Film cap polarity

[Mike McLane]

I was researching about signal caps only to discover that there IS a polarity to non-electrolytic caps. Apparently there is. . . . inner foil-dielectric layer-outer foil. . . the outer foil functioning as a shield similar to audio cables. The lead coming off of the outer foil should be oriented "toward ground". Would it be helpful if the capacitor slots in the PCB's were marked similar to diodes and electrolytic caps so we know how to orient them for the least noise?

 

[Brett]

I’ve read about this in threads for amp building but I’m not sure it makes a significant impact in low voltage circuits like pedals. To add to that, most film caps are not marked for polarity and marking PCBs for polarity may be confusing.

 

[Mike McLane]

It's easy enough to determine. . .

. But you may be right in that it only becomes apparent in higher voltage situations.

 

[Passinwind]

I was researching about signal caps only to discover that there IS a polarity to non-electrolytic caps. Apparently there is. . . . inner foil-dielectric layer-outer foil. . . the outer foil functioning as a shield similar to audio cables. The lead coming off of the outer foil should be oriented "toward ground". Would it be helpful if the capacitor slots in the PCB's were marked similar to diodes and electrolytic caps so we know how to orient them for the least noise?

I've seen quite a few old school polypro film and foil caps that do have polarity markings on them. IME modern deposited film caps in low voltage SS circuits for low distortion applications (the only kind I'm typically interested in for what I build) don't exhibit much if any difference in noise performance related to pin hookup, and after testing that on my old signal/noise test rig I stopped bothering with that pretty quickly. Always up for hard data that I can learn new things from though.

 

[Brett]

I've seen quite a few old school polypro film and foil caps that do have polarity markings on them. IME modern deposited film caps in low voltage SS circuits for low distortion applications (the only kind I'm typically interested in for what I build) don't exhibit much if any difference in noise performance related to pin hookup, and after testing that on my old signal/noise test rig I stopped bothering with that pretty quickly. Always up for hard data that I can learn new things from though.

Fair point and perhaps I should have clarified that most of the current production film caps that fit PedalPCB footprints are not marked to indicate polarity.

 

[Passinwind]

Fair point and perhaps I should have clarified that most of the current production film caps that fit PedalPCB footprints are not marked to indicate polarity.

As I said, in my limited testing it mostly only mattered with film and foil layups, not straight film which is far more common these days, especially for box caps. I’ve not yet built any PPCB boards and have no idea if and where it matters in that context, but I’m all ears!

 

[Mike McLane]

FWIW, I just built a tube preamp with Mallory 150's / 630v in the tone stack. Before installing them I turned my amp up all the way with a high gain pedal and tried reversing the leads back an forth across a live cable end (see YT clip above) to see if one orientation was louder than the other. I couldn't hear an appreciable difference.