What type of capacitor should I use?

The C/V "gotcha" is best mitigated by using a part that is overrated for voltage. The C/V effect is relative to the rated voltage so if that is several times the circuit voltage there won't be much effect. It's when you try to operate near the rated voltage that it causes problems. I've also seen data that indicates the larger package parts have lower coefficients of capacitance change with voltage.

You can also use C0G types which have a better dielectric which has a very low coefficient of capacitance change with voltage.

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t animal to the rest, ceramics are immune to the melting problems of some p lastic film caps, their light weight aids robustness, they're small, they t ypically handle way above rated voltage without trouble if ever necessary. Slight microphony is not a problem in lots of applications - it is only ver y slight. The C/V gotcha only applies to some, and obviously one need be aw are of it at design time and choose accordingly.

liable in a lot of situations. As with everything, not in every situation.

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mics as audio decoupling they need to either not have the C/V gotcha or be big enough to still have enough capacity down at 20Hz to not get in the way AND the dc component across them needs to remain steady.

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Picking a random Y5V, C is down to just 20% at 40% rated V, 40% C at 20% ra ted V. John Larkin tested a 4.7uF 50v cap and found 0.8uF at 30v, 1.33uF at 20v, 2 .86uF at 10v. It was down over 90% at rated V, 0.42uF.

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Of course. But one doesn't need C0G for run of the mill decoupling, bypassi ng etc.

NT

Yeah, if you are going to pick the worse possible type of cap it won't work as well. Try an X5R type and it works a lot better.

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It will be tough to find good ceramics in the values listed with voltage ratings high enough for tube gear. Polyester (Mylar) or Polypropylene are better choices.

As for the quality of ceramic capacitors, it depends on what kind of ceramic is used. C0G ceramics are about the best capacitors you can easily get. They are very stable, have very low loss, and are excellent in just about every other way. The one way they are not excellent is that, except for low values (less than around 1000pF - depends on manufacturer) they are large and expensive. Mid grade ceramics like X7R are less stable and less expensive. They are suitable for most audio frequency work. The really bad ceramics are the ones like Z5U. They are truly horrible in most ways and are suitable only for non-critical circuits like supply bypassing. They are, however, tiny and very cheap. Go to the manufacturer's data sheet for the capacitors you want to use to see if their characteristics match the application.

ack on that. it's always good advice to see the data sheet.

Somewhat recently, I bought some 500V 0.047uF ceramics that I use for high freq bypass in a 400V power supply. I checked, it's X7R. no problems noted. (got them from digikey along with others)

but yeah, the part selectors don't give you a whole lot of choice for capacitors at voltages about 100V, sometimes. Still, I've never had a problem with what I've purchased that way.

actually, I'd think that you just have to be careful and pick a reputable manufacturer.

that might be in a lot of cases. I haven't had that much trouble, but price DOES go up rather fast as the rated voltage increases. I'll consider mylar/poly capacitors also, test, see what happens.

A useful percentage of it (unknown China brands) is ok quality. A fair bit is pretty abysmal. Electronics seems to be worse than mechanical tools.

NT

On Wednesday, August 16, 2017 at 7:44:33 PM UTC-4, snipped-for-privacy@gmail.com wrote: Electronics seems to be worse than mechanical tools.

Not possible. Chinese tools are killers.

Peter Wieck Melrose Park, PA

I had a close call with one, but a lot of them are fine. Not really so with electronics.

NT