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
I don't know much about McIntosh, but always thought they had a great reputation.
What you are describing isn't something that should be happening.
You have done everything correctly, and the issue persists, so it would seem the problem is equipment related.
The only other cause would be the power coming into your house.
Do you live in a rural area, or use your own power source?
Second, if you bought from a dealer, he/she should be by your side getting this rectified. Period.
I hate it when good people get the run around.
B
Audio by Van Alstine make a relatively inexpensive but excellently built model.  They also have a generous return policy.  If McIntosh can't or won't help, it would be worth trying (if only to eliminate the possibility).
I would have expected the buzzing sound to come from both transformers if it’s due to DC riding in your AC line. Secondly, I’d also find it unlikely if it happens after all your efforts and also in your friend’s home. I’d consider getting it replaced if you bought it from a reputable dealer instead of going down a rabbit hole trying to fix the symptoms. A power conditioner rarely if at all addresses a transformer mechanical buzzing.
Agreed and this is usually a toroidal tranny issue. Strange. I don’t think it is DC, but rather a noisy tranny.

I buy from this oversees vendor.  Good pricing and great product. I buy the DC blocking nude circuit board for $15 shipped and populate them for about $25. Quiets toroidal trannys ( round flat ones) very well. 

https://www.atlhifi.com/shop/fully-assembled-devices/dc-blocker-trap-filter-assembled-in-case/
Emotiva CMX-2!  Killed the buzz from my Classé CA-200.  Now dead silent.
@kalali

I did buy from reputable authorized McIntosh dealer and the dealer replaced the first unit with a second brand new unit which has a louder buzzing and it is coming from the same left side of the amp. I am suspecting that somehow McIntosh has built defective transformers since these two amps were bought within one month period, but this is only a guess.
Did you try either amps at the McIntosh authorized dealer?  If it is ok there, then there is a problem with the power line.  If it isn’t ok, then the unit is defective.  At any rate, your dealer should be bending over backwards for you.  If not, I would demand a full refund. 
@stereo5

I returned the first unit to them and they had all this time to check it and tell me what the deal is, but so far I have heard nothing.I can return this one for a full refund that would not be a problem but I am trying to resolve this issue, and my question is why am i hearing the buzzing only from the left side and not the right, if I have a DC in my AC Line wouldn’t it both side be buzzing?
I own a Mac MC152 power amp and a MA6600 200wpc integrated and both are dead quiet. I have never heard of that. I will ask over at Audio Aficianardo Mac forum and see if others may have a clue. I’ll report my findings back here.  Did you or the dealer check to see if the transformer is bolted down tightly?

This is what I posted on Audio  Aficionado:

McIntosh MC8207 Transformer buzzing

I am asking this for an Audiogon member who is having a hard time with this amp. He bought from a reputable authorized dealer and the left power transformer buzzes so loud he can hear it from his listening chair 10 feet away. He returned the unit for another amp and it has the same problem. He contacted McIntosh service on 3 different occasions. They first told him he needs dedicated lines so he had a licensed electrician do that, having 2 lines installed both with separate grounds, but no change. Then service told him to buy a power conditioner and he bought an Audioquest Niagra to the tune of 4 grand and still no change. The last time factory service told him he needs a DC Offset Blocker.

It seems to me they are taking stabs in the dark. He brought both amps to his friends house 10 miles away and the same problem, the left toroidal transformer buzzes. His house is new, only 5 years old with a 200 amp service. He is quite ticked to say the least. I feel bad for the guy and I am trying to help him out. Anyone??
@stereo5 

I just got an email from the salesman I bought it from and told me that he would talk to service dept. to see if they can check or have checked the one I returned. I would also be bringing this one to them as well and have them plug it in while I am there no matter how busy they are.

And thank for posting in the other forum for me, I really appreciate that. I just don't want to spend another cent on trying to fix something that may not be fixable by me.
3 members of the forum told me there was a bad batch of the potted transformers which was confirmed by McIntosh.  Let the dealer know about that.  Best of luck and let us know how you make out.

@ tomiiv30 Your profile list country as N/A. By chance do you live 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.


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.

If you live in the USA the so called electrician is no electrician. Definitely not a qualified licensed electrician. No way in hell!

two copper polls for grounding for each outlet,
I assume you mean two earth driven ground rods.

DANGEROUS and not electrical safety code compliant. Not NEC or any AHJ in the USA.

IF the branch circuit wiring is Romex an isolated grounding type receptacle serves no purpose what so ever. Per NEC code the insulated equipment grounding conductor that connects to the isolated ground terminal on an IG receptacle shall terminate on the ground bar in the electrical panel the branch circuit is fed from.
Exception: NEC allows the insulated IG equipment grounding conductor to pass through a sub panel and to be connected to the equipment ground bar in the main electrical service panel.

