Revisiting the foil end of capacitors

[dscottguitars]

Hello,

I would like some help with this please. I read the previous threads here on this subject, went to the links on how to test for the foil side, googled for more information and I'm getting nowhere. The method did not work for me, but I don't know why.

I connected two wires to a input jack, pos and neg then to alligator clips. I connected the jack to an amp, clipped them on the leads to the capacitors and with both orientations the noise went silent. Unhook one and buzz. It did not matter which side I put the pos or neg on, the result was the same. I tried four completely different caps and the same result. In the picture you can see them. The smallest one is out of an old amp and had a band marked on one side, but still there is no noise difference with the test. Why??

I read Aikens claim that some caps don't have the foil 'shield'. But with four different types I would expect something.

I also read a link from google from a tech at Mallory that this orientation is just hype. Here it is: http://blueguitar.org/new/text/threads/from_adam/components/mallory-outer-foil.pdf

I am currently working on an amp and came across this subject in the archives and now I'm worried. I have always put the caps in position by orienting the writing to be in the direction of the path. EX: Coupling caps-from plate to next stage, Bypass caps- from cathode to ground, Tone caps- from volume to tone pot and from tone pot to ground.

I have always had a bit of noise in my amps but they were all in the high gain channel and thought that was why, but now this makes me wonder.

Thanks for your help,

Daniel

[sluckey]

I'm very anal about cap orientation. I always line them up like soldiers at attention. The writing is always visible and always pointing in the same direction. I can walk down the row of caps and read every name tag without having to stand on my head or turn around. The way you lined up the caps in your pic  is perfect and would pass muster with me.   

[PRR]

> It did not matter which side I put the pos or neg on

Put your finger on the body of the cap, to induce more hum/buzz. Be sure your room has plenty of hum/buzz (lots of AC wiring).

My impression is that large caps at audio, it almost never matters. The "problem" is 0.1pFd leakage from room hum field into the body of the cap, against >0.03uFd= 30,000pFd between the two foils of the cap. What is the difference 30,000.0 and 30,000.1? About none. Your 0.1 and 1.0uFd caps, even less.

I certainly agree about "easy reading".

[dscottguitars]

Thanks for the replies...

I did put my fingers on the body of the caps. I don't think I have very much AC wiring around to get hum, this apt. is only 3 years old. There is a lot of buzz coming from the amp with the wires coming out of the input jack though. They go to nothing when both leads are connected. With just one lead connected I touched the other lead and got loud buzz but when I switched leads the buzz was the same volume. I didn't try smaller caps. Maybe I'll try that. I have some 2200pF orange drops.

Sluckey, it sounds like you don't even pay attention to the foil end issue. Is that correct?

[shooter]

it sounds like you don't even pay attention

Can't answer for Steve, but I quit paying attention once I "cleaned up" my builds, layout and wire dress will solve 99% hum/buzz, the other 1% might be premature part failure, or damage from heat

[trobbins]

In the old days, caps were much bigger physically, so there was sometimes a chance that the large cap body was nearby to power or large signal wiring to allow a bit of capacitance coupling.  For audio gear, the input stage pentode would often have a large screen decoupling cap (eg. 0.5uF 400V waxy foil paper style) - that cap was typically huge compared to any other part related to the pentode or surrounding circuitry.  Outer foil to ground (or cathode) in that situation would have made sense.

Nowadays its a very different scene, as parts are small and so parts and wiring associated with high impedance nodes and high gain can be more easily laid out to give lots of distance.

[Gitbox6924]

Mr. Carlson's Lab on Youtube has a great explanation. If you have access to an oscilloscope.

[dscottguitars]

Unfortunately I don’t have an oscilloscope. Thanks.

[Ed_Chambley]

Usualy easier if you use a fuzz pedal going to the amp.  The sound is louder and therefore the differernce is more.


On another note, some caps buzz more than others.  Most lo gain circuts are fine to me with caps either way.  I have checked old Marshall and Fender amps stock and these are not oriented any particular way.  Especially the early 70's blue Fender caps.


I have reduce floor noise, but tonal differences I have not.  The noise reduction from a little hum you can hear if there is not other noise.

In the case of some types of capacitors, such as ceramic disks, multi-layer ceramics, or silver micas, there is no "outside foil", because the capacitor is made of a single-layer, or stacked layers of dielectric material and conductor.  The orientation of these capacitors makes no difference.  Also, some higher-voltage film caps (typically the 1000VDC/450VAC and higher values, such as the Orange Drop 716P high-voltage units) use a "series-wound" technique that has two separate sections, side by side, with a common "floating" connection layer, usually at the bottom of the layer stack.  These caps will have no inherent shielding either.