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Username: georgesdayout

Post Number: 14
Registered: 10-2007
Posted on Monday, October 22, 2007 - 4:20 pm:   Edit Post

OK, the wiring at our church must really need replacing at this point, or more specifically, the dimmers and ballasts in our lighting. I can't believe my Essence 4 is humming so badly. I get no hum whatsoever, even in front of the neons, at the local guitar store. I can crank one of their SVTs up and hear practically nothing. But when they turn on the lights at this church, it just hums (and worse, that buzz you get from the strong overtone at 180 and the other odd harmonics).

I would have thought the hum-cancelling in the Essence pickups would have grabbed that a little better. The sound does not improve with the pan control in any specific position (I don't know if there is a polarity reverse going on between the pickups, but suspect not). The sound is definitely in the bass - if I turn the volume control down, the hum/buzz goes away.

Any suggestions of things to troubleshoot this?

I wonder about the grounding (or lack thereof). We are running on old non-grounded circuits, but I'm not sure of the grounding path the bass's electronics anyway. I run from the bass on the 1/4 inch into the Boss GT-6B. The Boss has a power transformer/regulator so only goes to two prong power plug. I run 1/4 balanced into XLR on the mixing board. Assuming I can get proper ground to the power on the mixer or another component hooked to ground, will that provide the proper ground to the bass? I should try an ohmmeter on this idea to trace my ground out as far as I can. I fear that what might be happening is the entire unterminated ground circuit between all the ground wires both signal and power is floating and catching the EM (I got radio this Saturday at rehearsal).

- George
Username: mica

Post Number: 4876
Registered: 6-2000
Posted on Monday, October 22, 2007 - 7:12 pm:   Edit Post

George - It does sound like you've probably got some creative electrical work in the building. Is the hum directional? I mean, when you face different directions, does the hum change in volume?
Username: davehouck

Post Number: 5580
Registered: 5-2002
Posted on Monday, October 22, 2007 - 7:29 pm:   Edit Post

I don't know that this is it, but remove the cavity cover on the Essence and see if the ferite bead is there.

Also, your post didn't mention whether you were using a power conditioner/regulator.
Username: georgesdayout

Post Number: 15
Registered: 10-2007
Posted on Monday, October 22, 2007 - 7:44 pm:   Edit Post


Thanks for responding.

To give the building some credit, it has a great history. Washington's family (as in George) went there, but electricity was definitely an afterthought. They are renovating this coming year, so I have hopes of clean power in my future.

I did move around a little bit on Saturday at rehearsal to try to check, but there did not seem to much directionality on the hum/buzz. There definitely was directionality on the RF I picked up briefly, but I've never encountered that before.

The dimmers for the lights are about 20 feet below where I am sitting in the gallery, with the lights about 20 feet overhead about 10 feet in one direction and 20-30 in the other, so I am getting a bit swamped with signal from all directions.

Only thing related to the condition of the bass itself is that the nut on the output jack was getting loose recently. I just tightened it back down a couple weeks ago (snugged it by hand, not having a tool handy I would trust with the finish), but it had gotten loose enough to get a little wiggle when plugged in. When I had the cover off while tightening the jack, I did notice that the leads were run through the ferrite bead as expected for that year (1994).

I experimented by buying a new cord to see if my old cable had shielding issues, but that didn't make any difference. Oh well, replacing a cable every 10-15 years won't kill the budget too badly. The guitarist also gets a buzz (running straight out of the guitar into the board), but nowhere as bad as mine.

If there is anything else I can try to isolate the problem (or better yet, isolate me from the buzz), please let me know - it's been a long time since I taught Electronics lab and my soldering was never Mil-Spec, but I'm not afraid to troubleshoot hands on. I'm tempted to run my own ground and see if that makes things better or worse.


Username: georgesdayout

Post Number: 16
Registered: 10-2007
Posted on Monday, October 22, 2007 - 8:11 pm:   Edit Post

A couple updates...

- I'm sorry Dave, I can't do that.... OK, I already saw the bead a couple weeks ago when I first started investigating this issue. I just can't help the movie quote :-)

- I did verify that the GT-6 has continuity on the ground for input and output, so I would pick up a ground from the other end of the balanced cable if it existed.

- I do not have a power conditioner running. Perhaps I might pull the Furman out of my rack at home and trying it out. Or better yet, borrow one from my friends at the music store one block over and then get the church to buy it if it helps (the PA has a much lower but still noticeable hum as well).

