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Looking for advice on mechanical hum


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I'm looking for some advice. I have what I am assuming is transformer hum coming from my audio components. It's most prominently heard from my DAC (Lampizator Atlantic) though can also be heard from my amp (Classe CAP-2100) as well as a linear PSU (HDPlex).

I would describe the noise as a low pitched buzz or hum. It emanates from the components and is not heard through the speakers. The hum is present in the components even if everything is disconnected apart from the power cord. No hum when powered off. It's noticeable from the listening spot which is around 3-4 metres away. It doesn't seem to vary. It is present in the middle of the night also. I have tried different sockets in my house with no changes to the hum. I have not yet tried sockets outside my house but I will in a day or two.

I recently returned the DAC for testing and was assured that when tested there was no audible hum at all.

I have read into this to some degree but electronics is not my field. I have tried 2 different DC blockers (MCRU and ATL Hifi) and neither produced an audible difference. I also use a power conditioner (Audience AR4) but this has no effect on this noise.

Any insights or help here would be greatly appreciated.

There are 2 types of people in this world - those who understand binary and those who don't.

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Thanks for these replies.

 

5 hours ago, One and a half said:

The hum then is not through the speakers , so it is not a signal problem. 

 

I would attach a power scope to the AC and analyse the voltage waveform with intent on a harmonics up to the 31st should be enough.

 

if you have a ups even if it is small one to power up the amp and Dac separately and see what the hum does.

 

I agree that it is not likely a signal problem. I do not have a power scope, and as sandyk mentions, I fear that doing this would be beyond my level of expertise. I also do not have a UPS.

 

5 hours ago, Norton said:

I have exactly the same problem, although in my case it only affects one component.  But absolutely quiet when checked out (by me) at my dealer.  I'm told it's caused by "DC offset", but I have no idea what that is or how to remedy it.

 

It has been suggested to me also that it may well be DC on the mains, or DC offset. I have however tried at separate times 2 DC blockers, both feeding the power block and direct to the DAC - though neither made any difference in either configuration. Have you tried a DC blocker yourself?

 

5 hours ago, sandyk said:

 Even the steel top/lid of the case which is a little too close to the top of the transformer can cause this.

 

The same noise persists with the lid completely removed.

 

1 hour ago, One and a half said:

Remove the source.

 

Can be anything from a lamp dimmer, flourescent, heater controller, or a really large SMPS, but not RF.

 

 

Well, my understanding is that the sockets that my audio equipment is connected to is part of a ring circuit that does not include the large appliances - though I could be wrong. We do not have any dimmer switches or fluorescent bulbs. The noise was present in the middle of the night also. 

 

I will take the DAC to my work (which is around 4 miles away) and try there to see if a different power supply affects anything, and will report back.

 

There are 2 types of people in this world - those who understand binary and those who don't.

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Interesting to hear mourip. Did you try plugging the devices in anywhere outside of your own property? Good you cannot hear it from the listening position - I can hear it, as long as the room is completely silent. It's one of those noises that a newcomer might not hear, though when you've heard it, you keep noticing it. 

There are 2 types of people in this world - those who understand binary and those who don't.

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STC - interesting that your Classe amp had hum when voltage was more than 248V for a 230V rated device. When being tested at the manufacturer, they used up to 250V and still no hum was heard. 

 

rayooo - yes a few others have mentioned that DC on the AC line may be a potential cause. As mentioned above, I tried 2 different DC blockers (from MCRU and ATL Hifi) with no discernible benefit. 

 

one and a half - I think I have a standard multimeter in the garage - would this be suitable for measuring mains voltage from the plug? How do I do that? Yes, the problem was there before I got the AR4. I had wondered if the AR4 might have helped - it did deliver some sonic benefits, but did not affect the hum!

There are 2 types of people in this world - those who understand binary and those who don't.

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zoltan - I have seen the PS Audio Humbuster mentioned. I beleive that it is out of production and hard to find. If it worked, then surely there should be an equivalent product elsewhere?

 

As I mentioned, I have already tried 2 DC blockers, neither of which seemed to affect the hum very much.

 

One and a half/mansr - I will test the mains voltage and report back

 

Peter - interesting that you still reckon that it is DC offset, despite my 2 DC blockers not working. Do you think they were ineffective? The MCRU one was not cheap - around £350 or so I think. I do not have any PCs that run off SMPSs. The audio PC has a linear PSU from HDPLEX (which I have switched off, but this made no difference).

 

Regarding switching things off around the house - I can open the circuit breaker for all circuits in the house except the ring circuit that the hifi is on, and disconnect everything from that circuit apart from the DAC, to make sure that it is only the DAC that is drawing power in the house - is that what you mean? If I get it quiet with this procedure I would be overjoyed! What do you mean by USB isolator? Don't think I have one of those. My music is in another room on a NAS which connects to the audio PC in the listening room via ethernet; that then connects to the DAC via USB.

 

The only thing is, I could switch everything off in the house, but couln't it be a neighbours appliance that is affecting our mains? Can't really ask them to switch all their appliances off every time I want to listen to music :D

There are 2 types of people in this world - those who understand binary and those who don't.

