MANUFACTURER'S SPECIFICATIONS
Tuner Section, FM. Sensitivity, IHF: 2.0 µV. S/N: Better than 60 dB. THD, Mono: 0.3%. Capture Ratio: 2.5 dB. IF Rejection: 70 dB. Image Rejection: Better than 50 dB. Spurious Response Rejection: Better than 75 dB. AM Supression:-70 dB. Stereo FM Separation, 1kHz: 40 dB. Tuner Section, AM. Sensitivity, External Antenna: 20 V. Image Rejection:-75 dB. I.f. Rejection:-80 dB. Amplifier Section. Power Output, rms, both channels driven, 8 ohm loads: 50 watts per channel; 4 ohm loads: 60 watts per channel. Rated THD: 0.3% Rated IM Distortion: 0.3%. Frequency Response: 10 Hz to 50 kHz +1 dB. Power Bandwidth: 15 Hz to 30 kHz. Damping Factor: Greater than 50 at 8 ohms. Hum and Noise: Volume control at minimum, better than 75 dB; Phono inputs, better than 60 dB, with reference to rated sensitivity and output.
General. Dimensions: 18 1/2 in. W. by 13 3/4 in. D. by 6 in. H.
Retail Price: $550.00, optional walnut exclosure extra.
If the name seems unfamiliar, a word of explanation may be in order before discussing this outstanding receiver from BIC/LUX. BIC stands for British Industries Co., the people who introduced and popularized the Garrard record changers in the United States. Lux is a well-known and respected audio equipment manufacturer in Japan which has been in the business of producing high quality audio equipment there for over four decades. The introduction of the Model 71 /3R to this country (Lux products are already widely distributed in Europe) represents British Industries' entry into electronics, and a most auspicious entry it is, too. The amplifier section of this all-in-one receiver outperforms just about every separate integrated amplifier in this power category, while the tuner section sports a new form of center-tuning sensing circuitry which makes it a joy to use.
To begin with, the 71/3R is a BIG unit, ruggedly built and beautifully packaged. Signal source selection is accomplished by means of a vertical row of push buttons at the left of the panel. External inputs include a pair of phono stereo inputs (2 mV and 10 mV sensitivity) and a pair of high-level auxiliary inputs. The black-out dial area becomes illuminated in white light when the AM button is depressed and in green when FM is selected. When other sources are chosen, the dial scale itself vanishes and the selected source is designated in illuminated red letters in the lower portion of the blacked out dial area. The dial area also contains a signal-meter, a massive tuning knob coupled to an effective flywheel, and the CENTER-TUNE indicator light. Stereo reception is indicated by the word STEREO which becomes illuminated beside the CENTER-TUNE light. At the extreme right of the dial area are four miniature push-button/rotary control combinations. Three of these are used to pre-set favorite FM stations by means of adjacent miniature replicas of the main FM dial scale. Rotation of the pre-set knob sets desired pre-set frequencies while depressing the same knob (providing the main FM selector is also depressed) selects the given pre-set station automatically after it has once been set. The lowest of the four miniature controls is depressed for manual tuning.
This knob has two positions of rotation as well: one for "distant" FM reception and one for "local." The lower half of the extruded gold-anodized front panel contains the rest of the amplifier controls. Included are a pair of TAPE IN, TAPE OUT phone jacks (duplicating the tape jacks on the rear panel), a TAPE MONITOR switch, a stereo-mono MODE Switch, BASS and TREBLE controls (dual concentric knobs enable adjustment of bass or treble for left or right channels separately), switches for Low and HIGH filters and LOUDNESS compensation, dual concentric, clutch-action volume controls, MAIN and REMOTE speaker switches, a stereo phone jack, and a separate push-push power ON/OFF switch. Two departures from conventional receiver design should be noted. For one thing, there is no balance control. Since dual concentric, clutched volume controls are used, once relative level between left and right channels has been established, the two controls operate together, maintaining perfect tracking at other volume settings. Most conventional balance controls inevitably intro duce passive gain loss, but by eliminating their need in this way, the BIC/LUX 71/3R actually picks up a couple of dB of signal-to-noise advantage while still affording a means for perfect left-right balance. The second departure from conventional design are a pair of turnover selector knobs, each associated with its respective pair of tone controls. The problem with most tone control circuits is that however well calibrated they may be, they tend to lift or attenuate several octaves of the audio spectrum. Thus, if a bit of adjustment of, say, all frequencies below 150 Hz is required, resetting the bass control of most sets will also affect frequencies up to 500 or 1000 Hz. If attenuation is required, low and high frequency filters often can accomplish the desired effect, but if slight boosting of the "ends" of the spectrum is needed, this receiver's tone control arrangement facilitates such correction.
