capacitors for video

[steely3]

We've all seen discussions on what is a good audio cap.

I would like to know what is a good cap on video inputs and outputs (SVHS, composite, and component). I have typically seen plain electroyltics for DC blocking on schematic for my video stuff that I repaired.

What is good for video frequencies? do good audio caps imply good video performance?

[FastEddy]

'lectronics is 'lectronics ... video caps are pretty much the same as audio, except for "old fashioned" picture tube type video equipment, which can get into some pretty high voltages ... crackle, crackle, zzzzzzttttt

FYI: this short discourse applies to all electronics usage of capacitors except for the stuff greater than a few hundred volts:
"Robert: ... I was wondering how PPS film capacitors such as Panasonic's ECH-U series compare with the rest in your testing. (Polypropylenes have had superior soakage (dielectric absorption) and superior leakage (Tau = several years) /rap) I'm in an application where I have to use SMT, and I've heard that PPS does even better than NP0 for audio signal paths. (If you can use a big enough poly, it can sound better. If you use NP0 and you chintz because it's not big enough in C value, you can't blame it on the inherent quality of the dielectric. Many people use poly and other films where SMT is "required" because they are superior and worth it in terms of performance. Solder them in by hand. Have fun! /rap)
¥ Tyler Gleghorn
¥ Pease: Why are the PPS capacitors so good? Because they are polypropylene, which is a very superior dielectric. Some people think it's an octave worse than polystyrene. I think it is an octave better, for all the applications I have seen. There are many manufacturers of polypropylene and very few now of polystyrene. Polypropylene is comparable to NP0 for audio work, but you can get 1 µF or more in a reasonable package, whereas NP0/C0G is only available up to 0.1 µF. However, many film capacitors such as poly aren't very available in surface-mount (SMT) format. NP0/C0G is much better than poly for tempco, though for audio circuits, who's going to complain about Ð120 ppm/¡C versus (0 ±30)? If you think you can hear any difference, I suggest you try some A-B-X testing. I don't think anybody can hear any difference in an audio circuit. ..."

From Bob Pease's MailBox of Feb 15, 2007 ( http://www.elecdesign.com/Articles/A...762/14762.html )

So, whether it is power supply design for digital video (almost always + 5 VDC and +/- 12 VDC) or solid state analog audio (small signal PS usually +/- 15 VDC, large signal amp PS can be as high as +/- 100 VDC) or tube analog audio ( 6 volt heaters or 150+ volt grids ), the capacitor question is pretty much the same: If you want clean signals, consider the plastic capacitors (Bob says: polypropylene, I say: polystyrene) ...

Paraphrasing Bob above: " ... I don't think anybody can [see] any difference in a [video] circuit. ..." ...

[steely3]

For high frequency bypass ceramics seemed to be preferred over film types. So. I am wondering where do video frequencies for transmission fit it in. The post mentioned seems to mention audio frequencies specifically. Any, references/experience out there.

[FastEddy]

" ... high frequency bypass ceramics seemed to be preferred over film types ..."

Yes, for higher frequencies. Of course the processor speeds of modern LCD big screen displays are "higher frequencies", but all electronic devices, slow or fast, like large, electrolytic caps as power supply bypassing ... ... whether ceramics are added to suppliment these electro types is often a judgement call not based on engineering but on costs.

The reason that articles are written directed at audio is, well, you can hear it if its wrong. With digital devices (like LCD displays), digital either works or it doesn't ... and if it doesn't, digital device engineers don't pay much attention to capacitor types but more attention to cap sizes = for tweaking the RC time constants for speed / performance / propagation timing ...