I could be wrong, but I THINK the OP is saying that he has some DC on his speaker and it makes a hum. The hum is the same freq as his mains transformer hum. SO he is making the erroneous association that the DC on his output must be coming from his mains.
my water heater is old ones and compact in size, I guess it is the diode you guys said controlling the power of heater.
@enzo
yes, the hum's tempo on speaker is exactly the same as transformer hum.
I'll try add a DC filter after I fixed the emi/rfi filter.
is the hum can injected through 0volt ground trace close to input/signal trace?
@enzo
yes, the hum's tempo on speaker is exactly the same as transformer hum.
I'll try add a DC filter after I fixed the emi/rfi filter.
is the hum can injected through 0volt ground trace close to input/signal trace?
A ground loop within the amplifier or bad power supply filtering (some people have difficulty discerning 50/100Hz and 60/120Hz since both pairs are exact octaves) are more likely to be the culprit.
I assume you are referring to potential ground loops between equipment, e.g. a signal source and the amplifier. Yes, they can be an issue, and the easiest way to test is to just disconnect any signal source from the amp and ground the inputs using a 10k resistor and see if the problem goes away. If the hum persists, its's likely to originate in the amp itself (see above). If the hum goes away, you might have a grounding conflict between the amplifier and the signal source.
I still have difficulty buying into the mains DC offset possibility. It sounds far-fetched, while various other, more plausible causes have not been eliminated as far as I can tell.
@mastodon
my RCA ground, amp ground and.. all are connected to speaker ground and PSU without resistor in between. I'll add in a resistor tomorrow.
my RCA ground, amp ground and.. all are connected to speaker ground and PSU without resistor in between. I'll add in a resistor tomorrow.
Could you describe the exact grounding situation? Some photographs of your setup and especially the wiring would be extremely illustrative at this point!
As to the resistor: I'm not sure if you understood me correctly. What I mean is: try running the amp with no input, just a resistor clamped over the input terminals. This effectively ties the inputs to ground, so any noise you hear is sure to originate from the amp itself.
As to the resistor: I'm not sure if you understood me correctly. What I mean is: try running the amp with no input, just a resistor clamped over the input terminals. This effectively ties the inputs to ground, so any noise you hear is sure to originate from the amp itself.
@mastodon
I'm using a center-tapped psu. output, input, chip amp and..grounds are all connected together. without isolating the lower line with resistor from the higher power line.
I got it. Means listen to the ground condition with my amp?
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I just installed the Alta software, perhaps I can analyse the ground with it?
I'm using a center-tapped psu. output, input, chip amp and..grounds are all connected together. without isolating the lower line with resistor from the higher power line.
I got it. Means listen to the ground condition with my amp?
edited:
I just installed the Alta software, perhaps I can analyse the ground with it?
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Exactly. That should provide some clue as to where we should look. At present, there are just too many possible causes. It's key to isolate the problem in order to trace it back to a single cause.
Consider that you may be chasing at least two different problemens. 1) transformer buzz due to mains dc offset (I totally agree to Eva's explanations here; when a trasformer becomes audible that is normally due to saturation) 2) ground loop problems or similar between the audio components or within the amp.
I would first separate them. And you say that your speakers only buzz when the transformer buzzes. Two questions: can you confirm that your heater uses diode operation? Can you measure DC offset at your wall socket when you hear the buzz?
I would first separate them. And you say that your speakers only buzz when the transformer buzzes. Two questions: can you confirm that your heater uses diode operation? Can you measure DC offset at your wall socket when you hear the buzz?
@cent88
Does the hum come and go? Most water heaters and other appliances cycle on and off.
Any intermittent hum, noise or interference that can be linked to an external source has a much different solution than an always present problem.
Does the hum come and go? Most water heaters and other appliances cycle on and off.
Any intermittent hum, noise or interference that can be linked to an external source has a much different solution than an always present problem.
@tatus
I'm sure that heater causing the transformer to hum.
only either one of the heater(same model) in the house is enough to make it hum and I guess not the heater drawing too much current.
I tested three aircond(compressor running) on at the same time, can't hear any hum.
how to measure the DC offset at wall socket?
@speedskater
the transformer hum louder when heater is boiling water.
when I 1st bought the transformer, I can't hear any hum.
now without heater on, I also can hear very little hum from it.
(I guess long period of saturation caused damage to the trans, it can't even stand for little DC offset for now.)
I'm sure that heater causing the transformer to hum.
only either one of the heater(same model) in the house is enough to make it hum and I guess not the heater drawing too much current.
I tested three aircond(compressor running) on at the same time, can't hear any hum.
how to measure the DC offset at wall socket?
@speedskater
the transformer hum louder when heater is boiling water.
when I 1st bought the transformer, I can't hear any hum.
now without heater on, I also can hear very little hum from it.
(I guess long period of saturation caused damage to the trans, it can't even stand for little DC offset for now.)
From an earlier post of mine:
DC on Power Line
I did find 3 good discussions on the subject:
Mains DC and Transformers
http://www.diyaudio.com/forums/solid-state/2080-dc-filter.html
http://www.diyaudio.com/forums/soli...t-buzzing-toroid-transformers-what-right.html
Consensus was that these filters sometimes help.
However there was no agreement on what the actual problem is!
Or what the correct circuit is!
It's hard to measure because it's maybe a 1 Volt DC off-set riding on the AC line voltage.
DC on Power Line
I did find 3 good discussions on the subject:
Mains DC and Transformers
http://www.diyaudio.com/forums/solid-state/2080-dc-filter.html
http://www.diyaudio.com/forums/soli...t-buzzing-toroid-transformers-what-right.html
Consensus was that these filters sometimes help.
However there was no agreement on what the actual problem is!
Or what the correct circuit is!
It's hard to measure because it's maybe a 1 Volt DC off-set riding on the AC line voltage.
I would take a 100k resistor in series with a 1uF film capacitor, and use a dc voltmeter to measure the voltage across the capacitor. The two components help the voltmeter extracting the dc remainder on the mains voltage.
Hi,
take a standard sinewave and examine it carefully.
You will find that the area under the +ve curve exactly equals the area under the -ve curve.
Each pair of +ve and -ve curves sum their -ve and +ve areas to exactly zero.
This is a symmetrical AC sinewave.
The mains is not a symmetrical sinewave. It is distorted, it has extra artefacts added to it. These distortions are almost random and usually are not symmetrical.
Now examine the +ve area under the curve and compare it to the -ve area. Summing these does not always result in exactly zero area.
The difference from zero area is the DC effect.
A transformer sees the AC+distortion and interference as AC +- a small DC current that is not balanced from one waveform to the next.
It is this unbalanced millisecond to millisecond imbalance of +ve to -ve areas that the transformer responds to by making a noise.
I have no idea whether your proposed measuring technique can detect that imbalance.
What I can tell you is that the wave to wave imbalance is not the same as adding a small DC offset to a symmetrical AC waveform.
take a standard sinewave and examine it carefully.
You will find that the area under the +ve curve exactly equals the area under the -ve curve.
Each pair of +ve and -ve curves sum their -ve and +ve areas to exactly zero.
This is a symmetrical AC sinewave.
The mains is not a symmetrical sinewave. It is distorted, it has extra artefacts added to it. These distortions are almost random and usually are not symmetrical.
Now examine the +ve area under the curve and compare it to the -ve area. Summing these does not always result in exactly zero area.
The difference from zero area is the DC effect.
A transformer sees the AC+distortion and interference as AC +- a small DC current that is not balanced from one waveform to the next.
It is this unbalanced millisecond to millisecond imbalance of +ve to -ve areas that the transformer responds to by making a noise.
I have no idea whether your proposed measuring technique can detect that imbalance.
What I can tell you is that the wave to wave imbalance is not the same as adding a small DC offset to a symmetrical AC waveform.
I agree to everything except that the transformer reacts with buzz on each single half wave. What is causing that buzz is excessive current due to transformer saturation (as shown in figure 2 of Mains DC and Transformers). Lets assume that the transformer is unloaded at its secondary, then it can be seen as a simple inductor. Magnetic flux is proportional to current through the inductor, and current is proportional to integral of voltage. This means that the transformer adds up voltage imbalance over time, and will go into saturation after some time. That time depends on how much headroom the designer of the transformer has provided. When the dc imbalance persists, then it is the nonlinear remanence curve that keeps the transformer just at the saturation limit. The problem here that, naturally to an integral, even extremely small imbalances will slowly add up and let the transformer saturate.
My measurement method was targeting at that heater that supposedly uses diode rectification. A short simulation shows that it is effective. The remaining ripple of 7V rms should be okay for the voltmeter. If not, the capacitance can be increased.
Attachments
I agree that the DC effect is due to saturation. But not over one half cycle.
It's the difference between alternate pairs of half cycles that sum to a non zero area under the curve (your integral of voltage).
one cycle of +ve DC followed by one cycle of -ve DC (that randomness of the interference) will cancel out leaving a net zero DC effect (the upper and lower areas are identical over the two cycles).
The transformer can be competently designed and never saturate on no load when mains is at maximum design voltage.
This same competently designed transformer can become noisy due to dirty mains supply.
The same competently designed transformer will be well away from saturation when it delivers significant load current.
In this loaded situation it can still become noisy when dirty mains voltage is fed into it.
It is the imbalance over a series of successive cycles that causes the DC effect, not one half wave.
It's the difference between alternate pairs of half cycles that sum to a non zero area under the curve (your integral of voltage).
one cycle of +ve DC followed by one cycle of -ve DC (that randomness of the interference) will cancel out leaving a net zero DC effect (the upper and lower areas are identical over the two cycles).
The transformer can be competently designed and never saturate on no load when mains is at maximum design voltage.
This same competently designed transformer can become noisy due to dirty mains supply.
The same competently designed transformer will be well away from saturation when it delivers significant load current.
In this loaded situation it can still become noisy when dirty mains voltage is fed into it.
It is the imbalance over a series of successive cycles that causes the DC effect, not one half wave.
@don attack: not yet. I just finished my college exam. The transformer buzz too with only mains Neutral connected(Live not connected, power off).
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