When overwriting of tapes is often a need to apply audio-video (AV) to multiple recorders. The same problem occurs if the AV signal from one source (VCR, camcorder) need to apply for multiple monitors.
To solve such problems by using distributor of audio-video signal. One variant of this device four AV outputs was described in article I. Nechaeva "Splitter video and audio signals" ("Radio" 1999, No. 1, p. 13). It uses a microchip AD812AN company Analog Devices, which is a powerful dual channel high-speed op amp. If there are problems with the purchase of this chip, the dispenser of the AV signal can be collected and transistors.
The scheme is simple such a device is shown in the figure. It allows you to connect to one the source AV signal up to four VCRs or monitors (TVs).
The AV signal is sent to the distributor via connector X1 (in this case type SCART). Since the input impedance of the audio inputs of the VCR and TVs are relatively high, the task of distribution of audio (remove with contacts 6 and 2 connectors (XI) can be solved by introduction of the corresponding number conventional emitter followers transistors low power. They are made on transistors VT7-VT10 and to simplify the device by the bias network in the United two groups. The maximum input voltage for audio is about 2 V.
Since the video input of the VCR is a low-impedance load (usually 75 Ω), the solution of the problem using the emitter repeater on one the transistor is impractical. To ensure that the transmission coefficient is close to one, it needs to be made relatively powerful PA high-frequency transistor. The author described dispenser AV signal went on other way. He fulfilled the repeaters on a regular transistors low-power (VT3-VT6). due to the availability of matching resistors R16-R19 provided the transmission coefficient is somewhat less than 0.5. and the loss of video signal level compensated common to all four channels of a broadband pre the amplifier transistors VT1 and VT2 with a gain of about three.
The output signals from the repeaters served on four groups of three-pin output AV connectors (BB1-BAI - common wire. QQ2-BA2-common wire, etc.). They can to be of the same type, but if a ham radio operator uses equipment with different types connectors, such a dispenser can also be used as a kind of "adaptor". In this case, to each of the channels connect connectors of different types (BNC, DIN, RCA, etc.).
Transistors VT1. VT3 - VT10 can be replaced with any high-frequency n-p-n transistors low power, for example CTSB. Transistor VT2 - any high frequency silicon p-n-p transistor of low power, for example CTB. Diodes VD1 and VD2 - any high frequency low power, for example KDA. When work with stereo audio sources in series in the circuit 2 and outputs 6 X1 slots, you must install an isolation resistors 1 kOhm each.
Author: Jural Vajdullak