Capacitor polarity?

[Oscar South]

I took the capacitor from an old bass to put into the circuit of a newer one, I don't see any markings on it or any circuit diagram to indicate polarity, does it not matter which way round its attached?

Cheers,
Oscar.

[Stewart]

Unless it's a very odd manufacturer using strange components then no - they're not polarised

[BOD2]

I've never seen a polarised capacitor in a guitar tone circuit and when a capacitor is polarised it's pretty clear that it is and which side is which.

You'll be okay to put it in either way.

[Al Heeley]

The signal from the pickups is AC cos the strings wobble both upwards and downwards. If they put a polarising cap in, half the signal would be blocked, you'd only get tone control working on 1/2 the amplitude, the rest would be cut off. Now while that might be a blessing at one of our gigs this would generally be seen as an undesirable circuit mod.

[Tengu]

[url="http://www.interq.or.jp/japan/se-inoue/e_capa.htm"]http://www.interq.or.jp/japan/se-inoue/e_capa.htm[/url]

Loads of very useful information and even more useful pictures there.

[Paul Cooke]

[quote name='Al Heeley' post='369860' date='Jan 4 2009, 12:48 PM']The signal from the pickups is AC cos the strings wobble both upwards and downwards. If they put a polarising cap in, half the signal would be blocked, you'd only get tone control working on 1/2 the amplitude, the rest would be cut off. Now while that might be a blessing at one of our gigs this would generally be seen as an undesirable circuit mod.[/quote]


sorry, but that is so wrong... blocking half the signal is what Diodes do...

A polarised capacitor will still work in an unbiased low voltage AC circuit like the insides of a passive bass, but if there's a power rail and ground involved, then you have to get it the right way round otherwise it'll unform and go duff on you... the higher the incorrect voltage, the more spectacular the unforming can be...

Back in my RAF days, we had to take items from stores and power them up every couple of years to make sure the things were still serviceable... if there were any polarised capacitors in the circuits, then we had to apply the supply voltage carefully in steps until the full supply voltage was present or else follow a reforming procedure using a separate supply across the capacitors... while doing this, the item had to be in a cage to prevent people being hit by shrapnel from capacitors that failed while reforming...

you may have problems these days with New-Old-Stock capacitors that have been sitting around a long time... these will need reforming carefully

[url="http://www.nmr.mgh.harvard.edu/~reese/electrolytics/"]http://www.nmr.mgh.harvard.edu/~reese/electrolytics/[/url]
[quote]Electrolytics do not suffer idleness well. They can cause big trouble when idle for long periods, needing periodic charging to stay "formed" and maintain the oxide layer that insulates the conducting plates. Sometimes they can be "reformed" by a slowly rising return to working voltage (see below). Even with regular use, electrolytics fail with age by drying out or leaking electrolyte following internal corrosion. If the electrolytic bulges, shows obvious loss of electrolyte, or simply can't be reformed you must replace it.[/quote]

that's why I'd recommend running your amp every six months for a few hours to make sure the capacitors in the power supply are good to go when you need it... of course, if you are using it more often, then this is redundant, but beware when turning on items that have been sat around a long time... they may go bang and let the smoke out... a failed capacitor is the most likely reason.

Edited January 4, 2009 by Paul Cooke