Technics SH-R 808

 Infra-Red Wireless Remote Control

 Operation of Receiver

1. The receiver consists of a PIN photo diode, amplifier, LC tuning circuit, detection circuit, and wave-form shaping circuit (Schmitt Trigger), and it changes the infrared signal from the transmitter into the original 10-bit signal.
2. The 10-bit pulse signal is processed by the microcomputer, and then the necessary remote control signal is taken out from each output port.
3. The output interface is a circuit to facilitate the conection with each equipment, and it is an inverter using an open collector.

Operation of Transmitter

1. MN6025C is an 5-bit IC which can generate 25 kinds of signals. The oscillation frequency is 396 kHz and is divided by 12 to obtain 33 kHz which is used as modulation frequency. It is further divided by 16 to achieve 2,06 kHz which is the clock frequency of this IC.
2. When the keyboard is depressed, Mn6025C starts oscillating and generates series pulses of 5 bits plus inverse 5 bits, totalling 10 bits, according to the key position.
3. The 10-bit pulse signal is modulated by 33 kHz carrier.
4. The modulated signal from MN6025C is applied to the infrared LED and command eye LED drive circuits. With oscillation time is about 60 msec. required for 10 bits, while the lighting up time of the command eye is set at about 0,5 sec.

 Electronic Volume Control

1. In this control, five attenuators of -2 dB, -4 dB, -8 dB, -16 dB and -32 dB, and a muting circuit of -20 dB are turned On-Off by an analog switch for changeover in 32 steps renging from 0 dB to -6 dB and to ∞ by -2 dB each.
2. The analog switch is driven by a 5-bit binary up-down counter, which is provided with last sound function due to the back-up signal from the tuner pre-amplifier.
3. The volume control up-down switch gains 1 step in the initial 0,5 sec. of push, and keeping it depressed causes step-by-step volume control every 0,15 sec. When the switch is kept depressed, it takes about 5 secondes for the change from 0 dB to -∞ dB.
4. A 5-bit IC (LC7500) is used as the controller for the electronic volume. With this IC, the five attenuators can be selected in 32 steps. The internal oscillation frequency 800 Hz is divided into pulses of 0,15 sec. period, and the pulses are counted at the counter circuit to select the attenuators.

When the volume up-down switch is pressed, three pulses are first counted to select an attenuator and subsequently the attenuators are selected every pulse.

Specifications

Receiver Unit

Input Sensitivity / Impedance:  500 mV/27 k Ω

Maximum Allowable Input:  11 V

Total Harmonic Distortion:  0,015% (at rated output)

Signal-to-Noise Ratio:

At Rated Output :  90 dB (92 dB, IHF, A)

At -26 dB Output :  68 dB

Frequency Response:  20 Hz - 20 kHz , +0 dB, -0,5 dB

Residual Hum and Noise:  0,03 mV

Volume Control Range:  0 dB to -60 dB (2 dB steps),  -∞ in 32 steps

Muting:  -20 dB

Output Voltage [Rated/Maximum]:  500 mV / 3 V

Output Impedance:  2,2 k Ω

Channel Balance:  250 Hz to 6,300 Hz , ±1,0 dB

Chnnel Separation (1 kHz):  65 dB

Power Consumption: 6 W

Power Supply:  110, 120, 220, 240 V AC 50/60 Hz

Dimensions (W x H x D):  430 x 75 x 270 mm

Weight:  3,7 kg

Transmitter Unit

Effective Signal-Transmission Distance:  Approx. 7 m

Power Supply:  DC 3 V (two 1,5 V batteries)

Dimensions (W x H x D):  63 x 22 x 142 mm

Weight:  136 g (with batteries)