Crown FM Two Tuner Review

The Crown FM Two is an FM tuner of advanced design whose compact dimensions and appearance complement those of the company’s Straight Line Two preamplifier and Power Line Two power amplifier. Because of their unified design, the three components can be “stacked” in a single optional walnut cabinet to form a “receiver” of outstanding quality. The FM Two is only 1-3/4 inches high, with a satin-finish silver-color front panel fitted with handles. The panel is 19 inches wide and the tuner is 13-3/4 inches deep; it weighs approximately 9-1/2 pounds. Price: $599.

The Crown FM Two is a digital-synthesis tuner whose reception frequency is shown on a large fluorescent digital display in the center of the panel. The bright 1/2-inch-high numerals are readable from a considerable distance and can be dimmed by a front-pan-el switch if desired. To the right of the display are two flat momentary-contact scan/ tune buttons and a scan lock button. With the latter out, holding either scan/ tune button down causes the tuner to scan in the selected direction (up or down in frequency) in steps of 200 kHz, corresponding to North American channel assignments for FM. Export versions are set up at the factory for the channel spacings (such as 50 kHz) used in other parts of the world. A momentary touch on a scan/tune button will cause the frequency to step by one channel width.

If the scan lock is engaged, a single touch on a scan/tune button will cause the tuner to scan until it acquires a signal above the muting threshold, where the tuning stops and the FM Two unmutes. At the right side of the panel are a memory button and six preset buttons. A station frequency can be stored in any of the memory locations by pressing memory (which lights an amber indicator above that button) and then, within five seconds, pressing the desired preset button. The station can be recalled instantly at any later time by touching that button. A constantly energized separate power supply in the tuner keeps the memories “alive” when it is not in use, and a very large internal capacitor (0.47 farad) retains sufficient charge to support the memories for at least five days with no power available to the tuner.

To the left of the frequency-readout window (which also reveals a five-segment signal-strength readout and a stereo indicator) there are six round pushbutton switches. In addition to the power switch (with an adjacent red light), these include an FM de-emphasis switch (75- or 25-microsecond characteristics), a stereo-noise filter that blends high frequencies to reduce hiss on weak signals, a mute switch, a stereo/mono switch, and the fluorescent-display dim switch. With all the buttons in their “out” positions, the tuner is set up for normal operation.

The rear of the Crown FM Two contains the audio-output jacks, each with its own level control, and a coaxial connector for the 75-ohm antenna input. For installations using a 300-ohm antenna system, a 300- to 75-ohm balun matching transformer is supplied with the tuner. There is also a small remote connector whose function is not mentioned in the otherwise complete instruction manual.

The circuitry of the Crown FM Two is unusual in several respects. The “front end” has three cascode J-FET r.f. amplifiers whose seven tuned circuits give the tuner exceptional immunity to overloading by strong signals plus excellent image rejection. The first i.f. is at 10.7 MHz, with lin-ear-phase (constant group-delay) ceramic filters that make possible the tuner’s very low distortion rating of less than 0.05 per cent for both stereo and mono. There is a second conversion to 1.96 MHz, the operating frequency of the pulse-counting digital detector, which not only eliminates any alignment or drift problems in that part of the tuner but has an inherently wide bandwidth that accommodates excessive transmitter deviation without a significant increase in distortion. Although crystal-con-trolled frequency synthesizers are no longer a novelty in consumer-oriented tuners, the circuit in the FM Two operates rapidly and smoothly, and with no idiosyncrasies.

Laboratory Measurements

The 75-ohm antenna input of the Crown FM Two was driven through a resistive network that matched it to the 50-ohm output impedance of our Sound Technology 1000A signal generator. The “dBf ” notation of the tuner test standard makes sensitivity ratings independent of the impedance level. If one were to rate the tuner sensitivity in terms of microvolts, the numbers would be half as much as for a 300-ohm antenna input, and this might give a misleading impression of the tuner’s actual sensitivity.

