Quartz-locked PLL frequency synthesizer tuning Digital frequency display with 12 station memory Switchable wide/narrow IF bandwidth
All-electronic digital tuning becomes a reality in high performance audio equipment with the new Sanyo PLUS T55 tuner. The first radical departure in tuner design in four decades, the combination of electronically tuned varactor front end and digitally programmable guartz crystal reference oscillator used by the T55 give it superb audio performance, virtually perfect tuning stability, plus another extremely important benefit: it is impossible to mistune a station with the PLUS T55. As long as the station's frequency appears in the bright fluorescent digital display and the "center tune" indicator is lit, you are assured of being perfectly tuned at the exact point of minimum noise and distortion for the station of interest (this is not true of all tuners using quartz-lock in their designs)
In addition to this landmark development in tuning precision, the PLUS T55 offers a collection of other advanced features which add up to a level of operating convenience and audiophile sound quality seldom found in any component tuner, let alone at the T55's relatively modest price. Thus, the slim new T55 is yet another eloquent expression of the philosophy underlying Sanyo's PLUS SERIES.
CIRCUIT FEATURES
Quartz-locked frequency synthesizer tuning.
There is good reason for the increasing use of quartz crystal oscillators in home audio equipment — they are among the most stable and precise ways known for measuring time and frequency. In fact, commercial broadcasters rely on quartz oscillators to maintain the extreme frequency accuracy required of them by law. It is only the high cost of quality crystals that has prevented them from being used on a one-per-channel basis in home radio and TV receivers. Once it has been cut, a quartz crystal can be operated at only one frequency, and is useless for receiving other stations.
Recently, however, high speed digital technology has come to the rescue, and finally made the quartz-controlled receiver a practical possibility for home use. The breakthrough that made this advance possible was the development of the programmable Phase Locked Loop frequency synthesizer. This revolutionary circuit permits a single quartz crystal oscillator to serve as a reference standard for an almost unlimited number of other frequencies — with full quartz accuracy on all.
This is accomplished by digitally dividing the frequencies of the quartz oscillator and the controlled oscillator by different whole numbers, to produce a common lower frequency. The "divided down" signals from the two oscillators are then phase locked together, with a correction signal that automatically tunes the controlled oscillator to keep the two divided signals precisely in phase. (As a simple example, one could phase lock a 5 MHz oscillator to a 2 MHz reference by dividing their signals by 5 and 2 respectively, producing two signals of 1 MHz which can be "locked".)
Tuning an FM station involves two separate processes: tuning the "front end" circuits to respond to the desired station while rejecting other signals, and adjusting the tuner's "local oscillator" to a frequency exactly 10.7 MHz higher than the station frequency, so that when mixed with the RF signal, it will produce a 10.7 MHz "difference frequency" for further processing by the carefully tuned 10.7 MHz IF section (AM tuning is similar, with a 455 kHz IF.)
In the PLUS 155 both tuning functions are performed automatically under programmed control (see diagram). When a station frequency is entered in the digital display (either manually with the tuning knob or by recalling it from memory) the programmable counter is loaded with the proper frequency divisor to ensure quartz lock at the desired local oscillator frequency.
The voltage developed by the phase comparator and low pass filter is routed to four varactor tuning diodes in the FM front end. One of these varactors adjusts the local oscillator frequency to maintain "lock", while the other three vary the tuning of the three RF stages in the front end.
Thanks to the precise digital programming of the frequency synthesizer
system, it is always perfectly "on target". With other digital quartz locked systems, the receiver's front end may be significantly mistuned from the optimum reception point, and the system will still indicate "lock". But the T55 guarantees tuning perfection, with optimum audio performance without critical fine tuning for minimum distortion.
Selectable IF bandwidth.
The T55 provides a two position IF bandwidth switch which allows optimizing IF response for particular signal conditions. Choose narrow bandwidth for an incredible 80dB of alternate channel rejection —
unbeatable for separating stations on a crowded FM dial. Where interference is less of a problem, choose the wide position, and enjoy extra-low harmonic distortion for measurably cleaner sound reproduction.
12-station memory tuning
Once you have a favorite station tuned in, press the memory button to enter it in one of the T55's twelve station memories. From then on, tuning the station is simply a matter of touching one of the six memory buttons. An LED above each button lights to indicate which pretuned station is
selected. Each button stores both an AM and an FM frequency.
Variable FM muting threshold.
Rather than limiting you to a single FM muting threshold, the PLUS T55 provides a choice of two (in addition to "off"), so you can choose to hear only the strongest,
highest quality signals, these signals plus somewhat weaker signals, or all signals regardless of strength.
Fluorescent signal strength and centertuning display.
Conventional mechanical signal strength and center-tuning meters are replaced in the PLUS T55 by a unique fluorescent display. A 5-section "bar graph" indicates incoming signal strength, while a 3-point indicator shows when center of channel has been accurately tuned by hand (although this is not critical for proper reception).
Four pole, double-tuned FM MPX filter.
The PLUS T55's audio processing circuits contain a unique passive 4-pole LC filter to remove multiplex signals from the audio output. While most MPX filters are concerned with rejecting only the 19 kHz multiplex pilot tone, the T55's filter is double-tuned, with deep "notches" at both 19 kHz and 38 kHz (the frequency of the multiplex subcarrier). Thus, the high frequency subcarrier cannot interact with
the bias frequency of tape decks, producing audible "beats". The pilot tone canceling circuits used in some tuners cannot provide this 38 kHz rejection.
Band/mode selector.
