2. amps-preamps
  3. 142371-120446

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
nyev
1,020 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
15,657 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
1,020 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?
4krow
80 posts
 
I will be most interested in how this all plays out. When there is a problem like this, and it ONLY EXISTS with the unit being suspected, AND it has the same problem in someone else's home as well,, Good Lord, it is more than reasonable to get a Full refund. 
erik_squires
15,657 posts
 
The DC issues are two different things.


DC on your power (110VAC or 220VAC) causes mechanical vibration in the transformer, and otherwise rarely has ill effects.


DC on the input terminals (RCA or XLR) is different. Ideally there is none, or very little (millivolts). Amplifiers which are "DC coupled" can pass DC from the inputs to the speakers, which could be over 100V DC. More than enough to fry parts. They use a servo to adjust and stop this. And this works within range, but after a while the DC offset in the signal from the source (CD player for instance) is too great and the amp instead disconnects. It sounds like this input DC is what's happening, instead of DC on the power.


Best,
E
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