I am curious how the OP made out. I believe he was going to the dealer earlier this week to get it sorted out. I hope he sees this and replies.
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
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
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P.S. to my previous post: I didn’t mention the units that should be used for R and C in the various calculations. If R is expressed in ohms and C is expressed in Farads, the calculation described in my last paragraph will provide an answer expressed in seconds, and the calculation of bandwidth that is described earlier in the post will provide an answer expressed in Hz. Best, -- Al |
Hi Jim, They both appear to be reasonable values for this purpose. The 10 uF/100K combination will charge up to the final value about twice as fast as the 22 uF/100K combination, which isn't important, but it won't be down quite as far at 60 Hz as the latter. That difference probably isn't important either, although I can't say that with certainty as I'm not familiar with the internal design of modern digital multimeters. Specifically, the 3 db bandwidth of the low pass filter (i.e., the frequency at which 3 db of rolloff will have occurred) = 1/(2 x pi x R x C). Let's refer to that as "bw" (bandwidth). For 10 uF/100K, bw = 0.16 Hz For 22 uF/100K, bw = 0.07 Hz The rolloff at 60 Hz will be 1/(square root(1 + ((60/bw)squared))), converted into db based on 20 x logarithm of the resulting numerical value. (That looks more complicated than it really is; it could be illustrated more simply if it didn't have to be shown as text. Some people depict "squared" as "^2" and "square root" as "^(1/2)", but I'm not sure if for most people that would make the equation more clear or less clear). For 10 uF/100K that calculates to -52 db at 60 Hz, which would reduce 120 volts to about 0.3 volts. For 22 uF/100K that calculates to -59 db at 60 Hz, which would reduce 120 volts to about 0.14 volts. Also, the time to charge to very close to the full value of the DC that is present will be approximately RC x 5, which is how I derived the 10 or 15 second figure for the 22 uF/100K combination. Best regards, -- Al |
Al, (almarg) Thanks! 10 to 15 seconds..... I would have missed that for sure. What do you think about using a 22uF value for the capacitor? I chose the 22uF cap because that is what Eva (DIY member) said to use in her post. Elliott Sound Products recommends using a 100K ohm resistor in series with a 10µF non-polarized capacitor. What are your thoughts on the value of the capacitor used? Jim |
Jim (Jea48), good posts as always. My only comment on your low pass filter project is that with the 22 uf and 100K values it will take around 10 or 15 seconds after the AC is applied for the cap to fully charge up to whatever amount of DC may be present. Which is fine, of course, but it’s just something to be aware of when the measurement is made. Best regards, -- Al |
@ 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 . |
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. Google, first hit: https://www.stereo.net.au/forums/topic/75460-diy-main-dc-blocker/ |
@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. |
gdnrbob2,190 posts01-07-2019 1:21pm 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 . |
https://www.diyaudio.com/forums/solid-state/2080-dc-filter-6.html#post331815https://www.diyaudio.com/forums/solid-state/2080-dc-filter-6.html#post331815 . 22nd May 2004, 05:20 PM #71 Eva diyAudio Member . |
Food for thought. Quote from an Audio Circle audio forum thread about DC offset on the AC mains. HALhttps://www.audiocircle.com/index.php?topic=47973.0 . |
@twoleftears , Exactly. I bought a 2016 TTS that has a B&O sound system. It sounds like crap. My previous TTS had a Bose system that sounded leaps and bounds above the B&O-and that is saying something. B&O had some really interesting gear in the day, but now that they have been acquired by another company, they are just resting on the name recognition. Too bad for me, Audi trusted them- but, hey, it all comes down to money. B |
It's a story as old as the hills. A company spends decades establishing a really good name. A conglomerate swoops in and buys it up--and they're buying the name much more than the factory or the know-how. They proceed to try and squeeze every last drop of profit out of it--and then they'll throw away the dry husk when they're done. The attitude you've gotten--it's your problem, we really don't want to take it back (=we've already made our profit off of you)--is a classic demonstration of this. |
After some serious thinking I will just return this unit for a full refund, I shouldn’t be the one obligated to do all those things since everything else works perfect in my house I know that I don’t have problem with my power and it has been checked so many times, I don’t have to invest anymore time and money in any kind of aftermarket equipment to silence the buzz, I would try with the DC blocker like the Emotiva CMX-2 that was shipped to me by a forum member but that’s that, it will just mask the problem and nothing else. Yes taking it to the dealer and having no buzz there means that they use all kinds of power conditioners and dc blockers and what not would not prove anything to me, this unit does not work at my place and at my friend’s, I have taken this unit to two others and still buzzed. If McIntosh does not want to invest in a proper circuitry that will fix this problem that they are having and they do have this problem for a long time I can see that since there were many people on forums saying the same thing that I am saying and we as consumers should not be held accountable for it. There are some threads that I red about the MC462 being dead on arrival which is another thing that tells me that quality check is lacking, since I am also having issues with loose parts on mine. McIntosh you better get your sh$t together otherwise you would start losing some serious sales or maybe you already have. |
erik_squires4,643 posts01-06-2019 11:54am erik, keep this just between the two of us. Chuck is just plain ignorant when it comes to how to measure for DC offset on the AC mains. Jim |
tomiiv30 OP21 posts01-05-2019 12:47pm It is an amp that is 14,000 watts so it is sensitive to DC being present in the lines.I think you meant 1400 watts. 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." No,.... there’s nothing wrong with the AC power in your home. You measured for DC offset on the AC mains using your DMM and measured 0.9mv. You measured for DC offset exactly as McIntosh told you to do it. Exactly! tomiiv30 OP21 posts01-05-2019 10:40amChuck is the man, he should know. He is McIntosh’s expert on the subject. You followed his instructions to the letter. Can’t get any simpler than that. There is nothing wrong with the AC power in your home. The power transformer in the amp is defective. Period! . |
What about trying a 3000 microfarad 200v non polar cap in series with your line to block dc if there is any. Also if the line cord is flipped over (left prong on the right) shouldn’t the buzz move to the other transformer? Otherwise I’d think you should be able to see the offset at the box with a VOM. IMO you have a faulty unit that Mcintosh should replace. |
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. |
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. |
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. |
@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. |
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. |
@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. |
tomiiv30 OP17 posts01-04-2019 9:41pm How did you measure for it? The correct way. http://db.audioasylum.com/mhtml/m.html?forum=tweaks&n=140383&highlight=integrator+djk&r=...Re: Not trying to start a flame but.... . 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. . |
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 OP16 posts01-03-2019 12:48pm@jea48 @ 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... |
@jea48 From the MC8207 owner manual Power Supply CircuitsSee 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. |
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). |
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_squires4,593 posts01-03-2019 10:42amErik, 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. |
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. |
tomiiv30 OP14 posts01-03-2019 12:00am@jea48 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 |
From the MC8207 owner manual Power Supply CircuitsSee 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. |
