One path to ground!!

Chipper preaches the gospel of the one path, rant reprinted below:


Unless you have a REALLY high end sine wave UPS, get rid of it for all your audio gear, it doesn't have the balls to save you anyway. UPSs by thier nature inject all kinds of horrible hash onto the mains power. I mean get rid of ALL of them on the same phase as your audio gear. Don't even have'em plugged in in the same house if possible.

Repeat after me, as often as it takes,

One path to ground.
 One path to ground.
   One path to ground.
     One path to ground.
       One path to ground.

The ground point should be at the point of highest gain, usually the mix. The mixer should be grounded, everything else floats.

Common mode rejection. The way twisted pair works, the pair of wires, being twisted tend to cancel any IN PHASE signal that is common to both conductors. This is called common mode rejection.

Simple 1 conductor + shield wires have no common mode rejection, and rely on the shield for noise cancellation. Not too good that.

This is an inherent problem in most audio crap out there, unbalanced and balanced stuff with shields running all over the place, and more ground loops that anyone can imagine.

        One path to ground
           One path to ground.

What to do?

Guitar cables:
Pick an end, mark it somehow, this is the "Source" end. Snip the shield connection at the Source end. The shielding will be ground-relative to the destination. Keep it all going in the same direction.

Guitar(groundlifted)->(shield)Effect-gizmo(groundlift)->>-(shield)someothergizmo(groundlift)->(shield)DI-box

and so on to the amp.

       One path to ground.

Mic(shield-snipped)->(shield)mixer.

Actually, decent mics are so damned good, output xformers and such, with an op-amp on the mic-pre input, with quality xlr-balanced cables, are seldom a problem.

It's ALWAYS the keyboard guys who know EVERTYHING that are the problem, followed very closely by guitar folks.

These folks LOVE those Ernie-Ball brass connector-coax skinny little cables that have such low impedance, and they work okay, until they dont. Not worth it. Toss'em. use good switch-craft connected guitar cables prepared as I've
said.

There is some neato tricks you can play using balanced mic cable (Canare Star-Quad in particular) that will make guitar cables IMMUNE to noise, but they are beyond the scope of this document.

To the best of your ability, do exactly the same thing with the outboard gear (computer?) float all of it, and carry the ground to the mixer. Remember, keep the shield at the point of highest gain.

  One path to ground.
    One path to ground.

use transformers whereever you can. There is NO WAY a ground hum can pass a transformer, think about it, ground hum, (mains loop hum) is COMMON MODE.

Cabling up

Unplug EVERTYHING.

Set your mixer up. Neutral out all the knobs.

Plug 'er in to the wall. Lift the ground-pin and tie that little grounding hook to a piece of 14 gauge or better and get that to a drainpipe or something. Get it to a REAL ground if at all possible. Ground, as in earth. Deep earth. You want mother earth to take all the negative waves away.

Turn the mixer on, headphones, sample everything with the solo bus, listen carefully. Don't sweat it, unterminated busses and mic pre-s will make noise. But is there any hum or buzz?

Yes?

Do you have dimmers in the house? Turn'em all OFF. Hum or buzz gone?
No? You've got dirty power. There is an rf component to dimmers that are close to stuff that can be effected by low power rf/emi, but dimmers also
hash the neutral with squarewaves. If you had an o-scope, you'd freak out at what dimmers do to the power line. (or is that freq out?).

Anyway, try a different circuit, see if it gets better.

Basically, leave the dimmers off. Get some low output lighting.

Get rid of the dimmers.

Okay, you still have hum/buzz even with no dimmers active.

You've got SOMETHING in the power system , house mains power with a crossed neutral/hot. SOmething is wired incorrectly.

Sort it out.

Okay, hum/buzz gone?

Next, power-amp-speakers.

Remember, "telescope" those shields on the signal leads to the
amp. (yes the mixer has more gain than the amp, think about it
in terms of dbm, log man, log.) Tie the ground on the amp directly to the mixer, lift the gound on the powerlead.

        One path to ground.

Okay, add a signal source, cd player or something. how's it sound? Did it introduce noise? try a different outlet, you're crossing phases perhaps in the house.

Remeber, offtimes different outlets in a room can be on different phases of the house mains. You DEF want to be on the same phase. If your ac leakage across your audio gear is ocillating at 60hz Out of phase from each other, you loose your common mode rejection, cause it ain't common any more, and it will LOUD.

Okay, it's quiet now?

Cool, keep adding stuff until you get some noise, sort it out and move on the to the next,

   One path to ground.

Oh! Dimmers are evil, UPSes add noise to everything. What else?

You really don't need to fuss with the cables, that's just what we call A really good idea, and it works. But do the diagnostic cabling up first. That will tell you where your noise loops are.

And remember,

One path to ground.  ¶ 2:14 PM