[DecibleDude]

 A few weeks ago while listening to my AVA gear I noticed a slight buzzing sound coming from my DVA set 500 power amp and thought this ain't right. After a few minutes I was able to determine that the sound was purely a mechanical cause, because none of it came through the speakers. Well, that was a relief, but nonetheless still a little concerning as I started debating with myself whether it was an issue worthy of sending the amp in for repair. Owing to the fact that the amp is quite hefty and a hassle to move I began trying to think of alternatives to that nightmare scenario and thought I'd consult google AI first, which I did. I'm glad I did, because I learned a lot. Apparently, large transformers are quite prone to buzzing if you have any dc current in your household ac electrical. It's cause can be from things inside or outside of your home, but mainly in most cases inside. Things like dimmer bulbs, or malfunctioning appliances elsewhere in your home etc.

 In any event AI suggested I get a dc blocker which is something I've never heard of in the past, but whatever. There seems to be only one company I could find that makes them and that is "ifi" that makes Audio accessories of various types. They have two little units called dc blockers which plug into the power receptacle on the back of your amp and then which you plug your power cord into. Well for $149.00 for the bigger one and $129.00 for the smaller I ordered the ifi silent power dc blocker plus intended for larger amps on the off chance that it might actually work though I was skeptical it would. Lo and behold, it worked perfectly to the point I ordered the second smaller 
one for my preamp not because it was buzzing, but just because. I got the first larger plus version directly from "ifi" on their website and the second smaller one from Crutchfield for $129.00. Not bad prices in either case for something that actually works.

  Anyway to wrap up, I later discovered that my dc offset issue was being caused by a little space heater I use which had been set at 500 watts which is it's lower setting, which in turn creates the problem. I threw it out promptly, but am still using the dc blockers because from what I've read there's alway a tiny amount of dc in your household current regardless, and the dc blockers filter out all of it. Also, subjectively speaking I could swear that I heard an improvement in sound quality regardless. I understand this is likely psychological, as my AVA gear and associated equipment sound remarkable already, but who knows I'll take it.

  Lastly, and interestingly there another product on the Crutchfield site which is a fancy power cord for close to three thousand dollars. I won't comment on the wisdom of such a purchase, but noticed it had a built in dc blocker of their own.

[BadDNA]

I had the same issue, buzzing transformer in my old ADCOM GFA5500. I added AVA's Humdinger...... a DC blocker, and voila! Noise gone. I now have my M225 mono amps plugged into it.

[NIGHTFALL1970]

I had a buzzing in my AVA tube preamp. The AVA humdinger fixed it.

[DecibleDude]

 Well this is ironic, because if I had realized AVA made these devices I obviously would have gotten theirs. It's strange because prior in all my years of HiFi interest, I don't think I've ever heard of a dc blocker. Anyway, I may still get the AVA one if it can be put before my power strip and protect the whole system preamp, power amp, Tuner, CD player, Turntable, etc. I guess that would depend on how many amps going through it can handle, and I'm not sure you can use it that way. In any event, these devices actually work if the cause of your buzzing transformer is dc offset.

[FullRangeMan]

I had a buzzing transformer when it was saturated, too hot.
Never had DC on the lines.

[DecibleDude]

I had a buzzing transformer when it was saturated, too hot.
Never had DC on the lines.

 What was the cause of your over saturation, and overheating? I noticed that dc offset is one of the possible causes of your issue from what I've read. It's also possible that perhaps the dc issue is intermittent depending on what the cause is.

[danielgk]

Don't throw your heater out!  Simply switch it from low to high.  Most of these heaters have thermostats so the difference between low and high is only how long it takes to heat up the room (as well as the current used in doing so when the heater is actually heating).  A lot of these heaters use a diode to get the low setting.  In low, the positive goes to the heater and the negative is not used.  The result (for example) is 10 amps of current when the AC is positive and almost zero current when the AC is negative.  This results in an overall current average of 5 amps, a slight DC voltage on the AC line due to the imbalanced load, and a buzzing audio power transformer.

[DecibleDude]

Don't throw your heater out!  Simply switch it from low to high.  Most of these heaters have thermostats so the difference between low and high is only how long it takes to heat up the room (as well as the current used in doing so when the heater is actually heating).  A lot of these heaters use a diode to get the low setting.  In low, the positive goes to the heater and the negative is not used.  The result (for example) is 10 amps of current when the AC is positive and almost zero current when the AC is negative.  This results in an overall current average of 5 amps, a slight DC voltage on the AC line due to the imbalanced load, and a buzzing audio power transformer.

  Lol, too late the heater is gone. It's ok though, because the high setting produced too much heat for the space, and the thermostat on these cheapie heaters are almost worthless, being either too hot, or too cold, before they turn on, or off. I got a new single 500 watt setting one which is fine though, because nothing gets in the way of my stereo listening except possibly the Mrs.

[FullRangeMan]

What was the cause? I notice that dc offset is one of the causes of that saturation and overheating you describe.

DC voltage has been increasing in North America due home installations typically have only one wire net and one circuit breaker for the entire house.

The equips that usually causes DC component when they are unbalanced in a home electrical system are:
Battery chargers, laptops, TVs, household appliances that convert AC to DC, LED lamps, fluorescent lamps, dimmers, solar panels, power inverters, uninterruptible power supplies (UPS), grounding problems, deteriorated wiring insulation.etc.

[FullRangeMan]

What was the cause of your over saturation, and overheating? I noticed that dc offset is one of the possible causes of your issue from what I've read. It's also possible that perhaps the dc issue is intermittent depending on what the cause is.

The transformer I was using was old and had a rusty core.