In mono, the usable sensitivity was 11.6 dBf and the 50-dB quieting sensitivity was an almost identical 12 dBf. The stereo-switching threshold was 25 dBf, and the distortion was already under 1 per cent at that input level. In other words, clean and undistorted reception can be expected from any stereo signal strong enough to be heard in stereo at all. The stereo 50-dB quieting sensitivity was 35 dBf.

At a 65-dBf input, the total harmonic distortion plus noise was 0.11 per cent in both mono and stereo. The signal-to-noise ratio at that level was 74 dB in mono and 69 dB in stereo. To some extent, these figures may represent limitations of the signal generator (particularly the distortion, since the generator is rated at 0.1 per cent and has an actual residual distortion of about 0.06 per cent).

The IHF intermodulation distortion of the Crown FM Two was measured by modulating the signal generator 100 per cent with equal amplitudes of 14,000 and 15,000 Hz. A spectrum analysis of the audio output showed a second-order distortion product at 1.000 Hz that was some 70 or 71 dB below 100 per cent modulation at that frequency. The third-order distortion (at 13,000 and 16.000 Hz) was —51 dB in mono and —54 dB in stereo relative to the 14,000- and 15,000-Hz tone levels. As with most stereo FM tuners, there were a number of low-level intermodulation products in the stereo mode, but since their levels were all between — 65 and —80 dB, they were certainly not audible.

The tuner frequency response was perfectly flat from 30 up to several thousand hertz, rising slightly to +0.7 dB at 15,000 Hz. In spite of this very flat high-end response, the 19-kHz pilot carrier leakage in the audio output was at a barely measurable — 80 dB level. The internal hum was — 64 dB (mostly 120 Hz) relative to 100 per cent modulation. The channel separation was better than 40 dB over the full range of 30 to 15,000 Hz, and it was about 52 dB over most of the midrange. The maximum audio output from a 100 per cent modulated signal was about 2.5 volts, and at the minimum setting of the output-level control it was just under 0.6 volt.

Other measured FM tuner characteristics included a capture ratio of 1.6 dB at 45 dBf and 1.25 dB at 65 dBf; AM rejection was 70 and 72 dB at those input levels. The alternate-channel selectivity was a very good 81.5 dB, and the adjacent-channel selectivity was 8 dB. The image rejection was excellent at 92 dB, and the muting threshold was 20 dBf.

Comment

Although there were some minor differences between the measured performance and the published ratings of the Crown FM Two, most of them were easily explainable by differences in test equipment and setup. The Crown FM Two is clearly a superior tuner with consistently excellent performance where it really matters; distortion, noise, and interference rejection. Its wide-band digital detector not only has very low inherent distortion but is also unaffected by an occasional overmodulation peak that could create a burst of distortion from a conventional tuner using a quadrature detector.

Although the sound quality one achieves in FM reception is more likely to be determined by the broadcast signal than by the tuner, we noted that the Crown FM Two delivered a uniformly high-quality output from practically any signal we could hear in our suburban New York location. On one occasion, forty-four stations were receivable with an indoor folded-dipole antenna at ground level, and thirty-five of them were heard in fully quieted stereo. Switching to mono produced a fully quieted mono output from eight of the remaining stations, leaving only one that was still marginal under this deliberately extreme listening arrangement. The tuning and scanning were completely noise-free, the output of the tuner being muted until the program emerges with no thumps or noise bursts.

We noted with approval that Crown did not attempt to add AM capability to the FM Two. The AM sound from combination tuners is so consistently mediocre (to put it charitably) that its inclusion could only have degraded the user’s perception of this fine product. In our view, an excellent FM tuner should not be compromised by including a poor AM tuner, and a good AM tuner (which is perfectly possible, though rare) is likely to be at least as expensive as a good FM tuner.

The Crown FM Two, certainly a fine component for any music system, is ideal for use with matching Crown components. The combination of elegance and performance of such a grouping, though hardly inexpensive, would be difficult to match in any other way.

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