CAPACITORS (what i gathered searching DIY Audio forums and exploring web, mostly copy and paste work)
Capacitor ranking generally follows the dielectric constant of the dielectric: the lower it is, the better the cap. With a lower dielectric constant comes lower dielectric absorption and related losses.
Teflon and certain types of oil, wax and paper (DC ~ 2) are head-runners, therefore, followed by polystyrene (2.2) and polypropylene (2.3), mylar (3.1) being somewhat further down the list. Air, of course, is the best dielectric (1.0). The better Nordost cables sound so good because they achieve a very low dielectric constant in their insulating material (1.3), combining teflon and air in a manner allowing very little contact between cable and teflon, rendering a mostly air dielectric. Polyethylene (2.25) is also quite good (Jena cables, I believe, are insulated with this substance).
Ceramic multilayer caps have a sound as good as film caps.
Some further reference about audio quality of caps:
https://www.capacitors.com/picking_capacitors/pickcap.htm
The problem with low dielectric constant is a larger physical size capacitor is required for a given capacitance. Manufacturers may prefer a mylar capacitor over an electrically better performing cap simply due to size and $$ considerations.
well... here are the considerations you should make when selecting capacitors...
first of all... what function is the capacitor serving?...you shouldn't use a film cap if you are dc blocking... because film caps aren't polarized. if you are just filtering a power supply or power supply rails on the circuit then the type of cap is not so important.. in fact caps with poor high frequency response are preferable... just make sure you are operating within acceptable parameters for the circuit... proper voltages etc...
Silver mica caps are good if you are bandwidth limiting an opamp...
(a compensation cap in the feedback loop).
If a cap is used in the audio path then you should select one that has low esr (equivalent series resistance) and one that passes high frequencies well...
vishay/roederstein make great film caps for use in the signal path.. their polyester and polypropylene caps are excellent.
The metallised 5 mm pitch polyesters "small rectangular grey boxes"by Rifa Evox are good and so are the open ended stack foil polyesters (ugly as hell but sound wonderful!) by Siemens. They come in values up to 10uf!
Also look for Wima caps.
Good ceramic multilayer caps are those from AVX.
If you need a larger value poly film cap then you can use a nichicon 105c rated electrolytic bypassed with a .1uf poly cap... this will take care of the high frequencies.
Where?
I suggest you check the RS or Farnell catalogs.
The bigger film capacitors you can get them at Handmade
https://www.hndme.com/storesolen630a.html or at Wellborne Labs
https://www.welbornelabs.com/parts.htm, bigger film caps from Solen are not so expensive, specially in this sites; it seems to me that you should rather trust the audio quality of components from this two sites.
