The Pinnacle Studio MP10: Enhancing Output Signal Quality
The Pinnacle Studio MP10 is an external real-time MPEG1 codec equipped with composite video input and output. However, its output signal strength is only 0.7 V, insufficient for most video devices that commonly require 1-V signals. The low output level of the MP10 can be easily rectified. A dedicated correction circuit, complete with its own power supply, not only solves this issue but also finds utility in a variety of other applications.
Incorporating Analog Devices AD828 Dual Low-Power Video Opamp
To address the MP10’s low output level, an Analog Devices AD828 dual low-power video opamp is employed for amplification. Both opamps connect to the MP10’s output, enabling two separate devices to link to the correction circuit’s outputs. The amplifier IC offers an impressive combination of high bandwidth, substantial slew rate, and relatively low load current consumption. The circuit’s input and outputs maintain a standard 75 Ω impedance. Consequently, the amplifiers’ gain must be slightly below 3 (2 ÷ 0.7 = 2.86). Two trimpots (P1 and P2) are incorporated to adjust the output levels to the standard value and compensate for diverse component tolerances. The circuit features DC-coupled inputs and outputs to accommodate video inputs requiring a signal with a DC offset for proper black level maintenance.
Ensuring Stable Synchronization: Challenges and Solutions
When utilizing VHF/UHF modulators or video capture cards for PCs, unstable synchronization can be a common issue, especially with bright images. This instability arises due to weakened sync pulses caused by the asymmetric supply voltage, and the equipment in question lacks clamp circuitry. According to the IC’s datasheet, it boasts a no-load bandwidth of 85 MHz at a gain of 2, operating within a ± 5 V supply. However, under a 75-Ω load (150 Ω in total), the measured bandwidth is approximately 45 MHz (resulting in 1 Vpp across 75 Ω). To ensure stable operation, the IC’s supply voltages are meticulously decoupled by components L1, L2, and C1 through C4. Additionally, the power dissipation is minimized by limiting the supply voltages to +6 V and –5 V.
Strategic Voltage Design and Indicator Integration
In this setup, the positive voltage is set higher, accounting for the assumption that the signal is predominantly positive. Consequently, additional headroom on the positive side is crucial. The power supply design adheres to standard protocols, incorporating ample RF decoupling measures. The 78L06 and 79L05 voltage regulators are deployed to handle the modest current demands effectively. Within this design, LED D1 serves as the essential mains power indicator, strategically placed to ensure external visibility when the circuit is enclosed, enhancing user awareness and safety.
Efficient Printed Circuit Board Design
The printed circuit board layout is meticulously crafted using conventional components and has been optimized for compactness. During measurements, IC1 was placed in a standard IC socket; however, it is advisable to solder it directly onto the board for enhanced stability. The design of the power supply and amplifier section is intentionally kept modest, ensuring compatibility with a wide range of small enclosures, simplifying the housing selection process.
Optimizing Current Consumption and Availability
The IC exhibits a no-load current of approximately 13 mA when devoid of input signals. When both outputs are loaded and driven, the current rises to around 16 mA. Unfortunately, the PCB featured here is not readily available through the Publishers’ Readers Services, necessitating custom assembly for interested parties.