NO isolated ground rods allowed for IG receptacles.


stereo5
3 members of the forum told me there was a bad batch of the potted transformers which was confirmed by McIntosh.
That certainly wasn't publicly posted in the forum. Are you saying that AA users told you that privately?
tomiiv30 OP11 posts01-02-2019 8:10pm


@stereo5

I just got an email from the salesman I bought it from and told me that he would talk to service dept. to see if they can check or have checked the one I returned. I would also be bringing this one to them as well and have them plug it in while I am there no matter how busy they are.
Check the serial numbers of the two units. My bet is they are close to one another.
@cleeds...…………………….

I received 3 private messages.  There also were a few posts in answer to my post but they seemed like guesses.
@jea48 

I am in the USA
 
I will talk to the electrician when he comes back from vacation to find out what exactly he did, I may say things that are misunderstood since I am no electrician by any means, but for what I know is that I have an isolated 20 amp outlet that has it's own grounding and that's pretty much all I know and I know that there is a copper poll in the ground by the outside electrical wiring. I can tell you more once I talk to him.
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
@erik_squires 

But what makes one transformer to buzz but another not. Wouldn't you think that when you spend this kind of money for an amp to be quite even if there is a little DC offset in the AC line, plus there was another guy that said there is no such thing as DC in AC line, so which advice should I go for.
Even my electrician was confused as to what I was trying to fix, and when I told him how much money I paid for the amp he was laughing his arse off.
He was trying to make me happy and do whatever I asked him to do even though he did not wanna do anything because everything looked fine to begin with.

@ 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.
.

Not all transformers will respond the same. Try taking the amp to another building and see what happens.
He already did that.  He took the amp to a friends house and it still buzzed. 
@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.
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. 
From the MC8207 owner manual

Power Supply Circuits

To compliment the design of the MC8207, there is a high current power supply for the five power amplifier channels. Refer to figure 21. The very large Power Transfomer, has toroidal windings on a toroidal core and can supply over 35 amps of continuous current. Refer to figure 22 (golf ball is for size comparsion). It is enclosed in the legendary McIntosh Potted Enclosures and weighs over 12kg. The super size main filter capacitors can store over 340 Joules of energy for the seven amplifier channels, necessary for the wide dynamic range that “Digital Audio” demands. The power amplifier draws high current from the AC power line. Therefore, it is important that they plug directly into the wall outlet.
See page 15
http://stereobarn.com/wp-content/uploads/mcintosh-mc8207-amplifier-owners-manual.pdf

Where’s the second transformer? Am I missing something?

The very large Power Transfomer, has toroidal windings on a toroidal core and can supply over 35 amps of continuous current.
120V  X  35 amps = 4200VA. Just a guess the transformer is rated at 5Kva.


tomiiv30 OP14 posts01-03-2019 12:00am@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.

I agree, McIntosh should have incorporated a DC blocker circuit in the amplifier.

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.
The DC on the AC mains could/can be coming from a neighbors house that is fed from the same power company's utility power transformer as yours.

Just doing a quick Google search I found this manufacture of a DC blocker. You might give them a call and see if they can build you one to handle the power requirements of your amp. JMHO, the one shown is not big enough. Make sure you give them the AC power requirements info for the amp.

https://avahifi.com/products/humdinger-dc-line-blocker


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.
It is quite possible the two transformers are not the same. So differences in manufacturing can account for this.
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.
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
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).
@oldears 

How much are you looking to get for the PS Audio Humbuster
@jea48 

  From the MC8207 owner manual

Power Supply Circuits

To compliment the design of the MC8207, there is a high current power supply for the five power amplifier channels. Refer to figure 21. The very large Power Transfomer, has toroidal windings on a toroidal core and can supply over 35 amps of continuous current. Refer to figure 22 (golf ball is for size comparsion). It is enclosed in the legendary McIntosh Potted Enclosures and weighs over 12kg. The super size main filter capacitors can store over 340 Joules of energy for the seven amplifier channels, necessary for the wide dynamic range that “Digital Audio” demands. The power amplifier draws high current from the AC power line. Therefore, it is important that they plug directly into the wall outlet.
See page 15
http://stereobarn.com/wp-content/uploads/mcintosh-mc8207-amplifier-owners-manual.pdf

Where’s the second transformer? Am I missing something?

The very large Power Transfomer, has toroidal windings on a toroidal core and can supply over 35 amps of continuous current.
120V X 35 amps = 4200VA. Just a guess the transformer is rated at 5Kva.

In the manual it says "To compliment the design of the MC8207, there is a high current power supply for the five power amplifier channels". And this is a 7 channel amp so what about the other 2 channels. And why is there two boxes, what's in them if there is only one transformer. I am trying to understand what is what.
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.
You can find them on ebay for less than $100.00. We build them into all our amps.
tomiiv30 OP16 posts01-03-2019 12:48pm@jea48


In the manual it says "To compliment the design of the MC8207, there is a high current power supply for the five power amplifier channels". And this is a 7 channel amp so what about the other 2 channels. And why is there two boxes, what’s in them if there is only one transformer. I am trying to understand what is what.

