Technics RS-B905 Cassette Deck
Technics's RS-B905 contains most of the features that go into a thoroughly modern cassette deck, plus one feature that seems almost a relic of the past-albeit a useful relic. The deck is a two-motor, three-head model (with recording and playback heads in a single housing) and has a dual-capstan transport with different capstan diameters to prevent flutter-inducing mechanical resonances. Being absolutely up-to-date, the RS-B905 also contains the three main noise reduction systems (DBX and Dolby B and C). Also, as the label on the cassette-compartment door tells you in no uncertain terms, the deck incorporates the Dolby HX Pro head-room-extension system. Thankfully, the label can be peeled off.
Like most other new decks, the RS-B905 automatically selects overall bias and recording-equalization settings for Types 1, 2, and 4 tapes (ferric, chrome-equivalent, or metal-particle, respectively), depending on the molded cassette-shell keyways. A center-detented bias-trim knob has markings that indicate relative amount of bias applied: As you turn it to the " + " side, bias increases and high-frequency response decreases.
Unlike most decks we've tested recently, the Technics unit resurrects a valuable feature that can aid in making more accurate recordings: separate manual recording-calibration adjustments for each channel. These do not perform the same function as a conventional recording-level control (which, with the B905, is the large knob on the front panel that operates in conjunction with a nearby channel-balance knob). A recording-level control usually comes directly after the input jacks and before the noise-reduction circuits, which is the case with the B905. The two small, center-detented knobs-labeled rec calibration- at the lower right of the front panel are instead placed in the circuit after the signal has passed through the noise-reduction encoders (should noise reduction be switched in).
Judicious use of the recording-calibration controls permits superior recordings because the adjustment- which controls the amount of noise-reduced signal fed to the recording head-enables correction for the different sensitivities of various brands and types of cassette tapes. As explained in the manual, the intent is to adjust the recording-calibration knobs so that the sound level on each channel does not change while switching between source and tape monitoring during recording. Matching source/tape levels in this manner reduces mistracking of the playback noise reduction system. The Dolby systems are sensitive to the absolute level of the signal on the tape; Dolby C in particular can produce audible "pumping" and frequency-response aberrations should its playback circuits receive an encoded signal at too high or too low a level. While this is usually not a major problem, it can be exacerbated by use of tapes that have abnormally high or low sensitivities. The RS-B905 is one of the few decks allowing you to eliminate the response aberrations via manual adjustment (which can produce results superior to those of an automatic system because a wideband test signal, such as music or pink noise, can be used).
The source/tape monitor switching crucial for making the recording-calibration adjustment is automatic. That is, it automatically toggles to the tape setting during playback and recording-an excellent feature. A manual-override pushbutton is also provided. Other features include an automatic blank-seeking cueing system with repeat mode, a headphone output (with a separate volume control), a switchable multiplex filter, and a vacuum-fluorescent display incorporating two three-color (white, tan, red), 18-segment recording-level meters (reading from - 40 dB to +18 dB), as well as a three-digit tape counter.
Because the RS-B905 provides no objective means of determining when the bias and recording-calibration adjustments are correct, Diversified Science Labs tested the deck with these controls at their detented positions. With the TDK tapes used (AD, SA, and MA-X for Types 1, 2, and 4, respectively), response was consistently very good. Probably because of the action of the HX Pro system, the 0-dB response with metal tape and Dolby C (not shown in our graphs) was down by only 2 dB at 20 kHz with Dolby C, indicating excellent high-frequency headroom. Other 0-dB responses were down by 3 dB at 10 kHz and 11 kHz for Type 1 and Type 2 tapes, respectively, with either Dolby C or DBX. Dolby tracking was excellent and was free of the midrange response sag we often see. Playback frequency response was also very good, with the lab reporting a good-to-very-good match between the azimuth of the deck and the BASF alignment tape.
The distortion figures and indicator readings shown in our data prove to be about average-nothing particularly spectacular. Although DSL reported that there was a good bit of even-order harmonic distortion, we did not find it an audible hindrance (possibly because even-order distortion products are far less audible than odd-order ones). Likewise, the total harmonic distortion (THD) figures do not look out-of-line with performance on comparable decks.
Noise levels with and without noise reduction are on par with the best that can be obtained with present-day tapes and equalization settings. Flutter is a bit higher than we've lately been seeing with decks in this price class, but it was not noticeable even when dubbing piano and organ recordings. Speed accuracy is generally excellent, as is tape erasure. Sensitivity, overload, output-level, and impedance values should not pose any problems in typical installations.
The recording-level indicators are fast and accurate enough in their action to be considered "peak reading." We did, however, find that the tan-colored segments of the readouts (spanning 0 dB to +8 dB) are dimmer than the neighboring white and red segments. Nonetheless, making the desirable peak-level region for recording with Type 1 and 2 tapes a different color is a laudable attempt to ease the level-setting task.
The recording-calibration controls proved to be a mixed blessing: Setting them up with the bias-trim is not as easy as the manual makes it seem. On some tapes we tried, it was difficult to obtain a flat response and maintain proper recording-calibration levels. (These tapes, however, were of the souped-up variety that go for souped-up prices-the kind of cassettes that, for some reason, proudly show a deliberately rising high-frequency response on their cellophane wrappers, as if this were desirable.) In fact, we found this difficult even using a CD test record to supply pink-noise signals and monitoring the deck output with a 1/3-octave spectrum analyzer. It makes you wonder just how well decks with automatic tape-matching adjustments can do using only a couple of sine waves and a fairly crude level detector.
But with standard-grade cassettes, such as the ones DSL used in its tests, we were able to both optimize the recorder/tape match and make-with the aid of Dolby C or DBX-recordings almost indistinguishable from the originals. This is what a tape recorder should do. That it is possible with the RS-B905 is a tribute to the deck's overall design as well as to the welcome inclusion of the recording-calibration knobs.
