Audio Database

TX 9900 Image
Commentary

A high-end FM stereo tuner designed for truly high-fidelity FM reception.

A 7-row varicon dedicated to FM is adopted for the front end part.
This seven link varicon is combined with three dual-gate MOS FETs and has a three stage configuration of single -, double - and triple-tune for high selectivity. At the same time, double - and triple-tune are used in unique ways, such as L-coupling for double-tune and C-coupling for triple-tune, with a gain deviation of less than 0.5 dB over the entire receiving band.
In addition, the sensitivity is increased by using a FET that is specially SN selected.

It adopts a Phase Locked tuning method using APC (Automatic Phase Control) which adopts a unique sampling and holding method.
The APC samples the oscillation frequency from the local oscillator with pulses every 100 kHz obtained from a single crystal oscillator, and feeds back the voltage change obtained by detecting the phase shift to the local oscillator. The local oscillator always oscillates at an accurate frequency in increments of 100 kHz. Thus, the oscillation frequency from the local oscillator does not change linearly with the rotation of the dial, but changes every 100 kHz just like when many crystal oscillators are switched sequentially.
With this method, there is no oscillation in fractions of 100 kHz or less, so that there is no slight mistuning. When the dial stops rotating, the local signal is locked at that frequency, so that there is no drift.

Equipped with signal strength meter and lock meter.
When a broadcast is received, the hands of the lock meter point to the center to indicate the tuning point, and when the best center tuning point is obtained, the lock indicator lights red to indicate correct reception.

Two types of circuits with different selectivity characteristics are built into the IF stage. In addition, two types of detectors, narrow band and wide band, are prepared. The selectivity characteristics and this detector can be switched simultaneously according to the radio wave condition, and the circuit can be used properly.
This switch is integrated with the muting switch in consideration of practical usability.

As a wide-band detector, we have developed and installed a delay-type ultrawide-band linear detector.
This detector has a bandwidth as wide as 6 MHz and has excellent characteristics because of its high detection efficiency.

Before the output of the detector is input to the MPX stage, in order to prevent beat interference from adjacent stations at a distance of 200 kHz, an anti-birdie filter that cuts unnecessary high-frequency components is adopted, so that no unnecessary waves are mixed into the MPX stage.

The MPX section uses PLL (Phase Locked Loop) system.
The PLL is a loop circuit that corrects the deviation of the demodulation signal while comparing the MPX demodulation signal produced inside the tuner so that it always stays in phase with the pilot signal sent from the broadcasting station. Stability is improved compared with the conventional system.
The TX tx 9900, the IC used is carefully selected in terms of SN and distortion to further enhance the completeness of the PLL circuit. In addition, a low-pass filter with sharp high-cut characteristics provides a high carrier-leak suppression ratio and a flat frequency response in the playback band.

A 2-stage switching muting circuit using a relay is adopted.
Level 1 suppresses noise at the time of detuning and suppresses noise between stations. Level 2 also suppresses broadcast waves with a weak signal level and allows only high-level signals to be received.
In consideration of practical usability, it is combined with the selector switch for the selectivity characteristic. For narrow points, you can choose muting off or 1, and for wide points, you can choose muting 1 or 2.

It is equipped with an MPX noise filter to cancel high-frequency noise that tends to occur when receiving stereo signals in weak electric fields.

Two output terminals, variable and fixed, are and fixed.

Equipped with output terminals for multi-path observation.

Equipped with 4-channel MPX terminal.

Model Rating
Type FM stereo tuner
FM Tuner Section
Circuit system MOS FET RF2-stage, 7-train varicon, APC system フェイズロックト tuning
7-stage limiter with IF BAND switching, ultra-wideband detector, PLL MPX
Practical sensitivity Mono : 5 μ V (S/N 50 dB) / 2 μ V (IHF)
Stereo : 50 μ V (S/N 50 dB)
S/N Wide : 80 dB (mono), 75 dB (stereo)
Narrow : 75 dB (mono), 70 dB (stereo)
Harmonic distortion factor
wide mono: 0.08%(100Hz)
0.08%(1kHz)
0.08%(10kHz)
stereo: 0.1%(100Hz)
0.1%(1kHz)
0.3%(10kHz)
narrow mono: 0.2%(100Hz)
0.2%(1kHz)
0.2%(10kHz)
stereo: 0.3%(100Hz)
0.3%(1kHz)
0.6%(10kHz)
Capture ratio wide:0.8dB
narrow:2.0dB
Effective selectivity Wide : 35 dB (400 kHz), 20 dB (300 kHz)
Narrow : 65 dB (300 kHz), 12 dB (200 kHz)
Separation Wide : 50 dB or more (1 kHz), 40 dB or more (50 Hz to 10 kHz)
Narrow : 40 dB or more (1 kHz), 35 dB or more (50 Hz to 10 kHz)
AM suppression ratio wide:60dB
narrow:55dB
Carrier leak suppression ratio wide:75dB
narrow:70dB
Frequency characteristic 50 Hz to 10 kHz + 0. 2-0. 5 dB
20 Hz to 15 kHz + 0.2 -1.0 dB
Image interference ratio 120 dB or more
IF interference ratio 120 dB or more
Spurious interference ratio 120 dB or more
Muting action level 5 μ V/28 μ V
Antenna 300 Ω Balanced Type, 75 Ω Unbalanced Type
<General>
Output Level / Impedance Fixed : 650mV/5k Ω
Variable : 70 mv ~ 2V/3.5k Ω
4 ch MPX : 400mV/2.5k Ω
Semiconductor used Transistor : 49
FET : 9
IC : 15
Diode, etc. : 41
AC outlet Power switch not linked : 1 system
Power supply voltage 100 VAC, 50Hz/60Hz
Power consumption 22W (rated)
External dimensions Width 420x Height 165x Depth 385 mm
Weight 11.3kg