Testing non-electrolytic caps to find the "shielded" end

[gearhead63]

So I'm sure that most of us have installed Orange Drop non-electrolytic caps, or that type of capacitor, and never worried about which lead went where. But one lead is connected to the foil, or whatever kind of insulation or shield is wrapped around the outside of the cap. And it can make a difference.
I found a video on YouTube that shows an easy way to check these caps so that you don't install them in a way that may introduce electrical noise into the circuit. Pretty interesting. This guy uses his scope and a BNC cable with clips connected to the shield and center conductor to show how this works. But then he builds a fixture to put the caps on and check them.
Myself, just using the scope is plenty good for me. I have several that can measure down to 5mv or lower.

[mozz]

Some have a stripe marked on them.

[gearhead63]

Yep. some sure do, but that really doesn't mean much unless you actually check them.
The first part of his video will show you why.

[R.G.]

[...] But one lead is connected to the foil, or whatever kind of insulation or shield is wrapped around the outside of the cap.

There isn't any shield wrapped around the outside of foil caps, in general. They are made with two conducting/metal layers insulated from one another. Most are made by making a sandwich of layers, then rolling them up. The layers would be something like
- insulator
- foil (or metalization on one side of the insulator)
- insulator again
- foil or metalization again.
This sandwich is as wide as the finished cap is long, and as long as needed to get the total capacitance. The long, skinny strips are then rolled up in a spiral, and leads connected, one to each metal/metalization, and the capacitor insulated on the outside.

The sandwich/spiral construction being what it is, one of the two conducting layers winds up on the outside of the whole mess for the last full turn. That is your "outer foil".

There is a kind of cap which is sold as "stacked foil" which is not rolled up, but stacked in many layers. Neither of the two layers is wound around the outside of the last layer.

And it can make a difference.

Yes, it can - the operative word being **can**, not **definitely does**.

There is no magic, only the laws of physics. What matters in the choice of "outside foil" arrangements on spiral wound caps is what the leads are connected to. If one terminal is connected to a high impedance and the other to a low impedance, then connecting the outer foil to the low impedance side can make a difference.

But it can only make a difference at frequencies where the capacitor itself is a significantly higher impedance than the low-impedance side. At frequencies higher than that, the capacitance itself "shorts" the inner and outer foils together by its declining impedance. Sure, I can concoct a situation where that would be audible. But it is a process of concoction. I'm not sure how often it would be found in real tube amps.

It would make a difference in something like RF pickup if the "outer foil" side is grounded, and the self-inductance of the winding of the foils along with the distributed capacitance happened to tune to an RF source. But that's getting pretty far afield.

I found a video on YouTube that shows an easy way to check these caps so that you don't install them in a way that may introduce electrical noise into the circuit. Pretty interesting. This guy uses his scope and a BNC cable with clips connected to the shield and center conductor to show how this works. But then he builds a fixture to put the caps on and check them.
Myself, just using the scope is plenty good for me. I have several that can measure down to 5mv or lower.

What this does is to let you detect which lead connects to the outer final wrap of conductor. Detection is different from actually introducing electrical noise. Introducing noise requires that there first be noise to pick up inside a shielded amp chassis, and that the noise be a frequency that can be picked up by the differences in impedance, and that the noise that gets picked up, if any, is inside the bandwidth of the circuit.

It's far simpler to force the issue. Get yourself some adhesive copper tape. Wrap one turn of copper around the outside of the cap and then attach a wire from that tape/shield to wherever you think will make the circuit less noisy. Ground, or the low impedance source/load side of the cap itself might be good choices. This could be made into a real "shield". But you're also adding the possibilitity of piping noise in through the shield. It's almost like you have to know your circuits to tell what to do, isn't it?

And it's even better to enclose the whole circuit in a grounded metal box. This is a real shield, and it's far enough away from the cap in question to not effectively couple in noise to either foil of the cap.

It's very tempting to humans to want to polish and improve whatever they're working on. If it makes you feel good, like you've improved it, go ahead. But don't convince yourself that putting dual chrome exhaust pipes on your car makes it more powerful and smoother, either. Think about - even better, measure! - what you've done and see if you have actually made a difference, or just make yourself happy by tinkering.

[g1]

This was brought up in some previous thread I can't find, but I'll restate that no major manufacturer of amps pays any attention to the orientation of the (non-polarized) capacitors.
If there were significant gains to be made in terms of noise reduction, the manufacturers would do it and all circuit boards would be marked accordingly.
In the RF world it is a different story.

