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| Benta:
OK, look forward to your schematic. But honestly a lot of your problems relate to the breadboard. Those things are not usable for anything over 60 Hz, and certainly not for CVBS. Get a stripboard or something like that instead. 2.76 Vpp CVBS is high, but once it's loaded with 75 ohms it will drop to half. With the color burst on top, it's ballpark. |
| syntax333:
I will try to build it to a stripboard as you said. Until then, I uploaded the schematics. Please inform me about the problems that you see on it. |
| BrianHG:
--- Quote from: syntax333 on January 01, 2019, 10:52:34 pm ---I will try to build it to a stripboard as you said. Until then, I uploaded the schematics. Please inform me about the problems that you see on it. --- End quote --- In a circuit I once done, instead of your mosfet (Q1), I used a 4066 cmos analog switch, the enable control input tied to the sync separator, and a trim-pot at 1 input, adjusting the voltage from 0-5v, and the other side tied to the video source after a 1uf cap, or 0.1uf cap, not 100uf (C3). (Not if you want a true black level adjuster, tie the 4066's enable to the 'burst' output on the sync separator) At that video point, I used a 2n7000 mosfet in a source-follower configured amp. (video after 1uf cap tied directly to Gate of mosfet, 1k pulldown on Source which was video out) (No Q2/Q3/R3) I was then able to adjust the voltage output of the video to any level using the trimpot. |
| Benta:
Several points stand out: C3 is in the wrong direction. CSOUT is active low, so your switch logic is wrong. The MOSFET is HUGE! No wonder you get spikes when the puny LM1881 output has to drive all that gate capacitance. I strongly recommend a DG417 or DG419. Your decoupling is somewhat lacking. At least you'll need 100 nF directly at the LM1881. 12V should also be decoupled. Then let's see. |
| BrianHG:
--- Quote from: Benta on January 02, 2019, 10:46:33 am ---CSOUT is active low, so your switch logic is wrong. --- End quote --- Ooops, It's been so long. In the case of my example circuit, you would need to invert the CSOUT before feeding the 4066's analog switch enable. |
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