I just came back from Ratty Shack with this capacitor. There is no mention in the description that this is nonpolar/bi-polar, but there is no indication as to a +/- side. Before I go through the hassle of mail ordering something, is this really non-polar? I bought two for $1.60 each, so I want my money back if it's not right!
Ideally I'm looking for a 2.2 uF which is polarized. At least I think that's what I'm looking for. The source of the circuit mentioned possibly substituting metal film 1 uF, and Radio Shack had a pretty poor selection. The only 2.2 was nonpolar. In addition, some (not all) of the pictures of this circuit show a big rectangular thing, nothing like any of the capacitors in the store.
That is a non-polarised capacitor. It can be connected either way round. If it was polarised then it would most likely have this marked on..and the shorted lead would be negative.
Even so, that one should work fine even if you required a polarised type. Polarised types are normally electrolitic and can give different audio properties due to different charge and discharge specs etc.
To be honest, ive never seen a polarised cap at such a low capacitance.
Thanks for the confirmation. The circuit is pretty specific about the polarization (a plus sign on one side) and in the description it makes sense why. Digikey lists some polarized, aluminum, electrolytic 2.2uF capacitors, I'm just annoyed that I have to mail order one little part out of the whole project. And I hope I get the right part! The nice thing about Radio Shack is that if they have what you need, they likely only have one choice- at Digikey, the choice is bewildering, and to a novice like me it's impossible to know if I'm getting the best possible choice, or even something useable. I've narrowed it down, but the only catch is that it is axial instead of radial. But it's the right specs, and unlike some of the other choices, they sell it in quantities of less than 1000 ;).
Out of interest, is it a publically avaliable circuit? If so, any links to the schematic?
Thanks
P.S. I don't think it would make a whole lot of difference using a non polar cap, instead of a polar, if it is rated at the correct voltage and capacitance.
Since you asked...
http://www.geocities.com/ferocious_1999/md/micpreamp2.html
Including some variations from links near the top of the page. It might more closely resemble the "Juan" version since I will also be using a 12v power supply. Probably. At this stage it's all still pretty flexible. I'm a novice at all this (it'll be on a breadboard, I'm not ready to make my own PCB!), and I just want to try to build one that works, and then go back and try again to work on getting the lowest noise.
That cap is most likely there to filter out DC and only allow the AC signal to be amplified. Hense, a non-polarised cap should work fine in that situation.
EDIT: Should have read the page
But yes, I was right in thinking that the cap was a DC filter (why else use one? 
)
I honestly think you should stick with your non polar... I seriously doupt you will hear a difference.
I guess I'll try it, at least for the "prototype" phase, as long as you promise it won't make my $300 microphone explode...
Nope it should not make your MIC explode. Even if the capacitor was removed from that circuit, I doupt it would damage anything, except perhaps blow the op-amp, though I doupt even that would happen. The current is limited by the resistors.
As long as you use a cap rated at greater than 2.2uf and a voltage higher than around 18V, you should be fine.
That said, if you use something like an ATX psu to power this thing, expect fireworks if you have a short
Burning op-amps make a lot of smoke. Mains based PSUS can pump out way more current than the 9V battery would...
I assume you mean *no* higher than around 18v?
In general to be safe, one tends to choose a capacitor rating higher than the supply voltage.
Why? Because if you underspec a cap it will blow. Choosing a cap higher than your base voltage is to keep on the safe side.
It does not really matter what rating cap you use as long as its above 12V. The lowest I would probally use would be 13-14V as that cap is not under alot of stress. I mistyped my previous statement, sorry. I ment to say I would use an 18V capacitor or so...but if they were unavaliable, anything above 14V or so would be fine. You could use a 100V cap if you really wanted to! The only reason for using a cap at the lowest possible rating is to reduce costs, cap size and in some applications the slightly different discharge / charge caracteristics.
So go for anything above 12V, 14V and above to be cautious, 18V and above to be 100% safe
Gereral rule of thumb is to double your supply voltage...so 24V and above to be über safe :D.
Hope that cleared up some of the issues I brought up.
Edit: The cap you linked to (1uf version, if you are using these use 3 in parrelel to get 3uF capacitance) is rated for 250V, so this is definatly not going to blow and is fine for your application.
Oh and rating means up to...so a 10V cap is technically ok up to 10V...
Thanks for taking such an interest in this. I completely misinterpreted what you said- I thought the 18v referred to the power supply voltage, not the rating of the capacitor.
So if I am able to use three to get 3uF, do I wire it like this?
----cap-cap-cap-----
or like this:
......./-cap-\
---------cap----------
.......\-cap-/
Just to make sure I'm not mixing up the meanings of parallel and serial. Ignore the period dots, those are for spacing. I'm annoyed that the forums always get rid of spaces at the beginning of a line. Some of us like to indent paragraphs, and it really screws up ASCII art.
Nope, do not wire it like that. Caps in series will reduce the capacitance. So if you wire 3 1uF caps like that you will get 1/3 uF capacitance.
Yup, thats the way to wire it up. That should give 3uF capacitance, which should be fine for your application.
Like this: