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simon.plata

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About simon.plata

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  1. Ghosting could be produced by overdrive of the video signal, try to reduce the gain an see if the ghosting persist. If it persist then could be a mismatch of coupling impedance. Try a different video cable and different lengths the shortest the better.
  2. It sounds like a good idea. My concern is about the bandwidth and roll-off frequency. Darlingtons tends to have multiply the base-emitter capacitance of the hidden base, but should give a try.
  3. Hi ChildOfCv, In respect your first comment, you´re absolutely right . It's really easy (nothing to do really) to design the mod using an integrated video buffer in place of a discrete one. Indeed I ordered some video buffers to do another AV-mod for my VCS consoles. In this case I selected the TSH122. https://www.st.com/en/amplifiers-and-comparators/tsh122.html However the objective of this post, was to give an easy to built AV-mod which really works and was affordable for almost everybody in the world. In some places it's not easy or affordable to order uncommon electronic parts. Also I wanted it to be possible to assembly in an universal PCB or even a bread-board. Regarding your second comment, I might don't really understand your question. However I will try to respond. In the first post of the tread, I exposed two options: The first one is a one stage amplifier in common-collector configuration, which is the best approach as you said. However, given the high output impedance of the resistor network DAC (about 10.9KOhm), the current gain needs to be into the hundreds, which is in the edge of the capabilities of a general purpose transistor at 4.2MHz. The second one is a modified common-collector configuration like the first one, plus a preamplifier stage in common-emitter. I choose the common-emitter configuration for the preamplifier to take advantage of the high input impedance and the convenience of embedded biasing of the common-collector second stage. I hope I have responded to your question appropiately, otherwise please let me know your comments and I will try to do my best.
  4. Hi @slaanesh, PAL requires a higher video bandwidth (5.0MHz) than NTSC (4.2MHz), and this is the reason why you get the better results with your trim-pot all way down, which is the point of the highest gain for the circuit. To optimize the circuit for PAL's signal, it’s needed to move the knee point or the roll-off frequency point to the right (Higher frequency), which requires a complete redesign of the circuit, because it its DC coupled. The roll-off frequency is the result of the superposition of the RC low pass filters formed by the transistor's parasitic capacitances and the input/output equivalent resistances. You may try to change the C1 capacitor from 47pF to a higher value like 68pF or 100pF to increase the gain in the high frequency end. That trick could work but it’s not warranted. Unfortunately I’m being too busy at work, otherwise I would try to redesign the circuit with PAL bandwidth in mind. I will try when I have a truce from work.
  5. Hi @slaanesh, I'm pleased it worked for you. It was designed for NTSC so the optimum gain could be in the edge for PAL. Also I want to thanks @Djoulz for making it easy and accessible for more people.
  6. Hi and thanks to everybody who tryed this mod. May be I forgot to suggest to adjust the trimmer until you obtain the better picture in your set-up. The calculated value is for 0dB gain and 1Vpp output which is the standar composite video signal span. However due to the tolerance of the components in the VCS board and the in the mod, it could be lower or higher than that. The trimmer was included to correct that deviation. Best regards and enjoy!
  7. Hi stlouisrod, have you tried to reduce the gain of the amplifier? Gosthing could be produced by several factors, including unmatched impedance and overdriven signal. The RCA cable could increase the impedance and generate gosthing. I tested it on different LED TV and I have got nice video image. Best regards,
  8. By the way, the link to the mod is lacking tha "a" at the begining so is not working. Here is the correct link: http://atariage.com/forums/topic/271678-simple-diy-composite-video-mod Enjoy
  9. Hi mogul345, thank you for posting my mod in your list!!! Just one coment: my mod comes in one and two transistors versions. However two transistors version is better. Also I posted the PCBs if someone want to fabricate it. I wanted to fabricate a lot and have them available but due to my work I couln't ship them quickly. I have the Eagle files and would be fantastic if someone could fabricate a lot and sell them online. Best regards,
  10. Despite the mod is just a simple video amplifier, it exists several reasons to not work properly: One of them could be amplifier saturation to any or both rails. The real problem can't be found easily without an schematic or a signal analysis with an oscilloscope. The alternative is to revert the mod you did and try with the mod proposed in this tread which is proven and has worked for several people including myself. Best regards,
  11. The mod you're installing is not the same as the one stage (one transistor) posted in this tread. From the information you send it's very difficult and time consuming to reconstruct the schematic in order to analyze the circuit and verify the configuration. However it looks like a bandwidth issue or a unwanted low pass filtering. This could happen because: * The 2N3904 transistor is out of specs or in the lower limit for gain. I suggest to test it for a minimum gain of 200 or replace it. * May some of the minimum removal components are still in place. These components needs to be removed from the VCS board, otherwise they Will attenuate or filter the signal to unusable levels for this mod. If neither of the above Works for you, I suggest to implement the mod posted in this tread, then we can offer better support or advice. Bests,
  12. Hi, Can you share the schematic and component values you're using? I Will give a look and see if I found something. Looks like a bandwidth problem, it could make a color shift or distortion. Best regards,
  13. Hi, it was designed for NTSC bandwidth in mind which is a bit lower tan PAL. However "boggis the cat" used it on a PAL 2600A and worked fine (please see entry #11 above). That means it supported the PAL bandwidth. It should work on a sixer. Only needs to identify the components needed to be removed and the corresponding connection points. The two stage transistor design worked very well for me over all other single stage that I tested before.
  14. Hi, Please see the PDF files attached. Sorry for the delay. VideoAmp2S_MSK.pdf VideoAmp2S_SLK.pdf Best regards,
  15. Hi Darryl, Good to hear you will give it a try. Please let us know if it works for you. Regards, Simon
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