Preamplifier on the K284SS2 chip. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Preamplifiers
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The preamplifier on the K284SS2 chip is designed to amplify signals from various program sources. A distinctive feature of the device is the possibility of frequency correction of the amplified signal in separate frequency bands.
The amplifier is assembled on a K.284CC2 hybrid chip (the letter index can be any), consisting of four independent devices - source and emitter followers and two amplifiers - inverting and non-inverting with gains of at least 3000 and 200, respectively.
The main parameters:
- Rated frequency range, Hz.......20...35 000
- Rated input voltage (with an output voltage of 1 V), mV.......40
- Maximum output voltage (at harmonics up to 2%), V.......2,5
- Harmonic coefficient (at a frequency of 1 kHz with an output voltage of 1 V), %......0,4
- Tone control limits (at frequencies 60, 230, 730, 2 and 350 Hz), dB.......±7
- Input resistance, MΩ.......1
- Output impedance, kOhm.......3
A non-inverting amplifier (input - pin 13, output - pin 5) is used at the input of the device, an inverting one (input - pin and, output - pin 6) - at the output. A passive five-band tone control is connected between the emitter (pins 7 and 8) and source (pins 14 and 1) repeaters. The timbre is regulated by variable resistors R17 - R21, the volume - by a variable resistor R2. All resistors must be group B.
If necessary, the sensitivity of the amplifier can be adjusted by changing the ratio of the resistances of the resistors R10 and R11 (gain of the inverting amplifier K = R11/R10). The required capacitance of the capacitor C5 in this case is determined from the ratio C5\u6e l.10 / fnRXNUMX (fn is the lowest frequency of the nominal range).
Setting up the device is not required if resistors and capacitors selected with an accuracy of 5 ... 10% are used in the tone control circuits. The only thing to do is to measure the maximum output voltage, which should be at least 2,5 V. In the case of one-sided voltage limitation, it is necessary to select resistors R4 and R28 of dividers that determine the operating mode of the source and emitter followers, respectively.
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