The hum of death!?

[djmukilteo]

Have you tried just a regular power strip with all your equipment plugged into that without using the Furman?

[RemyRAD]

It sounds like you're dealing with some kind of ground loop? Even having everything plugged into your power conditioner with their electrical ground pins can cause you these types of ground loops. I've had horrendous problems like you are describing when plugging in a laptop with its switching power supply. I almost always lift the electrical ground on the switching power supply to the laptop and all problems are then solved. Well everybody wants you to have properly grounded equipment, equipment and close proximity all plugged into the same power source do not all have to be electrically grounded. Otherwise, you may never solve this problem. So your mixer should be grounded and plugged into your power strip. But your compressor and anything else like your computer also plugged into the same power strip/conditioner should not pose any electrical shock hazards. See don't need to have all of the electrical ground pins plug-in. Get yourself a couple of those 3 into 2 electrical power cord adapters and give that a try.

Please note, you do not want to have different pieces of equipment plugged into different electrical outlets not on the same circuit. So for recording purposes, it should not be a problem. Coupled with the PA system, this could pose a problem. Simply because the electrical load of power amplifiers generally need something more than a 15 amp power switch/conditioner. So if everything is in a rack box together, start lifting some of those electrical grounds of the equipment within the rack box. And that should do the trick. Just make sure you don't get to loopy before you do these jobs LOL.

I was keep handful of the little suckers available
Mx. Remy Ann David

[Jumpmonkey]

I'm rather certain the problem is the Furman. I have 2 of M8x2's. I swapped the old one I had in place of the new one and the hum disappeared. I believe its some rare fault in the new Furman. I am sending it back.


Thanks for all your help,
Adam

[RemyRAD]

I don't think so?

[TheJackAttack]

If it is the Furman that is fairly good news. They are easy to fix.

[dvdhawk]

I haven't seen this mentioned yet -

When you bolt multiple units into a rack, unless you have electrically insulated the rack rail / the rack screws, and the rackmount devices - you have bonded their chassis together enough to establish one common chassis. Sometimes that's a good thing, sometimes that's a bad thing. One problem child with a questionable ground and there goes the neighborhood.

[Jumpmonkey]

DVD,

If that's the case, how do I isolate it all. I got a little fancy with the electrical tape before I removed the Furman and got nothing for it. That said, you mentioned the screws. I figured those would be the weak point (unless the tape followed the screws into the rack. Which I believe is in the realm of physical improbability.)

Is there an electrical testing device I could use on my individual units to see if they're grounding out through the chassis?

Thanks,
Adam

[dvdhawk]

Don't get me wrong, the fact that your hum goes away when you swap out one of the Furmans is very telling. But it's possible the second unit bonded with (or didn't bond with) the rest of the rack differently for any number of mechanical reasons.

There are commercially available rack isolation tabs like Humfrees you can buy, or it's certainly something you could DIY.

A layer or two of electrical tape should be enough to insulate the devices from the steel rack rail, but that only does half of the job. A small piece of heatshrink tubing, or any similar tubing should keep the threads of the rack screw from directly making contact with the unit via the mounting holes to do the other half of the job. Although heatshrink is fairly soft and will get chewed up if the threads move against it very much.

This little tip is so low-tech I'm a little embarrassed sharing this, but when one of my kids was little we bought balloons for their birthday party. The balloons came with brightly colored "stick" something like this, which were essentially 2ft. long hollow plastic tubes. And as it turns out, they were the perfect diameter to act as an insulating sleeve over a 10-32 rack screw. I sliced them about 1/8" thick with a sharp knife to match the thickness of the faceplate of my recorders and used them on several racks. A let me tell you a 2ft. long 'stick' sliced into 1/8" pieces goes a long way (192 little bright green sleeves in fact).

It's not something I do all the time, but when I feel it's especially critical to keep things isolated that's all I use. Then all you have to do is make sure you're not making contact with any other metal rack parts and you're isolated. You have to watch for aluminum corner extrusions and recessed handles. I see I've got 10 more of those 'sticks' in assorted colors, so I'm good for another 1920 sleeves - if I ever get clear to the end of the bright green one.


You can use any RadioShack multimeter / ohm-meter to test for continuity (or any degree of contact) between the various pieces of equipment. If you're throwing yourself into the audio field, a decent multimeter is an indispensable tool that you should have (and know how to use). You don't need an expensive meter, just something reasonably reliable at this point. Analog and Digital meters each have their own strengths. At some point down the road, a case could even be made for having one of each, but either one would be $20-$30 well spent.

[Jumpmonkey]

DVD,

Thanks for all the info (again)! I don't know if I need 144 of those balloon sticks lol. I've heard about shoulder washer for doing the trick you're doing with those. My problem is I cant figure out what size I need and where to buy a sack of them (anyone got a link?) In the mean time I'll look for a smaller quantity of balloon sticks.

I'll be getting me a multimeter it sounds like. I haven't got one yet, but the further I get along in all this the more I've been seeing the wisdom of such a tool. Any reason I should start with one type of meter over the other? Dunno why, but at the moment I'm considering an Analog meter. Maybe because I like needle type meters and figure if it gives me bad news I can tap the glass once or twice, and it will tell me good news.


Thanks and God bless,
Adam

[dvdhawk]

Glad to be of some help.

You can probably go to your local WallyWorld and buy one balloon on a stick. Here's a link to shoulder washers.

Anyway, digital meters are easier to get an accurate reading - analog meters are much faster to respond to rapid changes.