On a supposedly robustly-designed power amp, I saw a 2.2uf X2 capacitor soldered right onto the IEC socket between Live and Neutral (as it should), before the power switch -- i.e., as long as the amp is connected to power, the capacitors are always on.
I know X2 capacitors are designed against catastrophic failure, but is this still an issue? I would think that, for example, in a lightning hit, the X2 capacitor could still short, causing fire/blown of house circuit, whereas if placed after the switch (an overrated DPDT), the high voltage may not get pass the switch to cause any damage.
I know X2 capacitors are designed against catastrophic failure, but is this still an issue? I would think that, for example, in a lightning hit, the X2 capacitor could still short, causing fire/blown of house circuit, whereas if placed after the switch (an overrated DPDT), the high voltage may not get pass the switch to cause any damage.
This is a non-issue:
1. If the X2 capacitor is actually safety approved then it will not fail short circuit. See http://www.kemet.com/Lists/Filestore/EvoxRifaRFIandSMD.pdf
2. If the house wiring is sufficiently poorly designed/installed that a lightning strike gets to the IEC socket then the X2 cap will be ok and the open switch will likely arc over and destroy any downstream circuitry.
3. The equipment line fuse should be suitably rated so that any 'bad' behaviour causes the line fuse to blow and isolate the downstream equipment. It can do this because even a metric 20x5mm fuse (the size you will find inside an IEC power inlet that incorporates a fuse) has enough clearance to prevent arcs at high voltage
To prevent switch arcing you put a 10-47nF X cap after the switch.
A cap before the switch is an attempt at mains filtering, or possibly power factor correction. Using a cap alone will not work very well as a filter because it is relying on mains wiring inductance to form the series element of the filter.
There are some people who believe that adding a big cap across their mains supply improves sound. Some put it in a distribution unit; others add it to a plug which then plugs in to the distribution unit.
A cap before the switch is an attempt at mains filtering, or possibly power factor correction. Using a cap alone will not work very well as a filter because it is relying on mains wiring inductance to form the series element of the filter.
There are some people who believe that adding a big cap across their mains supply improves sound. Some put it in a distribution unit; others add it to a plug which then plugs in to the distribution unit.
in a lightning hit, the X2 capacitor could still short, causing fire/blown of house circuit, whereas if placed after the switch (an overrated DPDT), the high voltage may not get pass the switch to cause any damage.'
I think it will make little difference having a 1mm air gap in the switch with a few hundreds of thousands of volts at many mega joules!
I suspect the 2u2 cap is an attempt to help with PFC.
I think it will make little difference having a 1mm air gap in the switch with a few hundreds of thousands of volts at many mega joules!
I suspect the 2u2 cap is an attempt to help with PFC.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.