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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
jea48
2,944 posts
 
@ tomiiv30

As for DC on the AC mains.

Nelson Pass

If you are experiencing mechanical hum from your
transformer, it is often caused by the presence of
DC on the line. Usually this comes from some appliance
using current asymmetrically, such as a lamp dimmer.

The hum comes usually from toroidal transformers, which
saturate easily with DC, and when they recover, they
draw an extra pulse of current, causing the noise.

You can put a pair of back-to-back electrolytics in series
with the AC power line to block this, and it works fine.
Makes sure the current rating of the electrolytics is
high enough, and the they are joined at a like polarity,
such as + to +.
https://www.diyaudio.com/forums/solid-state/2080-dc-filter.html




Re: Not trying to start a flame but....

"If your not comfortable with a meter get an electrician or tech that knows his way around test equipment. "

If you read the comments in the AA archives, you would have seen the ones from real engineers (Jon Ricsh, John Curl, etc)who have measured this. They report that most hand held DVMs cannot measure this (John Curl tried three different Fluke models with mixed results).

If you really want to try and measure the DC off-set on your AC line with a cheap hand-held DVM, try the following:

Put a 100K resistor in series with a 100µF cap (this is called an integrator). This now goes in parallel with the AC line. Measure the DC voltage across the cap.

Even a few tens of mV DC off-set can make a toroid buzz, especially low priced ones.

The image here is a PA Audio DC blocker. Note the two series connected bridges, this gives four forward diode drops vs the two of the Bryston circuit. Note also that the caps in parallel with the diodes are very small, just for RF suppression. The original LC Audio filter was similar to this PA Audio one as well, only they used three forward diode drops, and only small RF caps.


http://db.audioasylum.com/mhtml/m.html?forum=tweaks&n=140383&highlight=integrator+djk&r=...


JMHO, if the mechanical buzzing on one of the transformers is caused by DC on the AC mains, then both transformers would be buzzing.
.

erik_squires
5,268 posts
 
Not all transformers will respond the same. Try taking the amp to another building and see what happens.
stereo5's avatar
stereo5
2,766 posts
 
He already did that.  He took the amp to a friends house and it still buzzed. 
tomiiv30 OP
63 posts
 
@jea48 

With my amp only one is buzzing, the left one, so lets say I do have dc on my ac line why would only one buzz? IMHO I think that the one that buzz is a bad one comparing to the right one which is a good one. It would be the only explanation.
So what I did was, I turned off every switch in the house except the on the amp is plugged in and yes the buzzing sound got quieter but was still present. But having an expensive amp that has much better transformer than a cheap amp this little interference when all breakers are on should do nothing to it. 
I bet you that every house has the same problem when you have multiple things running in a house such as ac units, furnaces, washers and dryers etc, you can't tell me that there is going to be no interference at all, but this expensive amps should take care of that problem. - I could be wrong.
jackd
362 posts
 
Simple solution.  Take the second defective 8207 back to the dealer and get your money back and if he is the one that sold you the Niagara get your money back for it too.  Then find a HT amp from another reputable company with customer service and buy it.  There are plenty of multi-channel amps on the market even if they don't have blue meters that will work in your situation. If only one of multiple transformers on the same chassis makes noise then the problem is not your house.  Don't waste any more time or money trying to fix McIntosh's problems as they are not the McIntosh of old. 
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