Video Amplifier

[Darklegion]

Just wondering what you people use for a video amplifier,I need to get the signal up to around 4-5v but most consoles output around 0.7-1V,although the saturn seems to be outputting around 2v which is wierd.Anyway the CXA actually dropped the voltage when I input the saturn rgb into 2.2v down to 2.08(more or less) I assume this is as high as it will go,which obviously isn't good enough.The arcade people generally use a video amplifier released by ultimarc which does the sort of thing I am looking for,it is relatively cheap but I don't want to have to import it to Australia as I am too impatient to wait for international shipping and I figure a simple circuit will do the trick.....perhaps even pull-up resistors? Anyone know an equations that will work out the resulting votlage from a particular pull-up resistor?  Otherwise I'm sure the chip that the ultimarc uses is available,perhaps even one of my butchered consoles has one.

[Darklegion]

Seems there is a australia distributer (Ozstick) they are charging $35AU for it though which comes to $50AU all up with delivery.Seems they are adding on their middle-man profit too as buying straight from ultimarc is 15USD which converts to about $25AU.....but again postage costs and delivery time get me there.I'm tinkering with the idea of adjusting the CXA chip through changing the value of one of the resistors.Not sure if  that is how the amount of amplification is controlled though.I think its time for another look at the CXA datasheet....which I wish wasn't in japanese,some useful application notes are probably there for the taking.Also while I'm here,has anyone fed composite video through the composite sync input on the CXA, it could be used as a sync stripper also if it can.

[benzaldehyde]

Not too sure what you're up to there. 0.7V is standard RGB voltage (not sure if it's peak-to-peak or RMS, though). Composite video is 1V. I'm not sure why you get so high a reading on your voltmeter.

You are feeding the +5V in, right? The way you speak about using it as a sync stripper makes me curious. Are you connecting the signal sync to the circuit? I'm not sure if it has such a function, but if you don't connect C sync to the proper input, then the amp won't work.

[Darklegion]

I need 4-5V because I am feeding the rgb lines straight to the guns,much like what would be done with an arcade monitor....but with a TV.I am emulating what would normally done internally by a scart tv,with some switches and a few cut tracks...just need to get the rgb lines up to the correct levels......and verify that saturn is doing things properly.I think it is though,because I now have it set up so that I can switch between internal and external rgb and internal and external composite video/sync.And I would get a ghosted image when trying to run both regular composite video and external RGB at the same time......this is an indicator that the picture is shifiting to the right slightly which is what rgb tends to do.I might just get the ultimarc video amp though since I know it will work for this purpose and it comes with a prebuilt vga cable so I can test with something that is guaranteed to be setup up properly...i.e I don't have to troubleshoot several different stages.

BTW I was feeding the CXA 5v and had grounds and the rest all connected up.I was just using my sms2 mobo which had most of the required parts...I didn't use the 470uf capcaitors as I didn't have any,this wouldn't of stopped it from working though and putting them in wouldn't have raised the voltages in any case..the fact of the matter is even If i get it working through this chip,it will still end up being far too dim without pumping up the drive on the guns.....which I don't want to have to do since I want normal tv/composite operation,and also because it might damage the CRT.

As for sync stripping I was just curious that the standard sync input might be able to just grab the sync and ignore the rest....I don't know if this particular chip can do it,but I have seen some that can and it would be handy.There is no mention of it in the datasheet but than I can't read japanese :rolleyes:
Oh and you will get an output if sync doesn't work properly,you'll probably see a diagnolly rolling screen....at least this is my experience with this.

[Darklegion]

I ended up ordering the ultiamarc video amplififer....won't be here for more than a week though,but I could use a break from this anyway.Also I realised why the saturn was seemingly outputting 2v.....it was coupling with the sms2's output so thats why I was getting double voltage.I did not expect the 5v i was taking from the saturn to power other sections of the sms but there you go.Didn't think to lift the pins but then I didn't think i would need to....its useless for this purpose anyway its only designed to get to standard 1v p-p levels.....it ignores it if It is anything higher,which is what was happening with the slight voltage drop.

[RARusk]

Have you tried looking at this topic?.....

Using the CXA-1145 as a RGB Amplifier

I have been using this for a couple of years with no problems and it works great with all of my consoles including the N64. I created that topic thread to share my findings with the rest of the group. Maybe this might be helpful to you.

BTW, if you need to get some more CXA-1145s, you're better off going to a thrift store and buying some Genesis units cheap then hacking them to get the chip. Whole lot cheaper that way.....

[Darklegion]

Yeah I read your topic....thats where i got the idea from. :
Its not going to do the job for what I need it for though,it only pumps it up to 1 V P-P.There are plenty of chips around that can do what I need but they are mostly quite expensive and require a large circuit...usuallly they are full TV I'cs and I couldn't be buggered working with them.I'lll take a look at the ultimarc video amp when I get it and see what chip it is using.
Oh and BTW ,no thrift stores around here.Only ripoff second hand stores that charge more than ebay.

[Darklegion]

Also rather than creating a whole new thread,I am interested in creating a circuit that can control all of the switching.The method I have right now with dpdt switches is quite tedious and I am only using composite for the moment.Just a suggestion on an IC that can handle a lot of signals would be nice.I'd like to be able to hook up all my consoles to it and switch between any of them along with switching between internal rgb and external rgb.I'm thinking using a circuit with I.R in in it and a universal remote would be even nicer.I'll google around in any case but if anyone has done something like this berfore I'd like to hear your opinion.

