Equipment Profiles
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| Phase Linear Amplifier | 57 |
| Stanton Mark III Isophase Stereo Headphones | 59 |
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Fisher Model 201 Stereophonic AM-FM Receiver
MANUFACTURER'S SPECIFICATIONS
FM Tuner Section: IHF Sensitivity: 2.5 µV. S/N Ratio: 60 dB. THD: 0.5%. Selectivity: 36 dB. Image Rejection: 46 dB. IF Rejection: 65 dB. Capture Ratio: 3 dB. Stereo FM Separation (1 kHz): 35 dB.
AM Tuner Section: Sensitivity (loop): 270 µV/M. Selectivity: 44 dB. Image Rejection: 36 dB. IF Rejection: 50 dB.
Amplifier Section: Power Output: IHF Dynamic Power, 25 watts/ channel; RMS Power, 20 watts/channel. THD: 0.8% at rated output. IM: 1.2% at rated output. IHF Power Bandwidth: 25 to 20,000 Hz. Frequency Response: Phono, 35 to 15,000 Hz ± 2 dB; Aux. 1, 2 and Tape Monitor, 25 to 20,000 Hz ± 2 dB. Hum and Noise: Phono, -60 dB; Aux. 1, 2 and Tape Monitor, -65 dB. Input Sensitivity: Phono, 8 mV; Aux. 1, 2 and Tape Monitor, 200 mV. Damping Factor: Greater than 10. Tone Control Range (Bass and Treble): 24 dB @ 50 Hz and 10 kHz.
General: Dimensions: 15-11/32 in. W. x 4% in. H. x 14¼ in. D. Price: $199.95
Fisher Radio has joined a growing group of domestic high fidelity manufacturers who, in the interest of introducing lower cost equipment, have sought additional manufacturing sources abroad. Both the new Model 201 and the somewhat higher powered (and more expensive at $249.95) Model 202 Receivers recently introduced by this justly respected firm are manufactured for them in Japan. The "Fisher Touch," however, is unmistakable, and it would be our guess that design efforts, engineering and even production procedures were carefully initiated and executed by the home-based engineering and production talent. The front panel of the new Model 201 is replete with the familiar "bird-with-note-in-bcak" trademark.
The light-gold and black heavy anodized front panel features an upper dial area which is "blacked out" until power is applied to the unit. Controls arranged along the lower half of the panel include a combination power/speaker selector switch (including positions for main, remote, both sets of speakers or phonesonly), a bass control, treble control, balance and volume control as well as the usual source selector switch. In addition to these rotary controls, four "piano-key" buttons control loudnesscontour, stereo-mono mode, tape monitor and a novel new control identified as "volume." This latter control, when depressed, simply reduces volume level by a fixed 20 dB—a useful feature to use when the phone rings and you don't want to upset your
pre-set volume level for later listening. In the costlier Model 202 receiver, by the way, this control is replaced by an FM interstation muting switch—another difference between these two models.
The upper, blackout portion of the panel includes a wellcalibrated (every MHz) dial scale for AM and FM tuning together with a linear logging scale, a peak-reading tuning meter (above which is printed the word "stereobeam" which becomes brightly illuminated in the presence of an incoming stereo FM signal) and a large tuning knob, coupled to a moderately effective flywheel. Stereophone jack facilities at the lower left of the panel complete the front layout.
The rear panel includes input jack pairs for Phono, Aux I and 2 and Tape, a pair of Recorder Out jacks, an antenna terminal strip for FM antenna connection (300 ohms), and external AM antenna. Speaker terminals for both main and remote speakers are widely spaced to prevent possible shorts. An FM attenuator switch introduces a resistive attenuator network in the antenna circuit when switched to the "local" position. A pivotable AM ferrite antenna, an a.c. convenience outlet, fuses for a.c. and speaker lines, and a grounding terminal screw complete the rear panel layout.
Modular printed circuit board construction is used throughout the Model 201, as can be seen in the internal view. Separate AM and FM front ends are utilized, the latter being fully sealed in a metal shield housing. Separate modules are used for the i.f. stages, preamplifier, control amplifier, power amplifiers driver (a pair of identical p.c. boards), multiplex FM and power supply parts for a total of nine separate modules. Power output circuitry utilizes a pair of NPN transistors in a push-pull configuration, driven by a complementary NPN-PNP pair of drivers, eliminating the need for driver or output transformers. Supply voltage is 62 volts, with center voltage factory-adjustable to exactly 31 volts for perfect symmetry of output and absence of cross-over distortion. One channel of power amplifier circuitry is shown in Fig. 3. Tone controls are of the popular Baxandall (variable crossover feedback) type. The FM i.f. section includes integrated circuits for gain and limiting, an input bi-polar NPN transistor and a conventional ratio detector.
Fig. 1-Showing the rear panel of the Fisher Model 201.
Test Measurements
While the published specifications which appear in the instruction manual for the Model 201 are not specifically listed as guaranteed minimums, our measurements would tend to con-
firm that this is in fact the case-either that or Fisher is being extremely conservative in its statement of specs. Too many of the measurements we made turned out to be much better than claimed. For example, IHF sensitivity (which Fisher claims to be a modest 2.5 microvolts) was measured at 1.9 µV-the equal of far more expensive receivers. Ultimate signal-to-noise ratio actually measured a very superior 73 dB (as against only 60 dB claimed by the manufacturers). These findings are illustrated graphically in Fig. 4. THD in mono conformed exactly to the 0.5% claimed, and full limiting was achieved at just under 2 microvolts. As for stereo FM separation, the 35 dB figure claimed was exactly met at mid-band frequencies but, perhaps more importantly, at least 30 dB of separation was maintained all the way down to 50 Hz, while high end (15 kHz) separation was never less than 25 dB, as shown in Fig. 5.
