Electrolytic capacitor woes in simple preamp - diyAudio
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Old 22nd September 2004, 11:02 AM   #1
mattw is offline mattw  United Kingdom
diyAudio Member
Join Date: Apr 2004
Location: Oxford
Question Electrolytic capacitor woes in simple preamp


I have been building a very simple guitar preamp to interface my guitar to my PC's soundcard. I have based it on the 'guitar-to-hifi box' design in:


I have replaced R3 and R4 with a single 100K linear pot.

I bought my parts from Maplin Electronics, and the electrolytics I have received do not have the usual arrows pointing at the connecting leads. Instead, they just have a black band at one end. I have searched and searched and searched the Internet and it is really hard to find references to this way of marking an electrolytic (plenty on paper non-polarised caps however.) The very few answers I have found disagree amongst themselves - I found one that says negative at the black band, and another that says positive at the black band.

Can anyone please give me the definitive polarity answer for these capacitors?

Furthermore, what will happen if I connect them the wrong way around? I have been running the circuit on a breadboard with the black bands as positive.

Thanks for any help
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Old 22nd September 2004, 12:22 PM   #2
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Join Date: Jul 2003
Location: Newcastle, Australia
Usually the black band indicates NEGATIVE end, just as the arrowed markings usually point to the negative end. Does the capacitor body have a recess around it towards the other (non marked) end? - if so that end is positive and marked end is negative.

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Old 22nd September 2004, 12:32 PM   #3
mattw is offline mattw  United Kingdom
diyAudio Member
Join Date: Apr 2004
Location: Oxford
There is indeed a sort of indented ring towards the other end to the black band. Thanks very much for your reply!
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