YAMAHA CT-7000

Commentary

An FM stereo tuner designed with the assumption that all items will be marked with the best characteristics in the world.

In the development of the CT 7000, in order to thoroughly pursue the performance exceeding the limits of conventional measuring instruments, various measuring instruments with special specifications were newly developed first, and the limits that conventional measuring instruments cannot measure are pursued.

We are the first in the world to use an ultra-precision frequency number line 7-row varicon in the front-end section. By adopting a double-tuned antenna input circuit, we have obtained over 120 dB in image disturbance, 1/2IF disturbance, and local 2nd harmonic disturbance characteristics that cannot be measured by SG. This greatly improves multi-signal disturbance characteristics such as intermodulation characteristics and blocking characteristics at strong input.
Three low-noise -noise MOS-type FETs with excellent high-frequency characteristics are used for the two RF stages and the mixer stage to drastically reduce cross-modulation and realize a practical sensitivity of 2.0 μ V. In addition, the phase characteristics of the RF tuning circuit and the mixer stage are improved to suppress strong input characteristics and changes in sensitivity, distortion factor and separation depending on the tuning frequency.

In the IF stage, a block ceramic filter with a differential gain deviation within ± 0.2 dB is used Shinkai to achieve both low distortion rate characteristics and high selectivity.
In order to compensate for variations in the characteristics of conventional ceramic filters, this block ceramic filter is adjusted by combining L, C, and R with the input / output circuit of each filter element, matching the input / output impedance of each element, and realizing excellent filter characteristics close to the ideal.
Coupled with the excellent limiter characteristics of a high-gain 7-stage differential amplifier using an IC consisting of a constant current bias circuit, the IF stage of the CT 7000 achieves an effective selectivity of more than 85 dB, a capture ratio of less than 1.0 dB, an AM suppression ratio of more than 60 dB, and an SN ratio of more than 78 dB.

It uses a double IF circuit that can switch the IF band between Normal and Wide.
By switching the IF band to a wider band, it is possible to receive signals at a lower distortion rate for stations with strong electric field strength.

By developing and adopting a linear phase discriminator that minimizes differential gain deviation, we are able to support ultra-low distortion in block ceramic filters and broadband IF stages.
The characteristics are adjusted to minimize the distortion factor of each unit by a direct-viewing device, and the characteristics are maintained stable by adopting a direct-coupled two stage constant current drive circuit.

Yamaha's proprietary NFB switching method is used in the MPX circuit.
This circuit consists of a switching-type mean-value demodulation circuit with NFB as in the case of an audio amplifier. As a result, the distortion in the MPX circuit has an excellent value that cannot be measured by a stereo signal generator. In addition, this method does not require the conventional SCA filter, does not degrade characteristics by the SCA filter, greatly improves intermodulation distortion, and ensures sufficient high-frequency separation to provide excellent sound quality.
The subcarrier generation circuit uses a PLL to synchronize the phase with the input pilot signal. In addition, the 38 khz signal sent to the switching circuit is a square wave with duty ratio I, so extremely stable operation, high separation, low distortion rate, and high SN ratio demodulation can be obtained.
The PLL circuit is free from the influence of aging and temperature change like the tuning circuit by LC.

Yamaha's original active low-pass filter has excellent attenuation characteristics of more than 60 dB at 19 kHz and more than 80 dB at 38 kHz.
This filter also functions as a de-emphasis circuit, and has a value of ± 0.3 dB at 50 Hz to 10 kHz and + 0.5 -1.0 dB at 20 Hz to 15 kHz, providing clear playback sound up to the high range.

The low-pass filter and variable output terminal amplifier use a 3-stage direct circuit, and the buffer amplifier uses an emitter-follower circuit with a constant current load, so that the distortion of the audio amplifier system can be ignored.

Yamaha's original tuning circuit is used.
In this system, in order to maintain the tuning point with minimum distortion and maximum separation, AFC is applied to the FM front-end to limit the frequency drift of the FM front-end to 15 kHz at 25 ± 30 ℃.
This AFC circuit uses the electrostatic noise of the human body, and the Aita that is selected by touching the tuning knob is automatically canceled. Therefore, it can receive the weak radio wave adjacent to the strong electric field station without fear of the pull-in phenomenon.
In addition, the AFC/Station indicator lights faintly when the system is tuned to the station during tuning. When the system is tuned correctly and the knob is released, it lights brightly to indicate that the AFC is in operation.

The muting circuit is applied double to the input and output stages of the MPX circuit to eliminate all unpleasant inter-station noise and shock noise during 離局 and channel selection.
The muting level is variable, and a level adjustment knob is provided on the front panel to obtain the optimum muting effect according to the electric field strength of the receiving place. It can also be applied by changing the muting according to the purpose such as cutting the noise at the time of channel selection or receiving only strong radio wave.
The shock noise generated when the power switch is turned ON and OFF is also cut off by installing a muting circuit using FET.

