Technics RS-M270X Cassette Deck Review

The Technics RS-M270X is a two-head, two-motor cassette deck incorporating both the Dolby B and the dbx II noise-reduction systems. Its solenoid-operated tape transport is controlled by light-touch pushbuttons, with an IC logic system that makes it possible to press the buttons in any sequence without risking damage to the machine or to the tape. The transport controls can also be operated through a wired remote-control accessory that plugs into the rear of the recorder.

The tape-drive capstan is part of a direct-drive servo-controlled d.c. motor, with a second d.c. motor turning the tape hubs. The combination record/playback head (called the SX head by Technics) is made of permalloy and Sendust. Together with the Sendust-alloy erase head and high-power bias/erase oscillator, it makes the recorder fully compatible with metal-alloy tapes.

Tape selection is made by a small front-panel knob with positions marked normal, FeCr, CrO2, and metal. The cassette is loaded into guides within the well door, which slides out in a vertical position when the eject button is pressed. Most of the cassette can be seen through the glass window in the door. The pushbutton power switch is located just below the eject button.

The display area at the upper center of the panel contains two horizontal rows of fluorescent light segments that serve as level indicators for the two channels. They are calibrated from —20 to +8 dB, with the bars being blue-white below 0 dB and red above that point. The fluorescent indicators respond almost instantaneously to level changes and have a “peak-hold” feature that retains the highest reading for a second or two after the program level has dropped, making even short peaks visible to the operator. To the left of the level display is a three-digit index counter and its reset button.

The noise-reduction selector has a center off position, and its counterclockwise position turns on the Dolby system. A clockwise rotation turns on the dbx tape mode for recording and playback, and a further rotation to dbx disc enables dbx-encoded discs to be decoded for listening. Such discs can also be dubbed directly to tape without decoding, and in playback the tape will be heard with correct frequency response and dynamics when decoded by the recorder’s dbx circuits.

Recording levels are adjusted by two large concentric knobs (they are coupled by a slip clutch) at the upper right of the panel. The playback level is set by a small knob at the bottom of the panel next to the tape selector. A pushbutton switch selects either the MIC or line inputs (but not both simultaneously). Another button prepares the recorder for timer-controlled operation. It can be set for either recording or playback, coming on automatically when power is applied by an external timer switch.

To set the recording levels, the rec button is touched, placing the machine into a record-ready mode and lighting a red LED above the button. The level indicators then display the incoming-signal levels as set by the input-level knobs (in play, they show the playback level ahead of the front-panel output control). To start recording, the play button is touched. During recording, the input signal appears at the line out jacks in the rear of the machine. It is not processed by any of the internal circuits unless the machine is set for dbx disc operation, in which case the signals are processed by the dbx expansion circuits before reaching the line out jacks.

The pause button halts the tape without releasing the recording mode (to put the tape in motion again, a touch on the play button is required). Near the pause control is the rec mute, which when held in removes the recording signal from the tape without removing the erase and bias signals, stopping the tape, or affecting the signal at the line out jacks. This is convenient for editing out extraneous noises such as the thump of a stylus contacting a record. The other buttons control the fast-forward and rewind modes and stop the transport.

The “chassis” of the Technics RS-M270X is a large plastic molding (its circuitry is on printed boards) with the necessary shielding provided by the metal cabinet and bottom plate. In the rear of the machine there are only the LINE IN and LINE out jacks and a DIN socket for the optional remote-control accessory. The exterior of the recorder is finished in silver gray. It is approximately 17 inches wide, 13-3/4 inches deep, and only 4 inches high. It weighs 14 pounds, 5 ounces. Price: $500.

Laboratory Measurements

Our test sample of the Technics RS-M270X was supplied with the tapes for which it had been adjusted, and we used them for our measurements. The “normal” tape was Maxell XL-1S, and Technics XA-II was used for “CrO,” (it appears to be a high-bias ferric-oxide tape). The “FeCr” tape was Sony Duad, and the “metal” tape was Technics MX. Apparently the Technics-brand tapes are similar to the TDK and Maxell formulations.

