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In an instruction booklet written in 2001 for a Boss guitar effects pedal it says:

Do not connect this unit to same [sic] electrical outlet that is being used by an electrical appliance that is controlled by an inverter (such as a refrigerator, washing machine, microwave oven, or air conditioner), or that contains a motor. Depending on the way in which the electrical appliance is used, power supply noise may cause this unit to malfunction or may produce audible noise. If it is not practical to use a separate electrical outlet, connect a power supply noise filter between this unit and the electrical outlet.

Since this effects pedal is a consumer unit, it follows that there must be consumer power supply noise filters available, but I cannot find anything with that name available. Do they exist?

Another question: does this mean that it's a bad idea to plug something into a multi-socket extension along with anything that contains a motor or inverter?

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    This is 99.64% lawyerese hogwash and 0.36% anything likely to be a problem in real life. But they want an out if you hear noise from their cheap pedal... is it a typical Guitar Effects Pedal 9Volt DC supply external to the pedal?
    – Ecnerwal
    Commented Oct 4, 2020 at 18:58
  • @Ecnerwal "is it a typical Guitar Effects Pedal 9Volt DC supply external to the pedal?" Yes
    – EmmaV
    Commented Oct 4, 2020 at 19:00
  • Yes, they look like an oversized USB charging block, except instead of having a USB plug, they have a NEMA 5-15 plug. Actually they look a lot like smart sockets.
    – Harper - Reinstate Monica
    Commented Oct 5, 2020 at 5:44
  • Not really a home improvement question. You'll get better answers on a discussion focused on guitarists and/or sound reinforcement.
    – keshlam
    Commented Aug 4, 2023 at 13:17
  • For example, a sound tech would reach for a power conditioner, if and only if a problem was found. Not "consumer equipment," but commonly available as pro/semipro because some venues have questionable electrics.
    – keshlam
    Commented Aug 4, 2023 at 15:13

2 Answers 2

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Surge Suppressors are commonly available as consumer units.

Power Supply Noise Filters are not particularly common as a consumer unit, though they are commonly available as parts to be built into commercial electronics.

You could simply use a better-built 9V DC supply which has a filter built in - it's fairly common to have one large-amperage 9V DC supply powering your whole pedalboard (if you have a few pedals), rather than individual wall-warts for each pedal. Those will normally have excellent filters.

For test purposes (it's expensive beyond that) you can also use a 9V battery to completely eliminate the possibility that power supply noise is a problem.

As to the question of "what a power supply noise filter is" it's usually 3 capacitors and 2 inductors in a package. You'll find better results searching for "EMI filter" usually. But I seriously doubt you need to go buy one, if you can even find a "plug and play" packaged for consumers version.

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    Guitarist & EE here - This is the simple truth: "You could simply use a better-built 9V DC supply which has a filter built in - it's fairly common to have one large-amperage 9V DC supply powering your whole pedalboard (if you have a few pedals), rather than individual wall-warts for each pedal. Those will normally have excellent filters" Well done :)
    – Kyle B
    Commented Oct 5, 2020 at 1:48
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I'd use an Isobar

While dedicated (standalone) mains filters are generally not available as consumer products, the good news is that Tripp-Lite still makes their Isobar line of combination surge suppressors and AC mains filters. A two-outlet, plug-in Isoblok costs about $30 at the time of this writing, and is manufacturer specified to provide at least 40dB of mains noise suppression, which should be sufficient to keep your guitar pedal from emitting noises. Of course, using a wall-wart that's of a better grade than the cheapest thing that will pass FCC and UL testing (you could even use a medical grade supply, but that'd be overkill) will help with this, too.

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  • a surge supressor is about as much a filter as a fuse is a current source.
    – Jasen
    Commented Oct 5, 2020 at 4:07
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    @Jasen -- the Isobar is a mains filter/surge suppressor combination, as I said (i.e. it has both MOVs for suppresson and LC networks for mains filtering in it)
    – ThreePhaseEel
    Commented Oct 5, 2020 at 11:41

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