Polarized and non-polarized caps

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Polarized and non-polarized caps

Postby ianZeds » 14 Oct 2009, 11:42

I'm building a Dirty Little Secret, I posted a question about substituting a polarized cap, either with a different value or a non-polarized cap, the answer was a non polarized cap was fine, thanks Mike. http://freestompboxes.org/viewtopic.php ... &start=480

My question is as a rule of thumb when is it ok to substitute them with regular caps and what are the advantages and disadvantages of doing so?

Cheers!
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Re: Polarized and non-polarized caps

Postby sinner » 14 Oct 2009, 11:45

ianZeds wrote:I'm building a Dirty Little Secret, I posted a question about substituting a polarized cap, either with a different value or a non-polarized cap, the answer was a non polarized cap was fine, thanks Mike. http://freestompboxes.org/viewtopic.php ... &start=480

My question is as a rule of thumb when is it ok to substitute them with regular caps and what are the advantages and disadvantages of doing so?

Cheers!



I'm asking kindly the same question, as I would know aswell :)
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Re: Polarized and non-polarized caps

Postby Dr Tony Balls » 14 Oct 2009, 15:02

I have never shied away from replacing electrolytic (polarized) caps with non-polarized.

I could be wrong on this one, but I thought the main advantage of using electrolytics was that the construction technique allowed for high capacitance at a small size, and that the only rule you had to play by to use one is that they have a polarity associated with them, so put them into the circuit correct. So if a circuit calls for a 10uF cap you have your choice, an electro that's the size of a pencil eraser, or a non-pol that's 5 times that size. Most people opt for the electro.

I'm not sure that ANY circuit really NEEDS a polarized cap at any spot, but a schematic will usually show you polarity indicators where one would commonly use a polarized cap just because they're easier to find and fit onto the board.

Again, i could be wrong....im reasonably green at this. I'll await confirmation from one of the greybeards of the site.
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Re: Polarized and non-polarized caps

Postby ianZeds » 14 Oct 2009, 17:26

thanks for you reply, this is certainly something I will experiment with

http://geofex.com/Article_Folders/fuzzface/fffram.htm

from the above linked article, which I read, found interesting, but confess I didn't really understand...

The first transistor is set up with the simplest of arrangements - input through a DC blocking capacitor directly to the base


So a DC blocking resistor I'm assuming in this case it is the 2.2uf polarized cap, what is it doing and what happens if you put a non-polarised cap in a fuzz at the input?
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Re: Polarized and non-polarized caps

Postby Dr Tony Balls » 14 Oct 2009, 17:45

The DC blocking cap is there to separate any DC out of the input signal, leaving only the AC. In a pedal, the AC is the signal from the guitar or bass or whatever. Any DC is the power to the pedal, and you want to keep DC out of the signal chain. So all that input cap does is filter out the bad (DC) and let in the good (AC).

What happens if you put a non-pol cap in? I dont believe much of anything. I think a non-pol will do the job just as well, but its not that practical because it's gonna be BIG. Look at a site like smallbear. They're dedicated to parts for pedal building and the largest non-pol cap they have is a 1uF, probably because anything larger in value is gonna be too large in size for anyone to want in their pedals.
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Re: Polarized and non-polarized caps

Postby ianZeds » 15 Oct 2009, 08:34

great information, thank you very much this has helped me a lot
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Re: Polarized and non-polarized caps

Postby Geosh » 10 Nov 2009, 22:39

So in the case of the Fulltone OCD, why do they specify one of the caps to be Non Polar? (100n NP I think it was) Does it need an Non Polar electrolytic, or would any film or ceramic (non polar) cap work?
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Re: Polarized and non-polarized caps

Postby Dr Tony Balls » 11 Nov 2009, 16:32

Geosh wrote:So in the case of the Fulltone OCD, why do they specify one of the caps to be Non Polar? (100n NP I think it was) Does it need an Non Polar electrolytic, or would any film or ceramic (non polar) cap work?



All electrolytics are polarized (as far as I know). As far as why it specifies, I believe that non polarized caps are better in certain applications for noise reduction. It has something to do with voltage across the cap, but i'm not terribly sure about that. An electro cap will still work in the application, but a NP is preferred.
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Re: Polarized and non-polarized caps

Postby 5thumbs » 11 Nov 2009, 16:54

Dr Tony Balls wrote:All electrolytics are polarized (as far as I know). As far as why it specifies, I believe that non polarized caps are better in certain applications for noise reduction. It has something to do with voltage across the cap, but i'm not terribly sure about that. An electro cap will still work in the application, but a NP is preferred.

All electros are not polarized. I run into non-polar electros all the time when rebuilding/repairing effects. Here's a search page from Mouser that has non-polar electrolytic capacitors listed: http://www.mouser.com/Passive-Components/Aluminum-Electrolytic-Capacitors-Leaded/_/N-1b8ie?Keyword=non-polar+aluminum+electrolytic+capacitor&FS=True.

Polarity may or may not have an effect on noise reduction, but my ears have never been able to discern the threshold of difference between the two. From my experience, going from polarized electro to non-polar electro is minimal. Where I notice a difference is when replacing ANY electro with a film cap of equivalent capacitance. I get more detail (highs/lows/etc) from the reduced audio-frequency absorption characteristics of the film cap. This can also be a useful phenomenon in reverse, in that you may want to replace a film cap with a non-polar electro cap to use the audio-frequency absorption to "tame" or "lo-fi" a given section of a circuit.
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