Speakers buzzing when 'mame-ing' SOLVED

[clutch]

Got a Blast City cab in today and if I hook the monitor directly to my computer, it works fine but there is a loud buzzing coming from the speakers.

When I turn on the blast city hooked up to nothing, I get the buzz too.

When I turn on the blast city with a jamma board hooked up, I hear the buzz for a couple of seconds and then it goes away once the game kicks in.

Any ideas?

EDIT:  Turn your volume to 11 and the speakers will buzz.  Doh!

[BobA]

Sounds like the blast city power supply needs to be loaded by the jamma board to give the proper regulated voltage to your amp.  Is there an amp in the cab powered by an arcade supply?     You can replace the power supply to the amp with a small regulated supply and disconnect the arcade supply if you are going to convert the cab or you can load the arcade supply until it regulates the voltage to the amp and gets rid of the ripple (hum).

Replacing the arcade PS with a regulated wall wart is the easiest way to get rid of the hum as it will also take care of any potential ground loops as well.

[clutch]

That doesn't sound good.   I thought it might be because the speakers are disconnected when the jamma edge connector isn't plugged in?  Here is what I got inside the cabinet:

[gryhnd]

Could it be as simple as a ground loop hum?

[clutch]

I hope so.  Any idea how to test?  People have told me that these power supplies do not require a load.  Surely someone has mame'd a candy cab??

[MonMotha]

It sounds like there's an audio amp in there somewhere (if the system were a typical unamplified speaker setup, then you should get NO sound without something hooked up to JAMMA as the speaker is physically disconnected).  The input of the amp will pick up all sorts of stuff if nothing's hooked up.  Best option would be to unhook the power from this amp if you're not going to use it.

Plenty of candy cabinets have been MAME'd or otherwise altered, but each candy is different inside, especially those from different manufacturers.  Your wiring and power supplies look absolutely nothing like that found in my SNK Neo 29s, for example.

[clutch]

Thanks.  My jamma harness is jvs ready, so I have a connector that terminates in two rca type plugs.  Do you think if I ran these into my computer via an adapter, that would solve the buzz?  The audio amp for the blast city is inside the psu.

[clutch]

Problem solved.  Chalk it up to ignorance.  When I had the Soul Calibur PCB plugged in, I had to crank the volume wide open.  Of course, when nothing is going in and the volume is wide open, you will hear a buzz.  I connected the two rca cables to my audio out on the computer and I only have to turn the volume up just a bit to get good sound.  Whew.