- Finally, I should note that the buzz is not loud enough to be a problem while I'm actually playing a note, just very noticeable by the ensemble during rests or breaks before I get to the volume control

I'm still open to any other input while I try the power conditioner. I will have to search a little harder to find a good ground that I can reach. There must be one somewhere close without attaching to the lightning rod just outside :-) I've got two tons of organ pipes behind me - I'm sure those fans had to have grounds to pass code, right?

- George
Senior Member
Username: adriaan

Post Number: 1658
Registered: 6-2002
Posted on Tuesday, October 23, 2007 - 2:41 am:   Edit Post

Did you already try to eliminate either the instrument or the rig as the problem? If plugging in a different instrument eliminates the noise, then the instrument is the culprit. If plugging the instrument into a different amp eliminates the noise, then the problem is in the rig.

Alembic instruments are self-grounding - the electronics touch the shielding paint, and the back cover has shielding paint on it as well, so the cavity is completely shielded. However, if a pot or a switch or the jack socket is sitting loose, then the shield is not effective. Just tighten all the nuts on the pots, switches and jack socket (gently but snug) and make sure that the back cover sits snug as well.
Advanced Member
Username: cozmik_cowboy

Post Number: 219
Registered: 10-2006
Posted on Tuesday, October 23, 2007 - 6:02 am:   Edit Post

"Dimmers" is the key word here. I have never seen electronics on the same circuit as a dimmer that did not buzz. See if you can find a circuit to plug into that has no dimmers - and during the renovation, make sure they seperate lighting from outlets onto different circuits if they retain the dimmers.

Advanced Member
Username: dfung60

Post Number: 277
Registered: 5-2002
Posted on Wednesday, October 24, 2007 - 1:40 am:   Edit Post

George -

Based on what you wrote, I think you may have a wiring problem between your Boss pedalboard and the church mixer. If you want a balanced signal out of the board to the mixer, you would use the left or both <strong>XLR</strong> outputs. The 1/4" outs are unbalanced, not balanced. If you built a cable to connect the 1/4" outs to an XLR on the mixer, you need a transformer in there or you won't be delivering a proper signal to the mixer.

Testing if this is the problem is easy. Use a regular microphone cable from your Boss XLR outs the mixer XLR in, or run a regular shielded 1/4" guitar cord from your Boss 1/4" out jack to a high impedance or line-level input on the mixer.

You didn't say which volume you were turning down when isolating the buzz problem - on the instrument, on the preamp, or on the mixer. I would expect the buzz would only go away when you turn down the mixer gain, but there may be a noise gate involved somewhere in the signal chain that could muddle the results.

With an unbalanced ("regular") connection, the signal is the difference between the hot line and the ground line. If hum is induced into an unbalanced cable (e.g, gets through the shield), there's no way to reduce it since you can't tell what's your signal and what the noise is. With a balanced connection, the signal from your instrument is sent on two separate lines (+ and -) and the amplifier amplifies the *difference* between the two signals instead of an absolute level. These two lines are twisted together along their length under the shield (which is a separate conductor which is completely independent from the signal). The theory here is that if the cable is sitting in an RF field, the noise will be equally induced in the + and - signals, but when the amp takes the difference between the lines, the induced signal should cancel out completely.

A transformer is used to convert the unbalanced signal into a balanced one. That's what is in a regular direct box. That matching transformer will also normally play around with the impedance and signal level as well.

Without the transformer, it would be hard to build a cable adapter that wouldn't cause problems. You could put the unbalanced signals on + and - wires and connect the shield only on the XLR end and get something out, but the signal will probably be weak. If you tried to connect the XLR shield pin to the unbalanced ground too, it might hum less but you would almost certainly cause a ground loop, which would cause a different kind of hum. The mixer's ground lift switch might make it a little less noisy, but then you'd be back to basically running an unshielded cable and the original hum.

From your description, when you plug into an SVT, I'll be you were using a regular cable and not your Boss+adapter cable. That would be a quiet combo too.

Give the alternate connections a try. I'll bet that will fix your problem.

David Fung
Username: georgesdayout

Post Number: 18
Registered: 10-2007
Posted on Wednesday, October 24, 2007 - 9:08 pm:   Edit Post


I'm not sure this will fix the problem completely, because I had been using the XLR out into the mixer before and still had hum/buzz. But...I do think it is making it worse. Nice catch on the 1/4 in outs being unbalanced. I could have sworn the 1/4 in outs were balanced before I hooked up this way (just trying to have use of the volume pot on the back, since I was driving the mixer so hard with the XLR out).

