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Capacitor polarity- are we putting them in backward?
- Thread starter MarkWComer
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I had this quandry/dilemma/head scratcher/question about some Orange Drops I used when re-building a Heathkit tube integrated. I used Orange Drops to replace all of the, as the assembly manual called them, "tubular capacitors". The manual stressed that the capacitors be installed exactly as shown which referred to an end of them marked with a "bar". Being as how my understanding was that film capacitors are non-polarized, I installed the new ones without heed to a possible polarity difference. What I ended up with was the amp worked splendidly on all inputs except MAG PHONO which had a hum. Two people checked it out but neither could identify what was causing the hum. I also asked why the original capacitors were marked but again, neither knew. Maybe this stuff is before their time.
I formulated what I thought was stupid idea that maybe all the new components were picking up noise where the old ones were not. In doing a considerable amount of online reading, I learned that one lead of a capacitor is the outside layer. I thought perhaps that if I was able to identify which was which, I could mark the outside layer leads and re-install them as per the manual's direction. I posted this question on DIY Audio and got a few responses - some were over my head. But this suggestion was given for determining which capacitor lead was which:
To find the outer foil connect the cap to an amp input. Hold the cap in your fingers. Note the level of hum. Turn the cap around. Try again. Loudest hum means the outer foil is connected to the amp input. You can use a scope instead of an amp if you have one.
Since I have no scope, this is excellent information. I received this tidbit of knowledge only recently and have yet to put it to use. It will be soon though as I think this might be the answer.
EDIT: this comment preceded the above:
Normally the outer foil should connect to the lower impedance node - could be ground if it is a decoupling or filter cap, or the anode if it is a coupling cap.
If, as seems to be the case here, the cap can pick up significant hum then it is not only necessary to get it the right way round but also in the right position - distance from nearby AC conductors matters. Keep it well away from heater wiring, for example. This sort of thing was routine in the 1950s, but modern audio enthusiast have forgotten these old skills.
I formulated what I thought was stupid idea that maybe all the new components were picking up noise where the old ones were not. In doing a considerable amount of online reading, I learned that one lead of a capacitor is the outside layer. I thought perhaps that if I was able to identify which was which, I could mark the outside layer leads and re-install them as per the manual's direction. I posted this question on DIY Audio and got a few responses - some were over my head. But this suggestion was given for determining which capacitor lead was which:
To find the outer foil connect the cap to an amp input. Hold the cap in your fingers. Note the level of hum. Turn the cap around. Try again. Loudest hum means the outer foil is connected to the amp input. You can use a scope instead of an amp if you have one.
Since I have no scope, this is excellent information. I received this tidbit of knowledge only recently and have yet to put it to use. It will be soon though as I think this might be the answer.
EDIT: this comment preceded the above:
Normally the outer foil should connect to the lower impedance node - could be ground if it is a decoupling or filter cap, or the anode if it is a coupling cap.
If, as seems to be the case here, the cap can pick up significant hum then it is not only necessary to get it the right way round but also in the right position - distance from nearby AC conductors matters. Keep it well away from heater wiring, for example. This sort of thing was routine in the 1950s, but modern audio enthusiast have forgotten these old skills.
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Thanks Mark for the video link. Very interesting indeed. In analog / audio I can see this as maybe a concern but not so in digital. From what I've read about the WOPL design the noise level is so low that it is not audible no matter what direction you mount the non polarized caps in. I do believe that the distortion spec would come down maybe a little more, observed via a good distortion analyzer, if all of the so called non polarized caps were installed observing the caps common point. But with the distortion level so low all ready, what is the point really? As Gary noted, there are places that this kind of observance would be important.
We use plate capacitors, not wound capacitors in the White Oak Control board in all signal path applications. These are not constructed like the wound jellyroll ones referred to in the video. We use wound film capacitors on the backplane but only as high frequency power rail bypass, not in the signal path.