Lets you choose AM reception, or two FM modes: "auto", with automatic switching to stereo mode in the presence of a multiplex signal, and "mono", which suppresses stereo information in all signals, allowing noisy stereo signals to be heard with improved quality. In the auto mode, a front panel LED illuminates when a stereo signal is tuned.
Dual impedance antenna inputs.
The T55's built-in balun (balancer/unbalancer) lets it accept FM signals from either 300 ohm balanced antennas, or 75 ohm unbalanced feeds (including cable systems).
Sophisticated IC AM section.
The PLUS T55's AM section uses a sophisticated IC "chip" containing the complete front end, local oscillator, mixer,
IF, detector, and AGC subsystems. When combined with the double-tuned front end and dual-element ceramic IF filter, this advanced integrated circuit delivers clear, sensitive reception and reliable operation.
CHASSIS FEATURES
The PLUS T55's handsome, satin-black finish is designed to complement other PLUS SERIES components as well as professional-style components from other manufacturers. With the supplied rackmounting ears attached, the tuner fits perfectly into a standard 19" EIA equipment rack, occupying a single 134" vertical space. Unlike many "rack mountable" consumer components the T55 incorporates special precautions against the problem of ground loops when rack mounted with other components, a frequent source of hum, buzzes, and RF interference with incorrectly designed rackmount systems. To prevent any possibility of contact oxidation, the PLUS T55's output jacks are gold plated. Conventional output jacks may develop
thin metal oxide coatings which cause partial rectification of low level signals, serving to create harmonic distortion, and even operating as a "detector" for certain kinds of RF interference.
Like all PLUS SERIES components, the T55 promises a uniquely satisfying experience to the music lover who is sensitive to the fine points of audio reproduction.
Sanyo's new PLUS SERIES includes a variety of components in professional black finish, with rackmount capability. Handles (supplied with each unit) attach to the chassis sides, and permit secure mounting in EIA-standard 19 inch equipment racks.
PLUS SERIES philosophy
Sanyo PLUS SERIES ™— a new collection of ultra-high performance audio components designed, literally from the ground up, to excel in every way: outstanding specifications, useful "human-engineered" controls, features combining the best of traditional functions with unique new solutions, and styling of enduring beauty — plus , most importantly, audio reproduction quality that transcends simple formulas and numerical specifications.
This distinguished new series is the result of a unique design and production concept. Within one of the world's largest and most diversified electronics companies, we set up an independent team of audiophile-engineers and gave them full freedom to draw on Sanvo's massive technological capability. A major part of their assignment was to devote special attention to eliminating those small but audible departures from sonic reality - problems that seldom show up on spec sheets or test benches, yet can make the difference between sound that is merely good, and sound that communicates a spine-tingling sense of life, openness, and "air."
To support the PLUS SERIES group, Sanyo produces virtually every part required by their designs: transistors, capacitors, integrated circuits (both analog and digital), circuit boards, motors, meters, frames, knobs, cabinets to name only a few. We control our quality to tolerances far stricter than outside suppliers can match. We back up our production systems with 30 years of know-how from
our consumer and industrial electronics divisions.
Computerized component evaluation with automatic printout of test results.
The development of the Sanyo PLUS SERIES was one of the most difficult goals we have ever set for ourselves: to produce true "state of the art" audio components embodying the enlightened aesthetic and technological perspectives of the 1980's, and to make them available at a cost only slightly greater than the best of today's mass-produced audio equipment.
Our success — or failure — in achieving this almost superhuman goal can be evaluated now by arranging an audition with a PLUS SERIES dealer.
SPECIFICATIONS
| FM | THN | FD | SE | ст | ON |
| 101 | 95 | ••• |
| Frequency Range | 88-108 MHz | |
|---|---|---|
| Usable Sensitivity | ||
| Mono | 10.3 dBf (1.8 µV) | |
| 50 dB Quieting Sensitivity | ||
| Mono | 14.7 dBf (3.0 µV) | |
| Stereo | 36.3 dBf (36 µV) | |
| Total Harmonic Distortion (Narrow/Wide) | ||
| Mono 100 Hz | 0.15%/0.1% | |
| 1 kHz | 0.15%/0.09% | |
| 6 kHz | 0.3%/0.15% | |
| Stereo 100 Hz | 0.3%/0.15% | |
| 1 kHz | 0.2%/0.1% | |
| 6 kHz | 0.3%/0.2% | |
| Frequency Response | 20 Hz-15,000 Hz: | |
| + 1,-2 dB | ||
| Alternate Channel Selectivity at | ||
| ±400 kHz (Narrow/Wide) | 80 dB/55 dB | |
| Capture Ratio (Narrow/Wide) | 1.8 dB/1.2 dB | |
| AM Suppression Ratio | 60 dB | |
| Stereo Separation (Narrow/Wide) | ||
| 1 kHz | 42 dB/48 dB | |
| 10 kHz | 35 dB/40 dB | |
| Spurious Response Rejection (98 MHz) | 80 dB | |
| Image Rejection Ratio | 70 dB | |
| IF Rejection Ratic (98 MHz) | 90 dB | |
| Muting Threshold | 5 µV | |
AM TUNER SECTION
| Frequency Range | 525-1620 kHz | ||
|---|---|---|---|
| Usable Sensitivity (Ferrite - | |||
| External Antenna) | 300 V/m-30 #V | ||
| Signal-to-Noise Ratio (at 5 mV/m) | 45 dB | ||
| Selectivity | 35 dB | ||
| Image Rejection Ratio (1000 kHz) | 50 dB | ||
| IF Rejection Ratio (1000 kHz) | 45 dB | ||
GENERAL
| 17¼" x 1¾" x 10% | |
|---|---|
| handles attached) | |
| 8.4 lbs. | |
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