Touch volume control. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Audio equipment
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The regulator is made on the basis of an integrated five-channel switch K1KT901 (5 field-effect transistors with an insulated gate). The regulator can work with an ultrasonic frequency converter, the input impedance of which is at least 10 ohms, and the sensitivity is 0,1 ... 0,7 V.
The main parameters:
- volume control limits 0...50 dB;
- the gain at 0 dB is 1;
- the maximum input voltage is 0,75 V;
- the signal-to-noise ratio is 54 dB;
- loudness depth at minimum volume
- at a frequency of 30 Hz - 30 dB,
- at a frequency of 18 kHz - 10 dB.
The volume control circuit works as follows. When the power is turned on, the voltage across the capacitor C3 is zero, the field effect transistor A1.1 of the assembly is closed, and the LED in its circuit does not light up. Transistors A1.2 and A1.3 open with a negative bias through resistors R11 and R13, and the regulated signal circuit is practically connected to a common wire through capacitors C4 and Sb. In this case, the transmission coefficient of the device is minimal and is approximately 50 dB.
When touching the touch contacts E1 and E3, the capacitor C3 begins to charge and the voltage at the gate of transistor A1.1 increases, and the resistance of its channel drops, thereby reducing the voltage at the gates of transistors A1.2 and A1.3. As a result, the resistance of the channels of field-effect transistors, and consequently, the transfer coefficient of the device and the volume of the reproduced signal, increase. At a volume level of -40 dB, the V1 LED starts to glow, and at a level of -20 dB, V2 also glows, and the brightness of their glow increases to the maximum at the highest volume (0 dB). When touching the sensors E1, E3, the capacitor C4 is discharged and the regulation process proceeds in the reverse order. The rise in the frequency response at lower frequencies is provided by the capacitor C6, C0,2 (5 ... 1 μF), and at higher frequencies - by the oscillatory circuit L2C18, tuned to a frequency of 6 kHz. The higher frequency level is adjusted by selecting the resistor RXNUMX.
Microassembly K1KT901 can be replaced by field effect transistors KP310B; coil L1 is wound with PEV-2 0,07 wire until a standard three-section frame is filled and placed in an armored core from the IF filter of the Sokol radio receiver. Capacitor C3 is used with a low leakage current (for example, K73-11). During adjustment, the operating mode of the transistor A1.1 of the microassembly is set to direct current. Contacts E1, E2 are connected and an alternating voltage of 0,5 V with a frequency of about 1000 Hz is applied to the input of the regulator, and by changing the position of the potentiometer R15 slider, the maximum output signal level is achieved. The transfer coefficient equal to 1 is set by selecting the resistor R17. The harmonic coefficient of the controller depends on the volume level, and with an input signal of 0,5 V and a volume level of -10 dB, it reaches its maximum value (0,35%). At volume levels of 0 to 40 dB, the harmonic distortion is significantly reduced (less than 0,05%) When the input signal level changes from 0,1 to 1 V, the harmonic distortion changes in the range from 0,1 to 0,5%.
Author: V.Kozlovsky
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