Video Amplifier circuit - Pls explain

[stuboy78]

I have to make one video amplifier. can anyone please explain the following circuit diagram. I know all the parts except P1. Is it some kind of resistor? why is the symbol different?

Pls also tell me why all those parts are used like capacitors, resistors, transistors so i can understand the use of them in circuits in an easy way.

**broken link removed**

 

[Mikebits]

I have to make one video amplifier. can anyone please explain the following circuit diagram. I know all the parts except P1. Pls also tell me why all those parts are used like capacitors, resistors, transistors so i can understand the use of them in circuits in an easy way.

http://www.newcircuits.com/chimage.php?s=cir_vid001.gif

Pls hit the refresh as that site doesnt allow external linking.

P1 is a variable resistor. Should have the right ref designator like R1, some use VR1. I just use the former. If you want to learn about all those parts, I suggest you get a book. Too much to explain in a single post.
You might also look here.

 

[stuboy78]

In the above circuit, do the capacitors have to be os some VOLTS? or are capacitors always the same as long as the nF or uF value is matched?

 

[Mikebits]

The rule of thumb is to use twice the supply voltage. So if Vcc is 12v use caps rated at 24V or better. For coupling caps that see small DC or AC the V rating is not a big deal, most junkbox caps will work as a coupling cap. Example of coupling cap is C3. The other caps in your circuit should be 24v rating.

 

[Mikebits]

Someone else may know better, but that circuit does not look so good to use as a splitter as there may be some distortion in the 3 outputs. A normal pushpull has a balanced transformer. Important thing would be to use 1% resistors for R5 and R6.

 

[stuboy78]

cant i amplify the video signal by using just a Transistor and a few resistors?

im looking for such a project on the net.

 

[Mikebits]

So you just want a video amp? Is this standard video as what comes out of the yellow RCA jack, or is it the signal which comes out of the screw on connector?

The circuit you posted looks like a splitter ckt for baseband video and not RF.

 

[stuboy78]

What i want to amplify is Composite Video. Yes that comes from the yellow connectors.

i just want to make a small circuit that takes one Yellow Video In and distributes to 6 TVs in a TV Shop thru AV-in connectors that tvs have. (only video not audio).

i got one project a part of which amplifies video signal using this :

**broken link removed**

but how do i set the power in this... say i want 6 tvs and tomorrow he wants to hook 12 tvs... how do i know how much power this circuit gives?

 

[GonzoEngineer]

I used to design Broadcast Video Equipment years ago.

Google "Linear Technologies" and then do a search on Video Amplifiers.

Good stuff, and very easy to implement!

 

[audioguru]

StuBoy,
You want a composite video distribution amplifier, not a video voltage amplifier.
The extremely old circuit you found is too complicated and used parts that have not been made for 30 years.
The single transistor won't work.

You need a video distribution amplifier IC that has a gain of 2 so that you can add a 75 ohm resistor in series with each output for an impedance of 75 ohms to match the 75 ohm input impedance of each video monitor.

 

[stuboy78]

Can u suggest any IC?

 

[audioguru]

Most semiconductor manufacturers make video distribution amplifier ICs. About 15 years ago I used ones made by Motorola.

 

[stuboy78]

hi audioguru,

u said :

You want a composite video distribution amplifier, not a video voltage amplifier.

whats the difference?

can an IC from MAX like MAX4030E/MAX4031E be fine with me?

 

[audioguru]

whats the difference?

can an IC from MAX like MAX4030E/MAX4031E be fine with me?

The MAX4030 needs two resistors to set its gain to 2. A video distribution amplifier has the two resistors built-in.

 

[stuboy78]

i just found out about MAX9513. the site says its good for 2 outs. do u think its a distribution ic?

 

[audioguru]

The MAX9513 can drive only two video monitors and it is so small that you might not be able to solder to it.

 

[stuboy78]

what if i use one such ic for every 2 composite outs that i want? so 3 ics for 6 outs....

 

[audioguru]

You can use 3 ICs for 6 outputs. Connect the 3 inputs to one 75 ohm resistor to ground and to the input video signal.