Fun with foil caps
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[Deleted User]
Posts: 7,658
I've just confirmed a method, described in the DIYAudio forum, to determine the correct installation polarity of foil type caps. The goal is to determine the outside foil layer from the inside foil. This type of cap sounds slightly better if the outer foil is connected to the load. In order to do this you would need a Variac, oscilloscope, a small coil and a couple of clip leads. The procedure is to connect the cap's leads to a Variac and adjust the AC output to 10/15 VAC. Use two different colored clip leads so you'll know the polarity of the connections. I used a three-prong AC cord that has been cut so that the green, black and white wires are exposed plugged into the Variac so I can make individual connections to the white and black leads. Then connect one 'scope probe to one of the leads of the small coil and bring it very close to the cap. Set the 'scope to around .02V and 5mS sweep. You should now have a sine wave displayed, adjust the vertical position so you can measure the strength of the signal. Reverse the white, black wire connection at the Variac and note if the signal is stronger or weaker. Whichever connection gives the stronger signal the connection on the cap that is connected to the black wire is the outer foil side, since it couples better with the 'scope's probe.
I was testing some MIT Multi-caps and with a little practice I could easily determine the correct polarity.
Enjoy, Ken
I was testing some MIT Multi-caps and with a little practice I could easily determine the correct polarity.
Enjoy, Ken
Post edited by [Deleted User] on
Comments
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Ken, are we talking crossovers and/or power supplies, etc.?Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Coupling caps, possibly crossovers. Here's someone else who does the same thing: http://jimmyauw.com/2010/04/24/observing-inner-and-outer-foil-of-some-popular-capacitors/"He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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Hey F1nut,
I've not done very much work with speaker crossovers, except fixing a boatload when I worked for Polk (my wife and I still chuckle over rewinding a coil in our back yard, going from the front of the house to the alley in back). But, in general terms there seems to be a better sounding "direction" in putting a film type cap in any circuit. Some companies such as V-cap have a "green" lead and a "red" lead to tell you the "direction". Suppliers such as Michael Percy will mark one of the ends to tell you.
I had read that the MIT RTX caps were especially sensitive to direction and that the manufacturer's label weren't always a reliable indicator of which lead was the outer one. So, I did some searching to see what I could find. Believe me, this is no reflection on MIT, just on my audiophile paranoia. There seemed to be two methods, one I described and the other involved using a sensitive multimeter and holding the cap in your hand to induce a voltage into the outer foil. I couldn't get that one to work, so I tried the second.
Another approach would be to use clip leads to try the cap, in the circuit, with different orientations to see which sounded better.
Ken -
I love this hobby. Just when I think I know it all, something else pops up. Thanks!my wife and I still chuckle over rewinding a coil in our back yard, going from the front of the house to the alley in back
You're a good man, Ken.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Ken, I've used old open face fishing reels to rewind solenoids when the wire gauge is small enough.Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ * Signature Series Sonore Music Server w/Deux PS * Roon * Gustard R26 DAC / Singxer SU-6 DDC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *
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I thought this was going to be about tin foil caps to prevent the government from reading our minds.
Lumin X1 file player, Westminster Labs interconnect cable
Sony XA-5400ES SACD; Pass XP-22 pre; X600.5 amps
Magico S5 MKII Mcast Rose speakers; SPOD spikes
Shunyata Triton v3/Typhon QR on source, Denali 2000 (2) on amps
Shunyata Sigma XLR analog ICs, Sigma speaker cables
Shunyata Sigma HC (2), Sigma Analog, Sigma Digital, Z Anaconda (3) power cables
Mapleshade Samson V.3 four shelf solid maple rack, Micropoint brass footers
Three 20 amp circuits. -
I thought this was going to be about tin foil caps to prevent the government from reading our minds.
I too was going to speak of the fun I have with my tin foil hats.
Off to the optometrist I go!
And Ken....thanks for that tip.
