Aurex ST-720

Commentary

An FM stereo tuner that uses a pinboard preset system.

The tuning method employs a PLL frequency synthesizer method.
In this system, a local oscillator circuit is incorporated in a part of the PLL loop, and excellent tuning accuracy is obtained by producing an accurate oscillation frequency with crystal accuracy.

A newly developed FET and FET and 6-series varicap for the front end, 3-stage phase linear 4-pole LC filter and differential IC for the intermediate frequency amplifier stage, and PLL IC for the MPX part.

It uses a unique preset method, pinboard method.
On the front panel of the ST 720, there are four pinboard preset channels, each of which can be attached and detached as an FM unit like a cassette. When the FM unit is detached from the panel, a pinboard can be set inside the unit to adjust the receiving frequency.
The pinboard has a row of numbered teeth that can be folded to the desired receiving frequency to provide a plug-in switch that mechanically fixes the frequency.

Manual tuning of push type is also possible in addition to pinboard type.

Built-in 440 Hz oscillator for air check.

Equipped with a tuning error indicator using LED.

Frequency can be displayed digitally with 7-segment LED.

It comes with an observation data sheet that describes 4 items such as sensitivity, SN ratio, stereo separation and harmonic distortion factor.

Model Rating

Type	FM stereo tuner
Circuit system	PLL frequency synthesizer system using crystal oscillator
Receiving frequency	76.0 mhz to 89.9 mhz
Practical sensitivity	1.8 μ V (IHF)
Harmonic distortion factor (1 kHz, 100%)	stereo:0.15% mono:0.1%
Signal-to-noise ratio	stereo:68dB mono:75dB
Frequency characteristic	20 Hz to 15 kHz ± 1 dB
Effective selectivity	75dB(IHF)
Image interference ratio	100dB
IF interference ratio	100dB
Capture ratio	1.0dB(IHF)
Spurious interference ratio	100dB
AM suppression ratio	65dB
Stereo separation	48dB(1kHz) 30 dB or More (100 Hz to 10 kHz) 40 dB or More (400 Hz to 4 kHz)
Rated output	Fixed : 380 mv (400 Hz, 100%) Variable : 0 to 770 mV (400 Hz, 100%)
Output impedance	1k Ω (at maximum output)
Antenna terminal	300 Ω equilibrium 75 Ω unbalance
Reception frequency display	7-segment LED used, digital display
Semiconductor used	Transistor : 22 FET : 5 pcs IC (Linear) : 9 IC (Digital) : 16 Diode : 80 pcs LED : 5 pcs
Power supply voltage	100 VAC, 50Hz/60Hz
Power consumption	15W
External dimensions	Width 450x Height 148x Depth 365 mm
Weight	8.3kg