Bad AC Line

[Kosinki]

I moved into a new place (old house) and when I power on my Eico HF 87 I was noticing immediately that my power transformer was buzzing real good. I talked to a technician and he said it was small amounts of DC voltage that were causing it. Has anyone else experienced this? I've gone ahead and decided to order the AVA Humdinger DC Line Blocker, hope this solves the issue

 

[Brice]

Is the AC line voltage in your new place higher than before?
That could explain some buzzing.

 

[dspth]

DC blocker.

 

[Brice]

Hum,
The full primary current flows through the caps alternatively.
I hope they put good one in that device.

 

[gadget73]

I'd probably just get a nice heavy duty isolation transformer to solve the problem. Assuming of course that it is actually DC on the lines and not just the transformer having gotten jarred a little loose in transport from your old place.

 

[Brice]

Agreed. Isolation xformer is a better implementation.

 

[whoaru99]

http://sound.whsites.net/articles/xfmr-dc.htm

The potential problem with isolation transformer is itself might exhibit the same buzz/noise if there is DC on the line.

But, rather than build or buy anything right now, has there been a thorough process of elimination? Not long ago there was a thread where the OP received lots of recommendations for line.conditioners but the problem was resolved by simply unplugging an offending wireless extender.

 

[Freds.Bands]

Measure to see if the DC is there, which I doubt. And measure AC line too.

 

[Kosinki]

I'd probably just get a nice heavy duty isolation transformer to solve the problem. Assuming of course that it is actually DC on the lines and not just the transformer having gotten jarred a little loose in transport from your old place.

What aspect of the transformer would come loose? Thanks for the responses.

 

[gadget73]

The mounting screws / bolts mostly.

 

[Freds.Bands]

The mounting screws / bolts mostly.

that won't produce any DC.

 

[gadget73]

No, but it could allow mechanical noise to be generated. I'd personally be much more likely to believe the transformer is loose and mechanically buzzing than the power line has DC on it without any confirmation measurements. So far it seems the suspicion of DC on the power line comes from a tech saying thats what it could be. I don't think anyone has poked a meter into the socket to see whats actually going on.

 

[dewdude]

My question would be where is this DC coming from? Electricity passes through *several* transformers before it gets to you, and transformers won't pass DC.

So there shouldn't be any DC on your incoming line feed...at all.

 

[BinaryMike]

My question would be where is this DC coming from? Electricity passes through *several* transformers before it gets to you, and transformers won't pass DC.

The DC offset arises from local asymmetrical loads, i.e. anything that draws more current on the upper or lower excursion of the waveform. One obvious example would be a heating device with a low power setting that is achieved with a half wave rectifier.

 

[I LIKE MUSIC]

There are a number of potential sources of DC on the AC mains such as the use of high frequency ballasts within fluorescent lighting loads, and switch mode power supplies, even a simple halve wave rectifier circuit.

Modern equipment often draws current only during a very short period of the period of a power supply mains. This can cause unwanted non-sinusoidal and harmonic currents. In some cases even a single diode is used for rectification causing direct current (DC) in the mains supply.



Like AK, where terms are used somewhat loosely such as phase versus polarity, speaker sensitivity versus efficiency and others, DC on the AC mains is sometimes a catchall term for a less than correct AC mains waveform including DC offset. This may cause issues with power supply transformers.

 

[petehall347]

first try a different power outlet . or maybe ask the one that mentioned dc was causing it for the cure .

 

[dewdude]

I just take the opinion that it's better to fix the root cause rather than apply a patch. I've never seen this problem manifest itself as a symptom before so I'm really not knowledgeable about it.

 

[Kosinki]

I've plugged the power amp into all my outlets and I still get the loud buzz. The DC blocker finally arrived yesterday and it has significantly reduced the buzz. By about 75% I would say. I haven't tried plugging in a multimeter as I don't have one.

 

[Kosinki]

ALso the power transformer does not seem to be loose or have any loose screws.

 

[crispycircuit]

Does the house have a fuse box or breaker box?