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Which comes first, capacitor or resistor?


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Trying to understand if one way is correct/makes more sense than the other..?

 

Output from video chip -> resistor -> capacitor -> video input

 

Or

 

Output from video chip -> capacitor -> resistor -> video input

 

Does it matter which order the capacitor and resistor are placed? Electronically, is one way better than the other?

 

In my tests I can't notice any difference one way or another. I have noticed that most people tend to place the resistor first followed by the capacitor, but have also seen circuits where the capacitor is placed first.

 

Just wondering if there's a 'correct' way or electronic principle that stipulates which order is best?

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  • 2 weeks later...
Trying to understand if one way is correct/makes more sense than the other..?

 

Output from video chip -> resistor -> capacitor -> video input

 

Or

 

Output from video chip -> capacitor -> resistor -> video input

 

Does it matter which order the capacitor and resistor are placed? Electronically, is one way better than the other?

 

In my tests I can't notice any difference one way or another. I have noticed that most people tend to place the resistor first followed by the capacitor, but have also seen circuits where the capacitor is placed first.

 

Just wondering if there's a 'correct' way or electronic principle that stipulates which order is best?

 

Read the Sony diagram and follow that, but in my experience it makes no difference.

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Yeah doesn't seem to make a difference.

 

Funny cos the Sony datasheet specifies:

 

Video output from chip -> 470uF capacitor -> 75 Ohm resistor -> another 75R tied to gnd -> output.

 

This is inline with my tests in that using the two 75R's eliminates video artifacts that occur in specialised situations which most people probably never notice. E.g. play level 5 of The Ninja with a std AV mod on an MSII.

 

Yet the majority of people tend to use:

 

Chip output - 75R - 220uF - output

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Yeah doesn't seem to make a difference.

 

Funny cos the Sony datasheet specifies:

 

Video output from chip -> 470uF capacitor -> 75 Ohm resistor -> another 75R tied to gnd -> output.

 

This is inline with my tests in that using the two 75R's eliminates video artifacts that occur in specialised situations which most people probably never notice. E.g. play level 5 of The Ninja with a std AV mod on an MSII.

 

Yet the majority of people tend to use:

 

Chip output - 75R - 220uF - output

 

Yeah they do, but the correct value is 470uF, and on most displays you may not be able to tell much difference, if any at all. But if you view it on a reference grade display you will be able to see the difference.

 

Over on the NEO•GEO forums there has long been a load of garbage spread that early serial numbers have better RGB, but worse composite, while later consoles have it the other way round. This is total crap, and serial numbers have nothing what so ever to do with it. The fact is that every NEO•GEO console is capable of identical output, and the factory output standard follows revision numbers, not serial numbers. A very knowledgable member over there called MKL used to be regularly seen to say the 3-5 and 3-6 had perfect bright RGB right out of the box, and this is true, but was the opposite of what others said.

 

There is even a website where a guy compares different NEO•GEO consoles and shows close up shots that are made using a capture card that is scaling the image, making the results totally invalid. He makes claims of differing levels of interpolation etc, none of which are relevant to such an old console.

 

The only thing that makes the output different is the use of incorrect component values, by changing the values to 75ohm and 470uF, they all put out the same image, because they all share the same CXA1145 chip.

 

Its all a bit of useless info there Frank, but it shows that use of correct values can make all the difference.

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Leading on from this, it's the same scenario with aftermarket RGB cables. They all claim to be following the same standard as genuine cables, and all use 75R to 220uF cap. I've never seen/owned an official cable but would love to disect one given the opportunity.

 

To further cloud the issue, I traced back the composite video circuit of one of my Master System 1 consoles that has the CXA1145 - 75R to 100uF 10V cap which in turn is connected in parallel to a ferrite bead.

 

Even Sega aren't following Sony's schematic..?

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Leading on from this, it's the same scenario with aftermarket RGB cables. They all claim to be following the same standard as genuine cables, and all use 75R to 220uF cap. I've never seen/owned an official cable but would love to disect one given the opportunity.

 

To further cloud the issue, I traced back the composite video circuit of one of my Master System 1 consoles that has the CXA1145 - 75R to 100uF 10V cap which in turn is connected in parallel to a ferrite bead.

 

Even Sega aren't following Sony's schematic..?

SNK used that same sized cap, but a 68ohm resistor, in their early consoles. Later on, they switched to Sony's recomended values.

 

The thing about Sega using that combo is their SCART leads had caps in them, and i think they were 220uF.

 

I have a Genuine Nintendo SCART lead here that was purchased not working, and the common reason these failed was buggered leaking caps. Try getting a dead one cheap now that people know that...

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A lot of video output stages have a 75 Ohm resistor in series and run 2V p-p (peak to peak) at the output when measured without a load.

 

When the TV is connected, it's 75 Ohm input impedance cases the signal to drop back to the correct 1V p-p value due to the 1:1 divider action.

 

That's why if you parallel more than one monitor on a video output the picture gets darker with each one, becoming unstable at some point as the sync level drops too low.

 

It's also why some professional / security monitors have a termination switch. That enables / disables the 75 Ohm resistor on their input.

 

That way you can hook up a bunch on monitors to one output and only turn the termination switch on for the last one (so that only one of them is providing the 75 Ohm load).

 

It's unusual to see a second 75 Ohm resistor (the one going to ground) in a video output section. I'm not sure why that would be done unless they knew that the connected device never provided the termination.

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