Capacitor polarization help!

losacco · 17th May 2009, 05:09 PM

Hello, getting ready to start this build and I have newbie question. As far as capacitor polarization, are plus and minus marked on all capacitors? I’ve noticed on one of the capacitors I’m using, one lead is shorter than the other. From the circuit, can you tell the hook up direction? Are resistors hooked up in a certain direction?

Thanks for any help on this.
Patrick

http://www.diyparadise.com/simplepreamp.html

torrence · 17th May 2009, 05:46 PM

Hi Patrick,

Electrotytic (and tantalum) capacitors most definitely have a polarity
and must be installed properly. Electrolytics usually have the negative
terminal indicated on the can either with an arrow or a band. They
often have one lead shorter than the other as well. Confusingly,
Tantalum capacitors that I have seen usually have the positive terminal
indicated.

Other caps (polyester, polypro, metal film, ...) don't have a polarity
even though some expensive decoupling capacitors (like Auricap) have
different colored leads. This is for noise performance, not technically
for voltage polarity, and indicates which lead is attached to the outer
shield.

A nice visual example of identifying the polarity on electolytic caps
is provided by Tubelab:

http://www.tubelab.com/AssemblyManua...citors_SSE.htm

bereanbill · 17th May 2009, 06:02 PM

Just to add to what torrence said, electrlytic caps generally will have the negative lead to ground...i.e. when used as filters, or cathode bypass caps. One exception is when used as filters in a bias circut. Then they will have positive going to ground.

torrence · 17th May 2009, 06:44 PM

The capacitor needs to be connected so that the voltage drop across
the capacitor (from positive to negative terminal) is always positive.
If you are connecting between a grounded cathode and -35V bias on
a grid, then indeed the negative terminal should be connected to
the -35V side. The point is that if the voltage on the "negative"
terminal becomes more positive than the voltage on the "positive"
terminal, the capacitor won't work, and you risk a catastrophic
failure (explosion).

17th May 2009, 05:09 PM	#1
losacco diyAudio Member Join Date: Dec 2008	Capacitor polarization help! Hello, getting ready to start this build and I have newbie question. As far as capacitor polarization, are plus and minus marked on all capacitors? I’ve noticed on one of the capacitors I’m using, one lead is shorter than the other. From the circuit, can you tell the hook up direction? Are resistors hooked up in a certain direction? Thanks for any help on this. Patrick http://www.diyparadise.com/simplepreamp.html

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17th May 2009, 05:46 PM	#2
torrence diyAudio Member Join Date: Feb 2008 Location: Oregon	Hi Patrick, Electrotytic (and tantalum) capacitors most definitely have a polarity and must be installed properly. Electrolytics usually have the negative terminal indicated on the can either with an arrow or a band. They often have one lead shorter than the other as well. Confusingly, Tantalum capacitors that I have seen usually have the positive terminal indicated. Other caps (polyester, polypro, metal film, ...) don't have a polarity even though some expensive decoupling capacitors (like Auricap) have different colored leads. This is for noise performance, not technically for voltage polarity, and indicates which lead is attached to the outer shield. A nice visual example of identifying the polarity on electolytic caps is provided by Tubelab: http://www.tubelab.com/AssemblyManua...citors_SSE.htm

17th May 2009, 06:02 PM	#3
bereanbill diyAudio Member Join Date: Jan 2009	Just to add to what torrence said, electrlytic caps generally will have the negative lead to ground...i.e. when used as filters, or cathode bypass caps. One exception is when used as filters in a bias circut. Then they will have positive going to ground.

17th May 2009, 06:44 PM	#4
torrence diyAudio Member Join Date: Feb 2008 Location: Oregon	The capacitor needs to be connected so that the voltage drop across the capacitor (from positive to negative terminal) is always positive. If you are connecting between a grounded cathode and -35V bias on a grid, then indeed the negative terminal should be connected to the -35V side. The point is that if the voltage on the "negative" terminal becomes more positive than the voltage on the "positive" terminal, the capacitor won't work, and you risk a catastrophic failure (explosion).

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