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How to determine cause of guitar hum?

We've been trying to solve a hum problem. We know it's not the guitar (archtop with set in humbucker) because the hum only occurs in one particular place in the room. If we move the guitar even a couple feet away, the hum stops. Discovered that the hum is negligible when using a wood bridge and wood tailpiece. Worse with metal bridge and metal tailpiece. We know that the wiring and grounding of the hardware is correct. We've unplugged lights, computers, etc from nearby. So what could cause a low hum that goes away when you move the guitar from one specific position?

Comments

MC208 Sun, 04/28/2019 - 08:45
We're located in a residential basement, poured concrete walls and regular frame construction above like any other modern (2010) home. On the floor directly above is a living room with TV, and DirecTV box. Satellite dish is mounted to roof of garage above, and maybe 30 feet away. The basement was finished in 2015, so it shouldn't be a wiring issue within walls down here..

Boswell Sun, 04/28/2019 - 15:05
If you place the guitar plugged in on its stand in the affected place in the room, does it hum when you are nowhere near it? Does the hum amplitude depend on the guitar's orientation?

What do you see if you record the hum and then use a spectrum analysis plug-in on the signal? Is the hum reasonably pure 50 or 60 Hz, or are there high odd-harmonic levels?

pcrecord Mon, 04/29/2019 - 06:46
Hums are very common in many environement. Sitting at my mix place with my LesPaul always gives me noises and it I turn and point the guitar neck toward my right monitor, 90% of it is gone... Anywhere else in my rooms, it's clean..

There is numerous reasons that guitar pickups produce noises

  1. Bad house wiring, unconnected ground, etc.
  2. Electro-magnetic field, caused by AC adapters and various house appliances.
  3. Cheap or long wiring. Cheap guitar cables can even make a sound in the amp when taping on it.. But TR aren't made for long distance like TRS (balanced)
  4. Exagerated gain settings, the more you push the gain on pedals or your amp the more you'll get noises it's part of the game.
  5. Quality and Types of pickups. Some noiseless pickups are availlable.
  6. (please add more if I forgot something)
    class="xf-ul"> The quick solution is to find the right spot where it sounds clean in your room and stick to it.
    Other than this;
    • Use high quality cables.
    • Have an electrician check the wall wirings
    • Change pickups for noiseless ones.
    • having a clean power unit, like the furman can help too
    class="xf-ul">

MC208 Mon, 04/29/2019 - 07:26
Yesterday, we tried unplugging the TV, and the directv box on the floor above; it didn't have any impact on the hum sound.

Does the hum amplitude depend on the guitar's orientation?
Yes! We are shooting video, and the hum just happens to occur exactly where the guitar needs to be for the video, backdrop, etc. When I turn the guitar away, or lower it to near the floor, it goes away.

Computer is a desktop, so there is no battery. But not only did we turn it off, we also unplugged it from the wall.

This is the guitar cable we're currently using:
https://www.monoprice.com/product?c_id=301&cp_id=11509&cs_id=3011001&p_id=4794&seq=1&format=2
It doesn't specifically say it's a guitar cable. Could it be a problem?

Can wifi router cause any interference, I don't think we tried unplugging that yet.....

dvdhawk Mon, 04/29/2019 - 10:00
You posted a clip in a thread regarding compressors about a year ago. The guitar sounded perfectly fine.

What's gone sideways since then?
What has changed?
Taking you at your word that that is the exact cable you're using, which is 3-conductor TRS:
Are you plugging it directly into your mixer, or still passing through a DI and / or preamp first? (in what order?)
Do you have a standard 2-conductor TS instrument cable you can try in its place?
Is the noise present with a different guitar in the same signal chain?

MC208 Mon, 04/29/2019 - 10:09
We didn't like the reverb pedal, so we just disconnected the pedal board altogether to once again try and troubleshoot the noise.
So yes, we're plugging the guitar directly into the Hi-Z channel on the ZED.
We have other cables to try, but I think we tried other cables with no change in the outcome.
We notice that the noise, which isn't loud to begin with, is reduced when using a guitar with an ebony bridge and ebony tailpiece. It's louder with the gold bridge and gold tailpiece. Same pickup in both guitars. These are guitars that we sell, and no customer has ever complained about any noise which further supports that it's something environmental in this room/area.

dvdhawk Mon, 04/29/2019 - 14:22
What I'm getting at though is that when you plug a TRS cable into any of the the ZED 10fx inputs (Hi-Z or Line), it may be sensing that the Ring and Shield are not shorted together as they would be with a normal TS instrument cable. Naturally Boswell would be the leading authority on the ZED, but the way I'm reading the manual, even on the Hi-Z input the Ring = Cold (-) indicates it is a separate op-amp circuit. The guitar wouldn't provide anything on the ring conductor, so is it acting as an unterminated antenna at the ZED's Ring op-amp? Boswell ?
Attached files

Boswell Mon, 04/29/2019 - 14:57
Yes, agreed, but he said he had tried several different cables with the same result. Mind you, if they were all TRS cables...

