original famicom a/v conversion

[Rockard]

Well.. I have found various amplifiers on the net. mostly japanese ones.

Recently I built this one: http://www002.upp.so-net.ne.jp/jsrc/densi/fcav2.html

But, just like last time, the picture gets too bright, and then the picture gets all wobbly!
With the last mod, I installed a pot so I could adjust the amp. The wobbliness would disappear, but instead, the colors got totally off!

In super mario bros for instance:
bright - wobbly screen with correct looking colous (but too bright)
dark - stable screen but with a bit pale looking colorus, and totally off (pink sky)

AARGH!!

Have anybody succeded constructed a WORKING a/v mod for the original red/white famicom? I have an rgb-modded-nes, and will probably make a rgb-famicom also, but I really want to get this (simple??) av-mod working also, since the palette are more accurate.

thanks or any help.

[viletim!]

I don't have a famicom but I think I can help....

This japanese amp thing you posted is just a generic 'emitter follower' amplifier with a voltage gain of 0.5. It's also not very good because the output coupling capacitor acts as a high-pass filter and distorts the video signal. By just looking at the oscilloscope picture of the video at the bottom it's easy to spot the distortion.

To make the thing function properly, remove the output coupling cap. The 10k resistor isn't needed either (though it won't hurt anything). Next to the problem of too much contrast (you did mean contrast didn't you?). You can attentuate the signal by putting a resistor in series with the amp's input. The Zin of the amp is about 2.3k (two 4k7 r's in parallel) so a series resistor of the same value will attenuate the signal by 50%. Try different values till things looks right. With too much attenuation the picture tends to look too colourful.

[Rockard]

Thanks!

I found some other schematics for what I believe is various a/v mods, for some different models of famicom, but I'm not sure.

http://www.h7.dion.ne.jp/~beta-rev/virtual...ektronik01.html

Put the link in this translator to get an "english" version.
http://www.excite.co.jp/world/english/web/
There are two "radio" buttons. the left one is active. press the right one,
then the button with the orange outline.

Would any of these be any better?

thanks!
/Rickard

[viletim!]

These are much better!

I think the "Number of most small parts" (exite translation) and "Transistor one Koku addition" look like they'll work well, the latter being the most elegant. "Torangestani stone addition" looks a bit strange to me (what's the purpose of Qadd2 ?)... it's probably ok...I just don't understand it. I don't think they are for different models of famicom but rather just different circuits that accomplish the same thing.

The circuits will only work if the video section of the famicom matches the description. If there are different models of famicom (or clones??) that have different video sections then you may just have to build a generic circuit (like "Failure example") and go from there.