YAMAHA T-8

Commentary

FM/AM tuner which adopted CSL (computer servo locked) synthesizer system which refined the SLL synthesizer system adopted in T-6.

The newly developed CSL synthesizer system makes it possible to achieve both good digital operability and good analog reception performance and sound quality.
In this circuit, a computer controls a high-resolution PLL synthesizer that controls up to the order of 0.01 MHz, and an FM analog servo tuning system that achieves both high fidelity and high interference rejection characteristics, according to reception conditions.
The CSL system is very accurate because it operates in the PLL mode at the time of call for step tuning and preset tuning. If there is even a slight input signal, it switches to the analog servo mode and is locked to the center point of the IF band. At this time, the PLL operation stops and the interference to the low and high frequency ranges is almost 0. Since the reference frequency of the PLL system is 100 Hz, the frequency can be read in 0.01 MHz increments. In addition, since the IF offset can be adjusted with an accuracy of 10 kHz increments, the tuning point can be pushed more precisely.

Equipped with a random access memory function of 10 stations, you can preset up to a total of 10 FM/AM stations.
The memory uses non-volatile memory that does not lose its contents even when the power is turned off. It retains its contents semi-permanently without using a backup battery.

Equipped with two tuning modes, the tuning frequency is kept UP or DOWN until a broadcasting station is found in auto mode, and the frequency changes in 100 kHz steps only while the Tuning button is pressed in manual mode.

Equipped with last preset channel flushing.
When storing a new station, press the Memory button to flash the channel that was stored last, so that you do not store the same station in duplicate or erase the stored music.

Equipped with an initial station set function that can store music that can be received when the power is turned on.

The front end section is composed of an RF amplifier, a local oscillator with FET buffer, and a bipolar trunk circuit. The RF amplifier employs a 4-row twin varactor diode and a dual MOS FET. The antenna circuit is single-tuned and the stage is double-tuned to improve various interference rejection characteristics. The RF amplifier, a local oscillator with FET buffer, and a bipolar trunk circuit are used.
In order to achieve high sensitivity and high interference rejection characteristics, a newly developed RF servo gain controller is used. This circuit controls the gain of the RF amplifier. When there is no interference, the RF gain is maximized to enable high sensitivity reception. When there is interference, the RF gain is automatically controlled so that the reception state becomes discretionary according to the interference.

The IF stage consists of a low-loss uniresonance ceramic filter that achieves both high interference rejection characteristics and audio characteristics through the introduction of Yamaha's original differential gain direct-viewing analysis method, and a differential IF amplifier with excellent limiter characteristics. In addition, the IF stage employs an Auto-DX circuit as an automatic switching circuit for the IF band, enabling optimum reception according to reception conditions.
The Local-IF stage consists of two low-loss, uni-resonance ceramic filters, providing 25 dB of selectivity sufficient for normal use and excellent audio characteristics. The DX-IF stage consists of five low-loss, uni-resonance ceramic filters, providing 85 dB of effective selectivity.
The Auto-DX circuit automatically selects the IF circuit mode (Local-DX) mode (Local-DX).

An ultra-linear direct detector is used for the detection circuit.
This ultra-linear direct director has linear detection characteristics over a wide band of 1200 kHz (P-P) with a bandwidth of 150 kHz (P-PF), which is equivalent to 100% FM modulation, and has excellent characteristics with very little differential gain deviation in the band. This ultra-linear direct detector directly detects the 10.7 MHz IF signal without beat-down like pulse count detection, so its information transmission capability is five to ten times higher than that of pulse count detection.

A real-time C-MOS decoder is used for the MPX decoder.
This circuit consists of a pair of C-MOS bi-directional analog switches and a symmetric open-collector type high-speed DC NFB amplifier with emphasis on load stability at ultra-high speeds. The NFB switching circuit for one channel is used for both the left and right sides. This circuit has a simple and fully balanced configuration. This eliminates the carrier accumulation effect that is a problem with conventional bipolar transistors and realizes high-speed switching.

