whats a 1uf 'NP' ?

[The Captain]

Hi noticed on the tube screamer tonepad.com layout there's two 1uf 'NP'- what is the np mean? never come across before- the layout has larger spaces for these without polarity, so they're poly caps or summat? help appreciated, Captain.

[dai h.]

non-polarized

[Mark Hammer]

Which means they have no + or - side. You can just stick them in without having to pay attention to polarity.

Note that non-polarized is a state/category and not identical to a composition/material. Some are plastic and some are essentially fancy electrolytics (you can make an electrolytic NP by running two polarized caps in series with identical polarity sides in contact).

[Enzo]

If you do that, the two caps each must be twice the desired amount of the total. NP means non-polar, and some caps will be marked BP for bi-polar. That means the same thing.

FIlm caps and ceramics are non-polar by their nature. WHen you see NP in a schematic, or a part for that matter, it means the part is electrolytic but lacking polarity. A 1uf NP will be MUCH smaller than any other 1uf cap, but you could sub a film cap in for it.

[The Captain]

Thanks chaps, that was more complicated than I thought.. so in short its just shove a poly/ placcy/ film or whatever cap in there as opposed to a polar electrolytic which usually are 1ufs? the space seems larger I guess as 1uf polys are generally bigger..

cheers captain

[R.G.]

If you do that, the two caps each must be twice the desired amount of the total.

Actually, no, you don't need to make each one 2X because of the caps-in-series thing. Here's why.

Aluminum electros conduct in the reverse direction above about 1.5V, like soggy, poorly made rectifiers that reverse current causes to degrade. In the series-reversed-polarities setup, if the signal ever goes over 1.5V peak, the portion over 1.5V sees only one of the caps, the one with its polarity properly positioned to hold against that signal polarity.

It's only if you can absolutely guarantee that the signal is much smaller than that, perhaps unamplified guitar at 100mV or so, that you need to take into account the series caps stuff. There is a transition region between the two. cap values.

It's common in high-reliability designs where you simply MUST use the reversed-series connection to make an aluminum electrolytic bipolar to connect a Shottky diode across each cap so that the Shottky conducts in the reverse direction, not the cap. This ensures that even the minimal conduction in reverse polarity does not degrade the capacitors' oxide layers over time and wear them both out. Of course, using aluminum electros this way is very uncommon to start with, and has largely died out with the availability of high-value film caps.

Aluminum caps in reversed-series should be used only for field expedience, and never for values which set rolloff points and so on. Their value varies even more than normal electros because of the conduction effect. In fact, electros should never be used to set frequency rolloffs, period.

[R.G.]

Thanks chaps, that was more complicated than I thought.. so in short its just shove a poly/ placcy/ film or whatever cap in there as opposed to a polar electrolytic which usually are 1ufs? the space seems larger I guess as 1uf polys are generally bigger..

cheers captain

Yes. If you have the space, put in a polyester/mylar 1uF. These can be had in only about 3x the volume of 1uF electro if you're in the 50-63V range.

[Steve Conner]

To be pedantic, you only need to worry about series electros if the AC voltage drop across the capacitor combo is significant. That's not the same thing as the signal voltage, since they are typically DC blocking caps that appear as a short to the signal.

I once owned an old Studiomaster 16 channel mixer where ALL of the DC block capacitors were pairs of series electrolytics. In spite of that cheesy "feature" it worked fine. I'd still have it, if it hadn't been so damn big, I ended up getting a compact one.

The other place that people use non-polar electrolytics and I wish they wouldn't, is in some loudspeaker crossovers. I try to use plastic film wherever possible.

[oldrocker]

I used a 1uf NP cap at the bottom of my Nyquist Aliaser build. It's the big dark blue cap on an angle at the bottom of the board. I bought that at Radio Shack but after I bought them out they never restocked them. I was told they stopped selling them.
I always use 2 electro caps of the same value and hook the negative leads together when I make a non-polar electro cap. R.G. explains why and I just figured when connecting two electros together in this fashion that one cap sort of cancels out the other. Don't quote me on that though.