YAMAHA T-4

Commentary

FM/AM tuner equipped with newly developed high-performance uniresonance ceramic filter and MPX IC.

A high-precision wide-air-gap 4-row varicon is adopted for the front end section, the antenna circuit is single-tuned and the stage is double-tuned. The RF amplifier uses a J-FET with good linearity and low noise, which realizes excellent interference rejection characteristics.
In addition, by examining the operation level of the mixer stage and improving the variation of the distortion factor and separation depending on the strength of the antenna input, overall stable reception performance from weak electric field to strong electric field is obtained.

The IF section uses a newly developed uniresonance ceramic filter with extremely good transmission characteristics to achieve both excellent audio characteristics and interference rejection characteristics. In addition, the Auto DX circuit improves actual characteristics in actual use.
The Uniresonance Ceramic Filter is a ceramic filter for audio tuners developed through technical cooperation between Yamaha and Taiyo Yuden. It is an IF filter with a single resonance structure and a special electrode pattern that minimizes the differential gain deviation in the band. Compared with surface acoustic wave (SAW) filters and LC block filters, it has advanced transmission characteristics, low loss, low dispersion, and high stability. Moreover, the transmission characteristics can be controlled by an external additional circuit according to the purpose of use.

The local position of the IF stage employs an additional adjustment circuit in a newly developed 3-element uniresonance ceramic filter, a 6-stage differential amplifier circuit with a transistor stage and a current limiter. This local IF stage has excellent transmission characteristics with very little differential gain deviation.
In the DX position, high quality reception is possible by adding 2 elements to the 3 elements of the uniresonance ceramic filter for the Local position to make 5 elements, and combining it with a 2-stage transistor + 6-stage differential amplifier circuit with a current limiter.

The T-4 is equipped with an Auto DX circuit that automatically selects the IF circuit mode (Local/DX) by electronically detecting the presence or absence of interference with received radio waves in order to receive high-quality signals in any radio wave environment.
This circuit drives the Receiving Mode selection circuit by flip-flop with signals from the interference detection circuit and the tuning detection circuit, and drives the IF stage switching transistor switch and DX indicator.

The MPX circuit uses Yamaha's original DC / NFB switching circuit based on a high-slew rate DC amplifier. The subcarrier generation circuit uses an anti-interference PLL system with an anti-interference filter at the input, and is equipped with a tracking-type pilot pure cancel circuit that cancels the pilot signal before it enters the decoding stage.
The DC-NFB switching circuit is constructed by multiplying NFB by a switching circuit of Yamaha's original average value demodulation method using transistors. By multiplying NFB by DC, excellent transmission characteristics are obtained by multiplying NFB by DC, generation of intermodulation distortion is very little, and sufficient low distortion rate from DC to high frequency range is realized.
The tracking-type pilot pure cancel circuit uses a 19 kHz square wave generated by a PLL to generate a 19 kHz signal with the level and phase following the input pilot signal. Further, the signal converted into a sine wave by a waveform conversion circuit (the same level as the pilot signal but opposite phase) is added to the input of the switching circuit to cancel the pilot signal before the switching circuit. This circuit automatically follows the level and cancels the pilot signal even if the pilot signal level of each broadcasting station changes. Therefore, there is almost no leakage of the pilot signal.

The T-4 uses Yamaha's original MPX IC dedicated to the newly developed audio tuner. This IC contains 140 transistors, 140 resistors, and approximately 290 other elements such as diodes and capacitors in a 20-pin dual package. By adopting a large chip size, the degree of integration is not increased unnecessarily, and all parts that have a negative impact on sound quality and performance are composed of discrete elements. In terms of circuitry, all amplifiers for signals such as stereo decoders, output buffer amplifiers, and separation control amplifiers are DC-configured high-through-rate high-response amplifiers. Most of the newly developed balanced single-end phase detector PLL circuit, anti-interference PLL circuit, and tracking type pilot pure cancel circuit are integrated circuits.

The signal from the MPX circuit is amplified by a high-speed balanced DC amplifier and input to a low-pass filter.
Since the T-4 uses a tracking type pilot pure cancel circuit, the 19 kHz pilot signal has already been canceled at the entrance of the decoder. Therefore, by setting the cutoff frequency of the low-pass filter out of the audible band, a flat frequency characteristic up to 18 kHz is obtained. In addition, an excellent LC active low-pass filter that works effectively for the entire sideband wave band generated by stereo demodulation is adopted.
The output from the filter passes through the buffer amplifier of the active load emitter follower and becomes the output.

Equipped with a signal quality meter.
This meter can indicate a wide input level range from 1 μ V to 3 input level range from 1 μ V to 3 mV. In addition, with Yamaha's unique interference detection method, interference from multipath, fading, and noise sources can be indicated as a decrease or wamble without saturation from weak to strong input.
When the Muting/OTS switch is in the OFF position, the time constant of the meter circuit is set earlier to facilitate detection of interference.

