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Thread: Snubber / Safety Capacitor for a B&K EX 442

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    Forum Veteran VSAT88's Avatar
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    Snubber / Safety Capacitor for a B&K EX 442

    Howdy yall, quick question. My B&K EX-442 likes switches. Eats em right on up. I am not sure if I bought a bad switch from mouser but I am on my second one. the second one acts right but I would still like to see about putting a cap across it. I think it needs a snubber cap / safety cap across that switch. it uses a standard 15 A rocker switch. What value and voltage should I use ? Is there a way for me to calculate this or is there a standard value most use ? Thanks.
    Main System: PC-Audioquest Jitterbug / Technics SL-3300-Schitt DAC-Sumo Diana-B&K EX 442-Polk SDA2b's
    Confucius say, panties not best thing on earth, but next to it. Confucius say, man who like stereo love to boom boom.

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    If you're on 120vac wall power then I'd go with a .01uF/250vac X2 rated. In the old days manufacturers would've used a high voltage rated ceramic disc for this.

    You may have limited success with an arc suppression cap on the switch though. Does this amp have any inrush protection? Most amps use an NTC thermistor in series with the incoming AC power. If you need to add one I'd start with something in the 1.5 - 3 ohm range, don't go too high on the steady state current rating or the resistance will not drop an appropriate amount when in operation. Here's a link to some inrush protectors at Mouser.

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    Forum Veteran VSAT88's Avatar
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    The amp has no inrush protection. I have several NTC 47D-15's from my Fisher 500 project and the closest new high voltage capacitor I have "in stock" is a Dayton 400V PPT 0.22 uF . Close enough ? Should I use both or or just the one or other. I am at 120V home USA outlet voltage. The new Mouser switch is 20 A instead of the factory 15A.

    These are the specs for the thermistor.
    asic Info
    • Model NO.: NTC 47D-15
    • Function for Resistance: Protective Resistor
    • Material: Polysilicone & Tinned Copper Wire
    • Type: Thermal Resistor
    • Shape: Laminated Type
    • Application: Temperature Accurate Measurement
    • Technology: Ceramic Composition
    • Resistance Tolerance: -/+ 20%
    • Thermal Time Constant: 84s
    • B Value: Integral Series
    • Max Steady State Current: 3A
    • Trademark: Haiwang(HW)
    • Specification: CE RoHs
    • HS Code: 8533400000


    • Resistance: Sensitive Resistor
    • Installation: SMD Resistor
    • Packaging: Throught Hole
    • Quantity: Duplex
    • Resistance change scale: Log Scale
    • Brand: Hw
    • Zero Power Resistance at 25degc: 47ohm
    • Rated Power: 16 MW
    • Operating Temperature: -55-+200
    • Dissipation Factor: 25 MW/Degree
    • Capacitance: 47dmax. Shock Capacity
    Last edited by VSAT88; 02-11-2018 at 12:05 PM.
    Main System: PC-Audioquest Jitterbug / Technics SL-3300-Schitt DAC-Sumo Diana-B&K EX 442-Polk SDA2b's
    Confucius say, panties not best thing on earth, but next to it. Confucius say, man who like stereo love to boom boom.

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    The thermistor you listed will not suffice. You need one that is rated for at least the same amperage as the main AC fuse. If you have a 10A fuse on the incoming AC then get one rated for 10A maximum current. To give you an idea, Mondial used an SG-150 thermistor on the 8008 amplifiers and .01uF caps across the switches, these were very stout amps with > 1.5KVA transformers and 140k uF primary capacitor banks so they had the capability to produce a massive inrush however I've yet to hear of anyone having a dead switch on one of these amps.

    For the capacitor I'd only use an X2 rated film cap OR a ceramic disc. The reason being safety, an ordinary film cap could fail and burn. I may be going overboard on this but you can never be too safe when AC power is at play.

  5. #5
    Forum Veteran VSAT88's Avatar
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    Quote Originally Posted by mondialfan View Post
    The thermistor you listed will not suffice. You need one that is rated for at least the same amperage as the main AC fuse. If you have a 10A fuse on the incoming AC then get one rated for 10A maximum current. To give you an idea, Mondial used an SG-150 thermistor on the 8008 amplifiers and .01uF caps across the switches, these were very stout amps with > 1.5KVA transformers and 140k uF primary capacitor banks so they had the capability to produce a massive inrush however I've yet to hear of anyone having a dead switch on one of these amps.

    For the capacitor I'd only use an X2 rated film cap OR a ceramic disc. The reason being safety, an ordinary film cap could fail and burn. I may be going overboard on this but you can never be too safe when AC power is at play.
    Now I see where this leads. I understand now. Thank you I can do !
    Just to add a few amp specs. Capable of 75A 15 Amp fused.
    Last edited by VSAT88; 02-11-2018 at 12:36 PM.
    Main System: PC-Audioquest Jitterbug / Technics SL-3300-Schitt DAC-Sumo Diana-B&K EX 442-Polk SDA2b's
    Confucius say, panties not best thing on earth, but next to it. Confucius say, man who like stereo love to boom boom.

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