In the conventional signal meter, the meter drive circuit is saturated at an input of 30 dB or more, and accurate meter indication is difficult. In the CT 7000, the meter is linearly swung up to 100 dB according to the antenna input level by applying AGC to the meter circuit.
In addition, a new S-M (signal-multipath) meter can monitor the quality of the received signal.

Equipped with auto-blend circuit.
The SN ratio can be improved without loss of frequency characteristics even when the antenna input level is ratio can be improved even when the antenna input level is the antenna input level is small.

Equipped with multi-path detection terminal.
By connecting an oscilloscope to this terminal and adjusting the direction of the FM antenna while observing the waveform, we can accurately find the direction that is least affected by multipath phenomena.

It is equipped with two antenna terminals, 300 Ω balanced and 75 Ω unbalanced.
There is also a connector for coaxial cable that is not affected by external noise.

A low-impedance IF output terminal is provided to support discrete FM4-channel broadcasting.

There are two types of output terminals, fixed and variable.

It has a headphone amplifier.
The 3-stage direct connection SEPP-OTL system is used for the circuit so that excellent sound quality can be enjoyed even with headphones.

Equipped with an illumination switch, dial lighting can be turned ON / OFF.

The sealing panel uses a machined thick aluminum plate.
In addition, the cabinet uses a real wood finish with casters (stopper).

The CT 7000 measures not only static distortion characteristics (harmonic distortion and intermodulation distortion), which are generally measured, but also Nikaido distortion, which measures dynamic distortion by adding a signal close to the actually used music signal.

Model Rating

Type	FM stereo tuner
Receiving frequency	76 to 90 MHz
Practical sensitivity	IHF Normal : 2.0 μ V Wide : 2.5 μ V DIN Nromal : 1.6 μ V Wide : 2.5 μ V
S/N ratio 50 dB Chinese arrowhead level	Mono Normal : 4 μ V Wide : 4 μ V Stereo Normal : 50 μ V Wide : 50 μ V
Image interference ratio (84 MHz)	120dB
IF Interference Ratio (84 MHz)	120dB
Spurious interference ratio (84 MHz)	120dB
AM suppression ratio (IHF)	60dB
Capture ratio	10 μ V Normal:2.0dB Wide:3.0dB 1mV Normal:1.0dB Wide:0.7dB 100mV Normal:0.7dB Wide:0.6dB
Effective selectivity (IHF)	Normal:85dB Wide:18dB
Intermodulation Interference (2 MHz)	100dB
Signal-to-noise ratio	mono:78dB stereo:75dB
Total harmonic distortion factor	Mono 400Hz Normal:0.06% Wide:0.04% 50 to 10 kHz Normal:0.2% Wide:0.08% Stereo 400Hz Normal:0.06% Wide:0.04% 50 to 10 kHz Normal:0.3% Wide:0.15%
Stereo separation	400Hz Normal:50dB Wide:50dB 50 to 10 kHz Normal:35dB WIde:40dB
Frequency characteristic	50 Hz to 10 kHz ± 0.3 dB 30 Hz ~ 15 kHz + 0.5 -1dB
Frequency drift	SW-ON ~ 2 min : ± 10 kHz 2 minutes ～:± 5 khz ± 30 ℃:± 15 kHz
Carrier leak ratio	70dB
SCA interference ratio	70dB
IF harmonic whistle interference ratio (at 50 dB μ = 300 μ V input)	60dB
Muting level	3 μ ~ 30 μ V Variable
Stereo operating level	3 μ ~ 30 μ V Variable Linked with muting level
Auto-blend operation level	I : 100 μ V II:1mV
Antenna input impedance	300 Ω equilibrium 75 Ω unbalanced (F-type connector)
Maximum Input Voltage	300 Ω : 146 dB (20 Vrms) 75 Ω : 140 dB (10 Vrms)
Output level	Fixed:775mV Variable : 2 Vmax (continuously variable by -30dB)
Attachment mechanism	Muting (Variable) AutoBlend (two stage operation) AFC touch switch IF Mode switch Mode Meter display switch Headphone port
Semiconductor used	FET : 1 Transistor : 108 units IC : 7 Diode : 33 pcs Zener diode : 9 pcs
Working temperature	-10 ° C to 50 ° C
Power supply voltage	100 VAC, 50Hz/60Hz 100 VAC ± 15%, 45 Hz ~ 65 Hz
Power consumption	Illumination on:23W Illumination off:13W
External dimensions	Width 436x Height 144.5x Depth 352 mm
Weight	13.0kg
Measuring instrument
FMSG	MSG 282G (Meguro Radio Measurement)
Stereo modulator	MSG 211 fs (Meguro Radio Measurement)
Strain rate meter	333A or 334A(YHP)
RC oscillator	VP-722A (Matsushita)
Barbor	VP-960A (Matsushita)
Dummy antenna	Model100 (sound technology)