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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
4,553 posts
 
gdnrbob2,190 posts01-07-2019 1:21pm

@jea48 ,

Would you recommend getting a DC blocker for every system?
I know not all lines have DC, but just as a precaution?
Bob

No, I wouldn’t. There is not any need for a blocker unless you have DC offset on the AC mains. If you have a piece of equipment with a torid transformer that is buzzing loudly then it may be being caused by DC on the mains. The best way to find out is to measure for it. Measure for it the correct way.

I am surprised there is not someone building a low-pass filter device to use on the AC mains to measure for DC on the mains using a regular DMM.

For a DIY project it would be pretty simple to make one.

All you need is,
1 - male plug (to plug into the wall outlet)
1 - 100K 1 watt resistor
1 - 22uF non-polar capacitor
2 - alligator clips for the probes of the DMM 
Maybe a short piece of 2 wire zip cord 
Soldering Iron
Solder


You could even install the resistor and cap in a small PVC plastic box with cover. Connect a short 2 wire power cord and male plug. Install a couple of recessed insulated female jacks for inserting of the probes of a DMM.
Jim
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tomiiv30 OP
65 posts
 
@jea48 

I wish there was a video or some kind of a drawing of how to make this simple low-pass filter device  but yet too complicated for me and some others.
I am a graphics designer by trade and not an electrician but I am willing to give a go to make one I am no afraid but only if I see it how it is made. I do have a soldering Iron and solder plus those alligator clips so I am half way there.
I went to fry's electronics and the only item they were out of all the milion items they sell were the 100K 1 watt resistor and the capacitor. How unlucky I am that I drove like about 45 each way to get to the store. 
gdnrbob
4,469 posts
 
@tomiiv, 
I agree. 
For the electronically inclined, it is a walk in the park. But, those of us with limited skills (well, I can solder pretty well), seeing the list of items needed and putting them in the proper order makes me a bit uneasy. Mostly because I don't want to get fried.

Bob
atmasphere's avatar
atmasphere
11,996 posts
 
I wish there was a video or some kind of a drawing of how to make this simple low-pass filter device but yet too complicated for me and some others.
I am a graphics designer by trade and not an electrician but I am willing to give a go to make one I am no afraid but only if I see it how it is made. I do have a soldering Iron and solder plus those alligator clips so I am half way there.

Google, first hit:

https://www.stereo.net.au/forums/topic/75460-diy-main-dc-blocker/
jea48
4,553 posts
 
@ tomiiv30 OP and @ gdnrbob

I ordered the resistor and capacitor over the internet yesterday to build the simple low-pass filter. Hopefully I will have them in about a week.


100K 1 watt resistor
https://www.ebay.com/itm/5-pack-1-watt-5-carbon-film-resistors-100k-ohm/160460118738?hash=item255c2b...

22uf non polarized capacitor.
https://www.amazon.com/22mfd-Non-Polarized-Grade-Mylar-Capacitor/dp/B00B4DVXJE


Eva (DIY Forum member) didn’t give the voltage rating for the 22uf non polarized capacitor so to be on the safe side I ordered 250V.

I’ll post back with the testing results on how it works.


Here is a link of a wiring diagram that shows the wiring, configuration, of a low-pass filter. (Disregard the white paper for the use in the paper). It’s the best I could find for a wiring diagram of the simple circuit.
https://www.electronics-tutorials.ws/filter/filter_2.html

You need to redraw the simple circuit and add some wordage.
** ELIMINATE THE EARTH GROUND CONNECTION AS SHOWN ON THE BOTTOM LINE OF THE DRAWING. (This line will be the AC neutral.)

Note on the left side of the drawing the two Vin AC (sine wave) line inputs. You will connect these to the 120Vac male plug. I would suggest the top line (resistor) connect to the Hot blade screw terminal of the plug. The bottom Line (other end of the capacitor) to the neutral blade screw terminal of the 120Vac plug.

The right side of the drawing where it says (Vout) is where the DMM probes connect to.

Edit:
Another wiring diagram showing the Low-Pass Filter.
In the last post by atmasphere in the link he provided there is a post with this link showing an Intergator Low-Pass filter.

http://www.animations.physics.unsw.edu.au//jw/RCfilters.html#low
Low-Pass Filter
scroll down the page to, "Integrator" . Note the diagram is the same as the first diagram for a Low-Pass filter.


You don’t need an electrician to build, assemble, this low-pass filter to measure for DC offset on the AC mains. All you need to find is an electronic service tech. Or anyone with any experience in wiring a simple resistor capacitor circuit together.
Jim


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