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DC Offset Blocker/Killer - where to buy in the USA

   I have McIntosh MC8207, the first unit I bought from an authorized dealer came with a loud buzzing coming from the left transformer, and was replaced with a new unit which came with even a louder buzzing. The buzzing can be heard from 8 feet away. Then I was told to have install new 20 amp outlet that has its own isolated grounding.
   That was done professionally by an electrician who installed two isolated 20 amp outlets, two 20 amp circuit breakers, two copper polls for grounding for each outlet, each outlet has its own neutral and power line. After all this done the buzzing sound was still there.
   I was then told to buy a power conditioner which I did (Audio Quest Niagara) which was like $4000 and that did not help. Called back McIntosh and was told that I might have DC offset in my AC line and was told by McIntosh that I would need a DC Offset Blocker/Killer to which when I asked them where to buy one they told me to go on the internet and search to find one, to which I cannot find one.
  This bothers me a little bit, if you as a company think that I have dc in my ac and i need a dc blocker wouldn't you need to sell one as well. I brought this amp to my friends house and it was the same no improvement, so my guess is that he has dc in the ac line as well.
   So If anyone of you knows where to buy a DC Offset Blocker/killer please let me know, but even if this helps kill the buzzing wouldn't you guys think that this expensive somewhat hifi amp/brand should be silent from the factory. I mean this is two units in a row all purchased brand new.

My house is 5 years old, everything is brand new, the whole neighborhood is about 8-9 years old, my electrician says that I have perfect power coming to the house and everything looks fine.

Thank You

tomiiv30
almarg's avatar
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almarg
9,670 posts
 
That all seems perfectly consistent with the explanation I proposed in my previous post, Jim. The hairdryer draws considerably different amounts of current in the positive half-cycle than in the negative half-cycle. The resulting DC offset corresponds to that difference in current x the resistance of the wiring that current is drawn through, **for wiring that is in the path between the outdoor AC wiring and the measurement location.**

For example:

I then plugged the Low pass filter into the first outlet. (Outlet closest to electrical panel. First outlet on home run feed.)
Hair dryer left in farthest outlet.
Fluke measured 0.578Vdc....... (Note DC offset is decreasing)

At that measurement location the DC offset resulting from the current differential between the two half-cycles will not reflect the resistance of the wiring between the first outlet and the last outlet of that branch.

Regarding the 1.577 vs. 0.734 difference, note that 12-2 has about 60% more resistance per unit length than 10-2, and the length of the 12-2 was about 20% greater than the length of the 10-2.

0.734 VDC x 1.6 x 1.2 = 1.41 VDC.

The additional difference of 1.577 - 1.41 = 0.167 VDC is probably accounted for by a combination of the resistances of the connections to the several intervening outlets in the room with the 1.577, and imprecision in the estimates of the run lengths.

Best,
-- Al
jea48
4,313 posts
 
Thanks Al, (almarg) for the response.


The additional difference of 1.577 - 1.41 = 0.167 VDC is probably accounted for by a combination of the resistances of the connections to the several intervening outlets in the room with the 1.577, and imprecision in the estimates of the run lengths.

I don’t think so. All in and out wire connections along with the pigtail extended for the receptacle connection are twisted together and then made mechanically tight using Electrical Spring Connectors.

The live wire steel spring inside the connector is designed to expand and contract with the copper conductors. Varying loads placed on the circuit conductors can cause the copper conductor to expand from heat and contract from cooling as load falls off. The connector’s wire spring always keeps the connection tight.



Jim
nyev
1,026 posts
 
After reading this thread, I am second guessing a similar issue I’m having with an old Arcam P85 where I’ve noticed it buzzing, and the corresponding A85 integrated which has been switching off intermittently with a message that reads “DC Offset - Check Connections”.  The connections are all fine.

Figured the P85 was just old and was toast, but now I will try taking it somewhere else and plugging it in.

I’m concerned as I am considering an amplifier upgrade with a McIntosh MC462 as a candidate.  Also, this problem only started after we moved into a house we fully renovated, including a full replacement of the electrical.

Of note, there is no buzzing from the A85.

erik_squires
15,861 posts
 
After reading this thread, I am second guessing a similar issue I’m having with an old Arcam P85 where I’ve noticed it buzzing, and the corresponding A85 integrated which has been switching off intermittently with a message that reads “DC Offset - Check Connections”. The connections are all fine.



@nyev That’s probably a different issue. This sounds like you might have a bad source. Disconnect all your sources, and try adding them one at a time.

Best,
E


nyev
1,026 posts
 
Ok will do.  Only one source attached and it’s an Arcam DAC.

Would a bad source really cause the buzzing though, which sounds similar to the OP’s issue?
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