The buzz goes away several ways:

1. By turning down the volume control on the bass.

2. By turning the output of the Boss unit to minimum using the volume pedal.

3. By turning down the volume at the mixer.

So, I do conclude the noise signal is being injected inside the bass, even if additional noise is added later in the signal chain.

I think this is so much more noticeable now because the noise suppressor in the Boss unit used to gate out the noise before and now is not able to contain it.

I'll try a few things on Saturday and report back.

Thanks for the help so far.

- George
Senior Member
Username: adriaan

Post Number: 1662
Registered: 6-2002
Posted on Thursday, October 25, 2007 - 12:54 am:   Edit Post

Elimination is not done by turning down the volume, because if there's no signal being amplified then of course there's no buzz either. What you do is you take out different parts of your signal path one by one, keeping the volume open. You don't even need to play the instrument ...

Be sure to follow David's suggestions, as he knows more about this stuff than most people around here.

Just in case you ever need to do an elimination, here's the step-by-step program:

1. Use another bass or guitar, preferably one that does not have the buzz problem on its own rig. Plug it into the same unit in your rig that you use for the Essence, see if the buzz goes away.

2. Plug your Essence into a guitar rig that does not have the problem on its own. You don't need to play the bass, just have the volume open. If the buzz stays, the problem is probably in the Essence.

3. Use another instrument cable, and repeat tests 1 and 2. If the buzz travels with your original cable, and disappears with the other cable, then the problem is definitely in your own cable. The same goes for each cable in your signal path.

4. You appear to plug your instrument into a Boss effects unit. Now plug the instrument directly into the unit that comes after the Boss. If that next unit doesn't have an instrument-level input, then replace the Boss with a different unit that does not have the problem.

5. If you have a wall wart to power some part of the rig then make sure that the power line from the wall wart does not run parallel to any cable that is in the signal path.

... and so on.

(Message edited by Adriaan on October 25, 2007)
Advanced Member
Username: terryc

Post Number: 310
Registered: 11-2004
Posted on Thursday, October 25, 2007 - 3:10 am:   Edit Post

If it is worth anything since I am not as well learned as David, there are some venues I play which do the same with my MK Standard, I solved it by using a balanced 3 pin XLR direct from either my amp or my Zoom unit to the hum whatsoever.
I would be careful about attaching seperate earth(ground) to lightening rods or other ground areas as this can cause earth(ground) differential which can be dangerous..I hope you use a RCB device on your amp..these are indeed lifesavers if the mic becomes live along with your gear and you complete the circuit by touching the mic(personal experience!!!)
I must admit..when it occurs it is indeed the most annoying sound.
Username: georgesdayout

Post Number: 19
Registered: 10-2007
Posted on Saturday, October 27, 2007 - 9:25 pm:   Edit Post

Minor update:

Plugged in for rehearsal this morning. Hum still there, not so much buzz. Don't know what else is on Sunday that I didn't get turned on this morning. Or maybe, I just bother to actually turn the lights all the way to maximum, which generally generates less noise than partially dimmed in my experience.

I left the house without grabbing another guitar to eliminate the bass ash a problem, but I'll try to grab one of the kids electrics (I'm down to one bass anymore) tomorrow.

I did A/B the performance between the 1/4 in and XLR outs of the Gt-6 and did not find any difference. Left it with the XLR out based on desire to keep balanced as much as possible (have to love differential input stages).

I will also try out just running the 1/4 in out from the bass into the board.

I also tweaked the noise suppressor in the GT-6B and found that I had to raise the threshold up to 67 to eliminate the hum during rests.

I'm slowly working my way through the troubleshooting on this issue. Thanks again for all the ideas.

- George
Senior Member
Username: fc_spoiler

Post Number: 651
Registered: 5-2006
Posted on Sunday, October 28, 2007 - 1:55 am:   Edit Post

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Username: georgesdayout

Post Number: 20
Registered: 10-2007
Posted on Sunday, October 28, 2007 - 7:32 am:   Edit Post

Today's update:

Very small hum, no buzz! Argh, what changed since last week? Maybe no air conditioning with the cooler weather? Maybe they actually ran the dimmers on the lights up to full for a change? I even brought two items that could definitely help diagnose: another guitar and a battery powered amp. The mains kicked in with a nice hum half way through the service - maybe the gremlins just changed their target :-) (the band is on its own PA right now.)

I did check the shielding paint two weeks ago and it looks good.

I'll go ahead and work on cleaning up the power just on principle if nothing else and also try getting the buzz back by playing with the dimmers so I can further isolate the source.

- George

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