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Coupling Cap Polarity

From: dangerda–(at)–arthlink.net
Subject: Re: Q!!-Re Replacement Capacitors
Date: 16 Mar 1999 00:00:00 GMT
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Reply-To: dangerda–(at)–arthlink.net
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Hi Steve,

We’ve had some discussion on this topic recently.

Some caps are marked to show which terminal is connected to inner
foil, which is connected to outer foil.

The consensus seems to be that, in principle, if you orientate the cap
such that the outer foil is to the lower-z node, you may provide some
shielding of the inner foil from radiated/coupled electromagnetic
noise and interference. It would make sense for the seller to tell
you to hook the inner foil side to the load, as the source is usually
lower-z than the load, so the cap would provide more effective
shielding if orientated in that manner.

I presume that’s what you mean when you say “orient the inner foil
towards the output side of the circuit”.

Regards the effects of HF roll-off being dependent upon orientation of
a non-polarized cap, that is something I’m not familar with.

In my experience measuring HF roll-off at audio frequencies it depends
primarily upon the first order impedance of the devices, and to a
lesser extent is dependent upon the loss mechanisms in components like
capacitors and inductive devices. I suppose in some cases the loss
mechanisms might be orientation specific, but this would be a second
order effect, and probably of very small magnitude. The simple test
would simply be to measure the HF poles with the caps orientated in
both directions, and determine if there actually is a measurable
difference that has a real effect upon the audio properties of the
circuit.

Regards,
Dangerdave

>On Mon, 15 Mar 1999 17:04:42 -0500, “Pinky & The Brain” wrote:

>Looking to shed some light on the “replacement capacitor” subject as it
>applies to a Dynaco PAS-3. I recently purchased a set of 22 polypro
>replacement caps for my unit and was informed by the seller that upon
>installation I should orient the “inner foil” (right) side towards the
>output side of the circuit in all cases to avoid “rolling off” the High
>Frequencies I never realized that polypropylene tubular caps were “polarity
>sensitive”. Does anyone have any input on this matter? Any and all responses
>welcome!
>
>TNX
>
>Steve
>

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