YAMAHA CT-800
¥ 68,000 (around 1973)
¥ 75,000 (around 1974)
Commentary
FM/AM tuner equipped with NFB transistor switching system MPX circuit.
In the front-end section, three low-noise dual-gate MOS FETs are used for the two RF stages and the mixer stage to reduce cross modulation and improve practical sensitivity.
In addition, various characteristics have been greatly improved by adopting a 4-row frequency linear varicon for the tuning circuit.
The IF stage uses a high-gain IC differential amplifier consisting of a constant current bias circuit and a 6-element ceramic filter to obtain linear phase characteristics and excellent band-pass characteristics.
The MPX circuit is based on Yamaha's original transistor-switching averaging demodulation circuit with NFB, similar to audio amplifiers.
Since the conventional SCA filter is unnecessary, it is possible to receive FM broadcasts with transparent sound quality without phase disturbance or degradation of high-frequency separation.
In order to minimize input dependence, the FM front-end and IF stage are designed with an emphasis on phase characteristics and strong input characteristics. This is because large input dependence (the rate at which selectivity and separation change depending on the input level of the antenna) adversely affects various characteristics depending on the strength of received radio waves.
Yamaha's proprietary LC-type active low-pass filter, which also serves as a de-emphasis circuit, sharply cuts unstable elements such as 19 kHz pilot such as 19 kHz pilot signal and 38 kHz subcarrier.
AFC is applied to the FM frontby applying AFC.
This AFC circuit is automatically canceled while the tuning knob is touched by Yamaha's original auto-touch tuning mechanism, so that it is possible to receive weak radio waves adjacent to strong electric field stations.
The AFC/Station indicator lights faintly when it is synchronized with the station during channel selection, and lights brightly when it is accurately synchronized and released from the knob to indicate that the AFC circuit is operating.
Equipped with Signal meter and Tuning meter.
The Signal meter has an AGC in the meter circuit so that the pointer swings linearly from a strong electric field to a weak electric field without saturation. Therefore, the approximate electrolytic strength of the input radio wave can be confirmed from the fluctuation of the pointer.
The tuning meter is more accurate than the conventional one and is adjusted to minimize distortion and provide the best stereo separation when the pointer is in the center.
Double muting is applied to the input and output stages of the MPX circuit to eliminate inter-station noise and shock noise at the time of detuning and tuning.
The muting level can be controlled with the muting level adjustment knob on the front panel to obtain the optimum muting effect according to the electric field strength.
In addition, shock noise generated when the power switch is turned on and off is also cut off by installing a muting circuit using FET.
The tuning circuit of the AM tuner uses a triple chain system consisting of a triple varicon, ceramic filter and two tuning coils to improve the selectivity and various characteristics.
In addition, a dedicated AGC circuit is provided to cope with the increase in power consumption of AM stations to ensure stable reception without distortion.
The LC filter also eliminates interference from short-wave bands.
A multi-path detection terminal is installed so that the direction of the FM antenna can be adjusted by connecting an oscilloscope and observing the waveform.
Equipped with a high-blend filter that blends high-frequency components and reduces only noise without degrading frequency characteristics.
An IF output terminal for an adapter is installed in preparation for discrete 4-channel broadcasting.
Light-emitting diodes are used as indicators for Power, FM Stereo, and AFC/Station-ON.
Equipped with two output terminals, fixed and variable.
.JPG)
Model Rating
| Type | FM/AM Tuner | ||||
| FM Tuner Section | |||||
| Receiving frequency | 76 MHz to 90 MHz | ||||
| Practical Sensitivity (IHF, 84 MHz) | 1.7 μ V | ||||
| Chinese arrowhead's slope | 5 μ V : 55 dB 10 μ V : 60 dB |
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| Image interference ratio (84 MHz) | 100dB | ||||
| IF Interference Ratio (84 MHz) | 100dB | ||||
| Spurious interference ratio (84 MHz) | 100dB | ||||
| AM suppression ratio | 55dB | ||||
| Capture ratio | 1.0dB | ||||
| Effective selectivity (IHF) | 80dB | ||||
| Signal-to-noise ratio | mono:75dB stereo:72dB |
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| Total harmonic distortion factor |
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| Stereo separation | 45dB(400Hz) 35 dB (50 Hz to 10 kHz) |
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| Frequency characteristic | 50 Hz to 10 kHz ± 0.5 dB 20 Hz to 15 kHz ± 1.5 dB |
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| Subcarrier suppression ratio | 60dB | ||||
| Muting signal level | 10 μ V ~ 50 μ V Continuously Variable | ||||
| IF out level / impedance | 400mV/1k Ω | ||||
| Multipath level / impedance | Vert : 17mV/80k Ω Horiz : 400mV/1k Ω |
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| <AM Tuner Section> | |||||
| Receiving frequency | 525 kHz to 1605 kHz | ||||
| Practical sensitivity (IHF, bar antenna) | 52dB/m | ||||
| Selectivity (1000 kHz) | 30dB | ||||
| Signal-to-noise ratio (80dB/m) | 45dB | ||||
| Image interference ratio (1000 kHz) | 70dB | ||||
| IF Disturbance Ratio (1000 kHz) | 60dB | ||||
| Spurious interference ratio (1000 kHz) | 70dB | ||||
| Total harmonic distortion factor (80dB/m) | 0.8% | ||||
| <General> | |||||
| Output Level / Impedance (1kHz) |
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| Semiconductor used | Transistor : 58 pcs FET : 5 pcs Diode : 36 units Zener diode : 4 pcs Light Emitting Diode : 3 IC : 2 Ceramic Filter : FM6 Element, AM1 Element |
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| Power supply voltage | 100 VAC, 50Hz/60Hz | ||||
| Power outlet | Unswitched:500W | ||||
| Rated power consumption | 12W | ||||
| External dimensions | Width 436x Height 144x Depth 323 mm | ||||
| Weight | 7.5kg | ||||