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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
atmasphere's avatar
atmasphere
7,068 posts
 
Not all transformers will respond the same.
+1
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.
DC on the line is caused by things like an electric heater that is only running at half power and so only using half of the AC waveform. That causes that half to be lower amplitude- thus the DC on the line.
Its solved by a DC blocker, which is a simple and inexpensive circuit. Why Mac didn't include that in the amplifier, when toroids are known for being particularly sensitive to DC (and thus make a substantial amount of noise) is curious to say the least.

IOW the amp may be perfectly fine. The DC Blocker can be installed in the outlet junction box, or it can be a separate box of its own. Its probably a good idea to find one and try it, as its likely less expensive than the shipping of the amp.
erik_squires
5,268 posts
 
It is quite possible the two transformers are not the same. So differences in manufacturing can account for this.
jea48
2,944 posts
 
erik_squires4,593 posts01-03-2019 10:42am


It is quite possible the two transformers are not the same. So differences in manufacturing can account for this.
Erik, there is only one power transformer in the amp, not two.
See page 15

http://stereobarn.com/wp-content/uploads/mcintosh-mc8207-amplifier-owners-manual.pdf

I would guess it is a large toroidal at that. Probably rated at 5KVA. I don’t think that size of a toroidal would like any DC on the mains.
erik_squires
5,268 posts
 
DC blocking circuits are expensive to do right, and are very rarely needed.

That's why they aren't included in almost any linear power supply I know of.

I also don't know of any general purpose power conditioner that includes them. You have to either buy a specialized unit, just for DC blocking, or find a balanced power conditioner.

I recommend Furman. Especially when you can find htem on sale with LiFT and SMP
oldears
208 posts
 
A toroidial transformer can hum simply because of not being properly installed or positioned. I had a BAT tube preamp which hummed and left it with a repair tech. He called and said he had checked it out and it measured fine. I replied that the hum seemed mostly mechanical. He said "OK, I know about that"....he loosened the installation bolt, repositioned the tranny and solved the problem while on the line with me.However, if you need one, I have a discontinued PS Audio Humbuster III, new in the box, which I bought to see if it would solve the problem (it did not).
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