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NOT all caps are same linear. (long)

Posted by cheap-Jack (M) on April 18, 2007 at 10:42:20

In Reply to: Re: Why polystyrene caps? Where you put them? (nt). posted by Triode_Kingdom on April 17, 2007 at 19:59:02:

Hi.

Different dielectric materials, e.g. tantalum (oxide), mica, PP, PE, teflon etc etc yield different dielectric absorption. Of course, lower the better.

That said, lower dielectric constant does NOT warrant better linearity.

Let me put it in perspective, Ic=C.dV/dt. We can plot a linearity chart of various caps on this formula.

PP film cap (dielectric constant K=2.1) is lower than polystyrene film (PS, K=2.56). But it is not as linear as PS though the curvature difference is very very small. Why? Maybe due to the aromatic structure of PS being more easily ELECTRONICALLY oriented than PP resulting less mechanical change of polymer structure.
In simple language, the interpolarity charges in PS 'relaxes' faster than that in PP.

So your choice of PS caps is good for phonostage coupling & RIAA EQ.

Incidentally, I just completed built a very basic stereo phonostage using discrete SS biplars (sorry, not tube this time) in dual-monaural stereo format with battery power supplies. It is now singing like a nightingale after a 7-day non-stop 2.5KHz wideband white noise breaking in.

Obviously, thorough breaking is needed for new caps & new hook-up wires particularly for phono amps. For low cost, I used non-polarized small polyester (PE) film box caps, ying-yang parallel to build up the required uF values for I/P & O/P coupling. Also PP & PE film caps for the simple loop FB RIAA EQ. Ag plated oxygen free high conductivity (OFHC) wires in teflon dielectric, without shielding, are used for all signal paths.

I used PE (K=3.2) simply because of the uF values required that I can add up cheaply rather than resorting costly exotic large film caps. Yet, it sounds so gratifying, proving my choice is proper.

You don't want to know the tolerance those caps & so called 1% metal film resistors when measured. That's why trimming is needed.

c-J

PS: I built it in a small black plastic equipment box. Guess how I handle the EMI/RFI/hum issues?

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