speed varied slightly with the amount of tape on the supply hub but averaged about 0.6 per cent fast. Line-level sensitivity (315-Hz input for an indicated 0-dB on the fluorescent display) was 76 millivolts (mV), and at 0 dB the output level registered 400 mV.

Microphone sensitivity measured 0.25 mV, and the microphone stage reached overload at 47 mV, which is slightly above average. Dolby-level calibration was accurate, and Dolby-B and Dolby-C tracking accuracy was within ± 1 dB throughout the range of the deck, an excellent figure. Fast-forward and rewind speeds for a C-90 cassette were just over two minutes (85 seconds for a C-60), which is about average for a singlemotor transport.

Comment

With both prerecorded and dubbed material we found the sound quality of the RS-M234X to be very good. (Its two-head design made instantaneous source-tape comparisons impossible, so we had to compare finished dubs with synchronized playbacks of the source materials.) A prerecorded passage of Scriabin (on a Connoisseur Society cassette) that we frequently use to test for clarity on piano tones was more clearly reproduced on our $1,550 reference deck, but few people would value the degree of sonic difference that highly. Using very wide-range materials, such as Compact Discs, there were some audible losses from source to copy in the top and bottom octaves, but, again, we had to be really looking for trouble to find it.

The dbx system did not audibly “breathe” or “pump,” but rapid drum passages seemed slightly blurred, and the leading edge of solo trumpet tones seemed slightly dulled in comparison with Dolby-C. Dolby-B, on the other hand, left too much hiss, at least at the elevated levels we Use for critical listening.

Mechanically, the RS-M234X performed quietly and well. Our only criticisms here would be that the fast-forward and rewind buttons are awkwardly small and that the transport remains engaged if the power is turned off (by the power switch or a timer) during play or record. The simple solution to the latter problem is, of course, to push the stop button before turning off the deck. Overall, we found the RS-M234X, with its three noise-reduction systems, an extremely good value for its price.

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