Sherwood S-9200CP Stereo Receiver Review

The complete redesign Sherwood’s product line has undergone this year is well illustrated by their receiver lineup. It consists of five models offering a wide range of power outputs and control features at various price levels. This report covers the next-to-the-lowest-price Sherwood receiver, the S-9200CP, which is rated to deliver 20 watts per channel to 8-ohm loads from 20 to 20,000 Hz with no more than 0.08 per cent total harmonic distortion.

The silver-satin finish on the exterior of the S-9200CP presents an uncluttered, almost starkly functional appearance. The receiver’s most prominent front-panel feature is a large tuning knob, with an indentation for rapidly scanning the band with a finger tip. The words touch lock sensor above the knob are a clue to one of the receiver’s features; the AFC system is automatically turned off when the knob is touched. This simplifies tuning a signal close in frequency to a much stronger signal. When the knob is released, a locked light comes on to show that the tuning is locked to the station frequency. The other front-panel knobs are smaller and include bass and treble controls (with eleven detented settings each), balance, and volume (also detented).

A row of slender pushbuttons below the knobs select the inputs (phono, aux, fm, am), loudness compensation, tape monitor, SPEAKER A and SPEAKER B outputs, POWER, and the operating mode of the FM-tuner section. The last button, marked fm mute and off/mono, performs several functions that are somewhat ambiguously described in the manual. When it is out, the touch-lock system is operative and mono or stereo operation is determined automatically by the presence of a pilot carrier in the received signal (which also must be above a threshold level). Pressing this button in disables the multiplex section and the interstation muting as well as the AFC lock circuit. This mode is useful for receiving weak signals in mono in cases where stereo reception would be too noisy even if possible.

The dial window, which is all black when the receiver is off, contains a number of lighted displays. The tuner frequency for FM and AM bands is shown digitally by bright blue numerals at the right of the window. The frequency is shown to the nearest 100 kHz for FM and to the nearest 10 kHz for AM. (Note that the S-9200CP is not a digitally tuned receiver; the display is driven from a frequency counter that operates from the conventionally tuned local oscillator.)

To the left of the frequency readout are two horizontal bars (red and green) with a green dot between them. The dot, marked fine, is a critical-tuning indicator for FM and lights only when the receiver is set very close to the station frequency. To its left is a red stereo light, and the green light to its right is marked lock. Normally, the lock light is off while the receiver is being tuned. When the knob is released, the tuner locks to the station frequency and the lock light comes on. If the fm mute button is pressed in (its off/mono position), the lock and stereo lights do not operate but the tuning dot still functions as a tuning indicator.

Signal strength is shown by a five-segment green line to the left of the tuning display; its length is proportional to signal strength for both AM and FM. To the left of the line are LEDs that show when the aux, phono, or tape buttons have been selected. There is a small red pilot light above the power switch and a headphone jack at the lower right of the panel.

In the rear of the S-9200CP there is a hinged ferrite-rod antenna for AM, binding-post terminals for 300- and 75-ohm FM antennas and an AM wire antenna, plus the signal-input and -output jacks. Insulated spring connectors are used for the two sets of speaker outputs. One of the two a.c. convenience outlets is switched. The receiver is protected by a line fuse, and the speaker outputs are individually fused. The Sherwood S-9200CP is 16-1/2 inches wide, 11-3/4 inches deep, and 4 inches high. It weighs 17 pounds. Price: $259.95.

Laboratory Measurements

The one-hour preconditioning period left the top of the cabinet (over the output-transistor heat sink) quite warm to the touch. In normal operation the receiver remained quite cool. With both channels driven at 1,000 Hz into 8-ohm loads, the waveform clipped at 33.6 watts per channel. The 4- and 2-ohm clipping power levels were 42.3 and 38.7 watts (Continued on page 38)

per channel, respectively. The IHF clipping headroom (8 ohm) was 2.25 dB. With the tone-burst signals of the IHF dynamic-pow-er measurement the maximum power output was 39 watts (8 ohms), 61.7 watts (4 ohms), and 59.3 watts (2 ohms), corresponding to an 8-ohm dynamic headroom of 2.9 dB.

The 1,000-Hz harmonic distortion into 8-ohm loads was 0.0022 per cent at 1 watt (it was below the noise level at lower outputs) and increased smoothly to 0.01 per cent at the rated 20 watts and 0.017 per cent at 30 watts output. When driving 4-ohm loads the distortion characteristic of the amplifier was almost identical, rising from 0.003 per cent at 1 watt to 0.06 per cent at 40 watts. Even into 2 ohms (which often results in high distortion with amplifiers not specifically designed to drive very low impedances) the distortion ranged from only 0.006 per cent at 1 watt to 0.055 per cent at 30 watts.

The amplifier slew factor was greater than 20, and it was stable with complex simulated reactive speaker loads. The IHF intermodulation (IM) distortion with 19-and 20-kHz input frequencies was —65 dB for the third-order product at 18,000 Hz and —76 dB for the second-order (1,000-Hz) distortion, both referred to an equivalent sine-wave output of 20 watts.

The distortion at rated power into 8 ohms was less than 0.05 per cent from 20 to 20.000 Hz and typically between 0.01 and 0.02 per cent over the range of 100 to 15.000 Hz. At reduced power levels the characteristic was similar, but with distortion of less than half the full-power readings down to 2 watts output (-10 dB).

