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FolkU
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Apr 22, 2010

Grounding??

Hello ST. Hope you can help. I have submitted several posts recently so you may look at those for additional information. The following happened last Saturday night. I did see a post from 2007 where a follow Bose user found the problem to be a grounding issue caused by the metal ears is his rack. Have you ever heard of this. I called Bose and they are at a loss right now. I want to believe it is the drummers gear and not my Bose. He, our drummer, really want to place the blame on the Bose which, when he is not plugged into the Bose there is no problem. The trim knob on the power stand is very scratchy so we had to shut the unit down and spin the know to clean it, then it was fine. I think its important to mention that the entire unit shut of three times during songs (all trim knobs were green).
Help



We are a trio that typically operates out of two L1m2's. However, we are sometimes forced into very small spaces and need to scale down to a single L1 with two tone matches. This has proven to be problematic as we appear to be receiving an audio feed looping back along the AC line through the electronic drum rig. This causes unwanted audio to be present in all channels on whichever tone match the drums are connected to. In fact, even if we disconnect the drum rig mixer feed to the tone match the unwanted audio is still present across various tonematch channels. This only subsides when we actually unplug the drum rig mixer's power cable.
>>
>> As you might expect this additional audio appears to be overwhelming the L1 and distortion becomes present. We have nearly exhausted our troubleshooting abilities with the exception of trying to ground lift the drum rig (which we'll try at next gig). Wondering if anyone else has run into this and solved it. Any thoughts are greatly appreciated.
>>
>> FYI..The drummer is using a 12 channel behringer mixer with a combination of Octopads and triggers with an Alesis DM4 drum module.
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ST - Pro
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May 11, 2020

Re: Grounding??

Hi FolkU,

Is everything that is connected in any way connected to the same power source? (e.g. power bar)? That's the first thing I'd check.

Next I would try a DI with a ground lift between the drum rig and the T1®.

Please dont use a cheater plug
--?8T? Please click the picture for more details and an article about ground loops?T8?--

I know that it's probably inconvenient to swap out the L1® Power Stands (you'd have to get the guitarist to bring his in for this test). But you don't need him to bring the Cylindrical Radiator®s or his B1. If you swap the Power Stands and the problem persists, I'd be very confident that the problem lies elsewhere.

You could try things like disconnecting things from the drummers mixer: one thing at a time until the noise stops. If it doesn't (until you turn off the mixer), then turn off the mixer try plugging the individual sources (e.g. the Alesis DM4) that were going into the mixer... into the T1. If none of those devices are causing noise. Then I would be very suspicious of the mixer.
Le5
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Aug 22, 2006

Re: Grounding??

Hi FolkU,

In addition to ST's recommendation, I would like to add a few comments and suggestions:

I have witnessed a similar problem with someone using a larger Behringer console and also similar problems with another brand console within the same product category. I have also witnessed the grounding issue with the rack rails (metal ears) with a rack.

It is often easier to determine which piece(s) of equipment is causing the issue, but more difficult to resolve the issue or find the root cause.

Some of these problems relate to the audio grounding design within different products (by different manufactures). Without getting too technical, most audio equipment will have multiple grounds within the unit, power (chassis or AC) ground, audio ground (pin 1 of an XLR connector or the sleeve of a 1/4" plug) and digital ground for digital equipment. In many cases, all the different grounds are eventually internally connected to the power ground.

Where we run into problems is when we connect pieces of equipment that use different grounding schemes. For example, some devices have XLR pin 1 as chassis ground, but often older equipment will have XLR pin 1 as Audio ground. Unfortunately, if there is a potential difference (voltage difference) between the two grounds of the different pieces of equipment, even if all the gear is connected to the very same AC power source, issues often arise.

A defective internal power supply within a unit can lead to these same issues.

The first thing is to make sure that all units within the problematic system are indeed all connected to the same AC power source. Also make sure that the ground is a good ground where the system is connected. Have you tried the same setup in a different location (rehearsal space maybe)? Is the issue still present?

As ST recommended, try to isolate individual pieces of equipment within the drummer's rack. Then, if substituting (if possible) an identical piece of equipment does not resolve the issue, then it is likely a design incompatibility issue. But if if substituting an identical piece of equipment does resolve the issue, then the cause would likely be from an internal fault with the original unit. On the other hand, if you don't have access to an identical suspected unit and the replacement alternate did resolve the issue, it would be difficult to conclude whether there is a design incompatibility or a fault within the unit.

I apologize if this is confusing. Troubleshooting the fault you are experiencing is too often one of the biggest challenges we face in the audio world!

A DI, audio isolation transformer, Hum Eliminator or XLR pin 1 lift can sometimes resolve the issue.

I hope this helps rather than add to the confusion...
FolkU
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Apr 22, 2010

Re: Grounding??

Thank you Le5. We are playing out tomorrow night and will give it another go. You and ST are great and its nice to know that when you have a question, there are good people out there to get some answers for you.
I am a guitar player that has taken over the bass duties in the band. I see many posts about bass players that are very happy with their tone and others that want to go back to an amp. I'm in the middle. I think using my strat with the GK3 pick up into a GR55 sounds better than my expensive basses. That said I wonder is 4 B1's going to give me a better base feeling or, if the volume is not an issue, is 4 B1's just overkill. Do other bass players have more luck using a processor of some kind? I am just running through the T1 with little added other than the Tonematch. Not a big issue just figured I would ask.
Thank you for your help on the other, more important issue?
ST - Pro
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May 11, 2020

Re: Grounding??

Hi FolkU,

quote:
if the volume is not an issue, is 4 B1's just overkill. Do other bass players have more luck using a processor of some kind?


Lucky for you - you can probably answer this with a live test. If the guitarist will let you use his Model II Power Stand (and if he has two B1s). Don't bother doing anything that follows unless you have access to 4 B1s. Doing this with 3 will not hurt anything, but it probably won't help either.

On your Model II Power Stand (with two B1s) run the Bass Line Out to the guitarist's Model II Power Stand Analog Input. You can run that second Model II Power Stand without the Cylindrical Radiator®. No harm there.

Set the second power stand analog input trim to around 3 or 4. Do some playing and adjust the trim so that no matter what you do - you don't get any red flickers. You're looking for solid green with occasional amber. For the test you can use an unbalanced cable (Tip Sleeve) or balanced (Tip Ring Sleeve). The unbalanced connection will be lower but you can compensate for that with the trim control.

Make sure that all the B1s are physically touching (2x2 or 1x4). That should avoid any phase related issues.

You may not notice much difference until you push the volume up.

That's the way Bose designed things - at low volumes, 4 B1s should sound very much 2. The idea is to be able to turn up louder and while maintaining the overall spectral balance.

We have notes about that here:

Bass Line Out (Model II) and B1 Behaviour.

Does that help?