Non ADA Gear > Rack Gear
Rack Development
rabidgerry:
I'm pretty sure my hum is coming from the fact that two units are powered by a wallwart/power pack.
I'll give you an example, before I dropped the floor unit for FX I got hum going into the rockmaster. I was able to determine that this was because I had a ground loop being cause from running a pre in fx unit loop. I did this by detaching the earth in the rockmaster plug. Hey presto no hum. So the solution to this was use the Art Clean box II. Yes worked a treat.
Toward the end of the floor unit use I started running a different way, I was going direct into the pre and then having the pre out go into the return of the fx unit. This sacrificed the use of front end effect from the fx unit but also eliminated the need for clean box II which is a ground loop isolation box.
So moving onto where I am now. I use two unit loops, one for noise gate and one for FX. Using the clean box gets rid of the hum and basically the noise gate keeps it 95% unnoticeable. However there is still a bit of hum. And it's because there are two loops being used. The noise gates loop and the fx units loop. I could run the clean box in both loops I guess since it has two separate transformers for decoupling earth loops but I was just wondering if there are any other things I could try instead hence the question about isolating on the rack itself.
MarshallJMP:
Can you give a bit more info about those 2 loops you are using, maybe a schematic of the routing?
vansinn:
Some devices have everything internal fully insulated from ground, with only the earth pin in the power cable acting as ground.
This is the preferred way of ensuring single-point grounding, in order to avoid ground-loop [hum], because the builder can now use ordinary jack cables, and arrange single-point grounding for each device at the common mains summing point.
Other devices have their in/out jacks grounded to chassis.
This not preferable, as there's the possibility of ending up with grounding through both the mains prong and simultaneously through the signal cables - because of the chassis-grounded in/out jacks.
As Kim said, the builder can start with simply mounting and connecting the whole shebang, and see if all is ok.
If hum is present:
* either disconnect everything, and then reconnect one device at a time, until hum appears.
* or, disconnect devices one by one until the disappears.
Hum most often develops when using, say, external processors in send/return loops, simply due too signal cables carrying ground in a loop-structure, while this external device is also being grounded through the mains prong.
When the hum-hum device has been found, a usual remedy is to isolate it from the rack rails using insulated bolts and washers and maybe a strip of gaffer on the rails to avoid chassis contact.
Sometime it's possible to use custom signal cables having the ground flex connected at only one end - best option is to leave the open-ground end of the cable connected at the Send jack.
rnolan:
Hey RG, a thought, it may be a dud wall wart ? There were posts previously about the wall warts to phantom power the ADA midi pedals causing noise. Worth a try :dunno: .BTW, most of the ADA jacks don't earth to the case, eg Mike had really bad hum on his B200s when he changed the output jacks to standard, to fix he changed them to the plastic collard jacks that don't contact the case (as they came with).
At the end of the day, isolating each unit from the rack rails etc seems a good idea (though good quality units "shouldn't" need it).
Soloist:
Hey RG, you might want to isolate the velocity. In my experience the Rocktron equiptment is usually the culprit. Great gear, shitty ground loop hum. My old Pirhana pre amp was the same way. :headbanger:
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