Cap outer foil tester build -- Peegoo Custom Special

[King Fan]

In a recent thread, @chas.wahl designed and built a testing device to silently switch the connections of a film cap connected to an amp for much quieter testing (no pops and roars from reversing leads) with much more instantaneous A:B comparison. See that thread for lots of good discussion:

https://www.tdpri.com/threads/checking-cap-foil-lead-polarity-w-o-oscilloscope.1126408/

For a deep dive on finding the cap outer foil, see Mr. Aiken, who uses a scope. For those of us who don't own one, testing by ear is an attractive idea. All you need is a cap, a plug, a couple gators, and an amp.




But it's a slightly tricky proposition: Don't forget to turn amp down while switching clips, do try to remember exactly what volume setting to return to, do try to retain exact memory of hum loudness.

In the recent thread, I was massively impressed by an idea from our smart friend @Peegoo , who figured out that a 'make before break' switch would do this without pops and roars, and (wait for it) that a 3-way Tele switch was just that. Most impressive of all, he figured out the wiring. Whatever else you do, see his post, which explains the wiring and shows how it works.

https://www.tdpri.com/threads/checking-cap-foil-lead-polarity-w-o-oscilloscope.1126408/post-11854587

I was so impressed I just had to build one. I re-drew his diagram to make sure I could get the wiring right -- you want to know which switch direction connects the sleeve of the plug to which test clip.

Anyway, here's the result. It works *great*... much easier and way quieter and *way more obvious* than twisting the volume knob while unclipping.

Thanks, @Peegoo. Next I'll try to work up a quick video demo.

 

[chas.wahl]

Now we're cookin' with gas! I guess I need to make another one. +1 on kudos to @Peegoo!

 

[ahiddentableau]

Fun thread, and it was a nice gesture to draw it up in DIY Layout like that. Nicely done.

 

[Peegoo]

@King Fan

Hey brother, thanks for the props

When I originally mocked this up, I did it with alligator clip test leads and it worked great. I particularly liked the way the switch points at the cap terminals so you instantly know which side is which. I'll bet it's even more sensitive with shorter hookups on the switch.

I gotta say, your use of binding posts is a rockin' idea...I am stealing that!

For anyone else that wants to make one of these: if you have a cap that is difficult to determine a noise difference left or right, a thing that seems to help is this: Pinch the cap with thumb and finger of one hand, and wrap your other hand around an AC cable that's plugged into a wall socket. That brings up the noise floor immediately surrounding the cap.

^^^ That is a NICE build in that project box too ^^^

 

[King Fan]

OK, here's a little demo.



What's most impressive to me is how much quieter this setup is than my alligator clips to a bare plug. The amp here is on 7, and it's not at all loud; in the past I had to have it on 2 or 3 and 3 was pretty loud.

Likewise, you can see the switching is silent -- unclipping is a pop-roar thing unless you kill the volume, which also kinda hinders the A:B thing. Finally, this setup makes it a lot easier to hear the difference in hum.

Details:
• Aiken points out several kinds of cap that don't have an outer foil -- nice to know. E-caps are obviously not candidates for this testing, but also silver mica, CD, certain orange drops...
• You don't absolutely need to build a tester. I did this on a number of builds with just the crude clip-plug arrangement in the first pic. Just be very careful to reduce volume, and return it to exactly the same level.
• Don't feel bad if you aren't testing or orienting your outer foil -- thousands of good builds don't. OTOH, any step that can reduce noise is good, plus it's kinda fun. Or of course you can buy nicer caps that have an outer foil mark.
• Aiken discusses the technical factors that tell you which way to orient the outer foil -- they're complex. A nice feature of the plans drawn by maestro @robrob is many of them have outer foil markings.

 

[Peegoo]

Or of course you can buy nicer caps that have an outer foil mark.

Don't trust those marks even on mucho dinero caps. I've sometimes found them to be wrong.

While it is true you can build audio circuits with these non-polarized caps installed 'backwards', every little bit of noise that finds its way into the signal is additive. The more holes you can plug during the build, the slower your boat will sink

Nice vid!

