A
Quartz Synthesizer Tuner That ls a Worthy Source of High Fidelity
The ST-S7 tuner
provides listening quality which will convince you that FM broadcasts can, in
fact, be sources of superb sound. To achieve this high level performance, we
have departed from conventional tuner design in several areas. Two of the most
significant design elements are the incorporation of digital signal processing
technology and the introduction of DC amplification and detection (which is
impossible to achieve through conventional analog designs). Benefits of this
design include improved stereo separation especially in the low-bass range, for
a faithful reproduction of musical ambience. This is achieved along with a very
high selectivity of 85 dB (±400 kHz) indicating no trade off of selectivity vs.
Separation as is the case with conventional designs.
We've
also taken full advantage of the quartz synthesizer's potential by providing an
optional FM antenna tuning control with our remarkably effective SH-F101
compact room antenna. All this is contained in a sleek, slim tuner with a 43.6 mm (1-23/32") high front panel. In
appearance as well as performance, the ST-S7 is an excellent match for the
recently introduced Technics "New
ClassA" amplifiers.
DC Amplification, DC
Detection, and DC Stereo Decoding for Excellent Sound Quality
DC capability has
recently been introduced to amplifiers. Even though tuners are intended to
handle the same audio signals as amplifiers, little progress has been made,
until now, in DC tuner technology.
The instability of
the local oscillator frequency produces this situation. In a superheterodyne
dial-type tuner, a drift in local oscillator frequency creates inaccuracy in
the IF center frequency. This results in increased distortion, which is caused
by DC voltage in the detector. In a conventional analog tuner, this
"output without input" can be corrected, but not prevented. Analog
tuners employ AFC (Automatic Frequency Control) to correct this problem, but
AFC handles all the DC voltages in the detector stage as erroneous signals.
This makes it impossible to provide amplification and detection down to DC.
Unlike
the conventional analog tuners, a
quartz synthesizer tuner's local oscillator frequency is stabilized by the
extremely precise quartz oscillator frequency. Since there is no need for AFC,
this makes DC amplification (including the RF stage, DC detection, and DC
stereo demodulation) possible.
By taking advantage
of the inherent potential of the quartz synthesizer approach, we have produced
the world's first DC tuner. ln addition to such a significant innovation, we've
also added other useful features which imorove performance, like a balance detector
output tor connection to the MPX stage.
DC Peak Sample and
Hold MPX Circuitry Excellent Stereo Separation
The
ST-S7 exhibits very high FM selectivity of 85 dB (±400 kHz),a figure that is
rarely matched with conventional designs. Normally, tuners with such high selectivity
have sacrificed in the areas of distortion and stereo separation. But in
the ST-S7 the employment of DC peak-sampling holding circuitry has removed this
design conflict. Wide stereo separation (55 dB at 1 kHz) is achieved despite the high selectivity of
85 dB and distortion is only 0.15% stereo. The keys to success are DC
capability in the detector and MPX stages and the digital sample/hold processing of the 38 kHz stereo subcarrier, which
replaces the conventional switching decoder method. Because of the high
sampling rate, additional information is obtained from the stereo channels.
Moreover, frequency separation is
un affecled by the potential
instability of the 19 kHz pilot signal until the point of complete detuning.
25 kHz Quartz
Reference Frequency
The
reference frequency of the ST-S7's
quartz synthesizer tuner is 25
kHz; most other quartz tuners use a reference frequency of 5 kHz. This is but
one measure of the ST-S7's superior performance. Although it may seem
contradictory to find a reference frequency within an audio band, this arose
because of the ready availability of an lC that was originally developed for
car stereo tuners. When the 5 kHz reference frequency of this lC leak sin to the audio signal path, a low-level whistling sound is produced.
Distortion may not be audible in the relatively noisy environment of an
automobile; but it is undesirable, to say the least, in a high quality tuner like the ST-S7. Therefore, we developed our
own lC specifically for quartz synthesizer tuners. This new lC produces a
highly stable reference frequency of 25 kHz, safely above the audio frequency
spectrum.
Back-to-Back High-Q
Varactors and MOSFET Front End to Prevent lM Interference and Provide High
Sensitivity
On
a crowded FM band, it is particularly
important to eliminate lM interference (which is caused by interference of three nearby broadcast
frequencies) in the tuner's RF stage.
In the ST-S7, our back-to-back varactors (equivalent to a
four-ganged variable capacitor) control capacitance through an applied DC
potential rather than the manually controlled variation in capacitance found in
dial type analog tuners. These varactors exhibit a very high Q so that only the
desired broadcast frequency is selected, and intermodulation products from
nearby stations are effectively avoided. The 4-pole MOS FET RF amp provides
superb sensitivity of 20 µV (78 Ω )/46
dB quieting.
IF Staqe Ceramic
Filters Have Outstanding Group Delay
Characteristics to
Provide High Selectivity and Low Distortion Selectivity is extremely important
on a crowded FM dial. With conventional tuners, you have two choices: a wide lF
band with low distortion or a narrow lF band with higher selectivity and higher
distortion. Because of this, some tuner sare provided with switchable
wide/narrow lF bands.
