Build Your Own Arcade Controls Forum
Main => Main Forum => Topic started by: hiperco on January 03, 2005, 04:55:41 pm
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I'm contemplating building myself a video amp. Does anyone know which IC the Ultimarc video amp board uses? TIA!
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Have you ever built an op amp circuit before? It is a lot more difficult than it sounds. You have to select resistors and capacitors for the correct gain, while maintaining the clarity of the signal. The chip doesn't matter as much, except to audiophiles.
The best bet would be to lookup the CMOY pocket amplifier. You then have to change the diagrams to be a five channel amp. (R, G, B, H sync V sync) The best chip would probably be a dual channel op amp from TI, they give free samples to "students".
I think the gain is around 5, but don't take my word for it. I am too afraid to do my own, and I'm an EE. For 15 bucks, I think it is worth the lack of effort. You will spend at least 10 in parts (bread board, resistors, sockets, wires, capacitors) Besides, sending too much voltage could cause massive monitor damage.
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There is a pretty simple video amp circuit on the pc2jamma page.
http://www.mameworld.net/pc2jamma/hardware.html
I have this built and sitting on my bench, but I haven't had time to try it out yet.
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Thanks for the replies so far.
I've built a few op amp circuits in my day (they are pretty much hard to avoid when getting an advanced degree in Electrical Engineering ;D )
Something like the OPA3692 from TI looks interesting, (no resistors to add that might pick up noise etc), but only has a fixed gain of 2. http://focus.ti.com/lit/ds/symlink/opa3692.pdf. I'm wondering if something similiar (but with higher gain) is what is used on Ultimarc's version...
I've looked at the pc2jamma one, but I was too lazy (so far) to figure out how it works without converting the layout shown to a schematic. I'm curious to know how it works out for you, or, if you'd like to send it to me I'll be glad to check it out ;)
I don't think amplifying the sync signals is necessary, but I'll admit that RGB video wasn't a heavily covered topic in engineering school :)
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OK, I didn't realize that there is a hi-res picture of the amp on the Ultimarc web site. Upon closer inspection, it looks like a "standard" op-amp with external resistors is used (I'm sure its not a garden variety type, probably a medium/high speed device for fast transitions). I'll keep looking for an IC with a fixed gain of, say, 4. Let me know if anyone finds something interesting :)
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Don't forget that you need over 6 MHz of bandwidth for video. Some op-amps have internal low-pass filters to limit destructive oscillation in typical feedback circuits.
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I built the one on the pc2jamma page and it worked well, but not worth the trouble because of the price difference between it's parts and labor needed to assemble vs the ultimarc amp.
Later,
dabone
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How about something old? Like a TL082c on those old Atari boards. They cost about $1.
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I've built a few op amp circuits in my day (they are pretty much hard to avoid when getting an advanced degree in Electrical Engineering
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I've built a few op amp circuits in my day (they are pretty much hard to avoid when getting an advanced degree in Electrical Engineering ;D )
DOH! ;) You coulda said this before my EE banter, so I wouldn't have come off like an I'm an EE and you are not! >:( :D You have to admit that Op amps were one of the more difficult areas of EE.
How far did you go? I'm in my masters now, but in signal processing.
MSEE :)
(No offense taken, by the way, your words of caution are always appropriate. The "textbook" use of op-amps is easy, its the "real life" part that will get you every time (stability, noise, etc) ;D )