P.a. Noises

[professionalsounds]

TRYING TO FIND NOISES SUCH AS 60 CYCLE HUMS AND BUZZES.
SENARIO::smokin:

60 CYCLE HUM;:angry:
SOUNDTRACS MEGAS 32 CHANNEL BOARD - LEFT OR RIGHT OUTPUT - " XLR CABLE" - CREST AUDIO 7001 - SPEAKER.

ALREADY TRIED THE FOLLOWING:
TRIED LIFTING LINE GROUND WITH NO CHANGE.
TRIED LIFTING GROUND ON SOUNDTRACS POWER SUPPLY WITH NO CHANGE.
TRIED LIFTING AC GROUND TEMPORARILY WITH NO CHANGE.
TRIED LIFTING CHASSIE GROUND ON AMP, MADE HUM WORSE.
TRIED CHANGING AMPS USING CREST AUDIO 4001 WITH NO CHANGE.
TRIED CHANGING BOARD TO A MACKIE 24/4/2 WITH NO CHANGE.

Q: WHAT COULD BE DONE TO ELIMINATE THE 60 CYCLE HUM ?:scared:

ANYONE OUT THERE KNOW THE ANSWER ?:banana:

[cmchamp]

PLEASE DON'T SCREAM!

Double check to make sure that all audio gear is on the same leg of electric service. This doesn't mean necessarily that all circuits feeding the audio gear are on the same side of the breaker box. If your amp is on a different leg than the mixer, there is possibilities for different ground potentials, causing the ground loop humm.

C.

[professionalsounds]

Cory, I took the hydro distro out of the equation since we are normally running 3 amplifiers for LEFT and 3 amplifiers for RIGHT. Each amp rack runs to a 30A outlet in the hydro distro.

So, I ran both the board and amplifier from the same 110V circuit straight to the wall and not through the hydro distro.

There was still HUM comming from the amp.
Everything is quiet until I hook up the board.

So, I switched from the SoundTracs Megas board to a Mackie 24/4/2.
The HUM was still there.

Very frustrating! ! !

How can both boards deliver the same problem?

When the whole system is all hooked up the HUM spreads to all the amps, but only when you include the board.

There is a ground loop in there somewhere, but can't pin - point where.

Could there be a cold solder somewhere on the output of the board, a worn out resister on the output of the board or something else?

Can a worn out insert jack on the output of the board cause this problem?

Thanks for repying, Scott

[professionalsounds]

Cory, I took the hydro distro out of the equation since we are normally running 3 amplifiers for LEFT and 3 amplifiers for RIGHT. Each amp rack runs to a 30A outlet in the hydro distro.

So, I ran both the board and amplifier from the same 110V circuit straight to the wall and not through the hydro distro.

There was still HUM comming from the amp.
Everything is quiet until I hook up the board.

So, I switched from the SoundTracs Megas board to a Mackie 24/4/2.
The HUM was still there.

Very frustrating! ! !:scared:

How can both boards deliver the same problem?

When the whole system is all hooked up the HUM spreads to all the amps, but only when you include the board.

There is a ground loop in there somewhere, but can't pin - point where.

Could there be a cold solder somewhere on the output of the board, a worn out resister on the output of the board or something else?

Can a worn out insert jack on the output of the board cause this problem?

Thanks for repying, Scott

[cmchamp]

Does it hum with the amps on and nothing else connected?
How long is the line run from the mix position to the amps?
How long is the speaker level run and what gauge cable?
Are any cables run parrallel with any other AC power, by florescent lighting, etc.?
Does it hum with mixer connected, but Insert processing removed?
C.

