Audio Dynamics/ADC T-200 Tuner Review

The Audio Dynamics T-200, a moderately priced, high-quality digital-synthesis am/fm tuner, departs in several respects from most of its contemporaries. The most obvious difference is the tuning knob at the right end of its front panel. This once-universal tuner feature has all but disappeared.

Audiophiles who would rather push than twist need not feel neglected, though, for the T-200 also has a pair of small buttons marked seek, which cause the tuner to scan up or down until a suitable signal is acquired. The free-wheeling knob is used to tune to a specific frequency, especially one that does not contain a clear signal.

Other small buttons turn off the interstation muting, switch the tuner to mono, and activate the automatic if bandwidth and Schotz noise-reduction circuits. Two larger, square buttons select am or fm reception. A row of small station-preset buttons at the left of the panel can recall the stored frequencies of eight fm and eight am stations. The status of the several pushbutton functions is shown by red led’s.

The display window occupies the upper half of the panel over most of its width. Station frequency is shown in large red numerals. To the right of the frequency readout is a five-segment signal-level indicator and a tuning indicator, which consists of red left and right arrows with a green fm exact light between them. The arrows show the direction of knob rotation required for correct tuning of a nearby station, and the green light comes on only when the synthesizer and broadcast frequencies are matched.

At the right of the window are the stereo and if bandwidth indicators. When the auto if band button is engaged, the tuner’s bandwidth is determined by the signal strength and the degree of adjacent-channel interference. For reasonably strong signals, free from interference, the wide band is used; if the control circuits sense interference or the signal strength is insufficient, the tuner switches to a narrow band for greater selectivity. When the auto if circuit is disengaged, the tuner operates only in its narrow mode (although the manual seems to imply the opposite).

The Schotz noise-reduction circuit, licensed from its inventor, Larry Schotz, is designed to reduce background noise on weak stereo signals with minimal loss of channel separation. It monitors the signal strength (an inverse indicator of the noise added by the tuner circuits during reception of a stereo signal) and the frequency content of the program. The noise reduction is achieved by dynamically blending the left and right channels at high frequencies, which reduces channel separation as well as noise. When there is little high-frequency program content, the audible loss of separation is slight and a worthwhile improvement in the subjective signal-to-noise ratio can be obtained with little quality degradation. When the signal strength is adequate for quiet reception, the circuit automatically cuts out.

On the rear apron of the T-200 tuner are two pairs of line outputs, for fixed and variable levels; a small adjustment shaft is near the variable jacks. A coaxial F-type connector is provided for the 75-ohm fm antenna connection, and a 300- to 75-ohm transformer is furnished for use with 300-ohm antennas. There are screw terminals for an am wire antenna and ground as well as a hinged ferrite-rod am antenna.

The Audio Dynamics T-200 has a metal case finished in black with woodgrain side plates. It measures 18-3/4 inches wide, 12-1/2 inches deep, and 3 inches high and weighs 11-1/4 pounds. Price: $399.

Lab Tests

We measured the tuner’s performance in both of its if bandwidth modes. Although the tuner’s distortion was higher with the narrow band, and the usable sensitivity was also somewhat better in that mode, the more important 50-dB quieting sensitivity and signal-to-noise ratio (S/N) were unaffected by the bandwidth.

Surprisingly, channel separation was actually greater with a narrow if band, though it was very good in both modes. Neither the capture ratio nor the selectivity could be measured with a wide if band, since the tuner circuits persisted in selecting the narrow band under the test conditions. The narrow bandwidth, however, produced a superb adjacent-channel selectivity reading of 26 dB, though it also, as would be expected, resulted in an undistinguished capture-ratio measurement of 4 dB.

Another measurement, which had nothing to do with the auto if band circuit, gave results that were difficult to believe. The image rejection of the fm tuner turned out to be greater than 132 dB, the approximate limit of our measurement capability! Granted, the tuner’s image rejection is rated as 100 dB, a very impressive figure in itself, but a measurement of 132 dB is really extraordinary. The am tuner’s frequency response was considerably better than average, varying +3.5, — 6 dB from 20 to 4,800 Fiz.

The dynamic nature of the Schotz noise-reduction circuit made it impracticable to measure its effects. Nonetheless, by using an unmodulated signal (equivalent to one with no high-frequency program content), we established that the circuit had no effect on noise at signal levels of 55 dBf or greater and that it gave an A-weighted noise reduction of 7 to 8 dB at 45 dBf or less. While these results are roughly indicative of the capability of the system, they tell us little about its subjective effects. Unfortunately, in our area most stations are either fully quieting or too weak for stereo reception, preventing a complete evaluation of the Schotz circuit under actual use conditions.

Comments

The Audio Dynamics T-200 is attractive and easy to tune, and it has some unusual capabilities. We enjoyed the effortless band-scanning made possible by its free-wheeling tuning knob. One spin can cover about half of its tuning range, a clear advantage over most of the pushbutton tuning systems we have seen. The am quality was noticeably better than what we have heard from most other tuners in recent years, as well as being less sensitive to electrical interference.

While the auto if band circuit is a desirable feature, and one which we have found to work well in some other tuners, we feel that the default setting (with the circuit switched off) should be the wide rather than the narrow band. The automatic switching operates “transparently,” however, in the sense that one is never aware of a change except by seeing the wide or narrow legend in the display window. That brings us to another small criticism—the bandwidth legends are lit so dimly (dark green against a black background) as to be nearly invisible in a normally lit room. The tuner’s other display indications are bright and easily visible; why not these?

All things considered, though, the T-200 offers good value in a tuner. It works well, has a lot of versatility without external complexity, and sounds good, within the limits imposed by the broadcast signal.

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