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Re: -And that low-K capacitor thing?, OR, why aren't Z5U capacitors good enuf for audio - same deal.

You must first become familiar with the concept of dielectric absorption to understand what I'm talking about and try to get a little beyond the straitjacket of the 1930's vintage standard of steady state distortion measurements.

Higher K constants in capacitors pretty consistently have an inverse correlation with dielectric absorption performance. This amounts to a voltage deviation of up to several percent from the ideal capacitor charge/discharge characteristic for each capacitor exhibiting this characteristic or a recovery voltage of similar magnitude that can manifest itself for up to many seconds after external equilibrium is attained. Sonically, this usually manifests itself as a reduction in clarity, and particularly, perceived dynamic range. MILSPEC tests exist to quantify dielectric absorption, for precision Sample and Hold and other applications where high AC precision in capacitors is required.


These effects, of course, also apply to the silicon (K=12, in the general range of many mid-range ceramic, aluminum electrolytic and tantalum capacitors and far worse than any plastic film or mica capacitor) from which most semiconductors are made and its effects are expressed in their junction capacitances. A well known result of this is charge-storage effect in BJT's which makes it considerably more difficult to drive sand amplifier output stages at higher audio frequencies. MOSFETs also have quite nonlinear gate capacitances, partly as a result of silicon's relative high K.

Of course, if you believe that, simply because its effects often do not identifiably show up in steady state distortion measurements (which, unlike music, are specifically designed not to have any measureable transients), that nonlinear charge storage and release due to interelectrode dielectric absorption do not apply to audio, then you must also, to be consistent, believe that capacitor quality is unimportant for audio applications.

PS: the K of vacuum is 1.0000, so there is negligible dielectric absorption in the interelectrode capacitances of any vacuum tube used in audio.

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