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Started by viletim, September 21, 2008, 03:34:14 pm
Quote from: Link83 on September 22, 2008, 06:02:51 amThanks so much for this Viletim, I cant wait to try it So if I wanted to make this amp on veroboard would this be the right sort of layout for each line?:-Or is there a better/smaller layout I should use?
QuoteAlso, im just curious to know to know if it would be possible to make a similar amp which wouldnt require removing any components/lifting chip legs, or would this compromise the RGB quality?
QuoteLastly, if you have time I would love to know what the 'linking two points' boost method actually does to the RGB signal? Its shown here under 'another solution':-http://www.eurasia.nu/wiki/index.php?pagename=N64RgbBoosterYou can do the same thing by linking pins 22 & 23 of the VDC-NUS chip.For me it made the picture much brighter but also added interference to the picture
Quote from: viletim on September 23, 2008, 01:29:26 amI hate veroboard. The one pad per hole stuff is so much more flexable. See here for a layout (amplifier circuit is very similar).
Quote from: Link83 on September 23, 2008, 10:41:55 pmThanks Quote from: viletim on September 23, 2008, 01:29:26 amI hate veroboard. The one pad per hole stuff is so much more flexable. See here for a layout (amplifier circuit is very similar).Its does look like a much better idea than veroboard, but I cant seem to find it available anywhere Do you know what its called/brand name?
QuoteAlso, Just looking at the amp schematic some more and I am wondering if removing the capacitors C124, C125 and C126 from the board is actually necessary? Since they are all 1uf couldnt I use them to replace the C1 1uf capacitor used in the amp? (eg. remove the 75ohm resistors from the board, cut the RGB traces or lift VDC-NUS chip legs, then connect the ENC-NUS connection from the amp (from between R1 and R2) to the bottom of the C124, C125 and C126 capacitors?
QuoteAlso, I take it if I am not interested in keeping the Composite/S-Video output that I could just removed C1 entirely, and combine R1 and R2 into one resistor? Would 660ohms be the correct value to use?
QuoteLastly, could I just ask if you recommend using Carbon film or Metal film resistors for amps/video work? (In the Game Gear RGB amp it looks like you used a mixture of both?)
Quote(P.S. If you have a moment id appreciate your insight into the PAL N64 S-Video missing components I mentioned in this thread:-http://nfggames.com/forum2/index.php?topic=3203.40Expecially now that I know C14 should be 68nf - I just need to know if the component ordering is important, and if I can add the parts into the cable rather than the console)
Quote from: IJTF_Cinder on September 24, 2008, 09:17:17 amThis sort of stuff?http://www.radioshack.com/product/index.jsp?productId=2104052What's the difference between the board you're using viletim and veroboard (aka stripboard), they look the same to me?
Quote from: RARusk on September 24, 2008, 01:11:09 pmExcellent work. But I noticed the U5 chip in the diagram. If this chip can be safely removed from a dead N64 motherboard how useful could it be for making Composite Video and S-Video? This may be useful for consoles like the Sega Master System, TG-16, and the SNES Jr.
QuoteAlso, if the ENC-NUS would work, what would probably be even better is to use the 'S-RGB A' chip used in late model SNES consoles, as it not only produces S-Video and Composite, but also retains RGB aswell. Even better, if you google the chips code 'BA6596F' you should get quite alot of hits for Hong Kong suppliers who sell them for $2-3 each. I guess they were overproduced!
Quote from: viletim on September 24, 2008, 02:42:58 pmThese are custom chips made for one particular device that have been out of production for 13 years or so. I think $2-3 a piece is being a bit optomistic... That's less than the cost of an AD724 !
Quote from: viletim on September 25, 2008, 01:00:19 pmIt's probably not worthwile, anyone who wants one can just rip it out of a surplus SNES and I've never heard of anybody doing that.
Quote from: viletim on September 25, 2008, 01:00:19 pmBTW, when buying from chinese suppliers, you will probably have to pay by bank transfer which has high fees (at both ends!). They will only send parts by courier because if they used the postal system your warrenty might expire before you receive the parts, if you receive the parts.
Quote from: RARusk on September 25, 2008, 01:36:32 pmIn addition, did you measure the signal strength before you did anything? If you did, what did it measure?
Quote from: RARusk on September 25, 2008, 01:36:32 pmI also noticed that the U4 chip uses 3.3V. Would it make any difference if it was replaced with 5V or would Bad Things happen?
QuoteIn addition, did you measure the signal strength before you did anything? If you did, what did it measure?
QuoteId be interested in knowing the signal strength measurements too if you still have them? Also if you have the measurements from 'before and after' removing the board resistors and capacitors that would be great to know (I read the percentages in the Wiki - 35% and 60% - but am just curious as to what the actual values measured )
Quote from: RARusk on September 26, 2008, 01:27:27 pmOkay, so the voltage of the signal is correct, right? But if that is the case why is the video signal weak?*scratches head*
QuoteIC loaded with 45 ohms (original with TV connected directly), 0.7*0.35= 0.25Vpp
Quote from: Link83 on September 26, 2008, 09:29:45 pmSo can I just check i have this right - even though an RGB signal needs to be 0.7vpp, it actually has to be 1.4vpp before entering the TV. Is it only 0.7vpp inside the TV then?
QuoteMay I ask how you learn all of this stuff Viletim? I have had a look online but there doesnt seem to be much information out there on vpp and video signal levels. I wish there was some sort of 'beginners guide to video signals' or similar.