In this tuner, we
have succeeded in achieving both low distortion and wide selectivity by using
three very carefully manufactured and selected 4-element ceramic filters which
have very flat group-delay characteristics. Without resorting to lF band switching,
we've attained a very high selectivity of 85 dB (± 400 kHz), while distortion
is a very low 0,1% (mono); 0,15% (stereo)
Extremely
Easy and Accurate Tuning with Quartz Synthesizer Preset Buttons for a Total of
16 Stations, 8 AM and 8 FM, Plus Quartz
Lock Indicator
Perhaps the greatest
advantage of quartz synthesizer tuning is that virtually perfect tunig can be
achieved easily and quickly. Moreover, this completely electronic tuning system
readily lends itself to preset capability, thereby eliminating the need for
signal strength or center tuning meters.
To
"manually" tune the ST-S7, you just press the UP or DOWN button. This
lets you electronically scan the dial as long as you keep either the UP or DOWN
button pressed. When you reach the desired broadcast frequency, the locked
indicator lights up, indicating that the station that you have selected is
precisely tuned in.
Built-in
Programmable Timer for On/Off Tuning of Three Programs
The
Technics-developed micro processor.
Utilized for our quartz-synthesizer tuning, is so powerful that it can also
provide a programmable timer function. This allows you to program the tuner to
tune in the stations you want at the
times you choose. The programmable timer can be set to turn two programs off
and on every day, and an additional program for one particular time and day of
the week. So the tuning of three programs can be left entirely to the tuner.
The timer also controls the power to the tuner's switched AC outlet so that
your amp or tape deck will turn on at the same time as the programs are tuned
in.
This
tuner is equipped with a 24-hour quartz clock which provides great accuracy (+
10, -0 seconds per month). In fact, it can serve as a digital clock when the
TUNER OFF button is pressed.
To
program the timer, simply set the program selector to WRITE and Dress the preset buttons for the times you want. Of
course, you can cancel in the middle of a program (CANCEL) or check your
setting (READ). While listening to a program, you can check on the preset time
by pressing the CLOCK CALL button. The time will be displayed for about five
seconds; then the tuned-in station's frequency will reappear on the digital
display.
Specifications
FM
Tuner Section
Frequency
Range: 87,5 - 108,0 MHz
Sensitivity
S/N 30 dB : 0.95 µV (75 Ω
)
S/N 26 dB : 0.85 µV (75 Ω
)
S/N 20 dB : 0.75 µV (75 Ω
)
IHF Usable
Sensitivity : 0.95 µV (IHF '58 )
IHF S/N 46 dB Stereo Quieting Sensitivity: 20 µV
(75 Ω )
Total Harmonic
Distortion
MONO : 0,1%
STEREO : 0,15%
Signal-to-Noise
Ratio
MONO: 69 dB (77 dB IHF)
STEREO: 65 dB (72 dB IHF)
Frequency Response:
5 Hz - 18,000 Hz (+
0,2 dB . - 0,5 dB)
5 Hz - l8 kHz (± 1,5
dB)
Alternate Channel
Selectivitv: 85 dB (±400 kHZ); 55 dB (±300 kHz)
Capture Ratio: 1,0 dB
lmage Rejection (at
98 MHz): 80 dB
lF Rejection (at 98
MHz): 110 dB
Spurious Response
Rejection (at 98 MHz): 95 dB
AM Suppression: 55
dB
Stereo
Separation: 55 dB (at 1 kHz); 40 dB (at
10 kHz)
Carrier Leak:
At 19 kHz : -65 dB (-70 dB, IHF)
At 38 kHz : -48 dB (-50 dB , IHF)
Channel
Balance: 250 Hz - 6300 Hz ±1,0 dB
Limiting Point: 0,7 µV
Bandwidth
iF Amplifier: 180 kHz
FM Demodulator: 1000 kHz
Antenna Terminals: 75 Ω (unbalanced) F-type
coaxial
AM Tuner Section
Frequency
Range:
530 - 1620 kHz (10
kHz step)
522 - 1611 kHz (9
kHz step)
Sensitivity: 30 µV , 250 µV/m
Selectivity: 55 dB
Image Rejection at
1000 kHz: 45 dB
IF Rejection at 1000
kHz: 50 dB
Timer Section
Clock: Quartz-lock type 24-hour indication
Precision: Within 0 to =10 sec. Monthly (at 25°C)
Function: 24-hour programmable every day: 2 times; once
only: 1 time
Programmable
Contenet: Program source (FM,AM), Power
On/Off timing; Designation of preset stations
Setting
Intervals: 1 minute - 23 hours, 59
minutes
Priority Order: Once, everyday 2, everyday 1
Memory
"back-up": about 3 months
(without AC power)
General Section
Power
Requirements: AC 110/120/220/240 V 50/60
Hz
Power
Consumption: 9,9 W
Batteries: DC 45 V (3 "AA" size)
Dimensions (W x H x
D): 430 x 53 x 310 mm (16-15/16" x
2-3/32" x 12-7/32")
Weight: 4,0 kg (8,8 lbs)