The amplifier sensitivity for a 1-watt reference output was 34 millivolts (mV) at the aux inputs and 0.55 mV at the phono inputs. The respective A-weighted signal-to-noise ratios (S/N) were 86.4 and 80.7 dB. The phono-preamplifier input overloaded at 165 mV at 1,000 Hz, and at 20 and 20,000 Hz the overload limits (converted to equivalent 1,000-Hz values) were 157 and 230 mV, respectively. The phono-input impedance was 47,000 ohms in parallel with 300 picofarads.

The amplifier tone controls did not affect the midrange (300 to 5,000 Hz) significantly even at full boost or cut. The bass-turn-over frequency varied from under 100 Hz to over 300 Hz throughout the control range, and the treble curves were hinged at 5,000 Hz. The loudness compensation was very moderate (a maximum bass boost of 7 dB) and did not affect the high frequencies.

The RIAA phono equalization was as accurate as we could measure (better than ±0.25 dB) from 50 to 20,000 Hz, with no detectable departure from flatness over that range. The phono preamplifier has a built-in infrasonic rolloff in lieu of the usual switchable “rumble filter.” Its response was down about 1 dB at 30 Hz and 4 dB at 20 Hz. The phono response showed a gentle high-frequency rise when it was measured through the inductance of a phono cartridge, beginning at about 4,000 Hz and reaching +2 dB at 20,000 Hz.

The FM-tuner section had a mono IHF usable sensitivity of 10.3 dBf (1.8 microvolts, or μV), exactly as rated. The stereo sensitivity was established by the switching threshold at 26.8 dBf (12 μB), where the distortion was just under 1 per cent. The 50-dB quieting sensitivity was 15 dBf (3 μV) in mono, with 0.4 per cent total harmonic distortion plus noise, and in stereo it was 36.3 dBf (36 μV), also with 0.4 per cent distortion and noise. The distortion at a 65-dBf (1 ,000-μV) input was 0.11 per cent in mono and 0.18 per cent in stereo, and the respective S/N readings at that input were 78 and 71.5 dB.

The stereo FM frequency response was flat within ±0.5 dB from 30 to 15,000 Hz. The channel separation was about 44 dB in the midrange and exceeded 36 dB from 70 to 15,000 Hz (it was 29 dB at 30 Hz). The IHF IM distortion of the tuner section, using 14- and 15-kHz modulation for the signal generator, was —64 dB for second-order (1,000-Hz) and —48 dB for third-order (13 kHz) components in mono. The 1,000-Hz component is referred to 100 per cent modulation at that frequency, and the third-order distortion components are referred to the amplitudes of the modulating tones as they appeared at the de-emphasized tuner output (their combined peak value was equivalent to 100 per cent modulation). In stereo the distortion components were nearly the same (-60 and -47 dB), but as with most stereo tuners there were a number of additional responses in the audio range at levels of -60 to -70 dB.

The capture ratio was 1.15 dB, and the AM rejection was a good 62 dB. The image rejection was 60 dB, and the alternate and adjacent-channel selectivity measurements were 48.5 and 5.8 dB, respectively. The muting and stereo thresholds were identical at 26.8 dBf (12 μV). Stereo pilot-carrier leakage was -76 dB, and the tuner hum was a very low —77 dB (all 120 Hz). The frequency response of the AM-tuner section was down 6 dB at 95 and 4,200 Hz.

Comment

Our tests of most low-price receivers have shown them to be competent performers but generally lacking in meaningful features or performance that would set them apart from most of their competitors. This is to be expected in such a highly competitive marketplace. The Sherwood S-9200CP is a refreshing exception to that rule. Not only did it comfortably surpass many of its key performance ratings, but some of those ratings are well above the norm for receivers in its price class. For example, the FM S/N we measured on the S-9200CP was among the best we have yet found in a receiver at any price. The receiver’s ratings of 80 and 75 dB for mono and stereo S/N are most unusual for this class of equipment, and our readings of 78 and 71.5 dB are also well above average (the latter, in particular, is close to the residual noise in our signal generator). The only significant difference between our measurements and the tuner specifications was in the FM selectivity, which, although adequate, did not reach the rated 65 dB.

In every other respect, both the audio and tuner sections of this receiver were outstanding. Aside from sheer power, the S-9200CP could more than hold its own against most receivers selling for several times its price. The IHF dynamic- and clip-ping-headroom measurements for the amplifier show that under practical listening conditions it can deliver far more power than its very conservative ratings would suggest. Even with 2-ohm loads (which many supposedly powerful amplifiers cannot drive with a useful power output) the S-9200CP performs very well.

Instead of including the usual worthless “rumble filter,” the Sherwood designers have built an effective infrasonic filter into the S-9200CP’s phono preamplifier. The “Touch Lock” tuning works so easily it is easy to forget that it is there. It is impossible to get less than the best performance from the FM tuner. And its AM section, while not “hi-fi” by any means, is one of the best-sounding (and quietest) we have heard in years. In all, we are most impressed with Sherwood’s “new look.” It is as different in performance as it is in appearance, and the difference is all to the good.

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