Aiwa AD-M800U Cassette Deck Review

The Aiwa AD-M800U is a two-motor, three-head cassette deck with a microprocessor-controlled “DATA” system (Digital Automatic Tape Adaptation) that optimizes the recorder for any tape formulation in about 30 seconds.

The deck’s record and playback heads have separate gaps but are in a single shielded housing. The heads are faced with Sendust and the playback head is contoured to minimize the low-frequency “head bumps” that show up in the frequency response of most cassette recorders. The AD-M800U contains dual Dolby circuits so that a recording can be monitored with the proper decoding as it is being made.

The capstan is driven by a frequency-generator-controlled servomotor, and the recorder has a very low flutter specification of 0.04 per cent (weighted RMS). A separate d.c. motor drives the tape hubs. The transport is controlled by solenoids which are actuated by feather-touch buttons on the panel. The rec and play buttons must be held in simultaneously to engage the recording mode, and there is the customary pause button. The AD-M800U also has a rec mute button that removes the signals from the recording head while it is held down without affecting the level indicators or the signals at the line-out jacks (if they are from the source, rather than the tape). Small pushbuttons connect either the source or the tape playback signal to the line-out jacks, activate the Dolby system, and connect the mpx filter to remove any 19-kHz pilot carrier from the program when recording stereo FM broadcasts.

The cassette opening is flanked by the eject button and a power button, plus an infrared sensor for the remote-control accessory. Nearby are a phone jack and a small timer/repeat knob that sets up the machine for unattended timer-controlled operation in either the playback or recording mode, or for repeating a cassette playback indefinitely. The index counter and the memory switch can be set either to stop the tape when the counter returns to 000 in rewind mode or to go into its play mode at that point. Other front-panel controls include a pair of concentric record level knobs and two MIC input jacks for medium-to high-impedance mikes.

The level indicators are meters calibrated from —20 to +6 dB. Between them are LEDs that show instantaneous peak levels. These are marked to show the maximum permissible recording level for each of the basic types of tape for which the machine is designed; +4 dB for CrO2, +7 dB for FeCr and LH, and + 10 dB for metal tape (there are also lights at 0 dB and —6 dB).

Across the center of the panel are the controls and indicators for the DATA system. Although it is basically designed to do the same things other microprocessor-con-trolled recorder-optimizing systems are intended to do, DATA has some distinctive characteristics. One unique property is its ability to determine the type of tape being used without the need for preprogramming by slots in the cassette housing or by the operator. To do this, it records and plays back a 10-kHz test signal, measuring the playback level as the recording level is increased in steps over a wide range of amplitudes. From the maximum-output level (MOL) indicated by this test, the computer decides whether the tape is LH (or standard-bias ferric-oxide tape), FeCr (ferri-chrome), CrO2 (chromium dioxide or an equivalent high-bias ferric-oxide tape), or a metal-particle tape.

There are also four tape selector buttons on the panel, and although any of them can be used to preset the recorder adjustments manually, this is not necessary. The first step in the fully automatic DATA process makes this choice and lights a LED in the appropriate button. Next, a 6-kHz signal is recorded and played back while the bias is varied in steps to determine the maximum output level at that frequency. With the bias established, the machine sets its recording sensitivity by recording a 400-Hz signal at a — 20-dB level, playing it back and adjusting the recording gain until the input and output are at the same level. Then the midrange equalization is optimized by a similar procedure with an 8-kHz signal recorded in 128 steps and the equalization adjusted to match its playback to the low-frequency reference level. Finally, the same equalization is performed at a high frequency, which is automatically set at 12 kHz for LH tape and 14 kHz for all the others.

While the DATA process is going on, green lights below the meters are flashing, and as each parameter is optimized its light remains on steadily. At the end of the process, an ok light comes on at the right of the display. If the tape response has not been successfully optimized for any reason, the error indicator lights up, and if every step except the high-frequency equalization has been accomplished the OK light comes on but flashes. When an ok status has been achieved, the tape rewinds to the beginning of the test section. The user always has the option of moving the tape forward and initiating a new calibration process if the first has not been successful.

To start the DATA cycle, a data system reset button is pressed, lighting a green signal in the start button above it. Pressing start begins the sequence, which finishes about 30 seconds later when the tape rewinds to the starting point and stops. It is not necessary to repeat the entire process for every recording, since the machine has memories for all the data covering four tapes. After the DATA cycle has been completed, touching a memory in button followed by one of the four numbered memory buttons stores the data in that location, from which it can be recalled at any time by pressing the same button.

Another alternative is to use one of the basic tape-selector buttons, which are equivalent to the tape selectors of most conventional recorders. The bias can be trimmed slightly about each nominal setting with a small bias fine adjust knob that has a range of about ± 10 per cent. By recording interstation FM tuner hiss at a low level (such as —20 dB) and varying this control as the monitor button is switched from source to tape, it is easy to find a bias that gives the most accurate high-frequency response.

The infrared remote control included with the Aiwa AD-M800U is a compact unit on which all the transport-control functions are duplicated. It can operate the recorder over a distance of 25 feet or more at angles up to 45 degrees from the front panel. On the rear of the recorder the only features are the line-in and line-out jacks and a playback-level knob. The Aiwa AD-M800U is 18-3/4 inches wide, 11-7/8 inches deep, and 4-3/4 inches high. It weighs 17-1/2 pounds. Price: $770.

Laboratory Measurements

We tested the Aiwa AD-M800U with TDK OD tape for LH, TDK SA-X for CrO2, Sony Duad for FeCr, and Memorex Metal IV for metal tape. The frequency response and other performance data we obtained with these tapes left no doubt that essentially similar results can be expected from any comparable competitive tapes.

