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.
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.
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.
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.
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.
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.
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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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.
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.
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.
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.
No, the problem is switch damage due high inrush current on the make not break. Stock caps are fine unless they are shorted.
I have a HUGE junk box full of them, I'll get into them and see what is still good, some of them never lasted a year. That's great advice. I'm still a little fuzzy on the value. The orginal part was a .01/400v can not tell how long its been bad as I only got the amp around 3 months ago. I'm going to call around and see if I can find some one that can stamp out/cut the opening for a IEC inlet device, that will settle the other isue of the 2 conductor power cord and no filter. I have a order going into Mouser so if i need to I will order a new spark cap from them.
As to whether the risk to the power switch is turn off arc maintenance, or turn on burning, Both are risks in high power amps, turn on is less so in low power amps. Switches have gotten cheaper with less metal over the years, I am still using 1960 vintage switches in my ST70 and pas2 with no problems. But both had turn off pop sometimes, I put .02 @ 1000 across the switches twenty five years ago and that solved that. Lightning blew up one about 15 years ago, replaced it with another from the same R***** S***** surplus bag, still going strong. My point about UL/VDE listing on the power switch bypass cap in PC power supplies, yeah, they do use some dodgy parts so to get a UL rating now they have to use a rated cap on the input switch that has established reliability, or at least design.
Well it's a 700-800VA toroid with dual secondarys , 2x 25A bridges, and 60,000 uF. ( no slow start) By this, its turn on surge current is almost a function of instantaneous line voltage and primary line impedance. The turn off flyback V is a function of XFMR leakage inductance and steady state current. The former case is the pressing issue on this design!
The stock unit has a ceramic cap across the switch. These ceramics work at RFI much better than VDE film caps. The failure mode here is shorting, by an arc punch thru or carbon trail, hence spark gaps with lower breakdown than the dielectric. The line rated film caps ( self healing) use an extra floating plate to get double the diectric margin but at some RF performance hit.
The stock unit has a ceramic cap across the switch. These ceramics work at RFI much better than VDE film caps. The failure mode here is shorting, by an arc punch thru or carbon trail, hence spark gaps with lower breakdown than the dielectric. The line rated film caps ( self healing) use an extra floating plate to get double the diectric margin but at some RF performance hit.
This is exactly what I was looking for in an explanation. I was under the impression reading through the Vishay data on the X cap along with the common circuit designs I could not see any real benefit for RFI/EMI protection. Therefore I was looking for a simple solution for the inlet filter without going into cutting the panel for an all-in-one solution for that problem. I also would not mind building a simple slow start circuit for this unit depending on the overall cost associated with it. Infinai seems to have a broad understanding of the GFA555 design and I would appreciate any input you could give to further benefit my objective to; lower the MTBF of the switch and decrease or nullify any EMI/RFI introduced from the AC input. I did go through the DOA power supplies I have but the devices are of a very sub-standard design and much to underrate for this application.
1) Surge current protection in the stock configuration ie no slow start, the AC switch contacts are taking a beating because they are not rated for the peak currents on turn on. Lots on documented failures in the field of broken switches.
I have designed and build a simple slow start circuit documented on this forum. ( I used a surplus HD 110V relay across a large ceramic power resistor on the primary. The relay coils are energized by both secondary rail voltages ~160V DC along with dropping resistor and diode coil protection. I would recommend a power thermistor CL-60 instead of a power resistor now.) I posted pictures of the mod, please search the forum.
2) AC line switch spark protection on turn off is best with HV ceramic disk caps. Stock solution is good, no mods needed.
3) adding a EMI/RFI line filter thereby introducing a earth ground to the 555 amp. I'm not convinced this is a benefit. Perhaps a system level solution for problem installations? Maybe an external EMI/RFI filter box with a dedicated AC branch circuit for all audio components in the system.
I have designed and build a simple slow start circuit documented on this forum. ( I used a surplus HD 110V relay across a large ceramic power resistor on the primary. The relay coils are energized by both secondary rail voltages ~160V DC along with dropping resistor and diode coil protection. I would recommend a power thermistor CL-60 instead of a power resistor now.) I posted pictures of the mod, please search the forum.
2) AC line switch spark protection on turn off is best with HV ceramic disk caps. Stock solution is good, no mods needed.
3) adding a EMI/RFI line filter thereby introducing a earth ground to the 555 amp. I'm not convinced this is a benefit. Perhaps a system level solution for problem installations? Maybe an external EMI/RFI filter box with a dedicated AC branch circuit for all audio components in the system.
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