Interesting audio issue

[Breaker]

Hello all,

I've just noticed an odd issue with the audio on my (almost) completed CAB.

While doing some final testing of my wiring I noticed what sounded like a high-pitched whine from my speakers
while playing some games. After further testing I noticed that the whine was synchronized with the 'Numlock' indicator
on my keyboard. As a result I surmised that the whine was related to those games with lighted Player 1 and Player 2 switches.
The whine is not present when I first start up a game (using MAMEWAH) but, as soon as I coin-up, the whine changes to a beeping which coincides with the flashing of the Player 1 and/or Player 2 start buttons; once I press Player 1/2 to begin a game the beep changes to a steady whine (for those games that keep the Player button on during the game).

At this point it seems like my audio system is somehow picking up a tone related to the LED control feature on my IPAC.
I thought I'd post to see if anyone else has experienced this problem and has a solution?

Anyone have any thoughts?

Cheers,
Breaker.

[NickG]

Some stuff to try:
--eliminate suspicion of an audio system ground loop by temporarily substituting unamplified headphones.
--eliminate suspicion of the keyboard and the Ipac by removing them temporarily from the system.
--still hear it?  It may be motherboard related, especially if you are using onboard sound.  install a dedicated sound card.  Sometimes this can stop (nearly eliminate) chip-set crosstalk.  If you are still using that old broken ASUS board then you cannot do this step, but, well, there you are.

[Breaker]

Thanks NickG,

Here are the results of some further testing:

a) if I eliminate MAME/MAMEWAH by going into Windows and hitting the 'numlock' key while IPAC is connected-> whine is present
b) if I disconnect the IPAC and connect the keyboard directly to the computer -> 'numlock' produces no whine
c) unamplified speakers (using MAME/MAMEWAH/IPAC) -> no whine

I should note that I am using a set of Logitech speaker and have hacked the remote that comes with the set in order
to place a volume control on my CP. At this point it looks like it's a combination of a bad ground and/or something the IPAC
is kicking out when it turns on the 'numlock' LED on the keyboard. One last test will be to attach a different (unhacked) set
of amplified speakers and give it a try. If the whine persists, it points to the IPAC, if it goes away it must be my hack job.

I'll do some more testing and report back.
Breaker

[Breaker]

...OK, IO tried another set of amplified speaker (with MAME/MAMEWAH/IPAC) and no whining.
Looks like my hack is the issue...hopefully I can return the remote control to it's original state and
use Oscar's volume control design instead.

Breaker.

[Zebidee]

You could try using USB for your IPAC instead of PS2.  USB has better 5v reliability, apparently. Might be too much hassle though.