Each "turnover" selector has four settings (OFF, 150, 300 and 600 for the bass side and OFF, 6K, 3K and 1.5x for the treble) which determine the frequency at which boost or attenuation begins. In the OFF positions, the tone controls are removed from the circuitry entirely, insuring perfectly flat response for the purists. Variable crossover selection is sometimes found on the very best integrated amplifiers but this is the first time we've encountered it on a complete receiver.
The rear panel layout of the BIC/LUX 71/3R receiver, shown in Fig. 1, contains, in addition to the main line fuse, a pair of speaker fuses, one for each channel. Two unswitched and one switched convenience a.c. outlets are provided, and antenna connections are available for either 75 ohm or 300 ohm transmission lines, as well as for an external AM antenna wire. Speaker terminals are spring loaded so that the stripped end of your speaker wire is firmly gripped when the terminal is released. This arrangement almost precludes the possibility of "short circuits." An AM ferrite antenna rod can be swung away from the chassis surface to minimize the attenuating effects of the metal heat sink. The usual array of input and output jacks and a grounding terminal completes the back panel layout.
The internal layout of the chassis contains 11 modular sections, some of which are mounted below chassis surface and can therefore not be seen in Fig. 2. Of particular interest to us was the unique CENTER TUNE circuitry, which British Industries Co. (with some justification) has called a COMPUTER circuit. A close-up view of the FM i.f. and COMPUTER circuit board (Fig. 3) gives an idea of its complexity. Actually, the FM i.f. circuits occupy only the upper third of this p.c. board.
The entire lower section is devoted to the COMPUTER circuitry which utilizes no less than 18 transistors, eight signal diodes, and four extra tuned circuits. This circuit, in effect, senses three signal characteristics, noise, distortion, and accuracy of tuning. What's more, it operates for both FM and AM reception, allowing only perfectly tuned signals to be heard. In its FM use, the circuit is quite different from any conventional muting circuits which we have seen. When the LOCAL DISTANT switch is set to the DISTANT position, signals as low as 1.5 µV will be heard when properly tuned in, and yet there is absolutely no interstation noise present even when such weak signals are detuned. Further, there is no transitional region. That is, the signal is either received with minimum distortion or it is rejected-and no sound whatever is heard. As you tune across the dial, signals are received or "turned on" with absolutely no popping or clicking sounds and as you leave each one, the sound is again "turned off' without any "side effects." Interestingly, the signal strength meter (which might seem redundant) serves a useful purpose in the tuning procedure. As you approach a station frequency, the meter needle begins to deflect--often quite a bit-long before sound is heard. At one exact point in the "cresting" of the meter needle, sound comes on--and the CENTER-TUNE light becomes illuminated, indicating that perfect tuning has been achieved.
The power amplifier modules (seen mounted perpendicular to the chassis surface in Fig. 2) are fully d.c. coupled circuits, requiring no output coupling capacitor. Input stages are differential amplifiers and the output circuit is a complementary type. A schematic of this section (one channel) is shown in Fig. 4. Transistors Q758 and Q754, together with their associated diodes comprise a protective circuit and form a sort of bridge circuit in which the speaker load becomes one of the branches of the "bridge." Low values of load impedance, for example, cause Q759 and Q758 to turn ON and prevent the signal from being fed to the output stages when excessive current might otherwise flow. We can attest to the fact that the circuit is "short-proof" even when extended short circuits are maintained across the speaker output terminals. In fact, we wonder about the speaker line fuses--we could not cause them to "blow" under any conditions of short circuiting which we tried.
Fig. 1--Showing the back panel. Fig. 2--View from above.
Fig. 3--FM i.f. and COMPUTER circuit board.
Fig. 4--Schematic of power amplifier module (one channel).
Performance Measurements
Figure 5 plots various characteristics of FM performance of the 71/3R. As can be seen, measured performance exceeded claims, in that IHF sensitivity measured 1.7 µV. (IHF measurements are taken at 98 MHz. At 88 MHz least usable sensitivity was actually a bit better, measuring 1.6 µV, while at the high end of the band we measured 1.9 µV, again better than published claims). Ultimate S/N was a respectable 68 dB, but more importantly, S/N at a mere 5µV already measured 57 dB! To us, this figure is more meaningful than the IHF sensitivity, for it means that signals received with a signal strength of only 5 µV are noise-free and listenable. Interestingly, while the CENTER-TUNE circuits were set to about 1.5 µV in the DISTANT position, in the LOCAL position triggering took place for all signals having strengths above 5 µV. Thus, if you're interested in listening to stations that are both perfectly tuned and devoid of audible noise you merely have to set the switch to the LOCAL position and you are then assured that any station that "turns on" the computer circuits is arriving with a signal-to-noise ratio of at least 57 dB. Listeners who wish to DX have the option of the DISTANT position of the switch--at which setting they can receive signals down to 1.5 µV, which is about the practical and theoretical limit for FM. THD in MONO measured 0.2%, better than claimed, while in stereo we measured 0.4%. We could not pin-point the exact signal strength required for full limiting in Fig. 5, since it takes 1.5 µV of signal to "turn on" the audio, and by that time, full limiting was already in evidence! Stereo separation characteristics are plotted in Fig. 6 and, mid-frequencies the figure obtained was 42 dB (and was exactly the same in the opposite channel, not shown). At 50 Hz, separation was still in excess of 30 dB, while at 10 kHz we read a separation of 28 dB.
