Realistic STA-2250 Stereo Receiver Review

A little over a year ago, Radio Shack was one of the first hi-fi manufacturers to introduce a full-featured, digitally synthesizing AM/FM stereo receiver. The Realistic STA-2200 boasted an exceptional array of performance and convenience features as well as a relatively high selling price.

Although the STA-2200 is still in the Realistic line, the new Model STA-2250 brings its essential qualities, plus a few improvements, down to a much lower price range. The STA-2250 is rated to deliver 50 watts per channel into 8-ohm loads from 20 to 20,000 Hz with no more than 0.02 per cent total harmonic distortion (compared to 60 watts at the same distortion level for the STA-2200). The unit’s tuned-in frequency is shown on a large blue-green fourdigit fluorescent display in the upper center of the front panel. It is flanked by a five-segment green LED signal-strength indicator and a green stereo light. When the tuner section is not in use, these displays are blanked. To their right are eight small round buttons for the programmable station memories, plus a memory set button and light. To store the frequency of a station in the memory, the memory set button is pressed (lighting the indicator next to it), and pressing any of the station memory buttons assigns that frequency to its memory. Each button can be used for an FM and an AM station, for a total of sixteen stored frequencies. The programming will not be lost during brief power interruptions (up to an hour), but a longer period with the receiver unplugged will erase the programmed station memories, which will then have to be reprogrammed.

Five rectangular pushbuttons to the left of the display panel control the filters (mpx, low, and high), mono mode selection, and the loudness compensation. The other controls form a row across the bottom of the panel. For the most part, they are conventional knobs and switches. A rotary control selects the input source (AM, FM, FM with muting, phono, and aux) and there are separate tone-control knobs for the bass, midrange, and treble ranges. Each has eleven detented settings, with the center being a fully “off” flat-response condition. Below the frequency readout are two large concentric knobs for volume and balance (the latter with a center detent). Other controls include pushbuttons for individual speaker selection of two sets of outputs and the power switch with an adjacent red pilot light. There is a headphone jack on the panel. Next to the input selector are two three-position lever switches for the tape-dubbing and monitor functions with two tape decks (it is possible to dub from either deck to the other without interrupting one’s listening to a regular program source).

The tuning controls of the STA-2250 are two large rectangular buttons, marked down and up, mounted at a slight upward angle on the panel. Touching either one moves the frequency in the indicated direction. The normal tuning increments are 0.1 MHz for FM and 10 kHz for AM. The tuner frequency shifts by one increment each time the button is touched, and holding it down causes rapid frequency scanning until it is released. When the frequency reaches either end of its range, the tuner immediately goes to the other extreme and continues scanning. Above the tuning buttons is a small pushbutton marked search. When it is engaged, each touch of one of the tuning buttons causes the tuner to scan rapidly in that direction until a signal is encountered which is strong enough to unmute the receiver, and the scan halts at that point. This saves time when tuning across the band, since the receiver will stop only when a receivable signal is intercepted.

The rear apron of the STA-2250 contains phono jacks for the inputs and outputs, with DIN sockets paralleling the functions of each set of tape-recording jacks. Simple screw terminals are used for speaker outputs and antenna connections, and the terminals for speaker A are paralleled with phono jacks for simplified connection to speakers fitted with that type of connector and supplied with suitable connector cables (such as some Realistic models). There is a hinged ferrite-rod AM antenna and a single unswitched a.c. outlet. The front panel and controls of the Realistic STA-2250 are finished in pale gold satin aluminum, and it has a black metal top and rear. The wooden side plates are walnut veneered. The receiver is 19-3/8 inches wide, 13-3/4 inches deep, and 5-1/8 inches high; it weighs 30-1/2 pounds. It is available only through Radio Shack stores. The price is $429.95.

