Re: polar vs nonpolar capacitors

"Dave" (dspear99ca@xxxxxxxxxxxxxxxx) writes:
> I am interested in upgrading some audio components, and a lot of DIY tweak
> mention "replace the electrolytics in the signal path with Black Gate or
> other low-noise nonpolar capacitors." I know that polar capacitors cannot
> tolerate reversed polarity, and that bi-polars can as they are really two
> back-to-back capacitors. What is a non-polar? How is it different from a
> bipolar?
>
> Dave
>
>

Well, it must be a non-polarized capacitor.

Polarized capacitors exist not because of function but because of
manufacturing process.

There is no need for polarized capacitors.

But, in order to have higher value capacitors in reasonable sized
packages, the manufacturers have to switch to methods that result
in a polarized capacitor. The capacitor itself objects if the
wrong polarity is applied.

For a lot of applications where higher value capacitors are required,
that they are polarized doesn't matter, because they are mostly used
where there is indeed a well defined DC voltage applied to one of
the terminals. Thus, for filter capacitors in that power supply,
a polarized capacitor doesn't matter because you connect the capacitor
from a positive voltage to ground, so it's all very clear. A coupling
capacitor on the output of an amplifier running off only a positive
voltage has a positive voltage on that output, so again it's clear.

In a few cases, the capacitor won't actually see a clearly polarized
voltage source. Crossover capacitors in speakers are a prime example,
because the DC component has already been removed, either because
the amplifier feeding the speaker has a DC coupling capacitor on
the output, or has a transformer on the output (not likely in recent
decades). Here, there is no longer an AC voltage riding on a DC voltage,
so no matter what the AC voltage one side of the capacitor is clearly more
positive than the other; there is an AC voltage coming into that capacitor,
moving from positive to negative and back, in reference to the other
side of the capacitor. You need a non-polarized capacitor there, but
the issue of size and capacitance comes into play, and most capacitors
of the values needed will be electrolytic. A common trick is to put
two polarized capacitors in series, and sometimes they are manufactured
that way, so the capacitor is not polarized.

But there are issues with that sort of scheme. For someone fussing
with types of coupling capacitors in audio circuitry, they want non-polarized
capacitors. Thus the capacitors need to be manufacturered using some scheme
that will not inherently result in a polarized capacitor. If the values
are low enough, this is not an issue. If the values of capacitance are
higher, then one has to hunt around capacitors of mylar or polystyrene or
some other scheme that does not result in a polarized capacitor, and
the result may be a larger capacitor because those other formulations
can't be so compact.

Michael


.

Relevant Pages

  • Re: [BugTraq] Peter Gutmann data deletion theaory?
    ... Secure Deletion of Data from Magnetic and Solid-State Memory ... amplification would quickly move the voltage ... The question is whether the chip could be powered up ... Dynamic RAM involves a single transistor connecting a single capacitor ...
    (Bugtraq)
  • Re: Cap or Second Battery?
    ... Here are some functional differences between a cap and a battery: ... The operating voltage of a cap is defined by the charging voltage, ... depending on the car and condition of the alternator. ... This simply means that the capacitor has the ability to ...
    (rec.audio.car)
  • Re: Need to fix old valve radio
    ... to drop the line voltage from 230V to 115V. ... capacitor rated 30 uf or larger, ... If both pins of the capacitor are ... Is the sound clear at low volumes? ...
    (sci.electronics.repair)
  • Re: Simple capacitor circuit (slowly illuminating LED)
    ... >> across the capacitor is proportional to the charge it contains and second ... I took my multimeter and measured the voltage ... I left the circuit closed for two hours just to see if it ... > Now, at their lowest, the resistance of the capacitor and ...
    (sci.electronics.basics)
  • Re: Standing-Wave Current vs Traveling-Wave Current
    ... Although the argument about no energy crossing the zero-current node is compelling, I don't feel that an adequate argument has been given to justify the wave "bouncing" theory over all other possible explanations. ... A consequence of this is that either we have a whole inductor with zero current, or the zero current point occurs between inductors, at a node to which a capacitor is connected. ... So for half of the cycle, both are putting positive charge in the capacitor, and for the other half of the cycle, both are removing charge. ... The capacitor voltage goes up and down as a result, as we can also see by looking at the voltage at this zero-current point. ...
    (rec.radio.amateur.antenna)