QuoteOne other question, how does Waltarzars old N64 amp compare?http://www.eurasia.nu/wiki/index.php?pagename=N64RgbBoosterIt is directly connected to the VDC-NUS chip with no components removed - obviously this makes your amp more accurate (No offence intended to Waltarzar) but im just curious Knowing what parts he used would it be possible for you to say what Waltarzars amp would do to the RGB signal levels?
Quote from: viletim on September 27, 2008, 12:22:06 amI'd like a explain this further, but I'm short on time at the moment. To adequately explain everything will take some preperation... and pictures!
Quote from: viletim on September 27, 2008, 12:22:06 amVoltage gain of this amplifier is something like 0.95. The Vpp would be unchanged, there would be an additional DC offset added. The exact value of this offset would depend on both the average brightness of the picture, and gain of the individual transistor used. Makes it very difficult to predict.Basically, the idea is to reduce the impedance of the circuit to as low as possible then stick it into a TV. Then the 75 ohm load of the TV harly makes any difference to the amplitude.This circuit relies on tolerances which vary too much...it's a poor design.
Quote from: Link83 on September 28, 2008, 12:14:50 amWow, I have so much to learn Quote from: viletim on September 27, 2008, 12:22:06 amI'd like a explain this further, but I'm short on time at the moment. To adequately explain everything will take some preperation... and pictures!That sounds great With all your knowledge maybe you should consider writing a book on video signals?
QuoteIf it would help at all here is the datasheet for the BF494 used in Waltarzars N64 amp:-http://www.datasheetcatalog.org/datasheet/MicroElectronics/mXqwswz.pdfIt shows the transistors gain, although that might not be much use without knowing the brightness of the picture I guess?
Quote from: Link83 on October 11, 2008, 01:07:03 pmI would imagine with this method the ENC-NUS chip would still be generating a C-Sync signal but without Composite video? My TV was fine with this, but im curious to know if all Scart TV's would be happy with just a C-Sync signal on the Composite line - and not being able to strip it first?
Quote from: viletim on October 12, 2008, 11:58:35 amGood to hear you got it working.
Quote from: viletim on October 12, 2008, 11:58:35 amIt's no problem at all. The Dreamcast does exactly this when it detects an RGB cable is plugged in.
Quote from: viletim on October 12, 2008, 11:58:35 amTo be clear, you've lifted the R,G,B pins of the VDC-NUS and connected them to the amp?
Quote from: viletim on October 12, 2008, 11:58:35 amI don't know why you'd be loosing sync on bright images... there's no problem with the composite video output on the console I'm working on. The only thing I can think of is that you might be using a PAL N64 RGB cable with the extra 75 ohm resistor on the composite line.
Quote from: viletim on October 12, 2008, 11:58:35 amIt appears that the ENC-NUS doesn't like to have a high (in this case infinate) impedance source connected to its input (the CXA1645's datasheet warns about this too). What you normaly do with this type of input when you're not using it is connect a capacitor to ground. So just put some shorting links where the 110 ohm resistors used to be.
Quote from: Link83 on October 13, 2008, 01:43:06 amQuote from: viletim on October 12, 2008, 11:58:35 amIt's no problem at all. The Dreamcast does exactly this when it detects an RGB cable is plugged in.Really? How interesting. I wonder if that was this reason behind the issue this forum member was experiencing?:-http://nfggames.com/forum2/index.php?topic=3047.0Slightly OT but does the Dreamcast still generate C-Sync when in VGA mode?
QuoteSorry if I wasnt very clear - its only the RGB ouput that it seems to be having problems with the sync on bright images (Im assuming its the sync) the Composite output appears fine Its very strange and only happens for a moment.
QuoteI was thinking about the best way of making this N64 'auto-switch' to the AV1/RGB channel using Scart. Usually when making a Scart cable for an NTSC SNES/N64 I just alter the wiring so that the +5v line powers both pin 8, and pin 16 (through a 100ohm resistor) making sure to cut the +12 wire (if its even present) so that the +5v cant return back down the cable and along the C-sync line. This is the only easy way I have found to make the NTSC SNES auto switch (without using batteries) as it doesnt have a +12v line internally you can use. The side effect of this of course is the the Scart cable now auto switches to AV1/RGB channel in 'Widescreen mode'.I was wondering though - as the NTSC N64 does use +12v internally would it be safe to just directly link up the +12v line to the MultiAV output Pin 3? (making sure to isolate Pin 3 first by cutting the C-Sync trace on the board) This way it would auto switch to AV1/RGB in the correct 4:3 aspect ratio. Would this method be ok, or would I need to add a resistor/diode of some sort to make it 'safe' for both the N64 and TV?
QuoteLastly, out of curiosity you mentioned previously that to build an N64 amp without removing/lifting components would be "possible but would require an amp with voltage gain. It would be fairly complex with just transistors, a high speed opamp or similar would reduce the parts count but the're not always easy to obtain"I was just curious to know how many transistors would we be talking about? and how complex? I hope you dont mind me asking.
Quote from: viletim on October 13, 2008, 11:43:07 pmRight... When you wire up the RGB amp and connect RGB (from amp) + composite video (from normal output) you have the problem. It goes away if you either switch to composite video for the video source or disconnect the amp input to the ENC-NUS. That's a bit odd... can you try it on another TV?
Quote from: viletim on October 13, 2008, 11:43:07 pmI like to put a 220 ohm resistor in series with this SCART line. It protects the power supply in case of a short circuit.
Quote from: viletim on October 13, 2008, 11:43:07 pmDepends how it's done... a textbook example whould be to use the existing circuit and place a two common emitter (need two cause they invert the signal) gain stages between the two existing emitter follower stages. Maybe 4 transistors, 10 resistors per amp.