The power amplifier section did better than claimed as well. We measured 22 watts per channel rms before reaching the rated harmonic distortion of 0.8%, and that was with both channels driven. At all power levels below 18 watts per channel, THD measured less than 0.1%. As for IM distortion we did not reach the rated 1.2% stated by the manufacturer until the amplifier was producing a total of 23 watts per channel. The curves of these measurements are presented in Fig. 6 and in the case of IM, at all power levels below 12.5 watts, measured IM was less than 0.1%.
Power bandwidth, shown graphically in Fig. 7, was just a bit better at the low end than claimed and equalled the manufacturer's claims for the high end, extending from 22 to 20,000 Hz. Hum and noise on Phono exactly equalled the 65 dB claimed while in the case of high level inputs such as AUX and Tape Monitor, we measured hum and noise at 80 dB below rated output, as against the modest 65 dB claimed in the published specs.
Frequency response extended from 20 to 23,000 ± 2 dB with a fairly rapid roll-off above and below these frequency extremes. Tone control action, illustrated in Fig. 8 conformed with claims in the bass region, but was a bit less than fullrange in the treble range, where maximum range measured 22 dB (+12, -10) at 10 kHz, as opposed to the 24 dB total claimed. Square wave response for a frequency of 10 kHz tended to be a bit rounded because of the rapid roll-off above 20 kHz, but there was no evidence of "ringing" or overshoot.
Listening Tests
We used the Model 201 receiver with medium efficiency as well as with low efficiency speaker systems. In the case of the higher efficiency systems, we were able to produce "concert hall" volume for recordings having wide dynamic range with no evidence of break-up at either frequency extreme at volume settings of about "9 o'clock." In the case of the low-efficiency systems, however, the amplifier seemed to "labor" in an attempt to give us equivalent loudness and there was evidence of lowfrequency distortion, particularly when we tried to add a moderate amount of bass boost by means of the tone control. Twenty watts, however honestly produced, is just a bit on the low side for driving some makes of speakers-and it follows that an attempt to use two sets of low efficiency systems. operating simultaneously in different rooms, would further emphasize this limitation. Though we haven't had an opportunity to measure the Model 202 "first cousin" receiver, we suspect that its extra few watts per channel would have made the difference here. The Model 202 boasts 25 clean watts per channel rms. At lower listening levels, however, the 201's sound was extremely clean and the combined use of the loudness control at mid-volume settings, together with a moderate amount of bass boost and treble emphasis (to take care of our some-
Fig. 2-Showing the Fisher Model 201 from above.
Fig. 3—Schematic diagram of one channel of the power amplifier section.
Fig. 4-FM performance characteristics.
Fig. 6-IM and THD distortion levels.
Fig. 7-Power bandwidth.
what "soft" listening room), provided musical reproduction such as we have come to expect from more expensive units. Of course, frills such as high and low frequency filters are missing, in the interest of economy, but with good source material on hand, such devices are seldom used by most listeners anyway. Transient response was good, and hum and noise in all services was adequate. Tracking of the volume control, by the way, was excellent and we found it unnecessary to readjust the balance control even at very low background-music listening levels. Perfect balance was maintained when the "volume attenuator" described earlier was used, and it is, by the way, a worthwhile feature that might well be incorporated in other models.
In deciding whether or not to spend the extra $50.00 for the step-up Model 202, be guided primarily by the amplifier differences, since the tuner sections (aside from the muting circuit available on the higher priced model) are identical, we are informed by the manufacturer. And quite amazing tuner sections they are, as far as FM and stereo FM reception are concerned. Since the FM front end uses an FET transistor as an RF amplifier, we question the wisdom of having incorporated the "Local-Distance" antenna attenuator switch on the rear of the set. In our listening situation, we were never bothered by overload or alternate channel interference, despite the nottoo-impressive alternate channel selectivity specifications of the receiver. Of course, others close to strong local stations may find this feature useful but it seems to us to be just another switch which the customer may inadvertently leave in the "local" position, resulting in extremely reduced sensitivity (and a possible needless service call).
We logged over 48 "listenable" FM stations, using a 4-element directional outdoor antenna and a rotator. Some 20 of these were received in stereo, and we found the "stereobeam" indicator to be positive in its indication-never lighting on interstation noise. Calibration was accurate, and there was no significant evidence of drift even after several hours of use. The circuitry does not employ any A.F.C. by the way.
AM reception was adequate though sensitivity seemed a bit lower than that in other sets we have recently tested. The serious AM "DX'er" would probably want to avail himself of the external antenna provisions which come with this set. Alignment and calibration on AM were perfect, however, and the tuning meter is active in this service as well as in FM.
Fisher's entry into the "under $200.00" receiver market should be a welcome bit of news for those budget-minded beginners or even seasoned audiophiles who have always "wanted a Fisher" but could not afford one. The introduction of the Models 201 and 202 by that company is not likely to mar their "quality" image, as they have certainly built in about as much value for the price as anyone could.
Check No. 132 on Reader Service Card
Fig. 8—Tone control, frequency response, and loudness contour characteristics.
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