Hey Guys,
Two things here:
@ John, try your gate at the end of your effects chain, but before any delay or reverb effect. Tommy made that suggestion, and I've done that with an early rack rig I built, and it made a big difference. Although, I should mention now that I think about it, all the effects were in the loop of the MP-1 except the delays and reverbs, and the noise gates I placed between the outputs of the MP-1 and the inputs of the delays. The delay and reverb were between the MP-1 and the power amp, with the noise gates in front of them.
The noise gates I use for the MP-1 are a pair of dbx 463x Overeasy noise gates, and they work very well in any configuration I've used them in.
@ Chip, If you're getting hum, that's completely different from the white noise that gets generated by some rack units. You may have ground loop hum which no noise gate in the world can cure.
I would suggest isolating your rack gear from the rack mounting rails, and use insulating washers on the screws to mount them.
Additionally, check your cable routing in the back of your rack, and make sure none of your audio cables are running along side any of your AC power cables. This will definitely induce a hum.
When I build a rack, as a general rule, (looking into the rack from the back), all my power cables run down the left side of my rack between the rack case and the rack units. My audio cables run down the right side, and my control cables, (MIDI, and bypass switching), run up the center. If the audio jacks plug in near the center of a rack processor, I run that cable straight to the side of the rack processor to the right side before grouping them together.
If I ever run into a situation where it is impossible to avoid an audio cable and a power cable coming into close proximity with each other, then I will always try to have them intersect each other and avoid letting them run parallel.
With low voltage DC cables, they will not do much to induce hum in a rack, but there is always that oddball piece of gear that needs a wall wart to run, and that could be an exception to the rule.
Harley