 

[Peegoo]

@King Fan I stole your binding post idea and replaced the grommets and clip leads I had on this one.

I used a takeoff import switch I had in the junk bin. These have the solder tabs in a straight line, but they work the same way as a CRL or OG switch. They're not as robust, however.

This has the jack on the end so the plug is out of the way. I glued one of my picks on it.

If you want to use an import 3-way, here's the scoop:

 

[monkeybanana]

Awesome. I like the use of leftover PT wire too.

 

[2L man]

Great! Connecting capacitor other way does it produce exactly same result? If not those clip wires could be shorter?

 

[Peegoo]

Great! Connecting capacitor other way does it produce exactly same result? If not those clip wires could be shorter?

There's not enough capacitance in the wires to matter in this application. This test device is intended to measure noise differences, not capacitance.

Determining the noisier side from the quieter side of non-polarized caps does matter when using them in audio applications.

For a technical explanation of the purpose of all this wackiness, look here:

 

[King Fan]

Don't trust those marks even on mucho dinero caps. I've sometimes found them to be wrong.

Good to know. All of mine have been 'correct' so far, which is nice, since a marked cap is useful here on fire-up to confirm you have the wiring / interpretation correct. OTOH, you can actually *prove* that with a continuity tester, and then the Peegoo Custom Special makes it a trivial job to confirm that *all* of your boutique caps are telling the truth.

This has the jack on the end so the plug is out of the way.

Good idea. IMO yours wins on both size and appearance. I was just happy to find a big enough box that wasn't way too big, and decided a side porch might be useful. What are the dimensions on yours?

Connecting capacitor other way does it produce exactly same result? If not those clip wires could be shorter?

You're absolutely right, physical orientation doesn't matter, just electrical. The clip wires could be pretty short, and that'd be more elegant. I left mine "too long" for testing, and to make 'em fast and easy to clip on. I may trim them over time. And if I need longer for some reason, the binding post will take typical banana plug test leads.

As a related detail, I made both leads the same non-red/black color to emphasize that it's switch *direction,* not red or black, that points to the grounded lead. Peegoo's both-black binding posts are better; I just used what I had in the drawer.

One other wire detail: I had wondered if guitar cable might be better, but that speaker cable is so quiet I decided it would be plenty sufficient. And it doesn't have to be very long either.

Finally, different caps (different types and different uF values) have different noise levels. I'd still suggest starting with the amp volume on 1 and turning up to find a comfortable volume level. I also need to try this tester with Mallory 150s, which had been 'hard to tell' with my crude method.

 

[chas.wahl]

I also need to try this tester with Mallory 150s, which had been 'hard to tell' with my crude method.

Could this be because "Mallory 150s" (now produced by Cornell Dubilier, who also make "orange drops") are metallized polyester (metal deposited directly on film dielectric) as opposed to "film and foil", which presumably has more metal thickness? (One of the advantages of metallized polyester is that the cap size is smaller, for the same value & voltage.) There are a lot of metallized polyester caps out there now, and I believe that's a relatively recent technology compared to film and foil, paper and whatever.

 

[King Fan]

Could this be because "Mallory 150s" (now produced by Cornell Dubilier, who also make "orange drops") are metallized polyester (metal deposited directly on film dielectric) as opposed to "film and foil", which presumably has more metal thickness? (One of the advantages of metallized polyester is that the cap size is smaller, for the same value & voltage.) There are a lot of metallized polyester caps out there now, and I believe that's a relatively recent technology compared to film and foil, paper and whatever.

You mean my tarpaper and spruce-gum caps are obsolete?

You're right, it'd be interesting to know if some cap materials (or construction details) made them less sensitive to outer-foil direction even when they have an outer foil. I'd also want a guide to which kinds of orange drops have a non-directional construction. IIRC Mr. Aiken is a bit nonspecific. I tried to figure it out once, but since I am allergic to orange (just prejudice and various practical details, not sonic issues) I didn't pursue it. You, Chas, may know?

 

[Peegoo]

What are the dimensions on yours?

The box is 3.54" L x 2.56" W x 1.42" H. I got 'em from Armazon: These right here.

