There's a couple of different problems that can cause a buzz from the DS-5. Here's a couple suggestions of things to look at, sort of in order of easiest first.
Check all your cables. You may have a bad cable between the DS-5 and the amp, which is easy to test. Harder to test, but another thing to check is to see if there's a problem with the 5-pin cable. In the grand scheme of things, cables are almost always to blame!
You may have a ground loop between the DS-5 and your amp. Usually you can solve this by making sure that both pieces of equipment are plugged into the same outlet, and that that outlet is properly wired. If you have a voltmeter, you can test this by seeing if you read an AC voltage with one probe touching the DS-5 and the other touching your amp (faceplates in both cases).
Second, you can be getting noise induced into the preamp if it's near another piece of equipment's power supply. Try moving the DS-5 physically out of your rack and away from anything else and see if there's a reduction of noise.
If it's neither of those problems, then you may have a failure of the filter caps in your DS-5 power supply. When they go bad, 60Hz from the AC power will be induced into the audio.
Another thing to look at inside the case is whether a shield wire is loose somewhere inside.
The audio splitting in the DS-5 box is totally passive, so there's no interaction between the audio output from the bass and the power supply in this box.
I'd be willing to bet that you have a bad cable somewhere in the chain. If the 1/4 cable between DS-5 and amp isn't it, you'll need to figure out some way to test the 5-pin cable.
Good luck,
David Fung
