DENON TU-750
¥ 42,800 (around 1981)
Commentary
A synthesizer tuner that takes advantage of digital tuners to improve operability.
It corresponds to the frequency distribution of each FM/AM broadcasting station. It uses a synthesizer method that synchronizes every 100 kHz for FM and every 9 kHz for AM.
In this system, the reference frequency obtained from the crystal oscillator and the local oscillation frequency are compared in phase to form a phase-locked loop that controls the varactor diode. Therefore, there is no drift of the local frequency and good and stable reception is possible.
Built-in functions such as preset tuning (one touch tuning), auto tuning and manual tuning are also included.
Preset channel selection is equipped with a preset function for 7 FM/AM stations each. When you select your favorite broadcasting station, press the memory button and preset button (1-7) to store it.
In the Auto tuning mode, if you select Auto with the scan button and press one push of the tuning key up or down, the radio wave is automatically searched for whether the frequency is higher or lower and the radio wave stops at the correct tuning point. Pressing the tuning key again searches for the next tuning point.
Manual tuning can be performed by selecting the manual setting with the scan button and operating the up and down tuning keys. The received frequency is displayed with a digital counter enabling you to catch radio waves that cannot be caught with Auto tuning.
Equipped with an IC memory circuit, it memorizes all the conditions before turning off the power.
The memory circuit uses a backup power supply that operates for more than five years.
The front end is composed of a 4-stage varactor diode and a MOS FET, which is equivalent to an analog 4-stage varicon type.
The intermediate frequency amplifier stage (IF stage) employs a linear phase ceramic filter that achieves both low distortion factor and high selectivity, improving the distortion factor in all bands.
Quadrature detection ICs with linear detection capability over a wide band are used for the detection circuit, and PLL-MPX ICs are used for the MPX part.
In order to transmit music signals without degradation, a DC line amplifier without a coupling capacitor is used.
In order to improve the AM sensitivity and S/N ratio, the IF stage is composed of two 3-terminal high-selectivity ceramic filters with sharp out-of-band attenuation and a coil combined with the IF stage provides sound quality of 9 kHz without beat interference.
In addition, we have adopted a small low-impedance loop antenna that is resistant to noise in space. This antenna can be freely attached and detached from the back panel, and can be installed in a place with good reception within a range of approximately 1m.
The power transformer secondary winding of the power supply section is independent for digital display tube, synthesizer section and general circuit, and stable operation of each section is achieved.
You can adjust the brightness of the digital display in two levels with the dimmer switch.
Built-in oscillator for recording level check convenient for air check
The output level corresponds to 50% FM modulation at a frequency of 440 Hz.
Electronic switching is adopted for each function of FM/AM/Rec. Cal.
Power On / Off Built-in muting circuit to remove the following noise and inter-station noise.
Model Rating
Type | FM/AM Tuner |
FM Tuner Section | |
Receiving frequency | 76.1 mhz to 89.9 mhz |
Antenna terminal | 75 Ω, 300 Ω (Terminal Type) |
Practical sensitivity | 0.9 μ V/10.2 dBf |
S/N50dB sensitivity | Stereo : 15.8 μ V/35.2 dBf Mono : 1.5 μ V/14.2 dBf (μ V at 75 Ω, 0 dBf at 10-15W (new IHF standard) |
Image interference ratio | 80dB |
IF interference ratio | 90dB(76MHz) |
Spurious response | 90dB(83MHz) |
AM suppression ratio (IHF) | 55dB |
Effective selectivity | 60 dB (± 400 kHz) |
Capture ratio | 1.0dB |
Frequency characteristic | 20 Hz ~ 15 kHz + 0.2 -1dB |
Signal-to-noise ratio | stereo:75dB mono:80dB |
Total harmonic distortion rate (1 kHz) | Stereo : 0.08% at 90% modulation Mono : 0.06% at 100% modulation |
Stereo separation | 55dB(1kHz) |
Muting action level | 22dB |
Output level | 0.6 v (at 100% modulation) |
<AM Tuner Section> | |
Receiving frequency | 522 to 1611 kHz |
Antenna | Terminal type with loop antenna |
Practical Sensitivity (S/N20dB) | 18 μ V |
Selectivity | 50 dB (± 9 kHz) |
Signal-to-noise ratio | 55dB |
Total harmonic distortion factor | 0.6%(1kHz) |
Output level | 0.2 V at 30% modulation |
Level check Signal | |
Frequency | 440 Hz sine wave |
Output level | 0.3 v (at 50% modulation) |
<General> | |
Pwer | 100 VAC, 50Hz/60Hz |
Power consumption | 6W |
External dimensions (including knob, leg and terminal) | Width 434x Height 66x Depth 266 mm |
Weight | 3.1kg |