“SQC” Spark Quenching Capacitors” and “RFI” caps - diyAudio
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Old 29th July 2010, 05:36 AM   #1
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Default “SQC” Spark Quenching Capacitors” and “RFI” caps

I have a quick simple question about “SQC” Spark Quenching Capacitors” and “RFI” caps. I have an Adcom 555 I am restoring after a tragic failure of one channel. The power switch is also on its way out. I would like to change the spark cap also and add an RFI cap to the ac line. My question is would the Vishay X1/X2 line be ok for SQC and what value would be appropriate “.01~.1uf/500v ? This is on US current 120/60. The EMI/RFI cap I was considering a “across the line” type of arrangement using the Vishay X1/X2 metalized film type as it is also self healing. What do you feel would be the most appropriate for this unit? There just seems to be so many different type of cap technologies and circuit topologies that can be used it can be confusing. I would just go with an EMI/RFI block unit but space seems to be a problem in this unit. I would like to just do away with the 2/conductor power cord altogether but then I have no way to properly cut the chassis either. I would appreciate any recommendations.
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Old 29th July 2010, 11:16 AM   #2
AndrewT is offline AndrewT  Scotland
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Use X1 or X2 from line to line. (line is both Neutral/Cold and Live/Hot)
Use Y1 or Y2 from line to earth.
Use a switch suppressor across the switch. It is usually an integrated package of resistor + capacitor.

I have seen an opinion that the resistor interferes with the spark suppression and the Author suggested that a capacitor alone did the job better. I cannot recall who posted that opinion.
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Old 29th July 2010, 11:33 AM   #3
infinia is offline infinia  United States
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Why do you think your proposed changes will be an improvement?
There is plenty of room in these. I've added a huge relay and socket for in-rush current limiting to save the power switch from failing.
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Old 29th July 2010, 01:14 PM   #4
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I so appreciate your input but for the time being I need a viable solution that is very cost effective. I have the expense for parts and materials attributed to the repair. I can always at a later date make a more comprehensive solution as you have suggested.
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Old 29th July 2010, 02:41 PM   #5
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Quote:
Originally Posted by embrown057 View Post
but for the time being I need a viable solution that is very cost effective.
Solution for ?
I was just interested in your plans as to the why you want to do something like that. I believe there already is a terminal strip that has such a cap across the switch. You could move one of its wires location across the line. I wasn't suggesting anything but only relating my experience for the working room for mods.
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Last edited by infinia; 29th July 2010 at 02:49 PM.
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Old 29th July 2010, 05:17 PM   #6
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I do appreciate your insight otherwise I would not be asking for solutions. The spark cap that is already in place is “open” also there is no provisions for EMI/RFI filtering in Adcom 555. I thought it best to at least change the spark cap with the best solution that was the reason for the first question. Secondly, as I stated I have no provision to correctly cut the back panel to fit an EMI/RFI filter such as a IEC inlet filter/Power entry module, if I did then I could get rid of the 2 conductor ac cord.
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Old 29th July 2010, 05:54 PM   #7
infinia is offline infinia  United States
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Are you having RF noise issues? How will you switch the amplifier if you disable the power switch? My only advice is proceed with caution. You want to indroduce a new Earth ground to your system, the potential is now there for ground loops on SE single cabling actually making things worse.
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Old 30th July 2010, 12:25 AM   #8
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I never stated that I was going to disable the power switch.
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Old 30th July 2010, 03:50 AM   #9
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A source of UL listed switch pop eliminating caps is dead PC power supplies. Having a 250 VAC rated cap used to be enough, but UL/CSA/VDE have gotten into it and do establish some quality targets for the vendor. The logo is now printed on the cap. The PC supply I salvaged had a .47 uf cap. It is now residing across the power switch of my Herald disco mixer. Twenty years ago I put a .02 uf 250 V cap across the power switch of my PAS2 preamps. It is still suppressing turn off transients. Dead PC power supplies are available at any charity resale shop, or the trash can of your PC repairman. No shipping charge either.
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Old 30th July 2010, 04:04 AM   #10
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Yes surplus supplies are great source of parts, most of the PC stuff contains dodgy brands tho. There used to be scores of surplus shops in SoCa, but they consolidated online now.
No, the problem is switch damage due high inrush current on the make not break. Stock caps are fine unless they are shorted.
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