How to get rid of speaker interference?

[purbeast]

I converted a Time Crisis to JAMMA and I have it wired directly to my cabinet right now and am noticing a little bit of speaker interference.

When I first turn it on, before the speaker "pops" after like 2-3 seconds, I basically hear the fan in the speakers. But once it pops, the interference goes way down.

But while the game is on, if I put my ear closer to the speaker, I still hear a constant hum/buzz.

From what I gathered this is typically due to a grounding issue? Is that the case? And if so, like what is the best way to track down the culprit of this and actually resolve it?

 

[VectorCollector]

Fans are noisy. Marquees are noisy. Power supplies are noisy. Monitors are noisy.
Where "noisy" is more electrical EMI or RMS/pk-pk low/high frequency interference - either conducted or radiated.

You mention a fan. Disconnect it and see if the noise reduces or is eliminated. Same with other noise sources.
Some strategies are filters, cages, twisted pair wires (sound, video etc), shielded wires, isolated wiring (power away from signals), eliminating ground loops and more ...
Ideally, you need to figure out the noise source and determine if it is conducted OR radiated - and then choose the correct solution.

 

[Mahkeymike]

Get a ground loop isolator.
amazon link

 

[purbeast]

Fans are noisy. Marquees are noisy. Power supplies are noisy. Monitors are noisy.
Where "noisy" is more electrical EMI or RMS/pk-pk low/high frequency interference - either conducted or radiated.

You mention a fan. Disconnect it and see if the noise reduces or is eliminated. Same with other noise sources.
Some strategies are filters, cages, twisted pair wires (sound, video etc), shielded wires, isolated wiring (power away from signals), eliminating ground loops and more ...
Ideally, you need to figure out the noise source and determine if it is conducted OR radiated - and then choose the correct solution.

Thanks for this suggestion.

I unplugged the fan and to my surprise, it still made the same sound. I had remembered that the original fan on the cage was grounded to the cage itself, and when I replaced it with a 12v one that would work with the JAMMA harness, I ran the ground from the fan to the JAMMA harness. So I thought maybe doing that instead of grounding to the cage could have caused this problem. But when I took the fan off, the sound was the same.

I then unplugged the gun and pedal just to try more things with ground running to them and the sound was still the same.

When I listen to it before the speaker pop, it almost sounds like there is a little beeps in the interference. But I have to put my ear real close to hear that.

Then once the speaker pops and the interference is much less, I really have to put my ear right next to the speaker to hear it and it's only apparent in quiet scenes, which aren't much in Time Crisis.

One thing to note - this game is 4 PCB's inside of a metal cage. The metal cage itself is not grounded directly to anything inside of the cabinet like other the monitor frame or anything. Could it be something as simple as grounding the cage to the monitor frame could be needed to fix this?

I'm just a total noob about all of this grounding stuff so that may be completely off base.

EDIT:

I'm also wondering if the way I wired my speaker may be part of it?

Time Crisis is stereo and has SP1+, SP1-, SP2+, and SP2- on a connector.

I just wired SP1+ and SP1- to my JAMMA harness in the speaker +/- pins and ignored the SP2 completely. I didn't think this could have anything to do with it but thought I'd post the info in case it did.