Ground loop problem?

[Santy]

There is an audible buzz from the surround speakers. The preprocessor is connected to the studio monitors through an unbalanced 25ft DIY IC. It took me a great deal of effort to isolate the problem and conclude that the airconditioner is causing the interference. The noise goes away when it is turned off. I always keep the volume at 100% on the speakers so reducing the volume ofcourse, reduces the noise but that I do not think is an ideal solution. As per suggestions given in various forums, I have tried to fuse the pin 3 to the XLR casing on the speaker end, tried to lift the electrical ground from the power outlet (I know its not advisable), plugged everything (PC/prepro/sub/speakers and even projector) into a single power outlet, but the noise wouldn't go away. Surprisingly the monitors on the front do not have this problem (< 10 ft cable).

Anything else I can try to eliminate the buzz without spending too much? How to find out if the AC and power outlet are on same phase? Even then since the ground is common for all phases, will this solve the buzz problem? I think this would work but I wish to keep it as the last option: Behringer HD400 MicroHD . This seems to not only isolate the ground but also converts unbalanced to balanced so it would benefit in long cable runs.

 

[hydra]

...Surprisingly the monitors on the front do not have this problem (< 10 ft cable).

...

You might have covered these, but just in case, since the fronts don't have this problem:

- Did you try using the fronts with the same I/Cs as the surrounds?

- Did you try using the surrounds, powered from the same outlets as the fronts?

 

[jagdish_p]

If then humming is not present in the fronts it's an interference picked up by rear speaker cables due to running parallely with electrical wires or running close to the A/C motor.
BTW are your speakers active? In which case it could be due ground loop for the rears.

 

[Santy]

You might have covered these, but just in case, since the fronts don't have this problem:

- Did you try using the fronts with the same I/Cs as the surrounds?
- Did you try using the surrounds, powered from the same outlets as the fronts?

1. No. I will take the monitors to the rear and check tonight.
2. Yes, as I mentioned, I had connected every stuff to one outlet, the noise was still there. Its a faint buzz but its quite annoying.

If then humming is not present in the fronts it's an interference picked up by rear speaker cables due to running parallely with electrical wires or running close to the A/C motor.
BTW are your speakers active? In which case it could be due ground loop for the rears.

They do run close to AC cables of A/C but during troubleshooting I ran the cables far away from A/C but still the noise remained. Yes they are active speakers. Ground loop is the problem. And A/C load is causing it. I am wondering how to overcome it.

 

[hydra]

...
2. Yes, as I mentioned, I had connected every stuff to one outlet, the noise was still there. Its a faint buzz but its quite annoying.

Santy, if all the monitors are connected to one power outlet, and if the problem was power based, the fronts should also have the buzz, shouldn't they?

For this reason, it could be that the I/C (to the rears) is the culprit here. The AC could be messing with this I/C somehow, which is why the buzz goes away when the AC is turned off.

 

[Santy]

Santy, if all the monitors are connected to one power outlet, and if the problem was power based, the fronts should also have the buzz, shouldn't they?

For this reason, it could be that the I/C (to the rears) is the culprit here. The AC could be messing with this I/C somehow, which is why the buzz goes away when the AC is turned off.

Yes hydra, the IC seems to be the culprit. Its cheap and its long. But it has 3 core in it. So I thought I will convert into balanced cable and use Behringer HD400 to eliminate the ground noise. Should I go for it?

Any other suggestions? Has anyone else experienced this problem?

 

[greenhorn]

I always keep the volume at 100% on the speakers

That might be an issue.
Would suggest you reduce the volume on the speakers and pump up the volume levels at the Reciever/Preamp to reduce S/N

Otherwise you might need to invest in some fancy shielded cable, or add a line driver at the preamp output.

 

[hydra]

Santy, if the IC (and not power) can be isolated as the problem, shouldn't you just use another IC. If the problem is noise seeping into the IC because of something along the path it is going along, then you might need to re-route the IC. (But then you can continue using the same IC). Won't it be more expensive to get the Behringer HD400 and a long Balanced cable?

But if you prefer to use concealed wiring, and if the current IC is going along a concealed channel, then maybe it might be worth going the balanced route, to keep things concealed.

By not getting the HD400, you could avoid one extra item in the chain. (Though it may not matter much as far as the rears are concerned). I tend to be a bit OCD about things like this, and I'd personally prefer to fix the issue directly. I'd lose sleep knowing that the issue (noise seeping into an unbalanced IC) still persists

 

[Santy]

Nice thoughts!

With level adjustments on prepro, the lowest I could go is 50% on actives but I still hear the buzz. Even after 2-3 pegs. I am sitting hardly 5-6 feet from the surrounds and they are directed to my seat. I should have mentioned that I used to keep at 100% but right now it is calibrated at 50%.

