Audio mixer for video camera. Scheme, description

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Audio mixer for video camera. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Телевидение

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When shooting amateur videos, it is not always possible to get good sound quality and content. To correct it when dubbing from a video camera to a VCR, the device proposed for repetition was developed.

An audio mixer allows you to feed a signal to the audio input of a VCR from both a video camera and an additional sound source, such as a player or microphone (the latter is best used with your own amplifier), and also provides an overlay of one signal on another. If necessary, the device can increase the signal level from the video camera by 10 dB.

The schematic diagram of the device is shown in the figure.

Audio mixer for camcorder

The signal from the video camera is fed to input 1, and from an additional sound source - to input 2. From the sliders of the corresponding control resistors R1 and R14 through capacitors C2 and C7, the signals are fed to amplifiers assembled on transistors VT1 and VT2, respectively.

Amplified signals pass through a controlled divider R7R8R20 to a mixer made with resistors R9, R10. It is loaded through the capacitor C4 on the emitter follower, made on the transistor VT3. The latter reduces the output impedance of the device.

The controlled divider R7R8R20 is a regulator of the ratio of signals applied to the inputs of the device. The adjusting resistor R8 changes the mutual levels of signals from the video camera and an additional sound source coming to the output of the audio mixer.

In the event that the R7R8R20 ratio controller allows only one of the signals to be recorded (in the extreme positions of the variable resistor R8 engine), to control the second signal, the device has a power amplifier assembled on a DA1 chip, to the antiphase outputs of which a sound emitter is connected - a dynamic head BA1 or headphones, which are even more convenient. The controlled signal is selected by the switch SA1. The R21R22 divider provides the required volume level.

The device can be powered both from a network unit and from a galvanic battery ("Krona").

The audio mixer uses fixed resistors MLT and variable resistors SPZ-4aM. Capacitors C10, C11 - KM-6 or similar, the rest are oxide - K50-35. KT315V transistors are interchangeable with any of the KT315, KT3102 series. Instead of the KR1064UN2 chip, you can use EKR1436UN1. They are discussed in the article by D. Turchinsky "Audio frequency amplifiers EKR1436UN1 and KR1064UN2 ("Radio", 1998, No. 5, pp. 61, 62). Other microcircuits can also be used, for example, K174UN4.

Setting up the device comes down to obtaining a voltage of 4,5 V at the collector of the transistor VT1 by selecting the resistor R2 and the desired volume level in the sound emitter BA1 by selecting the resistor R22. However, before achieving the latter, it is necessary to set the nominal levels of the input signals, for which the variable resistors R1 and R14 serve. The easiest way to do this is experimentally by ear by the volume of the sound reproduced by the TV. First, they remember the subjective sound volume level when listening to a television program. Then, a signal is sent to the sound input of the TV from the output of the audio mixer, having previously connected signal sources to its inputs and turned them on. By moving the slider of the variable resistor R8 alternately first to one and then to the other extreme position, the signal is selected from the video camera (the slider according to the diagram below) or from an additional sound source (the slider at the top), and resistors R1 and R14, respectively, set the same subjective volume level, as when listening to a television program.

Author: V.Gurevich, Rostov-on-Don

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