At 1,000 Hz the input for a 0-dB recording level was 56 millivolts (mV) at the line inputs and 0.55 mV at the mic inputs (the latter overloaded at a very high level of 260 mV). The playback output from a 0-dB recording was about 290 mV for all the tapes except Sony Duad, which gave a 190-mV output. The playback distortion (third-harmonic) at 0 dB was 0.5 per cent with TDK OD and 0.7 to 0.8 per cent with the others. To obtain a reference distortion level of 3 per cent, we had to record at +7 to +7.5 dB with the two TDK tapes, +6 dB with Sony Duad, and +5 dB with the Memorex Metal IV.

The unweighted signal-to-noise ratio (S/N) referred to the 3 per cent distortion output level was about 52 dB with all the tapes except Sony Duad, which gave a 54-dB reading. Using the Dolby system and CCIR weighting, the S/N ranged from 63.5 to 64.5 dB with all the tapes, except for a 66-dB reading with Sony Duad. The noise increased by 9.5 dB through the MIC inputs at maximum gain but did not increase at all with the gain at more normal settings. Plugging a microphone into either channel input automatically disconnected the line input for that channel. The erasure of a 0-dB, 1,000-Hz recorded signal (with any of the tapes) was essentially perfect. The residual signal was lower than — 75 dB and not detectable in the noise background even with high-resolution spectrum analysis.

The playback frequency response with standard test tapes was exceptionally flat; it measured ±0.5 dB from 31 to 10,000 Hz with a BASF (DIN) 120-microsecond tape and +1, -0.5 dB from 40 to 10,000 Hz with a Teac 116SP 70-microsecond tape. The record-playback frequency response at a —20-dB level was virtually identical for all tapes. There was 2-dB overall variation from 40 to 17,000 Hz with the two TDK tapes. The extreme highs fell off slightly with the Sony Duad ferrichrome tape, which had a response of ± 1 dB from 45 to 13.000 Hz. The response with Memorex Metal IV was within 1 dB overall from 50 to 17,000 Hz.

The real differences between the tapes showed up in their 0-dB frequency response, which reflected their high-frequency headroom. Here there were no surprises; the TDK SA-X was only slightly better than OD at a 0-dB level, Duad rolled off gently above 2,000 Hz, and the metal tape was by far the best, with essentially flat response up to 13,000 Hz.

The MPX filter cut off the response sharply above 15,000 Hz instead of allowing it to fall off naturally. Its response was down 20 dB and still falling very rapidly at 18.000 Hz, where it ran off the bottom of the chart (it had a negligible effect at 15.000 Hz and lower frequencies).

The Dolby circuits tracked acceptably at all levels from 0 to —30 dB, and the difference between the response with and without Dolby was in every case just what would have been expected given the measured frequency response of the recorder. The Dolby system doubles any deviation in flatness of response due to the recorder or the tape. A standard Dolby-level test tape (200 nW/m) gave a reading of +2.5 dB on the recorder’s meters. The peak-responding LEDs lit at levels within 0.5 dB of the corresponding meter readings, and they flashed on 0.8-millisecond tone bursts with no loss of accuracy. The meters themselves read about 60 per cent of their steady-state values on 0.3-second tone bursts (slower than a standard VU meter response) and decayed to —20 dB in 0.3 second after signal removal.

The tape speed was 0.15 per cent fast, and the flutter was a very low 0.03 per cent weighted RMS or ±0.05 per cent weighted peak (DIN) with a TDK AC-342 flutter test tape. The flutter spectrum was broad and generally random, with a small peak at about 25 Hz. In fast forward and rewind, a C-60 cassette was moved from end to end in 67 and 80 seconds, respectively. All the operating functions of the AD-M800U, such as the timer and memory features and the remote control, worked perfectly.

Comment

The DATA system of the Aiwa AD-M800U virtually eliminates any audible differences between tapes, especially as far as frequency response is concerned, and for all practical purposes it does the same for their distortion and S/N performance. In view of that, it seemed strange to find that the instruction manual lists the recommended tape-selector settings for a large number of tape formulations. The DATA system makes that information, normally so important and so infrequently included in other cassette-deck manuals, quite redundant for this machine. Of course, tapes are not all equal. There are certainly differences in coating uniformity and high-frequency saturation properties, as well as in mechanical construction, that may make one tape preferable to another. Still, by and large they will all tend to sound pretty much alike when used in this recorder (with the possible, and occasional, exception of metal tape, whose high-frequency response at high levels is inherently better than that of the other tapes).

The machine worked flawlessly, leaving us with little to criticize. Its electrical performance has apparently been designed for the “real world” of cassette recording, with no attempt to extend its frequency response beyond 20 kHz or to compete with open-reel recording in dynamic range. These goals are possible in cassette machines, to be sure, but only at considerable cost. On the other hand, if we restrict ourselves to things that can be heard, it is worth mentioning that the flutter we measured was as low as we have ever encountered in a cassette recorder (or, for that matter, in consumer tape recorders of any type), and the figures we obtained may well be the residual levels on the test tapes (a combined record-playback measurement yielded very similar results).

In all the ways that count, the Aiwa AD-M800U is a superior product. It is extremely versatile, has excellent frequency response, distortion, and noise characteristics, a foolproof automatic tape-adjustment system, and is compact and easy to use. The remote control is a nicety that not everyone will use, but it works very well indeed. Even the price is right, especially when one recalls the prices of the first cassette decks with microprocessor controls a few years ago. This one does more for less money, and to us that spells progress.

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