YAMAHA T-6

Commentary

Yamaha's first digital synthesizer FM/AM tuner with SLL synthesizer and ultralinear / direct detector technologies.

The FM section consists of a 3-row twin varactor diode and a dual-gate MOS FET frontend, an IF stage with an AUTO DX circuit using Yamaha's original resonance ceramic filter, an ultra-linear direct detector, and a real-time decoder consisting of a bipolar DC NFB + antiinterference PLL + tracking type pilot cancellation circuit.
The circuit configuration of the AM section is cascode RF amplifier, differential mixer and triple tune IFT.
In addition, a newly developed station-locked loop (SLL) direct digital synthesizer circuit is used in the control section to improve operability without losing sound quality.

Equipped with Yamaha's original SLL (Station Locked Loop) direct synthesizer.
In this SLL synthesizer system, the voltage applied to the varactor diode for tuning is digitally synthesized directly from the reference voltage source to create a tuning voltage, and a loop is formed so that when a broadcast is received, the tuning voltage is locked at the center tuning point. With this configuration, the DC voltage for tuning is synthesized directly, so there is almost no interference from the synthesizer to the tuner. Thus, there is no decrease in sensitivity or deterioration of SN ratio due to interference over the entire receiving frequency band.
In addition, since the locked frequency matches the optimum frequency of the high-frequency signal system of the receiver, it is possible to receive signals in the condition in which various characteristics such as sensitivity, distortion, and separation of the set are the best.

The tuning system is an auto-tuning system with an up / down touch switch. This system automatically searches for a station by pressing the up switch when receiving a higher frequency than the displayed frequency, or pressing the down switch when receiving a lower frequency than the displayed frequency. When the station is locked, the station lock indicator lights and maintains the optimum tuning point.
In conjunction with the Auto DX circuit, the sensitivity of conjunction with the Auto DX circuit. When set to Auto DX, weak stations can be received, while when set to Local, only strong stations can be received.

Preset tuning is available for a total of 10 stations, 5 FM stations and 5 AM stations.
The T-6 has a built-in memory backup circuit with a capacitor that protects the contents of the memory within two days of power failure or unplugging the power outlet.
It also has a last-channel memory circuit that stores the last station received. When the power of the tuner is turned OFF and ON again, the last station received is received.

The front end consists of a 3-row twin varactor diode, a dual-gate MOS FET, a low-gain balloon amplifier with a RF-type pre-selector, a local oscillator circuit with FET buffer, and a bipolar mixer circuit.

The IF stage consists of a low-loss uniresonance ceramic filter and a 6-stage differential amplification IF amplifier with a current limiter that achieves both interference rejection and audio characteristics through the introduction of Yamaha's original differential gain direct-viewing analysis method. In addition, the IF stage is equipped with an interference detection type Auto DX circuit that automatically selects an appropriate reception mode according to the receiving radio wave environment.

In the Local IF stage, which can receive high-quality sound, complementary circuits are added to two low-loss uniresonance ceramic filter elements to obtain a selectivity of 25 dB, which is sufficient for normal use, while minimizing the differential gain deviation in band.
In addition, the DXIF stage, which enables high-quality reception in a reception environment with a lot of interference, is composed of four low-loss uniresonance ceramic filter elements to achieve constant distortion while maintaining an effective selectivity of 70 dB.
The Auto DX circuit automatically selects the IF circuit mode (Local-DX) based on electronic detection of interference with received radio waves.

The detector stage is equipped with an ultra-linear direct detector developed by Yamaha.
The Ultra-Linear Direct Detector has linear detection characteristics over a wide bandwidth of 1200 kHz (P-P) compared to the bandwidth of 150 kHz (P-P), which is equivalent to 100% FM modulation. It also has excellent little differential gain deviation within the band.
This ultra-linear direct detector directly detects the IF 10.7 MHz signal without beat-down like pulse count detection, so the information transmission capability is five to ten times or more compared to pulse count detection.

The MPX circuit consists of Yamaha's original high-speed bipolar, DC and NFB switching circuits based on a high-slew rate DC amplifier. The subcarrier generation circuit employs an antiinterference PLL system with an interference rejection filter at the input, and is equipped with a tracking-type pilot cancellation circuit that cancels the pilot signal before it enters the decoder.
The high-speed bipolar DC NFB switching circuit consists of Yamaha's original high-speed bipolar average-demodulation switching circuit with NFB, similar to the audio amplifier. This circuit has excellent transmission characteristics due to DC and NFB applied. The generation of cross-modulation distortion is extremely small. It can be fully coded from DC to ultra-high frequency band and has a sufficiently low distortion factor.

It is equipped with an auto-blend circuit to reduce noise components generated when weak radio waves are received in stereo.
The Auto-Blend circuit works in conjunction with the AutoDX circuit.

The AM tuner consists of an untuned high-frequency cascode amplifier stage equivalent to a double varicon, a differential mixer stage, a triple-tune + single-tune configuration IF amplifier stage, and a low-distortion detection stage.

The AM antenna is equipped with a Hi-Q type low-impedance antenna that is further improved based on the loop antenna.

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

Model Rating

Type	FM/AM Tuner
FM Tuner Section
Receiving frequency	76 MHz to 90 MHz
50 dB SN sensitivity	Mono DX : 4 μ V (17.3 dBf) Stereo DX : 27 μ V (33.9 dBf)
Practical Sensitivity (IHF, mono, 84 mhz)	2 μ V (11.2 dBf, 300 Ω) 1 μ V (11.2 dBf, 75 Ω)
Image interference ratio	62dB(84MHz)
IF interference ratio	100dB(84MHz)
Spurious interference ratio	100dB(84MHz)
AM suppression ratio	50dB(IHF)
Effective selectivity (IHF)	DX:70dB Local:25dB
Capture Ratio (IHF)	DX:2.2dB Local:1.5dB
Signal-to-noise ratio (IHF)	mono:82dB stereo:79dB
Total harmonic distortion factor	Local DX mono 100Hz: 1kHz: 6kHz: 10kHz: 0.50% 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% 0.1% 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)	55dB(1kHz) 45 dB (50 Hz to 1 kHz)
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	52dB
AUTO DX operating level	Automatic switching to DX MODE when the interference level in stereo is about -50dB
<AM Tuner Section>
Receiving frequency	525 kHz to 1605 kHz
Practical sensitivity	15 μ V (IHF)
Selectivity	26 dB (1000 kHz ± 10 kHz)
Signal-to-noise ratio	46dB
Image interference ratio	40dB(1000kHz)
Spurious interference ratio	50dB(1000kHz)
Total harmonic distortion factor	0.5%
<General>
Output Level / Impedance (1kHz)	FM (100% modulation) : 500mV/2.4k Ω AM (30% modulation) : 150mV/2.4k Ω Rec Cal (333 kHz, equivalent to 50% FM modulation) : 250mV/2.4k Ω
Attachment mechanism	Autosearch tuning Preset tuning for 5 AM/FM stations (with memory backup) Station lock indicator RX mode switch Last channel memory rec cal
Semiconductor used	IC : 10 Transistor : 40 FET : 3 Diode : 21 Zener diode : 6 pcs 7-Segment LED : 1 LED : 14 pcs
AC outlet	300W MAX
Power supply voltage	100 VAC, 50Hz/60Hz
Rated power consumption	9W
External dimensions	Width 435x Height 72x Depth 262.5 mm
Weight	3.1kg