It's difficult to see how an open-circuit ring connection would produce the reported place and orientation sensitivity. What it could cause is a sensitivity to how and where the cable is run along the floor.

I don't think we know the model of Zed mixer. A+H used a number of Hi-Z input circuits on the different models.

paulears Tue, 04/30/2019 - 00:51
If you are up to a quest, then remember that a pickup has it's maximum sensitivity perpendicular to the pickups, so essentially it's pointing out into the room forward, and through your body, backwards. You can therefore tell the direction the noise source is coming from. So move around the room, and swing the guitar finding the bearing of the noise source. Then move the guitar to the other side of the room, and repeat. look at the lines you have created. Do they cross? If they do - that is the noise source. Keep in mind that the source may NOT be at guitar height. I found one in my studio roof - a 12V transformer for the lights, which I always have on!

dvdhawk Wed, 05/01/2019 - 09:23
MC208, post: 460850, member: 49667 wrote: So you're suggesting to use a cable that doesn't have the extra ring?

Yes.

Typical instrument cables are basic TS. The standard instrument cable is coaxial, which is to say, one conductor down the middle of the cable and the spiral or braided shield is used for the 2nd conductor. (This shield should gather most outside interference and safely pass it to the chasis of the amp or mixer you're connecting to) Instrument cables much longer than 20ft. are to be avoided. Use a short instrument cable into a DI for longer runs.

Also, be aware of the fact that light duty 1/4" speaker cables look very much like instrument cables, and should be avoided for connecting instruments. The speaker cable is unshielded and will not reject outside interference. The cable should be marked stating whether it's an instrument cable or speaker cable, (usually imprinted on the outer jacket of the cable). If it's unmarked a quick look inside the connector will usually tell you - if you know what to look for.

If you use a TRS cable for a guitar, the ZED's Hi-Z and Line Inputs can interpret the TRS in a number of ways. When it senses that the R and S aren't shorted together it may be handling that like it would a balanced signal (and it is not balanced).

If the guitar is a normal passive (magnetic pickup, volume pot, tone pot, output jack) guitar it only has a 2-conductor (TS) output jack.
If the guitar has any active electronics in it that require a battery it probably has a 3-conductor (TRS) output jack which uses the extra contacts to engage the battery only when a cable is plugged in. With a normal TS cable that is not a problem. If you plug a TRS cable into that power switching jack then we open another can of worms.

Again, this may not be a source of any noise in your case, but it certainly isn't helping. It might not be a factor at all, but we won't know until we start at one end and do everything correctly.


Moral of the story and words to live by in general: "Just because you CAN stick it in there doesn't mean you SHOULD stick it in there." :)

Link555 Wed, 05/01/2019 - 19:18
It's hard to predict what the TRS will do, I had a line 6 amp, behave badly with a TRS cable into it....which is strange because it was a guitar amp with an unbalanced input.... upon investigation I found the used the ring connection a switch to indicate the guitar was there to further circuit. Normally with a TS this would a short, but with TRS connection it was open and amp did not enable the additional circuit....

dvdhawk Thu, 05/02/2019 - 15:01
MC208, post: 460850, member: 49667 wrote: So you're suggesting to use a cable that doesn't have the extra ring?


To expound on that a little bit... If you look at this Switchcraft Jack Schematics page you'll find the 39 Most Common pinout / uses for 1/4" connectors. (I and IV being the simplest version of TS and TRS respectively) The others have various combinations of contacts and separate switching contacts as well, depending on the job they were designed to do.

And the problem is, from the outside they all basically look this.




So it's important to have the right cables / connectors for the job. Like Link said sometimes a TRS cable will work in an application that doesn't require the Ring connection. Other times it just exposes you to a whole new array of problems. With more than 39 outcomes, it's pretty easy to see why having the right male connector matters.

Hopefully your noise problem is as simple as that, and if it isn't, you can move forward using the more common and less expensive TS instrument cable(s).
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