[professionalsounds]

Cory:Board to Klark Eq. to JBL crossover ( Stereo 3-way ) to amps.
Return lines are aprox. 100' . The speaker cables are 12' long and less and are of 12 guage wire TwistLock. The amps are Crest 4001,7001, and Carver PT2400 per side. :smokin:

When we hook up the board the noise appears, with and without the EQ. and X-over hooked up . All subgroup and main L & R faders are all the way up. We never run the board that loud at any show, but doing this enables us to find and reduce noises easier. NOTE: We are very sensitive towards "ANY NOISE" because we pride ourselves on having a quiet and clean sounding P.A.:smokin:

There is no noise when running only the amps to speakers.
Using inserts does not change anything.
There is no florecent lighting near the equipment but he garage we are using to test equipment has such lighting in the ceiling. We turned off all the lights and that did not change the P.A. noise.

Thanks for your reply, Scott:smokin:

[cmchamp]

Have you done this?
Amps => Speakers = no noise
Crossover => Amps => Speakers = Noise/No Noise
EQ => Crossover => Amps => Speakers = Noise/No Noise

Also, just to be redundant, when you hook up the mixers, are all inputs disconnected and muted, including aux returns?
C.

[professionalsounds]

Cory: Yes I tried that. I also tried measuring the voltages.:smokin:
ie; Starting at the source using a voltmetre set for measuring 120V.
Measure from HOT > NUETRAL = 120V
Measure from HOT > GROUND = 120V
Measure from NUETRAL > GROUND = 0 ( when we tested it read .3V)

One of our powerbars failed this test. When we eliminated it the noise reduced a little but did not disapear completely.:scared:

We also hooked up a isolation transformer between board and Eq. When the faders were pushed back up the noise did not change in volume. Without the isolation transformer, when the faders were pushed up the noise did increase in volume.

SUSPECT: Ground loop somewhere elusive.
Not sure where the 60 cycle is comming from either.:eek:

ALSO:Testing AMP>SPEAKER ONLY, Discovered that lifting the ground on the back of one of the amps did not change anything ( as it should be ). However lifting the ground on the back of one of the other amps increased noise dramatically.:angry:

Thanks for your reply,Scott

[gcjammin1]

Do you hear the noise when nothing is plugged into the board but the headphones are plugged into the headphone jack? Also, do you have a mono out and have you tried going through this output instead of the left and right to see if the hum is still there? Also, this may be a no brainer, but is everything disconnected from every input and aux send and returns and inserts? The reason I ask is because I had a hum in my system and it came from one of my reverbs connected to an aux send.

Gcjammin1

[professionalsounds]

gcjammin1: I've been trying to trace through every step of what I have already done. I do remember hearing the hum in the headphones but don't remember if it occured when the board wasn't hooked up to anything else. I will try that tomorrow to see what's what. As for inputs and aux.'s, nothing is plugged into the inputs or aux sends and returns.
The hum is present from amp to speakers at a very low level. A level that I do not wish to entertain. When I run a XLR from the board to any of the 6 amps running the stereo 3-way P.A. the hum's level increases to a level I do not want. I am sending one of the amps out for repair to resolve a different noise issue. When lifting the ground on the back of that amp I was getting a loud buzz. Clearly something is wrong with that amp that needs to be adressed.
Back to the 60 cycle HUM. The only thing I can think of doing next is to pull apart everything, and under a strong light using a magnifying glass, go over every circuit and solder joint of every piece of equipment I own until I am satisfied that there isn't a cold solder joint hiding out somewhere in my P.A. causing a possible ground loop. Thanks for your reply,Scott.

P.S. Somebody save me from having to do that much work.......anybody have any ideas? Let me know.Thanks

[professionalsounds]

gcjammin1: When it is just the board and headphones the 60 cycle hum is there.:scared:
However it is also there when the rest of the system is hooked up as well.
There is a ground loop somewhere.:scared:
I am still hunting it down. Do you have any more suggestions ?
Tomorrow I am going to find out why there is a .3V between the ground and the neutral of the garage hydro at all the 110V outlets. In a perfect world it should be 0.0V but .3V is alright ( so they say ). I checked out my friends basement hydro and he had a 0.0V between his ground and neutral.
MAYBE: The 60 cycle is due to the blead between the ground and neutral.
Thanks for your reply,Scott::smokin:

[gcjammin1]

If the hum is present when nothing is plugged into the board but the headphones, it sounds like the hum is coming from the board. One time I took my Soundcraft in to get the ins and outs modified for +4 and when it came back I had a hum. The problem was one of the nuts around the contol room pot was loose. I tightened it and the problem was solved.