But holy cats, the screw tunnels on three of the holes in the clamshell were too small for the provided screw heads, and all four screws could not easily pass through the first half of the clam. Goofy as hell. I had to drill things out so the screws could drop into place. What a hassle.

 

[24 track]

I posted about this in 2021 and have since tested for the foil side of 9/10th of all my caps marking the foil side with a black sharpy
building a tester is great idea

testing capacitors orientation

I came across this video about testing for polarity of unmarked capacitors like orange drops , chicklets etc I spent a good portion of today marking my stock for th e foil end of the cap this goes to the low inpedence side of the circuit , and as with almost every one else I believed that the...

www.tdpri.com

 

[chas.wahl]

I'd also want a guide to which kinds of orange drops have a non-directional construction. IIRC Mr. Aiken is a bit nonspecific. I tried to figure it out once, but since I am allergic to orange (just prejudice and various practical details, not sonic issues) I didn't pursue it. You, Chas, may know?

All I "know" is what Randall Aiken wrote:
"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."

I, too, am slightly biased against Orange Drop types, mainly irrationally; except that I also prefer the axial types in terms of layout topology. So I only have a few of them, and haven't tested those. Datasheets for capacitors are generally pretty opaque or lacking where construction is concerned, or at least it seems that way to me.

I don't even understand Aiken's description of film and foil capacitor construction:
"These capacitors are typically made by taking a long narrow strip of insulating material and placing a strip of metal foil on both sides of it. The two pieces of foil become the plates of the capacitor, and the insulator is the dielectric. This long strip is then wound into a cylindrical shape, leads are attached to the two foils, and the entire assembly is then potted in some type of material designed to keep moisture out of the capacitor and to keep the capacitor mechanically stable. Since the capacitor is wound into a cylindrical shape, one of the foil sides is on the outside, and the other is on the inside. The outside foil terminal connection is then marked with a band to indicate the outer foil position."

If the "film and foil" construction is really a foil/film/foil membrane rolled up, what keeps the two plates separated from each other electrically? Beats me.

 

[King Fan]

If the "film and foil" construction is really a foil/film/foil membrane rolled up, what keeps the two plates separated from each other electrically? Beats me.

I think it's one of those things that's hard to describe clearly. I agree his attempt is puzzling, but the wiki on it is only a little better. After I study it *and the pictures* long enough, I start to see that there really are two 'electrodes' there -- notice the contact layer(s) at the ends and the two *different* layers of metal, which alternate in a double spiral, each touching its own contact layer (or end). Hence "outer foil end."

 

[JPKmusicman]

I used a very primitive version of this to determine foil side of the orange drops for my 5E3. Worked great. There was an obvious difference in sound for me during the test. It's just a mono plug with a cable and two alligator clips. Yours is a trick setup.

 

[Peegoo]

If the "film and foil" construction is really a foil/film/foil membrane rolled up, what keeps the two plates separated from each other electrically? Beats me.

I cracked one open to have a look. His description is accurate; it's like a long narrow cheese sandwich. The bread is the conductive foil and the cheese is the insulator. If the cheese is larger than the bread, the breads don't touch! Which makes a really messy sandwich. I like bacon in my cheese sandwiches.

It's difficult to see in pics because the layers are so small and thin, but this is the idea.

Please excuse the crudeness of my model; I didn't have time to build it to scale or properly paint it

In reality, the strip of insulator (dielectric) is a teensy bit wider and longer than the two foil strips on either side. This prevents the opposing edges of the conductive foil from 'reaching around' the edge of the dielectric and making contact.

 

[Peegoo]

Thinking about this a little more...perhaps a better way to visualize capacitor construction and the extreme thinness of the layers, consider this.

Start with a roll of ribbon that is nonconductive:

Color one side of the entire ribbon with a blue marker. Color the other side with a green marker. If the ink is conductive, you have a capacitor. All that's left to do is attach a little wire to each inked side and roll it up.

The one thing I omitted from my diagram above is an additional layer of insulator that prevents the blue and green from making contact with each other. I think that may be why this all seems so confusing. There are actually two insulating layers. I'm not helping!