[Darklegion]

Well got the amp the other day and getting close to something workable :rolleyes: ,mainly seemd to be issues with consoles putting out non-standard levels which work ok with scart,but bugger everything over once these problems are magnified by the amp.VGA output works fine as far as colour is concerned,but software needs to be sorted for the scan rate.Dreamcast works somewhat as far as colour levels go but jump too high on white screens which gives visable retrace lines,and also interferes with the family set.....the dreamcast image was popping up on the other screen !  I 'm just running sync directly however,I may run it through the amp also,perhaps levels are getting  messed up because of the differences here.Also whoever said that the composite video  pin is disabled in rgb mode is correct,I have heard conflicting views on this.It seems to active at bootup however..

Xbox works with sync,and no interference but blue is missing and green is way to bright,possibly bad mode switch here.
Saturn is still giving out 2 volts,and is obviously way to bright for all the colours,retrace lines visable at all levels....don't know why its doing this but I'll have to take another look at it.
I'm going to run some potenionmeters on all  rgb linesso I can control things more easily,should fix the lines that are overdriving and will allow me to tweak things to the levels I like.

[Endymion]

Have you tried looking at this topic?.....

Using the CXA-1145 as a RGB Amplifier

Thanks along with the thread author for bumping this. I'd been pondering some amplifiers and couldn't recall the chip--this one looks really easy.

I just scored a Genesis on ebay for three dollars to eat its brains. If the CXA is as simple as it looks I'm thinking this could be sticky-worthy.

[Darklegion]

Apparently my multimeter was giving bad readings or I am idiot :rolleyes:
Just checked to see what my vga card was giving out after amplification(the only rgb I had gotten to work so far) and it read from 0.3 to 0.7 V,I could of sworn that it was giving out 4-5V and my tests on what the TV chip was giving out after splitting the rgb from composite video read the same thing,really wierd.I had tryed wiring up directly before with no good results....the white screen I was getting on several consoles wised me up to what was going on though.Now I wired up my psx directly and saw beautiful RGB....a slight picture shift to the left unfortunately but I have seen much worse on real SCART tv's.I also had to split the sync to get a good picture,I had the standard diagonal lines that you get with composite video otherwise.The only other blemish in the picture I can see is a possible grounding or interference issue,faint scrolling horizontal lines....only visible on white backgrounds.Several things I can try to fix that,will probably only need to match impedence inside the TV and run some bypass caps to ground,otherwise I will wire in a filter circuit to the LM1881,so that only the sync gets to the sync chip...should get a prefect picture after that

[benzaldehyde]

Glad you got it working. The shift to the left in the picture is a side effect of using the LM1881; something about timing adjustments while separating the sync.

[Martin]

Glad you got it working. The shift to the left in the picture is a side effect of using the LM1881; something about timing adjustments while separating the sync.

Dont some TVs have a feature that lets you overcome that problem?
I noticed on some TVs the picture doesnt shift to the left at all, and on others it does

[Darklegion]

The shifted effect is exactly the same with composite video used directly for sync,so that it is not the cause.It is the rgb lines that do it not the sync,it can be seen by having composite video running and swapping one of the colours to rgb,the particular colour will be shifted to the right...it is related to the TV's handling of high voltage I believe,and some TV's seem to be worse than others...or don't exhibit the effect at all.This TV is fairly good,about a 1-2cm border on the right of the screen..sometimes worse if the game has bad borders anyway....like grandia which has a black border on the right even in comosite mode and on different tv's.Some consoles seem to not cause the borders too,I believe the xbox is one that didn't seem to exhibit this,but I haven't really tested it enough on anything but the psx....

The psx seems to work directly without amplification because the output is at good levels without it,around 1-1.5V which is seemingly what my TV wants at the stage I am feeding rgb..It was a bit dim however...I had remebered that people were using 220 uf capacitors to boost the output... this actually made the output darker!

The saturn seems to be giving out a good output also,but sync was giving me issues..seemingly this one doesn't need amplification either.

The dreamcast looked good when I ran it through the amp,huge interference though,seemingly cause by the rgb lines and not the sync,since the effect lessened when I disabled 1 or 2 of the colours....possibly ground loops here or bad ground to the video amp...or maybe just something bad in the mess of wiring I had :rolleyes:

[Darklegion]

Well after getting the ultimarc to work properly,I've found that the signal is still too weak for my liking,even from a vga signal,which is what is designed for.Whether or not the weak signal is because of damage from me running high signals into it,like the psx and saturn or just the way it is built,it is not doing it for me.So I went back to the good old CXA chips .I tried using a broken saturn for this one  with the CXA1645m chip in it,however the buffering/boosting caps on the outputs were not working.So I tried connecting to the positive side of the caps and it worked but since I was cutting out these boosting caps it was too dim.I tried wiring in my own caps,didn't work still no voltage reading on the negative side.Then I tried using my sms2 again with the CXA1145p chip,wired up my own circuit for the output lines and input my rgb ins into the 0.1uf caps that were already in there along with the rest such as sync,power,ground.Got the exact same result,got an output on the positive legs,absolutely nothing on the negative.Now if it were only one line not working I would say the caps were shot,but it happens on all three rgb caps as well as the internal saturn ones.Also I have a 220uf cap wired in for the composite video out too,it had no negative effect on it whatsoever.Really annoying that this is happening and I can't for the life of me figure out why.