60 cycle hum - Page 2

wrench45us · #21 12-19-2012, 09:30 AM

This is something I'm trying to underestand as well, since there's definitely a directional aspect. If I face wsw or ene, the noise goes away when the amp is plugged into the noisy outlets.
Is it possible I'm somehow shielding the EMI with my body from the noise from wires in the wall and/or power cord to the amp?

There's no directional aspect when I plug the amp in what we're assumningb is the properly grounded outlet in the other room.

wcriley · #22 12-19-2012, 09:36 AM

Are you using an extension cord and standing in the noisey room when you aren't getting the hum? Or are you standing in the room with the properly gounded outlet?

SGD Lutherie · #23 12-19-2012, 09:44 AM

Quote:

Originally Posted by wcriley

How would that affect the airborn EMI in the room, as seems to be the case here?

Not being argumentative. Trying to understand and (hopefully) learn.

It's only airborne until it makes contact with the conductive parts of your bass. Then that noise is induced into your signal path. For shields to work the grounds on the other end have to be good. If you grounds are going nowhere, that noise isn't being dumped to ground, and you hear that annoying buzzing.

This is the same reason why un-grounding shields or your strings makes your bass noisier.

wcriley · #24 12-19-2012, 10:02 AM

But don't all the shields and other grounds get grounded through the neutral leg of the power line? Seems to me that if what you're saying is true, there would be no ground at all when using an outlet without a safety ground.

SGD Lutherie · #25 12-19-2012, 10:22 AM

Quote:

Originally Posted by wcriley

But don't all the shields and other grounds get grounded through the neutral leg of the power line? Seems to me that if what you're saying is true, there would be no ground at all when using an outlet without a safety ground.

The neutral is not really ground since it's AC and not DC. That's why this stuff was changed and the grounds were added. The ground pin really goes to the ground. It's usually connected to the water pipes, or a post or pipe stuck in the ground. Also, some outlets are wired up wrong. So if you have a 2 pin outlet, your neutral might be hot. Even three pin outlets are often miswired.

wrench45us · #26 12-19-2012, 10:24 AM

I carried the amp and plugged it into the non-noisey outlet in the non-noisey room and was standing in the non-noisey room for that test.

I did try the closest outlet in the non-noisey room and was still standing in the noisey room and did get the noise.

All noisey outlets in both rooms I tried were on the outside south facing wall. (so may likely be on the same circuit or romex wiring)
The non-noisey outlet I tried was on an inside west wall.

So it was only when amp and I both moved across the non-noisey room to the opposite wall that the noise went away.

No extension cords

wcriley · #27 12-19-2012, 11:05 AM

SGD: Still doesn't explain how any equipment sees ground when using a 2 prong outlet.
I always thought the neutral and ground were tied together at the breaker box.

wrench: Try using an extension cord or long instrument cable so you can plug the amp into the "quiet" outlet, but stand and play your bass in the "noisy" room. I think you'll find that the noise/hum you're getting is EMI from something in (or just outside/to the south of) the "noisy" room.

SGD Lutherie · #28 12-19-2012, 11:30 AM

Yes, they are supposed to be the same, unless the outlet is miswired.

wrench45us · #29 12-19-2012, 11:54 AM

I will try standing with bass in noisy room with amp plugged into quiet outlet.
EMI in the room may make more sense than ungrounded outlets given I don't have an outlet tester to verify their state.

And that noisy room is where all the wires from the poles across the back of the property enter the house: telephone, power, cable in the sw corner of that room.

Rune Bivrin · #30 12-19-2012, 11:58 AM

Quote:

Originally Posted by wrench45us

I will try standing with bass in noisy room with amp plugged into quiet outlet.
EMI in the room may make more sense than ungrounded outlets given I don't have an outlet tester to verify their state.

And that noisy room is where all the wires from the poles across the back of the property enter the house: telephone, power, cable in the sw corner of that room.

There wouldn't happen to be a big line transformer anywhere close? That would give exactly the symptoms you describe.

wcriley · #31 12-19-2012, 12:02 PM

Off topic and probably has nothing to do with your problem, but...
Until my local cable company replaced it's lines with fiber optic cable, there was so much leakage from the decades-old copper lines that a TV connected only to rabbit ears could pick up cable-only channels.

Crater · #32 12-19-2012, 12:18 PM

Quote:

Originally Posted by Meddle

Does the EHX hum debugger work as a very narrow notch filter, or does it actually contain a 60 Hz oscillator tuned 180 out of phase with the mains or what? I've heard criticism of it, as a pedal. Also, surely the UK version must be different from the US version as we run different power systems? Same with mainland Europe...

Based on the "gut shot" (pictures of the pedal's circuit board) I've seen it's obvious the pedal uses a DSP chip (digital signal processor) to digitally remove the hum.

Quote:

The neutral is not really ground since it's AC and not DC. That's why this stuff was changed and the grounds were added. The ground pin really goes to the ground. It's usually connected to the water pipes, or a post or pipe stuck in the ground. Also, some outlets are wired up wrong. So if you have a 2 pin outlet, your neutral might be hot. Even three pin outlets are often miswired.

The fact that the neutral is AC and not DC doesn't really matter. The difference between the neutral and ground lines is this: the neutral wire carries current (amps), the ground wire does not. Therefore, since there is always some resistance in a wire, the neutral wire will often have a small amount of voltage above ground. The more current on the circuit, the more this voltage can be.

wrench45us · #33 12-20-2012, 06:25 AM

ok I abandon the hypothesis of ungrounded outlest -- though I will still check that out.

If I plug amp and have amp in living room and all is quiet. If I walk the bass into the noisy room, it's just enough to get within 3 feet of the threshold and where all the wires come into the house, for the noise to start.

With the rig out of the room, the noise is much more directional -- of course, I only have limited cord length to explore that -- in any case the source is definitely in that corner of the room where power, cable and telephone all come into the house.

When comcast took over for Time Warner, they ran new cable into the house and the old Time Warner cable is still run into the house.
It's still a bit of a mystery, but thanks for all the input to get a better idea of what's going on.

I guess I picked the worst room in the house for my home studio and the idea of recording that bass.

wcriley · #34 12-20-2012, 06:38 AM

Just thinking out loud...and probably not very practical...and hoping someone in the know will chime in...

Would lining the walls in that corner of the house with aluminum window screen, tied to ground, help?

Rune Bivrin · #35 12-20-2012, 07:42 AM

What you've got is in all likelihood magnetic fields from the cables. There is no practical way to shield those, and pickups are fundamentally coils ideally suited to picking up varying magnetic fields. Humbuckers solve this problem by having two coils picking up the field with opposite polarity, effectively cancelling the hum.

10mm steel sheets in all the walls, ceiling and floor might help, but that's usually not a viable solution...