Is there truth to this?

[sr1200]

I came across this video and I'm sure if this is real or what? I understand that the old paper caps had markings for this, but on a modern ceramic/poly cap? If true, why dont manufacturers mark the caps? And why do we not denote it in our circuits?

Finding Polarity for NON polarized caps

 

[Sammas]

In'erestin'.

Anyone have any suggests for coupling cap-laden preamp designs to give this a spin with? It almost makes me want to try building a stereo microphone to test it.

 

[JohnRoberts]

old news...

The band or stripe represents the end connected to the outer wrap.

JR

 

[pucho812]

old news...

The band or stripe represents the end connected to the outer wrap.

JR

But does it make a difference or just a perceived difference?

 

[fazer]

suppose to make a difference on guitar and audio amps. I’ve just observed it in my old fender and Marshall amps. I’ve followed the hookup when replacing film caps in my amps. There are videos showing how you can determine which end to use on an unmarked cap using a scope and looking at electro magnetic radiation on the display drop when hooked up correct for lowest noise

 

[living sounds]

https://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitorshttps://e2e.ti.com/blogs_/archives/b/thesignal/posts/pcb-layout-tricks-striped-capacitors-and-more

 

[JohnRoberts]

But does it make a difference or just a perceived difference?

It depends on the circuit. To visualize what is going on, the outer wrap of the capacitor foil if grounded, or tied to a low impedance node (like an op amp output), can act like a shield protecting the inside of the capacitor.

Best practice is for high impedance circuit nodes to connect to the inner wrap of the capacitor, with the outer wrap connected to a low impedance. Ambient noise will get sunk to ground or low Z by the effective shield.

Of course there are different topologies. Filters using grounded capacitors obviously get the outer wrap tied to ground. Capacitors across op amp NF paths get the outer wrap tied to the op amp output, inner wrap to op amp - input.

In many cases this does not make a big difference but why not do it right?

JR

PS: Back in my kit business days I used lots of (cheap) polystyrene caps. They all had clearly marked outer foil wrap ends.

 

[sr1200]

https://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitorshttps://e2e.ti.com/blogs_/archives/b/thesignal/posts/pcb-layout-tricks-striped-capacitors-and-more

So the guy in the video showed an example of that line on the cap not actually pointing in the right direction. Guess its the same as testing the resistors even though they're labeled.

@JohnRoberts
What about the little ceramic guys where there is no marking? Are these effected the same?

 

[JohnRoberts]

@JohnRoberts
What about the little ceramic guys where there is no marking? Are these effected the same?

Ceramic disc caps are generally two flat discs, so don't have an inside and an outside.

JR

 

[sr1200]

Ceramic disc caps are generally two flat discs, so don't have an inside and an outside.

JR

Thats what i thought and why i even brought it up. Im guessing the multilayer are the ones that are in question here and the foil caps (polypro). Im just curious as to HOW MUCH of a difference it makes. I re-capped an old amp a number of years ago, didn't pay any attention to that as I didn't even know it was a thing, and I don't notice any more hum than any other guitar amp. I guess the possibility that i guessed correct on each one exists, but i doubt it.

 

[JohnRoberts]

Thats what i thought and why i even brought it up. Im guessing the multilayer are the ones that are in question here and the foil caps (polypro). Im just curious as to HOW MUCH of a difference it makes. I re-capped an old amp a number of years ago, didn't pay any attention to that as I didn't even know it was a thing, and I don't notice any more hum than any other guitar amp. I guess the possibility that i guessed correct on each one exists, but i doubt it.

Relax, it doesn't make that much of a difference for most circuits. When in doubt do it right, but don't lose any sleep over old builds, especially if they are working OK.

JR

 

[john12ax7]

There has been a lot of good sounding equipment built that has ignored this issue. So it is both a real thing and also one to not lose a lot of sleep over.

Get the prototype working properly and then build future ones the same way. In production the automation will provide consistent orientation. If building by hand then manually match things to assure consistent performance.

 

[user 37518]

But does it make a difference or just a perceived difference?

Noise can couple less into it depending on the orientation and potential across the cap.

 

[user 37518]

It depends on the circuit. To visualize what is going on, the outer wrap of the capacitor foil if grounded, or tied to a low impedance node (like an op amp output), can act like a shield protecting the inside of the capacitor.

Best practice is for high impedance circuit nodes to connect to the inner wrap of the capacitor, with the outer wrap connected to a low impedance. Ambient noise will get sunk to ground or low Z by the effective shield.

Of course there are different topologies. Filters using grounded capacitors obviously get the outer wrap tied to ground. Capacitors across op amp NF paths get the outer wrap tied to the op amp output, inner wrap to op amp - input.

In many cases this does not make a big difference but why not do it right?

JR

PS: Back in my kit business days I used lots of (cheap) polystyrene caps. They all had clearly marked outer foil wrap ends.

John beat me to it....