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I have a few computers connected to a mixer, which is connected to an amplifier, which powers two speakers. They are all on the same circuit. I have contractors over building a structure out back and they have their Skill Saw connected to an external outlet, which appears to be on the same circuit.

When they start their saw, I hear the cut through my amp. It starts as a buzz and then I head the distinct circular saw wzzzzeeeeeeer sound.

Is this normal, or is the fact that I am essentially hearing current draw in my amp a problem? If is it not normal, is this an amp problem, or a house circuit problem, or something else?

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  • If you want to avoid this completely, you can hook your equipment up to a "power conditioner" or "online/double conversion UPS". Those are going to be in the $500+ range, but they take the incoming power and filter it or generate a new AC sine wave to provide clean, (and with a UPS) constant power to sensitive equipment.
    – JPhi1618
    Commented Aug 26, 2021 at 20:14
  • you are not hearing current draw ... you are hearing electrical noise that is produced by the electrical motor ... it is caused by arcing at the motor brushes ... if the motor is brushless, then the speed regulating switching circuit injects the noise into the power lines
    – jsotola
    Commented Aug 27, 2021 at 0:48

3 Answers 3

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Tools like a "skillsaw" employ what is called a universal motor. These have brushes and a commutator which creates tiny sparks which generate electrical noise. That noise is getting into your audio system at some point although it will take some detective work to determine exactly where.

I'm not saying it's "normal" but it's not uncommon. It's best to have things that power portable power tools on a separate circuit. If this is a long-term prospect, you may want to look at some line noise suppression equipment to isolate your audio circuits from the AC line noise.

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  • Cheers for the comment on the noise suppression equipment, did not know about that. It may help with my other issue: "new gaming PC makes a noise in AMP when moving the mouse" but that is something.
    – Chris
    Commented Aug 27, 2021 at 0:58
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It is totally normal for noise especially with motor driven equipment on the same circuit. Because of the EMF of the motor it is not recommended to have motor driven equipment on the same circuit as your computers or other sensitive equipment like your amp. Depending on your power system even having a motor load on the same leg can be problematic. So yes it is normal with motor loads.

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  • Interesting, good to know this. Fortunately it is just for a short time, and unfortunately there is no other outside plug and I cannot move this setup, so I'll just bare with it for a while. Just glad to know there is not some issue, like stripped and exposed wire behind the wall somewhere or something like that.
    – Chris
    Commented Aug 27, 2021 at 0:56
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Does your location have a different power circuit? Moving the saw to a different circuit may help reduce noise in your circuit.

I once saw pro's deploy a generator to power a huge jobsite bench/chop saw, that was causing issues on startup, just to protect the site's power network (which was admittedly shaky.)

Consider unplugging your computer while they're working.

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    I would definitely ask them about that if they were planning months here, but it will only be a couple of weeks, but interesting to know all this, cheers
    – Chris
    Commented Aug 27, 2021 at 0:59

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