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I've read about the mod of installing poly caps across the A/C mains, usually Auricaps. Has anyone done this using other brands/types of caps? What were the results/differences if any?
TIA
Follow Ups:
Hey RickeyM,Do a seach of Al Sekela's posts. He offers some comments on different caps used in this manner.
If I recall correctly, he uses (or likes/prefers) siver mica caps.
FWIW: I use two 0.47-µF Auricaps between L & N in my CD/DVD player (after fuse) and two 0.47-µF Auricaps before my Class-D amps (after a circuit breaker & surge suppression)and both sets made nice improvements in the sound, to my ears. Though, I have not tried other caps, yet.
Good Luck,
Doug
The only caps that are safe are those rated "X," X2," or "Y." These are designed to be self-healing after breakdown, without causing a resistive leak. They are rated for (typically) 250 or 275 volts AC. I don't know if Auricaps have this property, and would not trust them without knowing this for sure.A capacitor by itself is not a good filter for AC line noise, because it reflects higher frequencies. A better design is a resistor in series with the capacitor, where the resistor is selected to match the AC power cable impedance. 120 ohms is a good match to typical plastic AC (Romex-type) cable. Wire the capacitor in series with the resistor and connect them to short leads of a molded, unplated plug. Better yet, use several R-C networks in parallel, where the C values are selected to decrease in decades, such as 0.47 uF, 0.047 uF, and 0.0047 uF. Each capacitor will have a different self-resonance frequency, so the collection will span a wider frequency range. Connect the capacitors to the hot lead and the resistors to the neutral lead.
If the resistors are not flame-proof, enclose the filter in something that will contain the flames that will come out if one of the capacitors fails to a short-circuit. A half-watt, 120-ohm resistor flares up like a kitchen match when exposed to line voltage.
If you can sort through bins of parts, take a small magnet and look for capacitors and resistors that are not attracted to the magnet. There are such X- and Y-type capacitors, but the resistors are harder to find. Steel parts in these components add an undesireable sonic characteristic.
Make up several of these filters and try them in unused outlets. Some outlets will give more benefit than others.
The Hammond 193L choke tweak uses the magnetic core losses to dissipate RF noise in place of the resistors in the R-C filter tweak. If you can find a big filament transformer, wire appropriate R-C filters to the secondary. The core losses will function like the choke tweak, and the R-C network will dampen noise at lower frequencies and keep the transformer from ringing electrically. The core will protect the capacitors from line spikes, so X- and Y-rated caps are not needed. It is still a good idea to use a fuse or circuit breaker, however.
The only caps that are safe are those rated "X," X2," or "Y." These are designed to be self-healing after breakdown, without causing a resistive leak.It was suggested to me quite a long time ago (by an electrical technician who works for a big name aerospace company) that carefully enclosing the cap with heatshrink (which is normally quite thick) would provide that "extra" margin of safety in the rare case of a pinprick material failure, thereby creating or approximating the outer material thickness with which an X or Y cap may be made. If I were to wrap a cap, I would probably use Kapton, which if memory serves, has a heat-resistance rating of 500F as well.
In both cases, wrapping the cap also creates the benefit of additional resonance control. Your thoughts on all of this?
Non-X- or Y-rated caps may develop resistive leakage paths internal to the cap body upon exposure to AC line spikes. Repeated spikes can and will decrease the resistance to the point where significant power is dissipated by the leak. The cap will get hot and eventually catch fire or set something nearby on fire.Your friend's tweak would be a good way to improve the outer insulation of a cap that had to be used at a high voltage with respect to ground, and may improve the sonics by reducing the acoustic response. However, it will not affect the internal leakage issue.
However, it will not affect the internal leakage issue.Wouldn't that depend on the build quality of the cap in question? And if a particular company addresses that potential failure in its intrinsic design?
The right choice of insulator and metal film are necessary, but so are test procedures. This is not a "defect" issue per se, as any capacitor dielectric will break down if stressed with a sufficiently high voltage. The issue is how well the dielectric + conductor film system heals itself after the breakdown event.With the best of design intentions and knowledge, and the best uniformity of materials, a capacitor made on a manufacturing line that does not perform testing for the self-healing requirements would be at risk for failure in a highly dangerous application. Whoever makes Auricaps may well use the test methodology as well as a self-healing design, but if they don't get third-party approval and mark the capacitors as X- or Y-rated, then how are we to know?
I was just asking about other caps used. On my CDP, I used two .47uF Dayton film & foil caps just because I had them laying around. I'm about to mod another CDP and I was wondering about the effectiveness of higher quality caps in this application.
I've tried Rifa PME 271 (metallized paper), but now I'm happy with Wima MKP-X2
(metallized polypropylene), imo much better sound than Rifa.
I didn't tweak any of the system components, but I've made some boxes with caps series inside: now I'm using 1uF, 0.47uF, 0.1uF, 0.01uF, 0.001uF in parallel in every ac line in
my house. The av system filter has caps dumped with blu tack, and all the boxes are connected with shielded cord. I live in Switzerland, in the 240V (230) part of the World.
This is my first post in the asylum, and I would like to greet everybody here, and thank
Al and Jon for all the suggestions.Ciao
M
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