As I mentioned, I ran the cable far away from the A/c line but the problem persisted. So I thought the noise is not picked up enroute but probably originating from source equipments due to some ground loop.

But as it is pointed out, if front monitors are not having this problem then yes, it could be the problem with IC or the length of it (both front & rear are same grade cables).

Also, the cable as I mentioned is of 3 cores. I planned it that way so that if I get a balanced prepro in future I could convert them into balanced cables. So I don't have to buy another cable if Behringer is to be used.

Truth is, I can afford to buy ICs of high quality for 2-3 m lengths but 30+30 feet of IC

 

[greenhorn]

A DIY Line driver is a cheap solution if you are open to some soldering. An op amp stage with some 5-10 gain (use preset pots) running off split 15 or 12 V rails, and a passive attenuator (optional) at the speaker side.

PS. Try moving the speakers around, bring it to the front, and try to figure out if the speakers or the IC is picking up the hum.

PPS: are the rear speakers earthed ? Are they running off a different power line compared to your Reciever/Preamp? If that's the case, try running an extension cord to the rear speakers from the power point where your reciever is plugged, and see if the hum is still there

 

[jls001]

@Santy: you have a PM.

 

[Santy]

@greenhorn
Thanks. What is the primary objective of going for line driver. I believe you are suggesting to boost the signal to get better SNR? But will it not amplify the noise also if it is originating from source. Did you mention it needs 12v power supply?

Yes the speakers are earthed. As I mentioned already, I have tried connecting every gadget that consumes electricity in my HT from single outlet but in vain.

Actually I have been reading about audio transformers (1:1) like this one from Jensen but again, its quite expensive.
http://www.jensen-transformers.com/award.html
http://www.amazon.com/Jensen-CI-2RR-IsoMax-Isolator-Jensen/dp/B00ASVWYCS

@jls
Thanks for the suggestions. It was very helpful. I did not know that these branded pro-grade cables are available locally. Will have to check them out.

 

[greenhorn]

if the noise is coming from the source, then either the source is faulty, or it should be reflected in all channels equally.

My guess is that the long Line level wiring is picking up EM interference along the route. If the Output impedance of the line driver is sufficently low, and the output voltage is high, then it should be enough to bring down the EM interference relative to the signal. The line driver should be at the preamp side, so that your output voltage is already high.

 

[ranjeetrain]

May I suggest a low-cost experiment such as this. Nothing much to lose even if you don't benefit.

A bit expensive but more functional: http://www.amazon.com/EBTECH-HE-2-E...dp_s_cp_5?ie=UTF8&refRID=03YW7K9YZ081YK2396QB

 

[darshanjoshi]

Santy
Did you swapped speakers ?
Just remove XLR from surround speaker and connect it to front speaker and check whether noise is still cumin

Since it is DIY IC i would suggest remove all wires from XLR connectors from both sides and rewire them. Nothing to loose.

We had similar problem in our speakers in office which were connected from PA Amplifier with DIY IC. Problem was samll humming sound.
I removed, cut the old ends of cable, made new ends and rewired. All humming went away.

 

[Santy]

@ranjeet
Thanks. But if that is the ideal solution, I would prefer to get the Behringer as its a known/ reputed brand in pro audio. It also converts unbalanced to balanced so the cable length concern is also taken care of.

@darshan
Yes that experiment is still pending. I also plan to connect the rear speakers to my DAC and see if the preprocessor is the source of noise.

I am thinking of getting pro grade cables as suggested by jls if problem persists.

 

[omishra]

As greenhorn and others pointed out, it looks like interference from outside into IC. You can try making shield connected to ground at source end. RCA/ connector Live and return path (ground) connected within two cores of wire. Shield can protect cores from interference.

Making balanced cable is another solution if you select quality converters. Otherwise it would highly deteriorate SQ.

 

[Thad E Ginathom]

I would prefer to get the Behringer as its a known/ reputed brand in pro audio.

It has the reputation of being relatively low cost and relatively huge value for money

I'm hoping that you do try this solution because I'm looking forward to hearing if there is any sound quallity difference with the box

 

[Santy]

I observe that the headphone also picks up the same faint buzz both from DAC and prepro (when A/C is on). So cable or its length is not the actual problem I believe?
The cable replacement I plan to do anyway but it's clearly some ground loop problem. Don't know how I am gonna fix that.

 

[Santy]

Update:
While I am still trying to get the balanced cables (the dealer is hesitating to supply in small lengths), I checked the power outlet last Sunday and I was shocked to note that the Line and Neutral were swapped. Incidentally both the two different outlets that I use for A/V are wired that way. I fixed it and verified the problem. The buzzing noise on surrounds have come down significantly, I would say by about 40%.

Now one more observation was that there is a 1.6 V supply measured between neutral to ground connections. I checked in the living room, it was 0. I am not sure if this could cause the buzz since this voltage is sensed with or without the A/C switched on.