Laboratory Measurements. The Realistic STA-2250 is rated for use only with load impedances of 4 ohms or greater, and its internal protective circuits are designed to shut it off if one attempts to drive a lower load impedance. Into 8-ohm loads, the measured total harmonic distortion in the output was between 0.008 and 0.016 per cent from 20 to 20,000 Hz at 50 watts per channel output. Most amplifiers’ distortion rises at either the low- or the high-frequency end of the range, but the distortion plot for the STA-2250 did not show such a trend. At lower power outputs the characteristic was similar, except that the distortion readings were even lower (at 5 watts, for example, the distortion was typically between 0.003 and 0.005 per cent).

At 1,000 Hz, the distortion into 8-ohm loads rose smoothly from less than 0.003 per cent at 1 watt to about 0.01 per cent between 20 and 60 watts before clipping at 68.5 watts. The 4-ohm performance of the amplifier was quite similar except for slightly lower distortion readings at most power levels and a power output at clipping of 93 watts per channel. Despite the warnings about not using loads of less than 4 ohms, we measured the amplifier’s performance into 2 ohms, since some speakers rated at 4 ohms impedance may dip to close to 2 ohms at certain frequencies. We were never able to reach the clipping level, since the protection system shut off the receiver at about 76 watts, well before clipping occurred. The first time this happened, we were at a loss as to how to get the amplifier working again. The instructions do not explicitly state that the power must be turned off for a while and reapplied to turn the receiver on after the protection has tripped, although this is implicit in the manufacturer’s suggested trouble-shooting procedure.

The IHF clipping headroom was 1.37 dB, based on the STA-2250’s 8-ohm ratings. Since it is not rated for the other impedances, we can only note the maximum power outputs we measured at the clipping points. With the tone-burst test signals of the IHF dynamic-power test, we measured maximum unclipped outputs of 81 watts, 128 watts, and 156 watts per channel into 8-, 4-, and 2-ohm loads, respectively. The maximum 2-ohm power, even with the 20-millisecond tone burst of this test, was limited by the tripping of the protection circuit. The 8-ohm dynamic-headroom rating of the amplifier was 2.1 dB. The overload-recovery time was less than 5 microseconds, a totally negligible figure, and complex loads had no effect on the amplifier’s waveform or its stability. The IHF slew factor was greater than our measurement limit of 25.

The amplifier sensitivity for a 1-watt reference output was 22.5 millivolts (mV) through the aux input and 0.29 mV through the phono input. The respective A-weighted noise levels were —81 and —79 dB, referred to 1 watt. The phono preamplifier overloaded with a 180-mV 1,000-Hz input. Equivalent overload inputs at 20 and 20,000 Hz were 240 and 115 mV. The phono-input impedance was 47,000 ohms in parallel with 270 picofarads. This capacitance is slightly high, although most modern record players will add only about 100 picofarads to it, placing the total capacitance within the usable range for most good cartridges.

We also measured the amplifier’s intermodulation distortion with two equal-amplitude input signals, at 19,000 and 20,000 Hz, whose combined peak value was equivalent to that of a sine-wave signal of 50 watts output. The third-order distortion at 18,000 Hz was —67 dB and the 1,000-Hz second-order product was —84 dB, both referred to a 50-watt output.

The amplifier tone controls had conventional characteristics. We noted that the midrange control affected frequencies from 300 to 4,000 Hz, although it had relatively little effect near those extremes. With the knobs at their center positions, the frequency response was perfectly flat, obviating the need for a tone-control bypass switch. The loudness contours were well chosen, affecting only the lowest frequencies (under 200 Hz) and to a slight extent the frequencies above 7,000 Hz when the volume setting was reduced. The cutoff slope of the low-frequency filter appeared to be approaching 12 dB per octave below the audio range, but the high filter had a gradual 6-dB-per-oc-tave slope. Their respective — 3-dB response frequencies were 40 and 6,000 Hz. The RIAA phono equalization was accurate within 1 dB overall from 35 to 20,000 Hz. There was a slight change in the high-frequency phono response when it was measured through the inductance of a typical magnetic phono cartridge (about a ± 1-dB variation).