[DrGonz78]

This was brought up in some previous thread I can't find, but I'll restate that no major manufacturer of amps pays any attention to the orientation of the (non-polarized) capacitors.
If there were significant gains to be made in terms of noise reduction, the manufacturers would do it and all circuit boards would be marked accordingly.
In the RF world it is a different story.

This is the one you speak of...
http://music-electronics-forum.com/t39867/

[Enzo]

Every amp forum has this same discussion on a regular basis.

In all my years, the only place I have ever seen it matter was places like RF circuits and a pentode screen bypass needed to be "right".

It is easy to find which lead is outer foil, but as RG points out, all that means is which side of the double strip wound up on the outside after rolling.

When I have a resistor from a plate over to my cap and from there another resistor to a grid, plus any wires in between, of that whole antenna of a circuit, I am supposed to worry that the little half inch that the cap represents is where noise will be picked up?

[tedmich]

I'm also very interested in minimizing thermal/shot and Johnson–Nyquist noise in my resistors, please discuss!


A cut open ($360) Bybee Quantum Purifier

[Justin Thomas]

[ATTACH=CONFIG]36521[/ATTACH]
A cut open ($360) Bybee Quantum Purifier

(Blows raspberries)...

Justin

[trobbins]

Back in the days when a 0.1uF 400V waxed foil screen bypass was the largest part below the chassis and often straddling the input EF86 circuitry, then maybe there could be sufficient capacitive coupling to g1 wiring and parts if some care wasn't taken, especially for grid leak bias.

[Leo_Gnardo]

I'm also very interested in minimizing thermal/shot and Johnson–Nyquist noise in my resistors, please discuss!

[ATTACH=CONFIG]36521[/ATTACH]
A cut open ($360) Bybee Quantum Purifier

Looks like the connection on the right side of the 0.025 ohm resistor isn't soldered.

Is "that" what makes it work?

On second blink, the left side solder looks missing too. What are you s'posed to do, stand there and shake this thing while you hope some current passes thru? (put witch doctor with rattle smiley thing here.)

[R.G.]

I guess there's always someone willing to either consciously perpetrate fraud or to believe their own press enough to stomach taking money from people like this. I find it disgusting.

But as H. L. Mencken noted:

“No one in this world, so far as I know — and I have searched the records for years, and employed agents to help me — has ever lost money by underestimating the intelligence of the great masses of the plain people. Nor has anyone ever lost public office thereby.
[...]
The mistake that is made always runs the other way. Because the plain people are able to speak and understand, and even, in many cases, to read and write, it is assumed that they have ideas in their heads, and an appetite for more. This assumption is a folly.”

Over time, this longer quote came to be paraphrased and misquoted, most commonly in the form “No one ever went broke underestimating the intelligence of the American public.”

[Tom Phillips]

Looks like the connection on the right side of the 0.025 ohm resistor isn't soldered...
On second blink, the left side solder looks missing too...

I do not condone the hype sales technique. However, the soldering appears to conform to the standards you see in the NASA soldering course publications. Most people use far too much solder.

[Leo_Gnardo]

I do not condone the hype sales technique. However, the soldering appears to conform to the standards you see in the NASA soldering course publications. Most people use far too much solder.

I'm not much a fan of hoodoo voodoo "improvements" either, the more expensive, the more skeptical.

Squint as much as I can, I don't see any solder on those resistor/wire leadout connex. I know NASA tries to keep things light, minimize payload weight, get all the bang for the buck you can out of a launch. But if this squantum percolator was ever part of the manned space program, I expect we'd be hearing <static burst> "Houston, we have a problem."

Looks like a 1966 date code on the resistor too. You'd think the hoodoo voodoo company could sell you something made with fresh stock for that price. Shame on them. Say "Bybee" to your money. Wonder how many they sold?

edit: found a "six moons" review. My review, Mr Bybee closely resembles a well stocked deli cooler shelf: full of baloney. Have a read, try to not let your beverage exit via your nose.

http://www.6moons.com/audioreviews/bybee/bybee.html

Another review, of sorts. Last paragraph the best.

http://redspade-audio.blogspot.com/2...ke-oil_16.html

Let's not forget to mention this magnificent device is cryo-treated, de rigeur for any proper hoogle skoogle item these days, especially one rated for NASA standards. Hey, it's cold out there! Gotta be prepared. Wear your scarf & hat.

[tedmich]

Supposedly its the (VERY special) ceramic in the second from the bottom tube which imparts the miraculous properties (not the resistor which has changed several times during production). The tube ceramic is a "near superconductor" which forms Cooper pairs at room temp which, rather than just not adding appreciable noise to the signal, actually remove all noise from the signal !! That's one smart ceramic...