Are film capacitors directional?

Hi Bryon,

I looked through the Fluke 115 literature. The one notable thing I found is that I think you should perform the measurement using the "AC Volts" mode, not the "AC Millivolts" mode. The meter's input is AC-coupled in the "AC Volts" mode, meaning that any DC that may be present (which might otherwise confuse the measurement) will be blocked in that mode. "AC Millivolts" is DC-coupled, which is undesirable for what you are trying to do. The "AC Volts" mode can resolve down to 1 mv, which should be more than adequate.

On the Model 115 the "AC Volts" mode corresponds to the large rotary mode select switch being at the position that is immediately to the right of the "Off" position.

Also, given my uncertainty about the need for connecting the ground wire to an outlet screw, try it both with and without that wire, if necessary and if you already haven't.

Hope that helps. Best,
-- Al

Since Al's valiant effort to help me determine the directionality of these caps has failed to produce an answer, I emailed Parts Connexion, who sold me the Mundorf caps. They said this...

Regarding the caps...while caps aren't polarized.....some people "feel" they sound better, if the outer foil is connected to the INPUT side....and the input side is on the left, when reading the case printing from left to right.

.

But this seems to contradict what I read on the auricap website, which said...

The idea is to always have the outside foil connected to the lower impedance to provide outside foil shielding to noise. Circuit OUTPUTS are always lower impedance than inputs and should be connected to the outside foil.

So does the outer foil connect to the INPUT or the OUTPUT?

You can see a picture of the crossover I'm building, prior to soldering, here. The + outputs, which haven't been added yet, are marked "OUT" in red. Assuming the outer foil is connected to the LEFT lead of each Mundorf cap in the photo, do I have the caps oriented correctly?

Thanks,
Bryon

Hi Bryon,

Yes, the Mundorf's are probably oriented correctly. The two wordings are consistent, although confusing. The lowest impedance in this context is the output impedance of the amplifier. So by orienting the outer foil of the capacitor towards the input of the speaker, which is the same as orienting it towards the output of the amplifier, you are orienting it towards the lowest impedance point.

The reason I say "probably" is that if the values of R2 and R4 are particularly high, conceivably the lowest impedance path to the amplifier's ground could be through the corresponding driver and its interconnected crossover components. What are the values of R2 and R4?

Best,
-- Al

YES- in the photo; you have the Mundorf outer foil leads connected to the x-over's inputs, which is correct(for a series circuit). Reread point three, of the auriCAP advisory, regarding connection in a x-over circuit.

You owe me a Coke, Al. We must have hit, "enter" simultaneously!