Im a serious novice..so...how does one figure the worst case dc offset?
I think a more important consideration is that higher rated voltage capacitors will show fewer losses than those with a lower voltage rating. This is shown on the datasheets as "tan-theta" or the tangent of the loss angle, basically the real component of loss. This isn't quite ESR, but the combination of all dielectric losses. So, while the cap may never see more than a few volts of offset, a capacitor rated for 25V, 35V, or even 50V will probably perform a lot better regarding tan-theta, and thus should be more linear overall.
the ones I have are the UVP series. Would you advise against? What's to be gained from the "muse" UES series?
thanks for all the help!
A little while back, I made some APx 555 distortion measurements of a Nichicon UES1C221MPM1TD (220µF 16V) capacitor being driven at 2kHz with a +15dBV signal through a 100Ω resistor to the cap to ground, which is basically putting 56mA of 2kHz signal through the cap, and looking at the distortion voltage across the cap. In that test, there are no distortion voltage components greater than around -165dBV, the noise floor of the FFT used to measure the distortion residual. That's a lot of gobbledygook to digest, but the important point is that, compared with most other "normal" high quality electrolytics, this is an extremely low distortion level. Almost all other caps at the same drive level will show some distortion component, either 2nd or 3rd harmonic, but no harmonics were visible at all. For example, a 470µF Panasonic FR series (which is polarized, but driven with 22V DC bias) will show a tiny bit of 2nd harmonic and -140dBV of 3rd harmonic.
I have not measured a UVP cap under these conditions, but tests with dozens of other types of high quality caps almost always show some distortion component, either near residual or significantly higher. So, the point is that measurements seem to show that the UES series caps are measurably cleaner than most other types. I will make no claims of audibility, or whether this is significant, but if it's a simple choice and you have a part that measures better, I see no reason to not use it. Or, if you think this 'improvement' is insignificant, there's no reason to make a choice - use whatever you want and be happy
edit: re-reading, you say you already have some UVP, and those will probably work fairly well, so why not use them. A comparison will probably not show significant differences but if it comes time to buy more, it's worth trying the UES series. Leaning toward the higher voltage size and larger capacitance will also help, The drawback to a large capacitance cap will be increased leakage, which may be important for some circuits, so gross excess is probably not wise. But generally sticking to larger caps with larger voltage ratings will result in a cleaner cap. Setting any LF time constant to around 1Hz or so is "large enough" IMHO, and will help to reduce the signal voltage across the cap and make it misbehave less.