The AM tuner section is configured with low noise and distortion while maintaining high sensitivity and high dynamic range by high frequency amplification stage using cascode circuit, differential mixer stage, triple tune IFT, etc.
Furthermore, by switching the RX mode switch to Local-DX, you can switch between the Hifi-Receive-DX receive and playback frequency bands.

A low-impedance loop antenna is used for the AM antenna. This antenna has a feature that it is difficult to pick up electric noise due to its low impedance.
If the FM antenna is installed outdoors, you can enjoy AM DX reception by using the attached combination bar because it uses Yamaha's unique combination feeding system.

Equipped with a convenient OTS (Optimum Tuning System) that turns off the AFC during tuning and automatically locks the frequency from the station to the correct tuning point after tuning.
In addition, the dial indicator works as a bright station indicator when tuning with the station during tuning. When the tuning knob is released after tuning, the dial indicator winks to indicate that the station is locked.

It is equipped with an FM Blend circuit that reduces noise when receiving stereo signals in weak electric fields.
When this circuit is active, the brightness of the stereo indicator is reduced by half.

Equipped with two outputs, fixed and variable.

A Rec Cal circuit is mounted. The signal of the Rec Cal circuit corresponds to 50% modulation output at 333 Hz FM.

Model Rating

Type	FM/AM Tuner
FM Tuner Section
Receiving frequency	76 MHz to 90 MHz
50 dB SN sensitivity	Mono : 3 μ V (14.8 dBf) Stereo : 35 μ V (36 dBf)
Practical Sensitivity (mono, IHF, 84 mhz)	75 Ω : 0.8 μ V (9.3 dBf) 300 Ω : 1.6 μ V (9.3 dBf)
Image interference ratio (84 MHz)	90dB
IF Interference Ratio (84 MHz)	100dB
Spurious interference ratio (84 MHz)	100dB
AM suppression ratio (IHF)	65dB
Effective selectivity (IHF)	DX:88dB Local:50dB
Capture Ratio (IHF)	DX:2.5dB Local:1.2dB
Signal-to-noise ratio	mono:86dB stereo:84dB
Total harmonic distortion factor	Local DX mono 100Hz: 1kHz: 6kHz: 10kHz: 0.05% 0.05% 0.08% 0.05% 0.1% 0.3% 0.7% 0.1% stereo 100Hz: 1kHz: 6kHz: 10kHz: 0.05% 0.05% 0.08% 0.1% 0.5% 0.5% 0.8% 1.5%
Intermodulation distortion factor (IHF)	mono: 0.05%(Local) 0.5%(DX) stereo: 0.08%(Local) 1.0%(DX)
Stereo separation	Local DX 1kHz: 50 Hz to 10 kHz : 55dB 50dB 30dB 25dB
Frequency characteristic	50 Hz to 10 kHz ± 0.3 dB 30 Hz to 15 kHz ± 0.5 dB 10 hz ~ 18 khz + 0.5 -3.0 db
Subcarrier suppression ratio	65dB
Muting level	DX : 5 μ V (19.2 dBf)
AUTO DX switching level	50 μ V (39.2 dBf) (Interference level approximately -50dB at stereo)
<AM Tuner Section>
Receiving frequency	525 kHz to 1605 kHz
Practical sensitivity (IHF)	15 μ V
Selectivity (1000 kHz ± 10 kHz)	27dB
Signal-to-noise ratio	52dB
Image interference ratio (1000 kHz)	40dB
Spurious interference ratio (1000 kHz)	50dB
Total harmonic distortion factor	0.3%
<General>
Output Level / Impedance	FM (100% modulation) VR min ~ max : 0.1 ~ 1V/220 Ω VR Center : 500mV/2.5k Ω AM (30% modulation) VR min ~ max : 25 ~ 250mV/220 Ω VR Center : 125mV/2.5k Ω Rec Cal(333Hz) VR min ~ max : 50 ~ 500mV/220 Ω VR Center : 250mV/2.5k Ω Fixed output FM (100% modulation, 1 kHz) : 1V/220 Ω AM (30% modulation, 1 kHz) : 250mV/220 Ω Rec Cal (333 Hz) : 500mV/220 Ω
Accessory function	FM blend switch Recording calibrator FM Muting & OTS / Meter Speed Switching Interlocking Switch Interference detection signal quality meter Low-impedance loop antenna
Semiconductor used	Transistor : 35 IC : 5 FET : 2 Diode : 19 units Zener diode : 1 unit LED : 2 pcs Ceramic Filter : 5 Pieces
Power supply voltage	100 VAC, 50Hz/60Hz
Rated power consumption	8W
External dimensions	Width 435x Height 95x Depth 337 mm
Weight	5kg