For a 0-dB recording-level indication, a line input of 60 millivolts (mV) was required at 1,000 Hz. The line input overloaded at a satisfactory 3.5-volt input. The microphone-input sensitivity was 0.17 mV, and it overloaded at 29 mV. The playback output from a 0-dB-level recorded tape was about 300 mV with any of the tapes. Although the rated output is 420 mV, our measurements were made with the IHF standard load of 10,000 ohms in parallel with 1,000 picofarads, which reduced the output level somewhat (this load is standard for low-level amplifiers and is expected to be part of the E1A tape-recorder test standard now in preparation).

The third-harmonic distortion at an indicated 0-dB recording level was only 0.56 per cent from the XL-1S and MX tapes, 1 per cent from the Duad tape, and 1.4 per cent from the XA-II tape. In order to obtain the reference 3 per cent third-harmonic distortion in playback, we had to record at a high + 6 dB with all the tapes except the MX, which required +7 dB.

The unweighted noise relative to the playback from those recording levels was between —59 and —60.5 dB for all the tapes except XL-1S, which gave a —53-dB noise level. With the Dolby system in use and with CCIR weighting, the noise level from XL-1S tape was —62.3 dB, the XA-II and MX tapes gave readings of about — 64.5 dB, and the lowest noise was measured with Sony Duad at —66.3 dB. The noise increased by 8.5 dB through the mic inputs at maximum recording gain.

When we used the dbx system, the entire behavior of the recorder was radically altered. For example, the playback distortion from a 0-dB recording was reduced to 0.3 per cent for XL-1S and XA-II tapes, 0.4 per cent for MX, and 0.56 per cent for Duad tape. In order to reach the reference condition of 3 per cent distortion, we had to record at a + 17-dB level for all the tapes. We never did reach 3 per cent third-harmonic distortion with XL-IS tape, since the recorder’s electronic circuits overloaded before the tape saturated, and there was evidence that with all the tapes the maximum level was set by the electronics rather than by the tapes (the playback output was nearly 10 volts from the + 17-dB input). In each case, the playback noise was not really measurable, since it was at or below the minimum 100-microvolt reading of our meter and at that level seemed to be composed largely of external-noise pickup rather than actual tape noise. All we can say is that the S/N was better than 80 dB. a fantastic figure for a cassette deck.

The noise reduction could be seen more clearly on our spectrum-analyzer screen. The Dolby system reduced the noise by about 10 dB at all frequencies between 5,000 and 10,000 Hz and by even more at higher frequencies. The dbx system dropped the playback noise floor by about 22 dB (compared to no noise reduction) over the full audio range. An even more dramatic demonstration was to play a blank tape at maximum volume settings of the recorder and amplifier. With no noise reduction the hiss was, of course, loud and disturbing. Dolby reduced it substantially, but it was still plainly audible at the system gains we used. Switching on the dbx silenced the system—totally! With an ear close to the speaker, we could hear a faint hiss from the external amplifier, but there was hardly any change when the recorder was shut off entirely.

The playback equalization was measured with TDK AC-337 (120-microsecond) and Teac 116SP (70-microsecond) test tapes. Both were played back flat within ± 1 dB over their full ranges (40 Hz to 12,500 and 10.000 Hz, respectively). The overall record/playback frequency response was measured, with each of the tapes supplied, at levels of 0 dB and —20 dB (without noise reduction). The — 20-dB curves were almost identical for all the tapes. The low-bass response was down by about 9 dB at 20 Hz but reached the midrange level by about 40 Hz. From 50 to at least 12,000 Hz the response was flat within ±0.5 dB. There were minor fluctuations at higher frequencies, followed by a sharp cutoff above 17.000 or 18,000 Hz. The rated frequency-response variation of ± 3 dB over a range of 30 to 15,000, 16,000, or 17,000 Hz (depending on the tape) was met easily, most of that variation resulting from bass rolloff rather than high-frequency effects.

