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So I setup my Grandfather clock today and I'm getting some annoying audio hum intermittently. When the audio is running the hum disappears but comes back again when nothing is playing. The clock has a lot of moving parts, it runs a servo for a talking skull pendulum using a Scary Terry board. The pendulum swings using a wiper motor and the whole rig runs off an ATX power supply. The audio source is a tablet PC and currently splits using an adapter so one line goes to the ST board and the other to a set of computer speakers. I also tried just using the passthrough on the ST board instead of the spliter with no difference.

I've tried to isolate the problem by keeping all of the power and audio cables as far apart as possible and things seemed okay and then it started up again this evening. I'll try messing around with it again tomorrow as it's too late now and the family needs to sleep. Just looking for any advice on a possible easy solution or any ideas.

Thanks!
 

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Your problem is simple, when there's no audio signal going to the speakers, they're gonna hum. This is typical of any audio amplifier. An easy fix is to incorporate a relay with a N.O. set of contacts. Connect the N.O. contacts to either the speaker power or a speaker lead. Have the relay energize when the audio starts and de-energize when the audio stops.
 

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Your problem is simple, when there's no audio signal going to the speakers, they're gonna hum. This is typical of any audio amplifier. An easy fix is to incorporate a relay with a N.O. set of contacts. Connect the N.O. contacts to either the speaker power or a speaker lead. Have the relay energize when the audio starts and de-energize when the audio stops.
Well that sounds simple but not sure how I could trigger the relay when the audio starts and stops. It sounds like a project and there is no time left to work on it. Our party is Saturday and too many other things left to be done. Thanks for the answer.
 

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This is a long shot but worth checking. Try running audio without the prop running. This will help determine if it's the motors in the prop causing the "hum". My guess would be its coming from the audio splitter. Those splitters can be temperamental and pick up stray feedback, which gets amplified from the powered speakers. Could be as simple as touching the splitter and it goes away or returns. If that happens, try taping the connections well and see if it helps.
 

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This is a long shot but worth checking. Try running audio without the prop running. This will help determine if it's the motors in the prop causing the "hum". My guess would be its coming from the audio splitter. Those splitters can be temperamental and pick up stray feedback, which gets amplified from the powered speakers. Could be as simple as touching the splitter and it goes away or returns. If that happens, try taping the connections well and see if it helps.
Yes I played with the splitter and that seemed to make things worse at times. I tried removing the splitter and using the passthrough on the ST board and still the same issue.

So I started thinking about what J-Man said about the lack of a signal to the speakers and here is what I came up with. The audio is run by an app on the PC that I wrote in Visual Studio. It's a media player playlist starter. On the hour and other random times it plays a WMP Playlist. The playlists have my clock chimes and then a track for the skull to talk. Then nothing plays until the next event's time is reached. I created a silent MP3 using Goldwave and added it to the end of each playlist. The silent track runs for an hour but is stopped when the next event starts. The silence playing seems to have eliminated the speaker hum with no signal. It's been running all night and no audio hum.

Maybe tonight I'll be able to sleep. Thanks for the advice.
 

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Yep, that'll work too. Any audio signal will get rid of the hum, even if it's a silent track. I would have suggested that but I didn't know how your audio was triggered or played. Good job!
 

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Glad to hear you got that figured out. It's always those little things that'll drive you crazy... like hum in an audio system... or mirrors that don't quite align for a projection effect.. no, wait.. that's the problem *I'M* dealing with! LOL
 
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