Step 15: Add the Video Amp

Picture of Add the Video Amp
What you need:
2N4401 Amplifying Transistor
33ohm Resistor (Orange-Orange-Black-Gold)
220ohm Resistor (Red-Red-Brown-Gold)
Soldering Iron

The RF box did more than just turn the composite to RF. It also amplified the video signal. When we took it off, the video signal became weak. We need to build a small video amp to boost the signal.
The second picture explains it all.

Solder one end of the 33ohm resistor to the emitter of the transistor.

Solder the 220ohm resistor to the other end of the 33ohm resistor. That point is your video out. We will connect that to the screen later.

The amp is finished. Clip the leads on the transistor, then solder the base of the transistor to the weak video signal, and the collector to 5v.

All this may sound a little confusing, but pictures 2 and 3 explain it all. Picture 4 has the schematic, if you prefer.

I soldered the resistor leads very close to the transistor, but you may not wish to do this. If you heat the transistor up too much, then it won't work anymore. Feel free to make the circuit on a small piece of perfboard.
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my nes died. cpu gets hot fast and blue screen when powered on. i have replaced the connector. anything else i can do?
also i reverse engineered a portable dvd player lcd to work without the dvd player control circutry and it now takes composite. 7 inch diagonal screen
Exiumind4 years ago
I, can you make a tutorial on how to create a composite multiple outputs(3) video amplifier?
I have 3 car monitors and want to connect them to the same source without having signal loss..

thanks =)
bperez294 years ago
I can use this 2N4401 to amplifier the video signal of my computer vga output to convert an rca signal?
1up (author)  bperez294 years ago
Uh, no. If I understand what you're saying.
bperez294 years ago
I can use this to amplifier the video signal of my computer vga output?
redsoup4 years ago
Is this optional if you use a clone
When I connect everything from this point on, I get power to the board indicated by the power light I still have intact, but no video signal. What did I do wrong?
I think the signal is still weak because I managed to get an image once for a quick second.
I'm not quite sure but doesn't the base work as a switch for turning the transistor "on" when voltage is applied and "off" when voltage isn't supplied? If that is true, then voltage would have to go to the base, the weak signal into the collector and the emitter would be the output video signal.
Ok. I've got it to work. One of the main problems is that for video to appear, audio MUST either be grounded or connected to the tv screen at the same time. Also, depending on the screen, you may need to add a resistor between the power source and the transistor that accepts the 5V in to strengthen or weaken the signal. I use a 33ohm resistor on my portable. Work around that number until you're satisfied.
TheLHP5 years ago
I got my transistor from radioshack..on the package it says the base is the middle pin (2) , but on your picture there it looks like you're using pin 1 (or 3) as the base..im confused.
1up (author)  TheLHP5 years ago
No, on mine the middle pin is the base. I think you need to take a look at the photos again.
TheLHP 1up5 years ago
Yes, but in photos 2 and 3 the middle pin (base) of the transistor is not soldered to any resistor, but above you say "Solder one end of the 33ohm resistor to the base of the transistor," while in both the photos the 33ohm is only connected to the first pin. Sorry if I'm not understanding this correctly.
1up (author)  TheLHP5 years ago
Oh, wow, I can't believe I never caught that when I was proofreading it. Thank you! :) I fixed it now. The text was wrong but the photos were correct.
TheLHP 1up5 years ago
Ok makes much more sense now haha thanks alot :)
Davide3115 years ago
Can i use another NPN transitor, like the 2n2222 or the 2n3904, to amplify the video signal?
1up (author)  Davide3115 years ago
I'm not sure. You can try it, but the 4401 is made specifically for amplifying.
qwertzui5 years ago
i bought the transistor and i made the video amp and everything. i just cant figure out how to hook it up to the screen. could you tell me how to get all the wiring?
qwertzui5 years ago
would this be the regular NPN transistor?
1up (author)  qwertzui5 years ago
qwertzui5 years ago
where could I buy the amplifying transistor?
1up (author)  qwertzui5 years ago
RadioShack, or online at Mouser or Digikey or some place like that.
hey dude its me again about this video amp uh what kind of electronics could i get the transistor from and ive got 2 7805 voltage regulators but they both have short pins like really short and my soldering iron was stolen by sombody and right now dont want to spend money so how do i use one of the voltage regulators? also iv got a 7805 regulator with 5 pins could you get me a schematic of how to connect that?its real name is l78mr05.
1up (author)  flame boyyyy5 years ago
You'd be best off buying the transistor from RadioShack. I don't know where to get them otherwise. And if the 7805 pins are too short to solder to, you'll need to buy a new one. I don't know about that 5-pin regulator, either. You can't make a portable without a soldering iron, so get one. Some intelligent Google searches can answer your questions.
glueman5 years ago
great instructable. I am trying to make my own, but am having difficulty with the video amp. this may be a dumb question, but the voltage for the video signal should be higher after going through the transistor correct? it is lower for me.
1up (author)  glueman5 years ago
I'm not sure how video signals are measured, but if it is volts, then yes. Did you burn out the transistor when soldering it? Are there any shorts?
glueman 1up5 years ago
no, I even switched it out with a new one and have the same problem.... I don't know what to do.
1up (author)  glueman5 years ago
Perhaps it's your NES. Did it work before you took the RF box off? It might not be loading the cartridge, too.
would a 3903 amp transistor work
1up (author)  devicemodder5 years ago
You could have put all three questions in one post... I'm not sure if any of those will work.
Could I pull these (or acceptable substitutes) out if the RF modulator box?
1up (author)  nevermind15346 years ago
I don't think so. Nice thinking, though. :wink:
would an lm386 op amp work
I thought that in Benjamin's book it said that the parts could be retrieved from the RF box? Although there were a few mistakes in the book and I haven't read that part in a while.
After looking, there are three resistors on the board. I just don't know what the difference would be, seeing as they aren't the same ones. I'll probably just end up getting those two new ones.
1up (author)  nevermind15346 years ago
I wouldn't know, I don't have his book.
bwah6 years ago
im going to work on a ps2 portable are there any alteration to the instrutions for the ps2?
Is this the right transistor?
I only ask because it says "switching transistor" and not "amplifying transistor", I was wondering if there was any difference.
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