As expected, there were some differences between the tapes in their response at 0 dB. The XL-1S tape response began to roll off above 7,000 Hz, intersecting the —20-dB curve at 14,000 Hz. With the XA-II tape, the intersection was at 16,500 Hz. Although the response from Duad tape began to roll off at about the same frequency as the others, the slope was more gradual and remained above the —20-dB curve all the way to our 20,000-Hz upper measurement limit. The metal tape really showed its mettle (!) in this measurement, with the 0-dB response curve being virtually identical to the —20-dB curve (±0.5 dB from 50 to 15.000 Hz).

The apparently very large upward extension of dynamic range afforded by the dbx system led us to measure the record/playback response of the metal tape (with dbx) at levels of —20, 0, and +10 dB (the last level would be unthinkable with any ordinary cassette recorder, and with most nonprofessional open-reel decks as well). There was little difference between the three curves up to 10,000 Hz, although the + 10-dB response began to droop at higher frequencies. There was a slight peak in the response at 15,000 Hz for the 0-dB response at —20-dB levels as well as a shallow depression in the midrange between 500 and 5.000 Hz. The depression was only about 1 dB deep, and the peak was less than 2 dB at ± 20 dB and 1 dB at a 0-dB recording level, so it is clear that we are talking about very good response in every case.

The final frequency-response measurement was made, also with MX tape, at levels of —20 and —30 dB with and without the Dolby system. The “tracking” of the record and playback Dolby characteristics was excellent, as shown by the fact that at either level the two curves (with and without Dolby) differed by no more than 0.5 dB up to 15,000 Hz or higher.

The Technics RS-M270X carries some other rather impressive specifications, such as a flutter rating of 0.035 per cent (wrms). We measured the flutter as 0.033 per cent, both in playback of a TDK AC-342 test tape and in a combined record/playback measurement. The weighted peak (CCIR) flutter was only ±0.06 per cent in a combined record/playback measurement and ±0.05 per cent from the test tape. The flutter spectrum was broad and decreased smoothly with frequency, with small but distinct peaks at 20 and 35 Hz. The tape speed was about 0.7 per cent fast.

In fast-forward and rewind modes, a C-60 cassette was handled in 82 to 88 seconds. The level indicators were calibrated with their Dolby-reference level at about +2.5 dB (the nature of the display makes it difficult to determine its readings closer than about 1 dB). A standard Dolby-level tape (200 nW/meter) gave indications about 1 dB higher than the indicated marks. The fluorescent display responded very rapidly, with no loss of accuracy on tone bursts as short as 40 milliseconds. The error was — 1 dB at 20 milliseconds and — 5 dB at 10 milliseconds. The peak-hold time was about 1 second. The volume through the headphone jack was fine, even with 200-ohm phones.

Comment

When we recorded interstation FM-tuner hiss and compared the playback with the original signal, the results were about what one would expect from the measurements we had made. At low levels (—10 dB or so) all the tapes gave nearly perfect reproduction of the random noise. At 0 dB, the XL-IS sounded slightly dull, the MX tape was still essentially perfect, and the rest fell between those extremes.

Even though the response curves we had measured with the dbx system should have prepared us for its behavior, it was still startling to find that the setting of the in-put-level knob had very little to do with the final sound quality when using dbx. We deliberately turned it to maximum, so that the FM broadcasts and records we were taping kept the level indicators at and beyond their maximum readings through the entire recording. Both FM hiss and a variety of musical programs were recorded and reproduced with audibly undiminished quality under these highly unorthodox conditions. For all practical purposes, it seemed to be impossible to saturate the tape or cause the machine to distort when using dbx.

At first we found it necessary to look carefully at the controls of the RS-M270X to be sure what we were doing, but in time their use became almost automatic. In any case, we would have liked to see more physical distinction—spacing, size, shape, or some other characteristic—between the various transport-control buttons. We also noted that the large illuminated dbx logo on the panel confusingly has nothing to do with whether the dbx system is in use or not.

Nit-picking aside, the Technics RS-M270X is one of the most impressive cassette decks we have seen in some time. Performance is exemplary, especially for a two-head machine. With the RS-M270X, the improved high-frequency headroom of metal tape is a reality rather than a promise, and the ability to use the dbx circuitry for disc decoding in addition to tape recording is both a money-saver and a welcome convenience.

Read all

Technics reviews

Read all