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#173271 - 01/06/08 04:28 PM low voltage switch suppressor for audio pops
Haligan Offline

Registered: 02/25/04
Posts: 112
Loc: Berkeley, CA USA
Whenever the igniter starts on the furnace, lots of pops come out of the stereo speakers. An audio person recommended a switch suppressor for the furnace.

Anyone familiar with these? They seem to be used for security systems. In theory it sounds like they should work. In theory.

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#173277 - 01/06/08 05:52 PM Re: low voltage switch suppressor for audio pops [Re: Haligan]
LarryC Offline

Registered: 07/05/04
Posts: 776
Loc: Winchester, NH, US
Assuming the ignition source for the furnace is a spark, versus a hot surface, the source of noise is probably the igniter. First thing, verify the burner is bonded to the electrical ground. The igniter is part of the burner assembly if it is an oil burning furnace.

If the bonding to the furnace is good, the next thing to check is if the furnace and stereo are on the same branch circuit, the same phase, or the same multi wire branch circuit. If they are, try moving the furnace to a dedicated circuit, the other phase, or a dedicated circuit.

If these all check out, verify what audio source the noise is coming in. For example, if the noise is showing up only when the turntable is selected, the stylus leads probably need better shielding, if it shows up on the tuner, perhaps the antenna lead needs to be rerouted, if it shows up on ALL inputs, the amplifier inputs needs shielding or the noise is coming thru the power lines.

How close is the stereo amplifier to the furnace? Does the popping noise show up on any other radio or sound equipment? Does anything else create noise that is picked up by the stereo? Things that make electrical noise include light dimmers, motors in mixers, dishwashers, AC units, pumps for aquariums, hairdryers, clothes washers, clothes dryers, etc.

Switch suppressors work with switched inductive loads and relay coils. They are typically a small capacitor and a resistor in series. They absorb the inductive kick of the collapsing magnetic field of an inductive load.

Larry C

#173314 - 01/07/08 10:02 AM Re: low voltage switch suppressor for audio pops [Re: LarryC]
Haligan Offline

Registered: 02/25/04
Posts: 112
Loc: Berkeley, CA USA
It's a gas furnace. I'll check the grounding.

Yep. Furnace and stereo are on same circuit. Dedicated line seems to be the way to go. First I'll try running an extension cord as a test to get the stereo on the other leg.

Popping shows up on all inputs, only when igniter is firing. No other device seems to leak into the stereo that I've noticed.

Sounds like the switch suppressor is not the right solution. An igniter seems to be a controlled arc. That's a pretty significant electrical disturbance.

#173448 - 01/09/08 07:31 PM Re: low voltage switch suppressor for audio pops [Re: Haligan]
JoeTestingEngr Offline

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
Isn't the furnace supposed to be on a dedicated circuit anyway?

#183352 - 01/05/09 06:53 PM Re: low voltage switch suppressor for audio pops [Re: JoeTestingEngr]
Trumpy Offline


Registered: 07/05/02
Posts: 8532
Loc: SI,New Zealand
I'd try a snubber circuit over the thing first.
Let's face it, these days if you're not young, you're old - Red Green grin


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