When we started to measure the power amplifier performance of the Model 71 /3R, we thought that perhaps we had gotten hold of a higher powered model (B.I.C. has announced a second receiver model which will feature higher power than the 71/3R while most other features will be similar.) Talk about conservatism! (Is it synonymous with the "British" in British Industries?) This amplifier section was not even near ready to quit at 50 watts per channel, both channels driven. In fact, we reached rated THD at 63 watts per channel, with 8 ohm loads. Intrigued by this "under-rating," we measured the output using 4-ohm loads and read 82 watts per channel before reaching rated THD (0.3%). At rated power output THD was a miniscule 0.07%. At no power level below rated did the THD exceed 0.1%, as can be seen in the curve of Fig. 7.
Power bandwidth was equally incredible. Only when we realized that BIC was quoting power bandwidth in terms of-1 dB from rated power (IHF standards dictate a-3 dB or "half power" reading), were we able to explain the discrepancy.
Using the -3 dB reading, the power bandwidth we obtained extended from 8 Hz to 35 kHz. More important, when we confined our measurements to the 20 to 20 kHz range, we were able to obtain 50 watts per channel at every frequency at less than rated THD. This is illustrated graphically in Fig. 9, along with THD readings at other, lower power levels. Figure 8 is a plot of power bandwidth, using the conventional IHF references.
Fig. 5-FM (mono) characteristics.
Fig. 6-Stereo FM separation characteristics.
Fig. 7-Distortion vs. power output.
Fig. 8-Power Bandwidth.
Fig. 9-THD vs. frequency at 1 watt and 50 watts per channel.
Fig. 10-Tone control range at the various crossover selections.
The action of the various bass and treble crossover settings is graphed in Fig. 10 and helps to further explain the advantage of this feature. The HIGH and Low frequency filter action is plotted in Fig. 11 and is seen to have slopes of only 6 dB per octave. Normally, we like to see 12 dB slopes in these filters but, frankly, with the extra flexibility inherent in the tone control variable crossover features, you're not likely to depend upon these filters for much anyway.
British Industries makes a point in their literature about the ability of this receiver to reproduce square waves accurately throughout the audible spectrum, so we thought we'd check this out as well. Rather than photograph square-waves at 100 Hz and 10,000 Hz, as is our normal practice, we decided to make things a little bit more difficult and used 20 Hz and 20 kHz. The results speak for themselves in Fig. 12. The only comparable square-wave performance we have ever run across was in an amplifier-preamplifier combination of somewhat higher power which sells for $700.00. The upper trace in each case is the input square wave as produced by our square wave generator. This is shown because it is not perfectly square at 20 Hz and we would not want to fault the 71/3R which is, in fact, reproducing just about what is fed to it.
Fig. 11--Filter characteristics.
Fig. 12--Square-wave response at A 20 Hz and B 20 kHz. Upper trace is input.
Listening Tests
Station logging with the BIC/LUX 71/3R we were able to receive 52 listenable stations when the receiver was set in the DISTANT setting. In the LOCAL position, this figure was reduced to 46, which means that six stations were previously received with signal strengths of between 1.5 and 5µV and were considered quite listenable. The gain of the FM section is such that it is possible to attain quite high listening levels at about 1 o'clock on the dual volume controls and it was therefore early in our listening tests that we began to realize that this amplifier was not the typical amplifier portion of a receiver. No matter what listening level we used this amplifier just refused to quit and exhibited a transparency and crispness which belies description. Fortunately, we do have a few carefully transmitted FM signals in our area (all too few, I must confess) and it is to these few that we listened extensively. One thing about a piece of equipment such as this is that it must be fed with good, clean program sources if its reproduction capability is to be fully appreciated. A new Columbia release of Santana served as our audition record in the PHONO input department and it is replete with those percussive and dynamic sounds that separate the superior amplifiers from their lesser cousins. The BIC/LUX 71/3R is definitely in the former category. In fact, this receiver should be auditioned by anyone interested in finding out what state-of the art solid state design has been able to achieve after only a decade of popular use. The tuner section is fine, the center tune feature is great to use, but that amplifier has got to be heard to be believed.
-Leonard Feldman
(Audio magazine, Feb. 1972)
Also see:
BIC America Venturi V-604 Speaker (Equip. Profile, March 1997)
B-I-C Speaker Systems (advertisement, Nov. 1978)
B-I-C VENTURI speakers (Sept. 1974)
VMPS FF-3 Speaker (March 1997)
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