@ tomiiv30

The box on the left houses the power transformer. The box on the right houses the DC power supply. Rectifiers and electrolytic caps.

Scroll down page to photo of amp.
http://www.hifishock.org/gallery/electronics/mcintosh/power-amplifier/surround-sound/mc8207-1-mcinto...

Link to the video I uploaded on youtube where you can clearly hear the MC8207 buzzing loud.

Also I have measured for DC offset in my AC line the the result was 0.9mV, which is not enough to cause the transformer to buzz

https://www.youtube.com/watch?v=ucbBaD2eIgg
tomiiv30 OP17 posts01-04-2019 9:41pm
Also I have measured for DC offset in my AC line the the result was 0.9mV, which is not enough to cause the transformer to buzz

How did you measure for it?

The correct way.

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.


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

.


Here is another Link for measuring DC on AC mains.
http://sound.whsites.net/articles/xfmr-dc.htm#dc1
However, if you must (and PLEASE take extreme care), you need a 100k resistor and a 10µF non-polarised capacitor, wired in series. Connect this circuit across the mains (power off!), and connect a DC voltmeter across the capacitor. This attenuates the AC enough to prevent the front-end of the meter from being overloaded, and the DC voltage is easy to measure. Expect to see the DC vary around the zero voltage, with a normal variation of ±25mV or so (typical - residential areas). The alternative method is to measure the DC across the diode/capacitor network in the circuit of Figure 3. Do not connect or disconnect the meter with the circuit live, and use alligator clip leads to make the connections.

.
@jea48 When I called Chuck at McIntosh and told him my problem he said and these were his words" 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. 

I would try the other methods too but I feel like I have done everything they told me to do or was told to do, and I don't feel comfortable to spend any more time and money on this matter. I have other equipment in the house that does not buzz, hum or make any sounds out of the ordinary. I think that their amp is poorly design and that they should be the ones making sure this amps are not buzzing by maybe installing their own DC blocker/killer or whatever you want to call it in their amps so none of us consumers would have to deal with this what I am dealing right now. Not many have my patients.

Also I have turned off all the breakers except the one for the whole house and the one for the outlet where the amp is plugged into, the buzz was still there and you could still hear it 6-8 feet.


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.
You have been great, but now its time to take it back.  If it hums at the store take your refund and look for another unit.  I am assuming the problem is not your electricity and that you have run another unit in the past without the hum.  Sorry, don't want to reread all.
@erik_squires I tried every possible combination and nothing worked. The only thing left to do is wait for my DC blocker which a member of another forum shipped it to me and it is the Emotiva CMX-2 to come in and see if that will help and even if it does I would still be not satisfied with this amp, it should hum/buzz at all.
And this is what I get from the dealer:

"Ron from McIntosh says he might hear of this buzzing issue 5 times a year. It is an amp that is 14,000 watts so it is sensitive to DC being present in the lines. He said it has to either be the electrical coming from the pole or something within your house that is introducing DC in the AC of the lines ie. Faulty/poorly designed dimmer switch or something similar. So it is certainly not the amp or us, it is something going on at his specific home. It could be something as little as 1 volt of DC that can cause this issue." 

Does this look like the McIntosh is siding with the dealer and not me, is it my f'ing problem that I spend over $20K on Mac product to be told that I am in the wrong.
tomiiv30 
... even if it does I would still be not satisfied with this amp .
Why prolong your agony? Why not return it for a refund?
I would tell the dealer you are returning everything involved for a full refund unless they do as you ask. Sounds like they are jerking you off with no happy ending.
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
I hope Tom bought it from a very good dealer with a lot of cash flow.  Some stores would be unable to refund that amount of money as many rob Peter to pay Paul.  I hope for a happy ending.
I did buy it from a big cash flow dealer but that doesn't meant they would want to refund it, we will see how it all plays out next Tuesday. Also I am not trying to return everything I am just trying to get an amp that works that's all, but dealer and McIntosh are saying that it's me with the problem and not them which makes it more difficult for me to return it for a refund or another exchange.
I had same problem with my amps due to DC offset in the AC.  I tried AVA DC blocker. It did work, but the bass dynamics became restricted, and sound was lifeless.  I couldn’t live with those compromises.  Van Alstine tried to convince me it was all in my head. Ha! I bought Gigawatt power conditioner with built in DC blocker. Problem solved with no limitations of the AVA dc blocker.  It’s on the expensive side though. 
“Sounds like they are jerking you off with no happy ending.”  Stereo5

Sounds like you’re speaking from experience. Lol!