DIY Stompboxes > Building your own stompbox

Mouser ordering question

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newbie builder:
I need a 3.3uf Non polarized capacitor for a pedal, and i'm ordering the  parts from small bear. Does:    

Capacitor, Electrolytic, Axial 16 V

Mean that it is polarized? If so, can i just use two and link together the negatives do I have one non-polarized capactitor?
Thanks--

rockgardenlove:
^Nope, that won't work.  They are polarized.  In most cases a polarized cap will work fine though, what circuit are you building?

newbie builder:
AMZ Mini Boost. ;D

R.G.:

--- Quote ---Mean that it is polarized?
--- End quote ---
Every electrolytic capacitor is polarized unless it explicitly and clearly says otherwise. The notation may be "bipolar" or "non-polar".


--- Quote ---If so, can i just use two and link together the negatives do I have one non-polarized capactitor?
--- End quote ---
Yes, you can. You can make a quick and dirty NP cap by tying together the negatives of two equal-sized polar caps.

In the series-NP connection, the capacitance value is funny. Normally caps in series are a smaller capacitance than either cap by itself. If you had two 3.3uF polyester caps, then the expected value for two of them in series is 1.65uF. However, electrolytic caps actually conduct in the reverse direction, so two 3.3uF polarized aluminum electrolytic caps act like they each have a diode in parallel with them that conducts when the voltage is backwards for that one cap. So two 3.3uF caps hooked up as series non polar (i.e. negative to negative) look like a single 3.3uF NP cap.

... except for tiny region near zero volts where they withstand a tiny reverse voltage, so they look like 1.65uF there...

ACK~!!!

But yes, you can use two polarized electros in series negative to negative to do the job.

NB: Mouser has NP caps...

newbie builder:
Thanks! I was going to order from mouser, but instead I think I'm going with Small bear so if I can get everything there it makes life easier, I have no problem with connecting the negative leads of two capacitors. Another obviously newbie question is when looking at the mosfet boost schematic calls for a "9.1v zener" Whats that?
Thanks!

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