(Topic ID: 24704)

Data East speaker noise - ideas for a cure


By roc-noc

7 years ago



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  • 517 posts
  • 136 Pinsiders participating
  • Latest reply 17 hours ago by Robotworkshop
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#44 6 years ago

Go to your breaker box and start shutting off power to various appliances in your home. I betcha the source of your hum goes away.

Transformers act as low pass filters, but they aren't complete line filters. Especially considering the primary and secondary grounds are tied together physically, so high freq hum will come through the ground.

#46 6 years ago

Just for shits and grins, temporary lift the ground on the primary of your transformer. Not a permanent solution, but a test.

#48 6 years ago
Quoted from Matt_Rasmussen:

If that were the case, wouldn't my williams machine buzz too?

Not necessarily.....Lots of factors go into audio buzz. Obviously disconnecting breakers or lifting the ground aren't solutions. Trying to identify the source.

#106 6 years ago
Quoted from Crash:

True, but I keep the boards grounded and include all the screws. The hum is still there on Hook.

The fact that the points are grounded could very well contribute to the noise. That's the origination of ground loop problems.

It's why very early in this thread I suggested to start isolating grounds in an attempt to pin point the source of the noise. It went unnoticed as everyone went down the path of sound board design, and that's fine, but I suspected all along that the source of the noise is the power supply, and very likely a ground loop issue.

Wiki's got a pretty good writeup on how ground loops affect audio equipment:

http://en.wikipedia.org/wiki/Ground_loop_(electricity)

#115 6 years ago
Quoted from Crash:

Did that regulator fail under stress or did you drop something on the board? Other people with this issue should check this component on their sound boards to see if it has failed like this.
Back to the ground loop issue though, I'm starting to "get it" now. Basically this means the sound board has more than one path to ground which completes a circuit and it's picking up noise from the other boards? Where would the second path to ground be besides the ground plate? Found a couple of videos if others are having trouble understanding:
» YouTube video
» YouTube video

The paths to ground are likely numerous. You have the ground plate as mentioned. You also have interconnects that carry grounds between boards where other boards are grounded. You also have the main power distribution which is grounded to your wall outlet and the ground braid in the game.

#117 6 years ago
Quoted from Crash:

The ground plate isn't connected to the ground braid? So really what needs to be done is remove all connections to ground but one (the ground braid) and that should solve it?

Everything is eventually connected to the ground braid and then the transformer ground and then the incoming ground. The problem is that there are multiple paths with varying impedance to ground. The likely culprit is some ground interconnect between power board and audio board. Both these boards have their own ground via the mounting screws...the ground interconnect between the two (probably the common of a DC voltage), supplies a potential ground loop. That's why when a clean PC supply was installed in one test, the hum went away...you no longer had the ground interconnect between power board and audio board.

You might have success lifting the audio board completely from ground, assuming all the ground points on the board are interconnected and make their way back to the power supply board. I haven't even cracked the schematics so it's all supposition.

1 week later
#133 6 years ago

Classic audio ground loop and what we suspected very early on.

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