In order to cancel the pilot signal at the input of the switching circuit using a sine wave of the same amplitude and opposite phase, a tracking type pilot pure cancel circuit is mounted. This circuit accurately follows the pilot level and cancels the pilot signal before it enters the decoder even if the pilot level differs depending on the broadcasting station.

The Antiinterference PLL System is used in a PLL circuit that generates a 38 kHz subcarrier for demodulation of a composite signal from a 19 kHz pilot signal. In this circuit, a tunable antiinterference filter is added to the input to minimize subcarrier disturbance caused by stereo audio signals.

Equipped with Rec Cal (recording calibrator).
When the Rec Cal is set to ON, a 333 Hz signal is output, which is equivalent to FM monaural 50% modulation. To adjust the recording level, set the level meter on the cassette deck so that it reads from -6VU to 0 VU to ensure reliable recording.

It is equipped with an Auto Blend circuit to reduce noise components when weak radio waves are received in stereo.
Since this circuit operates in relation to the Auto-DX circuit and signal quality, the service area of the stereo broadcast transmission is greatly expanded and improved compared to the conventional one.

Equipped with a 3-point LED type signal indicator.

The circuit configuration of the AM tuner section consists of an untuned high-frequency cascode amplifier stage equivalent to a double varicon, differential mixer and triple tune IFT to ensure high excess and high dynamic range. Also, by switching the RX mode switch, you can choose between DX position and Local position in the AM tuner section.

The AM antenna uses a Hi-Q type low-impedance loop antenna that is an improved version of the conventional loop antenna.

Model Rating

Type	FM/AM Tuner
FM Tuner Section
Receiving frequency	76 MHz to 90 MHz
50 dB SN sensitivity	Mono : 3.0 μ V (14.7 dBf) Stereo : 32 μ V (35.3 dBf)
Practical sensitivity (mono)	75 Ω : 0.9 μ V (10.3 dBf) 300 Ω : 1.8 μ V (10.3 dBf)
Image interference ratio	80dB
IF interference ratio	100dB
Spurious interference ratio	100dB
AM suppression ratio	65dB
Effective selectivity	DX:85dB Local:25dB
Capture ratio	DX:2.5dB Local:1.2dB
Signal-to-noise ratio	mono:90dB stereo:84dB
Total harmonic distortion factor	Local DX mono 100Hz: 1kHz: 6kHz: 0.02% 0.03% 0.05% 0.05% 0.3% 0.8% stereo 100Hz: 1kHz: 6kHz: 0.04% 0.04% 0.06% 0.6% 0.6% 1.2%
Cross modulation distortion factor	mono: 0.03%(Local) 0.3%(DX) stereo: 0.04%(Local) 0.6%(DX)
Stereo separation	Local DX 50Hz: 1kHz: 10kHz: 60dB 60dB 50dB 28dB 28dB 25dB
Frequency characteristic	50 Hz to 10 kHz ± 0.3 dB 30 Hz ~ 15 kHz + 0. 3-0. 5 dB
Subcarrier suppression ratio	65dB
AUTO DX switching level	40 μ V (37.3 dBf)
<AM Tuner Section>
Receiving frequency	518 kHz to 1615 kHz
Practical sensitivity	10 μ V
Selectivity	DX:17dB Local:27dB
Signal-to-noise ratio	50dB
Image interference ratio	45dB
Spurious interference ratio	50 dB or more
Total harmonic distortion factor	0.3%
<General>
Output Level / Impedance	FM (1 kHz, 100% modulation) : 0.5V/2.2k Ω AM (1 kHz, 30% modulation) : 0.15V/2.2k Ω Rec Cal (333 kHz, equivalent to 50% FM modulation) : 0.25V/4.7k Ω
AC outlet	Unswitched : 1 line, 300 Wmax
Power supply voltage	100 VAC, 50Hz/60Hz
Rated power consumption	12W
External dimensions	Width 435x Height 72x Depth 320.5 mm
Weight	4.0kg