Cabinet Amplified Speaker Hum


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Posted by Tom A. on 18, 2000 at 1:45 AM:

Hi folks,

It's me again. First let me thank Saint, Tom61 and all the wonderful people on this site. If it wasn't for you guys, I would have a lot more money and more free time. ;-) Seriously, I appreciate all the help and encouraging words.

Ok, back to my question. Now that I have my 29" arcade monitor working I'm trying to get the amplified speakers to work well. I am using DOS MAME, ArcadeOS and a SB64 Gold which has line level outputs.

My JAMMA connector only has provisions for a mono lead, the right channel has no wire on the pin so I didn't hook the speakers to my JAMMA fingerboard. But there is an audio amp at the bottom of the cabinet that has stereo line in RCA jacks. I hooked up my SB64 line out jacks to these inputs and it worked but I get an annoying hum. The inputs have a ferrite ring that the wires are wrapped around, but apparently it isn't enough. What's odd about the inputs is that the left channel has two leads as you would expect but the right channel only has one...signal, no ground.

I figured that my SB64 would work better with two leads for each channel but even when I unplug the right channel from the cabinet (which only has one lead) the left channel (two leads) still hums.

I had an old Radio Shack ground loop isolator in my "junk trunk" that I used to have in a car with an EQ that had a hum, albeit a different type. I tried this but I guess the isolator is expecting a higher signal input as it cut the sound totally. Even with the mixerset util set to master volume 255 (/ma:255;0) it still has no sound output.

I wonder if I change the cabinet's audio right channel input to use two leads with the left channel, if it would work? I thought maybe I could use the ground from the left channel with the right. Am I risking damage by attempting this? Is it a total waste of time?

This problem can simply be fixed by using a pair of PC amplified speakers but if possible, I would like to use the cabinet speakers for looks and quite frankly cost. I did test the cabinet using my PC's Altec Lansing speakers with sub and it sounded just dandy, no hum whatsoever.

-Tom A.


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