Neither? DC is not noise, although both are unwanted in a mains supply.
DC, if present, must involve both conductors as richie00boy says.
Noise may come on both or just one, so mains filters handle common-mode and differential-mode noise.
DC, if present, must involve both conductors as richie00boy says.
Noise may come on both or just one, so mains filters handle common-mode and differential-mode noise.
my speakers producing the same buzzing sound as transformer when DC present.
good high current DC blocker too expensive to DIY.
good high current DC blocker too expensive to DIY.
Are you sure you have a problem with DC on your mains? That usually causes the trasformer itself to buzz, not through the speakers. Buzzing from your speakers is more likely to be caused by a ground loop or possibly a bad ground connection between components in the system. If you do have a DC problem, it's not that difficult or expensive to fix it, check out Rod Elliot,s site or do a search right here, lots of good info.
My transformer buzz itself for sometimes(don't know what is the source of DC) and on water heater confirm will cause it to buzz. my speaker only buzz when the transformer buzz, put my ear 3-5cm near to speaker only can hear it.
Yes. I found a lot of DC blockers. This is the one I trusted.
Mains DC and Transformers
most of the high current application DC blocker required high capacitance capacitor equal to high cost and Rod Elliot,s required high inductance, which is very costly isn't it?
I have two audio system here, my pc(750watts)+LM3886(225watts) and hometheater 1000-1500watts.
is there any alternative way to do to the mains instead of DC blocker?
Yes. I found a lot of DC blockers. This is the one I trusted.
Mains DC and Transformers
most of the high current application DC blocker required high capacitance capacitor equal to high cost and Rod Elliot,s required high inductance, which is very costly isn't it?
I have two audio system here, my pc(750watts)+LM3886(225watts) and hometheater 1000-1500watts.
is there any alternative way to do to the mains instead of DC blocker?
If DC is the problem then only a DC blocker is the solution.
If noise is the problem then a mains filter should help.
If noise is the problem then a mains filter should help.
DC is extremely rare, and often misdiagnosed. The presence of 120Hz will make a meter read some DC residual; I can measure this on the secondary of my power transformer (definitely no DC getting through there) but the meter says there is DC present. It can be ignored, and is likely not the source of noise you are describing.
DC should not be present in a power system unless there is equipment connected that does not belong, or a system that is lacking. A DC blocker is a band aid to a larger problem.
You say the noise increases when your water heater turns on ?
DC should not be present in a power system unless there is equipment connected that does not belong, or a system that is lacking. A DC blocker is a band aid to a larger problem.
You say the noise increases when your water heater turns on ?
@zigzag
most of the time I can't hear any little buzz from the trans.
the noise occur when heater turns on. some one told me before that the heater injecting harmonic 120hz, 180hz, 240hz, 300hz or...into the line.
most of the time I can't hear any little buzz from the trans.
the noise occur when heater turns on. some one told me before that the heater injecting harmonic 120hz, 180hz, 240hz, 300hz or...into the line.
While it's unlikely that true DC will get on our AC power lines (although it occasionally happens) . But distortion of the AC power sine wave can create asymmetry which can be viewed as a DC offset. This DC offset can and does upset some poorly designed or selected power transformers.
I am not aware of any electric water heater that would produce harmonics; they are thermostatic-controlled passive resistive heaters.
Do you have a scope that you can use to monitor line voltage at the time you are getting this buzz? Either your voltage is distorting at this time, or you are picking up magnetic induced hum due to the high current consumed by the heater. Normally this would require close proximity, though.
I suppose this could be explained by miswiring somewhere in the chain, so any further details about the water heater and amp will help.
Do you have a scope that you can use to monitor line voltage at the time you are getting this buzz? Either your voltage is distorting at this time, or you are picking up magnetic induced hum due to the high current consumed by the heater. Normally this would require close proximity, though.
I suppose this could be explained by miswiring somewhere in the chain, so any further details about the water heater and amp will help.
Even if there is asymmetry in the AC waveform, the transformer primary inductance is a voltage integrator and will just move the zero crossing point to suit, it is impossible to integrate a DC component. If you have DC in the mains there is no need to protect the computer or any other device with an SMPS because they are not affected by DC in fact some SMPS's can run off DC.
I'm with zigzagflux on the water heater.
I'm with zigzagflux on the water heater.
but I can hear the buzz from the speaker too.
the DC can cause damage to the trans or other components?
the DC can cause damage to the trans or other components?
I also doubt that it is DC or harmonic distortion (unless the heater uses eletronic regulation - what type is it?).
What happens when a large load is connected to one of the phases in a household installation is that it creates a small AC voltage between N and PE (as N seen as a resistor takes the full load current, whereas PE has no current). This can be tested by an electrician by shorting N and PE, this will normally trigger the RCD in your installation provided the load is large enough. In a bad installation with large transfer resistances, the voltage can be high enough so you can even feel it.
If you now have some devices in your audio equipment that connect to PE, this can become audible in your speaker. As a test, you can interrupt all PE connections by (temporarily!!) isolating them at the mains connectors using tape. If the hum is gone, you are one step further.
Things can get even worse when you have devices connected that use different mains phases. In a bad household installation, this can already be the case when using different wall sockets. To test against this (for the case), reassemble all mains connections to only use one wall socket.
What happens when a large load is connected to one of the phases in a household installation is that it creates a small AC voltage between N and PE (as N seen as a resistor takes the full load current, whereas PE has no current). This can be tested by an electrician by shorting N and PE, this will normally trigger the RCD in your installation provided the load is large enough. In a bad installation with large transfer resistances, the voltage can be high enough so you can even feel it.
If you now have some devices in your audio equipment that connect to PE, this can become audible in your speaker. As a test, you can interrupt all PE connections by (temporarily!!) isolating them at the mains connectors using tape. If the hum is gone, you are one step further.
Things can get even worse when you have devices connected that use different mains phases. In a bad household installation, this can already be the case when using different wall sockets. To test against this (for the case), reassemble all mains connections to only use one wall socket.
Tatus you are right on the money there, and hot water heaters often use magnesium dioxide insulated elements which can get damp and leak to earth, It is unlikely that an RCD would be installed on this service. Many times I have tripped an RCD with a heating element and even with pyrotenax which must have got damp.
Many electric heaters (of all kinds), particularly old ones, use a diode in series with the heating element for half power operation or even for 120V/230V operation.
They draw DC from mains line and create a DC offset voltage that makes transformer saturation worse, particularly in big toroids with low primary DC resistance.
A saturating transformer produces strong leakage magnetic fields with high odd harmonic content, that are picked up by any signal circuits and wiring close enough. That's how "transformer buzz" ends up in your speakers.
They draw DC from mains line and create a DC offset voltage that makes transformer saturation worse, particularly in big toroids with low primary DC resistance.
A saturating transformer produces strong leakage magnetic fields with high odd harmonic content, that are picked up by any signal circuits and wiring close enough. That's how "transformer buzz" ends up in your speakers.
Without a doubt some legacy appliances had series diodes for low power modes of operation. But few of us still use these old appliances and almost all being intermittent in operation would cause the hum/buzz to come and go.
- Status
- Not open for further replies.