I have built a small amplifier with a pair of ECL82/6BM8 valves in single ended configuration and a EZ81 rectifier valve (with 50uf - 3H - 50uf filter) PSU
I notice occasional pops from the speakers when switching the mains off. I suspect this is coming from back EMF from the power transformer primary, causing short duration spikes on switch-off. My transformer is a Hammond DAX370, with the primary configured for 240VAC
I am considering fitting a 100nF + 100R snubber across the 240V primaries. Has anyone any experience of using a snubber this way?
I notice occasional pops from the speakers when switching the mains off. I suspect this is coming from back EMF from the power transformer primary, causing short duration spikes on switch-off. My transformer is a Hammond DAX370, with the primary configured for 240VAC
I am considering fitting a 100nF + 100R snubber across the 240V primaries. Has anyone any experience of using a snubber this way?
I'd go with a 400 VAC rated cap for 240 V mains. You might get excursions up to 264 V.
I bet the pop is caused by arcing in the mains switch. You may find that a snubber across the switch works better to prevent the pop than a snubber across the primary. It'll also help prevent wear on the switch points.
Tom
I bet the pop is caused by arcing in the mains switch. You may find that a snubber across the switch works better to prevent the pop than a snubber across the primary. It'll also help prevent wear on the switch points.
Tom
Me, I'd try the snubber-across-load (in this case, across the power transformer primary) first. Only if this arrangement's behavior fails to satisfy you, reluctantly try snubber-across-the-switch as your Plan B, then decide whether it increases your satisfaction. Keep the load-energy-dump as local as possible.
Exactly as PR Mallory described the action of the "Quench-Arc"I bet the pop is caused by arcing in the mains switch. You may find that a snubber across the switch works better to prevent the pop than a snubber across the primary. It'll also help prevent wear on the switch points.
Tom
I have a bag of them from a heavy equipment company in Ohio -- to bad you're in England or I'd send a dozen!
The source of the transient is usually the inductor, specifically the leakage inductance of the primary, so logically place the snubber across the transformer primary, with short leads/low loop area. However mains voltage is high enough without back-EMF considerations to cause arcing anyhow - some switches are better than others mechanically (break the contact faster) and wear and tear on a switch can affect this.I bet the pop is caused by arcing in the mains switch. You may find that a snubber across the switch works better to prevent the pop than a snubber across the primary. It'll also help prevent wear on the switch points.
Placing a snubber across the switch will lead to electricity consumption when the unit is switched off, note: 100nF will leak 7.5mA at 240V, which is 1.8W of apparent power on your bill (about 16kWh per year).
Its also possible to get a shock through a snubber. 7.5mA is definitely enough for that.
Yes, I do that a lot.I have built a small amplifier with a pair of ECL82/6BM8 valves in single ended configuration and a EZ81 rectifier valve (with 50uf - 3H - 50uf filter) PSU
I notice occasional pops from the speakers when switching the mains off. I suspect this is coming from back EMF from the power transformer primary, causing short duration spikes on switch-off. My transformer is a Hammond DAX370, with the primary configured for 240VAC
I am considering fitting a 100nF + 100R snubber across the 240V primaries. Has anyone any experience of using a snubber this way?
LCR in Wales make/used to make these , in 100nF/100R and 220nF/100R, with Class X2 rated caps for UK mains.
They Work. Try your snubber - and keep the wiring as short as practicable to the Trafo primary connections.
NB - even small caps used in a snubber across a switch, at 240VAC, pass enough current for a sting' ; the limit here would require class Y caps, at 2.2nF; less effective. And still enough to feel ... quite fizzy. But way less effective.
I know Tom, he is first rate!Tom Christensen (tomchr) is in Calgary, Canada, much closer than England.
Unless you have a different Tom in mind.
That was my thoughts Mark. I have fitted my R-C snubber across the transformer primary leads and this seems to have stopped the pops on switch-off.The source of the transient is usually the inductor, specifically the leakage inductance of the primary, so logically place the snubber across the transformer primary, with short leads/low loop area. However mains voltage is high enough without back-EMF considerations to cause arcing anyhow - some switches are better than others mechanically (break the contact faster) and wear and tear on a switch can affect this.
Placing a snubber across the switch will lead to electricity consumption when the unit is switched off, note: 100nF will leak 7.5mA at 240V, which is 1.8W of apparent power on your bill (about 16kWh per year).
Its also possible to get a shock through a snubber. 7.5mA is definitely enough for that.
I was not comfortable fitting a snubber across the input and output of the switch (or two, as I have a 2-pole switch for isolating Live and Neutral). Apart from the energy leak you mention, I would probably be tripping the RCD circuit breaker in my consumer unit!
Martin, I found a compact R-C snubber from CPC Farnell and have installed it across the transformer primary leads. So far, so good. (Probably manufactured by LRC!).Yes, I do that a lot.
LCR in Wales make/used to make these , in 100nF/100R and 220nF/100R, with Class X2 rated caps for UK mains.
They Work. Try your snubber - and keep the wiring as short as practicable to the Trafo primary connections.
NB - even small caps used in a snubber across a switch, at 240VAC, pass enough current for a sting' ; the limit here would require class Y caps, at 2.2nF; less effective. And still enough to feel ... quite fizzy. But way less effective.
But you don't pay for apparent power, you pay for real power. A snubber's impedance is nearly all capacitive, therefore the leakage current contributes nothing to real power. The units are 1.8VAR, not 1.8W. You pay $0 for VAR, and kWhr is close to 0 per year.100nF will leak 7.5mA at 240V, which is 1.8W of apparent power on your bill (about 16kWh per year).
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