Gcjammin1

[professionalsounds]

To all: When just the board is hooked up there is no noise in the headphones.
When the rest of the system is hooked up there is no noise in the headphones.:D

When just the amp and speakers are hooked up there is a 60 cycle hum.:eek:
When the rest of the system is hooked up there is a 60 cycle hum.:eek:
The 60 cycle hum is a little louder when the boards mains are all the way up.

I tried two separate hydro sources::smokin:
1: Systems hydro distro which is hooked up to the garage hydro.
2: Hydro from the house.

The garage hydro has a 0.3V bleed from the ground to the neutral.
The house hydro has a 0.0V or NO bleed from the ground to the neutral.

Either hydro source, makes no change in current 60 cycle hum.:scared:

Can anyone suggest something I haven't tried yet.
Please read "all" threads related to this problem.

Thanks for your replies, Scott:smokin:

[dementedchord]

why are your panties in a twist take a breath... buy a vowel ...whatever.. relax... ssshheeees take it logically.... start at the speakers and work your way back to the board... are all the amps noisey when they alone are hooked to their speaker??? if so how much?? are they the same amount??
you call yourself professional sounds... been doing it a while have ya?? well when did the noise start what did you change ??????

[professionalsounds]

dementedchord:Anyone else out there::scared:
I've Been doing this a real long time.:smokin:
Very,very,very fussy regarding noises. 60 cycle hum is pretty low.
Trying to reduce 60 cycle hum completely.
All the obvious things have already been tried before I started this thread.
I am looking for any possible "new" ideas/suggestions.

Amp>Speaker= NO NOISE:bounce:
Board>XLR cable>Amp>Speaker= NOISE:bounce:
Already tried, different board,cable,amp & hydro source.:bounce:
Exausted every combination of the above mentioned.:bounce:
Checked printed circuit boards on all the amps for the following:
Discoloured/burned out resistors & capacitors.:bounce:
Cracked or cold solder joints.:bounce:
Also checked all the grounding on all plugs for all pieces of equipment.:classic:

The 60 cycle hum although pretty low in volume should not be there.
If you have any new ideas/suggestions, Thanks,Scott:smokin:

[cmchamp]

Scott:
How old are the amps?
Have you tried different amps?
I have a Carver PM1400 that had developed an anoying hum as you may be experiencing. Factory serviced - problem gone.
Just a suggestion.
C.

[professionalsounds]

CMCHAMP: Some amps 6 years old and some are older than that.
Crest 4001,7001 and Carver PT 2400.
Amp to Speaker = NO noise.:banana:
It seems that only when I hook up either board that the 60 cycle hum exists.:scared:
SoundTracs Megas 32 ch. OR Mackie 24/4/2.
I still think it is an elusive ground loop. What is bothering me is that it is happening with both boards.:scared:

Keep in mind that the noise is pretty low, but should not be there.
I would still like to track down the reason for the noise and get rid of it completely as I am very fussy about any noise.:bounce:

Thanks for your reply,Scott:smokin:

[professionalsounds]

Thanks everyone for your help. I will keep looking for ways to reduce even the smallest noise in P.A. 60 cycle hum is really low and acceptable signal to noise ratio. I pride myself on having a clean and quiet running system. I don't think that I will ever run the board full out, as I have it when I am checking for noises. If anyone has any additional information that would help reduce the 60 cycle hum even further send me an e-mail.
All e-mails are welcome at the following adress: professionalsounds@hotmail.com
Thanks again, Scott.:smokin: