Nonpolarized capacitor Polarity,for hum rejection, 8)).

[Mosaic]

Ok,
Have a look from the 10 minute mark (for 2 min) for the proven significance of this unmarked polarity!

I learned something new!

 

[Willen]

Dear mosaic,
Members with poor internet (like lame snail) like me, will not able to get benefit from the video (impossible to streaming). I am excited to know what you leaned new. Because title of your post is amazing. I thought that non-polarized caps will never face 'Backward' problem, but...? Any article or can you teach me some basic in short please? (short because I don't want to irritate you more).

 

[KeepItSimpleStupid]

Neat!

==

"Polarity" is used loosely in the video. What the author did was to show how you can identify the foil side of a "non-polarized" capacitor manually using an oscilloscope. The technique is to hold the body with your fingers and reverse the leads. The lower amplitude connected to the negative lead is the foil side.

Early caps were marked foil with a band.

He then said the foil side of a cap should be connected in a tube/valve circuit to the lowest Z point. This makes sense.

Later, he went through a "design process" and showed the fruits of his success by making a gizmo that has two short shielded leads with alligator clips, and limits the output to +- a diode drop, and electrically reverses the leads using a version of the 4066, a Flip flop and a 555 timer powered by a 9 V battery and connects to the scope. A green LED lights at the side that should be marked negative when the amplitude is at a minimum.

 

[dr pepper]

Interesting vid.
By 'backwards' he doesnt mean wrong polarity he means that the end of the rolled foil is nearest the non ground or sensitive side of the circuit.
One thing I learned is that some caps are marked incorrectly, or the dot or line doesnt mark the end of the foil roll.

 

[audioguru]

He tested huge high voltage plastic dipped capacitors used for upgrading old vacuum tube geetar amplifiers because the original "waxed paper" capacitors were too old and leaked DC current. One end of the capacitor is the outside connection that makes a good shield but many capacitors have no marking or are marked wrong. The small low voltage Epcos metalized plastic capacitors I use in sold state circuits make very little different for their "polarity".

 

[Mosaic]

The video raises an interesting concept though. Intra circuit crosstalk via electric fields impinging on A.C. coupling capacitors in high impedance areas.
audioguru would foil encapsulated capacitors with a 3rd lead to ground be a useful component in the quest for low noise A.C./audio circuitry?

It might be an interesting exercise to add some grounded foil shielding to the caps in a modern preamp and note the effect. Of course there are less significant sources of interference these days (no high current Tube heaters or heavy transformers) unless there's a buck/boost nearby. I have seen a nearby cell phone mess with a preamp though.....it's EM squawk (when receiving msgs) ringer and vibrator produce interference. While shooting a (my experience) commercial video a powered phone in your pocket WILL screw with the audio signal and get onto the recording if it receives a message. Silent mode does not help.

Willen when I had dial up I'd start a streaming video and pause it , then come back in 15 min after it had buffered. You can give that a try!

 

[audioguru]

I have never had a problem with film capacitors "wrong end" picking up hum or interference.
In the olden days my vacuum tube amplifiers did not have a pcb so they had wires all over the place (passing by old waxed paper capacitors) and the capacitors were passed by AC wires for the tube filaments. They were built with the correct polarity of the old capacitors that were marked correctly.

 

[dr pepper]

I cant remember where however I think I've seen caps with a shield, probably something thermionic.