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

Showing 11 responses by erik_squires

erik_squires
16,730 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.
erik_squires
16,730 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
16,730 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


erik_squires
16,730 posts
 
Balanced power conditioners also work.

But seriously, the best way to tell if this is a power issue or defective manufacturing is to take the amp somewhere else.

Best,
E
erik_squires
16,730 posts
 
Agreed.

If you measure that little, you need to take the amp back and prove it there.

Best,
E
erik_squires
16,730 posts
 
I can understand McIntosh not wanting to change their gear based on frequency of events.

However you should also get a full refund if it does not perform normally in your home.
Best,
E
erik_squires
16,730 posts
 
Get a multi meter and stick probes one into the neutral the other into the phase and measure for DC mV, and that’s what I did. I am not going to do anything more than what they suggested.

That’s pretty smart. :)

I never thought of that, as I was worried about the meter being damaged, but reading around the net it seems safe to do with a digital, and with a mechanical, just set it to the highest range first, then come down.

Glad you tried turning everything off.

One other thing you could do, is try moving your amp to another phase. Usually the circuits breakers alternate phase going down.  So if your amp is now on the top breaker, try the second fourth or sixth down.
erik_squires
16,730 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
erik_squires
16,730 posts
 
It is quite possible the two transformers are not the same. So differences in manufacturing can account for this.
erik_squires
16,730 posts
 
Not all transformers will respond the same. Try taking the amp to another building and see what happens.
erik_squires
16,730 posts
 
You got a bit of bad advice.
Mechanical transformer hum comes from having DC on the AC line.

Isolated lines or ground do not help you.

First check your AC for DC. An electrician should do this.This can be caused by lights and dimmers elsewhere in the home, so you may diagnose this by shutting off everything but your amp.

Fixes include:


- Switching to other phase

- Using a balanced power conditioner.
Most power conditioners are not balanced so won’t help.

Best,
E
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