Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Tube DIY Asylum ]

---

[ Alert Moderator ]

---

RE: Reasonable sounding question but likely missing the boat.

Posted by Russ57 (A) on July 25, 2016 at 14:59:16

In Reply to: Importance of the "polarity" of a film capacitor posted by Lew on July 25, 2016 at 08:22:25:

As TK mentioned it has a lot to do with impedance. The outer foil lead should go to the lower impedance side of the circuit.

Consider a coupling cap. Be defintion (i.e. for it to be coupling) the AC voltage across it must be near zero. That pretty much means your impedance at each end is roughly the same. The part a lot of folks miss is the impedance of the coupling cap itself. The stuff you are concerned about happens when one end is many kilo/mega ohms to ground and other end is at ground.

I suppose the point I'm trying to make is....when you have high impedance signal carrying wires/parts....it is more important to keep them away from unwanted noise signals. Don't think the "outer foil of the cap stuff" makes up for having that cap too near AC heater wiring!

I'll admit I can manage a "thought experiment" where outer foil location matters (and by all means it can't hurt so do as you wish)....but there are many areas where signal purity/intergity is far more important.....be it aerospace/defense/medical imaging/diagnostics/etc.....yet never once have I seen such caps marked, or tech notes suggesting one pay any mind to which lead goes where on a film cap.

This post is made possible by the generous support of people like you and our sponsors:

Atma-Sphere Music Systems, Inc.

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---