The FM tuner section had an IHF usable sensitivity of 11.8 dBf (2.1 microvolts, or μV) in mono. The stereo sensitivity was set by the switching threshold of 21 dBf (6 μV). The 50-dB-quieting sensitivity was 13.8 dBf (2.6 μV) in mono and 37.8 dBf (40 μV) in stereo. At a 65-dBf (1,000-μV) input the distortion was 0.19 per cent in mono and 0.11 per cent in stereo. The respective noise levels were —72.5 and —68 dB. A two-tone intermodulation-distortion measurement was made with the signal generator modulated 100 per cent by equal-amplitude signals at 14,000 and 15,000 Hz. Spectrum analysis showed third-order distortion components at 13,000 and 16,000 Hz at a —45-dB level relative, to the primary modulating tones, and a second-order component at 1,000 Hz at — 50 dB relative to 100 per cent modulation at that frequency.

The stereo frequency response was flat within ±0.7 dB from 30 to 15,000 Hz. It was at its maximum at the high-frequency end of that range, but the suppression of the 19-kHz pilot carrier to a low — 70-dB level in the audio outputs suggests the use of either very effective filters or a pilot-canceling circuit in the tuner section. The tuner’s stereo crosstalk was low and very uniform, changing from about —42 dB at 30 Hz to — 37 dB over most of the audio range and dropping to —32 dB at 15,000 Hz.

The FM-tuner capture ratio was 1.5 dB at 45 dBf (100 μV) input, and the AM rejection was 62 dB at that level (both figures were slightly better at 65 dBf). The image rejection was an excellent 90 dB. Alternate-channel selectivity was also excellent at 81 dB, and the adjacent-channel selectivity was 4.4 dB. The muting and stereo thresholds were identical at 21 dBf (6 μV). The tuner hum level was —68 dB. The AM-tuner frequency response was down 6 dB at 30 and 3,100 Hz.

Comment. When we tested the Realistic STA-2200 receiver we were highly impressed with its absolute performance and with the value it represented at its $600 price. The new STA-2250 made an even greater impression on us, since it is in many ways improved over the STA-2200 and certainly shows no signs of any performance sacrifice. The principal omissions in the new model, compared with the older one, are the deletion of the Dolby FM decoder and the clock, plus a few control simplifications such as removing the power indicators, selectable tone-control turnover frequencies and bypass switch, and automatic scanning of the programmed channels. The only significant omissions in the STA-2250, in our opinion, are the separate preamplifier out-puts/main-amplifier inputs found on the STA-2200.

To counter these deletions, the lower-price (by $ 170) STA-2250 has more memories (eight compared to six), a midrange tone control, audio filters, and what we consider to be an improved front-panel layout.

Also, in the FM tuner we found image-rejection and selectivity characteristics, among other things, that were outstanding for a receiver in this price range.

Despite the manufacturer's repeated warnings about not using the STA-2250 with load impedances of less than 4 ohms, it seems better able to cope with such operation than most receivers we have tested. The protection circuit is highly effective (it gave the impression of being infallible, but that is always a risky inference), and we doubt that anything could be damaged if one were to use the receiver with a low-impedance loudspeaker load. Even though the output shut off at some 158 watts into 2 ohms with a 20-millisecond signal repeated twice per second, the waveform distortion was negligible up to that point, and we doubt that most very brief program peaks would trip the protection system.

Although we do not allow the AM performance of a receiver to affect our overall appraisal of its merit, it is worth mentioning that the STA-2250, whose AM frequency response is no better than that of similar receivers, sounds very much better than most of them. This is because it has a high effective sensitivity and does not seem to be susceptible to the buzzing interference that usually makes AM reception a practical impossibility at our location. By assigning the AM and FM outlets of a well-known good-music station to the same programmed button, we could make A-B comparisons between them; the STA-2250 acquitted itself very creditably, the major difference being the expected loss of high-frequency response in AM reception. From the standpoints of noise and distortion there was remarkably little difference.

When the STA-2200 first appeared, fully digital receivers were far from common. Today, most manufacturers include at least one such product in their line, so the STA-2250 is not unique even in its price range. Nevertheless, it impresses us as being at least as good a buy as its predecessor, and it comfortably met or surpassed all of the performance ratings for which we could test. We found it a thoroughly fine receiver at a very reasonable price.

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