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
erik_squires
15,861 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
erik_squires
15,861 posts
 
So to check if this is a source issue, leave the CD player off, and turn on the amp.

Let it run for a while. Then turn on the CD player. If that, or playing music from it, causes the error, you have your answer.

Sometimes this can also be caused by ground loops.
nyev
1,026 posts
 
Thanks for the explanation Erik.  So I have two issues to figure out...  I wonder what the odds are of the buzzing issue persisting if I upgrade to the Mac 462...  I’ll be demoing the 452 shortly so I will find out then.  If the buzzing continues i’llbe in the same boat as the OP....


4krow
80 posts
 
Well,  If you find yourself in the same position as the OP, then demand a full refund, and find unit that does not have this problem. Been there, done that.
jea48
4,313 posts
 
@ nyev



See page #17. It appears the power transformer is an EI type. EI type power transformers as a rule are not affected by DC offset on the AC mains

https://www.manualslib.com/manual/1460643/Mcintosh-Mc462.html?page=17#manual

Question is why would you still want to buy a McIntosh product after hearing the way they have treated the OP? Ron ( McIntosh representative) said maybe 5 complaints a year about torid buzzing power transformers. You want to beat the number of complaints is actually higher than 5?

How much would it have cost for McIntosh to incorporated a DC blocker in the MC8207 amp? I would be willing to bet the design engineer first designed the amp with a DC blocker. No doubt the design engineer new that a large torid power transformer would vibrate/buzz if there was DC offset on a customer’s AC mains.
How much you think them pretty covers cost that cover the transformer and DC power supply inside the MC8207? Or them big pretty blue front meters?
They sure look pretty though don’t they?

Charlie Randall (top USA dog now) is already starting to make ARC equipment look like McIntosh.

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