Harmonic Current??
- Thread starter 1sparky2
- Start date
- Status
tryinghard
Senior Member
- Location
- California
Electronic ballasts do contribute to harmonic issues but I believe the greatest contribution to noise like this is the neutral incorrectly bonded past the service disconnect (250.142(B)). If this is the case every time 120v circuitry is used the unbalanced load will travel ALL PATHS to source and most often this includes sound systems as one of the paths. I believe a good place to start troubleshooting is to qualify correct bonding.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Do the speakers use twisted pair leads? Non twisted pairs can pick up all kinds of interference. In a larger building with longer speaker leads it can become more noticeable.
tryinghard
Senior Member
- Location
- California
The techs for sound systems often want zero potential equipment grounding, this is achievable with an equipment grounding conductor from the sound equipment?s power source panel to the sound equipment. But this will not eliminate neutral bonding problems - if these exist it will simply be another route for any unbalanced load current meaning noise will occur here too.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
110115-2008 EST
1sparky2:
Find one fixture that when on and all others are off will produce at least some noise in the sound system. In this fixture install a Corcom 5VR1 filter, about $18 from Newark, and see if this will essentially reduce the problem.
If this works, then find the next noisiest fixtures and install filters in them. If this produces substantial reduction, then make a decision if this is a cost effective approach.
Fluorescent lights are an arc discharge type device and these generate substantial radio frequency interference.
In the early days of radio sparks were used to generate radio frequency energy for signal transmission. In fact a spark generator was the very first radio transmitter.
http://www.juliantrubin.com/bigten/hertzexperiment.html
http://www.sparkmuseum.com/BOOK_HERTZ.HTM
http://www.localhistory.scit.wlv.ac.uk/Museum/Engineering/Electronics/history/radiohistory.htm
.
1sparky2:
Find one fixture that when on and all others are off will produce at least some noise in the sound system. In this fixture install a Corcom 5VR1 filter, about $18 from Newark, and see if this will essentially reduce the problem.
If this works, then find the next noisiest fixtures and install filters in them. If this produces substantial reduction, then make a decision if this is a cost effective approach.
Fluorescent lights are an arc discharge type device and these generate substantial radio frequency interference.
In the early days of radio sparks were used to generate radio frequency energy for signal transmission. In fact a spark generator was the very first radio transmitter.
http://www.juliantrubin.com/bigten/hertzexperiment.html
http://www.sparkmuseum.com/BOOK_HERTZ.HTM
http://www.localhistory.scit.wlv.ac.uk/Museum/Engineering/Electronics/history/radiohistory.htm
.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
That is why I asked if he had twisted pairs supplying the speakers, non twisted pairs have a tendency to pick up radio frequencies and have some effect on the speaker output.
I remember when I was a kid the church we went to would sometimes hear truck drivers passing by talking on their CB radios - through the sound system in the church.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
110115-2228 EST
kwired:
It is probably a good idea to have twisted pair speaker wires, but I doubt the noise is entering the system at this point.
Speakers are relatively low impedance and narrow band devices. Unless transformers are used the impedance level is probably below 16 ohms.
There are other high impedance and high sensitivity components that are more likely the entry point of the noise. In particular microphone circuits.
Your comment about CBers getting into an audio system probably points to something in the amplifier at a sensitive point acting as a detector of the high frequency signal. You could take a small loop of wire, a solid state diode, small capacitor, and earphones and go near a broadcast station, detect, and listen to their broadcast.
There have been reports that being near very high power AM stations, WLW at 500,000 watts, would cause some bed springs or other metallic components of neighbors to demodulate the broadcast and produce acoustic output.
There are ham radio operators with 1 KW of output power that when pointing their beam antenna at a neighbor's house would light close lights.
Power level, and existence of detection devices at points of high sensitivity, will be the determining factor in the effect of noise.
Microphone circuits may be 100,000 ohms or more for input impedance, and sensitive to millivolt levels. Good radios will have input sensitivities in the microvolt range but lower impedance than microphone inputs.
.
kwired:
It is probably a good idea to have twisted pair speaker wires, but I doubt the noise is entering the system at this point.
Speakers are relatively low impedance and narrow band devices. Unless transformers are used the impedance level is probably below 16 ohms.
There are other high impedance and high sensitivity components that are more likely the entry point of the noise. In particular microphone circuits.
Your comment about CBers getting into an audio system probably points to something in the amplifier at a sensitive point acting as a detector of the high frequency signal. You could take a small loop of wire, a solid state diode, small capacitor, and earphones and go near a broadcast station, detect, and listen to their broadcast.
There have been reports that being near very high power AM stations, WLW at 500,000 watts, would cause some bed springs or other metallic components of neighbors to demodulate the broadcast and produce acoustic output.
There are ham radio operators with 1 KW of output power that when pointing their beam antenna at a neighbor's house would light close lights.
Power level, and existence of detection devices at points of high sensitivity, will be the determining factor in the effect of noise.
Microphone circuits may be 100,000 ohms or more for input impedance, and sensitive to millivolt levels. Good radios will have input sensitivities in the microvolt range but lower impedance than microphone inputs.
.
- Location
- Illinois
- Occupation
- retired electrician
Often this is cause by a poor connection at the lamp socket. The high voltage arc at the poor connection causes the static on the system.
BILLY101
Member
- Location
- Telford, Pa
First, the audio equipment rack should be on a dedicated circuit. Wireless microphone receivers should on this circuit.
Second, the input wires from microphones etc. should use twisted pair wire with XLR connectors. This allows canceling of unwanted rf noise.
Third, if that doesn't help use an isolation transformer to power the rack such as a Tripp-lite Model IS1000 or similar equipment.
Reference NEC art 640.9 A2 and 647.7
BILLY
Second, the input wires from microphones etc. should use twisted pair wire with XLR connectors. This allows canceling of unwanted rf noise.
Third, if that doesn't help use an isolation transformer to power the rack such as a Tripp-lite Model IS1000 or similar equipment.
Reference NEC art 640.9 A2 and 647.7
BILLY
- Status