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Ray - sorry, I had somehow missed your earlier post. I was considering a P5 at one point. I have heard however that the P5 itself has transformers and is liable to hum. Also, it is a rather expensive solution to solve a problem of hum which shouldn't be there in the first place! I would be keen to try a P5 or equivalent though, just to see if that fixed the problem.

There are 2 types of people in this world - those who understand binary and those who don't.

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Well, I just opened the circuit breakers for all circuits in the house except the one the DAC is on, and turned off all items except for the DAC (including the NAS, good point Peter). And no change to the hum. So perhaps that rules out something else in the house generating noise on the line.

 

I do own a multimeter - or if I didn't, they're cheap enough to buy. I am going to test the mains with it to see what the AC voltage is doing; hopefully report back with this in the next few days.

 

As far as I know there is only one earth here Peter.

 

I am also going to take the DAC to my work to see if it hums there. And if it does, I will take it maybe to an audio store that is a bit further away to see if it hums there.

There are 2 types of people in this world - those who understand binary and those who don't.

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Don - thanks for the specific suggestion :P Yes I will look into that. Won't such a transformer dampen dynamics and limit peak draw?

 

Peter - you're saying that measuring DC offset on the mains using a multimeter is not a viable option? Perhaps a more powerful oscilloscope is required for such measurements? I did not try the power amp or HDPLEX on their own, no - I'm mainly concerned about the DAC as that has the most prominent hum. And no, I have not yet tried the DAC elsewhere - what I did do was send it back to the manufacturers (in Poland) where there was no hum found.

 

What I will do in the next few days is try the DAC elsewhere in the UK, first at my work and if it still hums there (it is only 5 minutes drive away) then I will try it further away (e.g. a music shop 30 minutes drive away). If it does turn out to be silent at work I will be pleased as it will be a clue as to the problem!

There are 2 types of people in this world - those who understand binary and those who don't.

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Thanks for the ongoing insights here - though some of the technical discussion is a little above my head :)

 

I have 4 further small findings that might help in the quest to remove the hum;

 

1. I took the case off (again) to see if the rod that holds the transformer needs tightening or loosening. What I found before getting to that however, was that the casing seems to be contributing to the noise. With the case removed, the noise is definitely less. It is still audible, though perhaps heading towards the level that would not be noticeable from the listening spot. I had tried removing the case before and don't remember a particular reduction in noise, but there you go. So I got some thin rubber pads and tried to insert them in-between the front panel and side casing. Once the screws were again tightened, this did not seem to improve the noise. Flexing or moving the top casing also seems to affect the noise somewhat, though inserting anything in-between this and the base is quite tricky. Either way I did not have the impression that inserting further bits of rubber would likely affect the noise, given my findings with the rubber at the front.

 

2. Trying again to isolate the area that the hum is coming from, I think it is coming from a different component to what I had expected. I had thought that the noise was coming from the main transformer (a big round thing which I have labelled 'A'), though it appears to be coming from somewhere nearby. The exact culprit is difficult to determine, though I'm wondering if it is coming from the component highlighted in my photo below (which I have labelled 'B'). I'm not sure what this component is but am wondering if it is also a kind of transformer?

 

2nvy0ki.jpg

 

3. I noticed that one of the bolts/pillars holding the PCB to the casing appears to have current running through it (if that is the right term) - when I touched it, I felt a small shock. I can't remember if my other hand was touching the casing or not. I also don't know if this is normal/expected or not. The unit was powered on at the time. Maybe I was stupid to be prodding around inside with the power on. I don't know if the other 4 bolts are the same (I didn't fancy testing)! I have highlighted this bolt in the picture below also.

 

28u3gp4.jpg

 

4. I took the DAC to my workplace and plugged it in there. Same hum. It is however only about 3 miles away as the crow flies - don't know if this is relevant or not.

 

Thanks again for the help here.

 

There are 2 types of people in this world - those who understand binary and those who don't.

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Thanks for this reply Bob. 

 

I don't think I can feel a vibration when touching the case. Although I say that I can hear the hum/buzz from a distance, it is still relatively quiet. Regarding the over-voltage, I am going to use a multimeter to check the mains voltage in the house in the next day or two. 

 

You are correct re the tubes - 1 rectifier tube and 4 DHP tubes. I will make sure it is off in future when poking around inside :) I doubt that it could have been static - the shock was a little too pronounced, and it happened twice. 

 

Item B (the transformer/choke) is bolted to the base of the case via 2 of the 4 available bolt points. I will look further into this with a plastic rod as you suggest.

 

Yes, the fact that my Classe amp hums (though to a lesser extent) and my linear PSU (now to a lesser extent also - I think it used to be worse) makes me wonder about my mains. I still plan to measure this as mentioned above, and try the DAC a bit further afield.

There are 2 types of people in this world - those who understand binary and those who don't.

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OK One and a half - I looked back at the post you mentioned. Here are my findings:

 

Black probe to earth, red probe to active: 246V

Black probe to earth, red probe to neutral: nothing registered on my multimeter - 0.00V (however the lowest "setting" for AC V is 200V)

Black probe to neutral, red probe to active: 246-247V

 

You initially said that it should read 230V. Does this therefore seem quite high?

 

There are 2 types of people in this world - those who understand binary and those who don't.

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9 hours ago, chetthejet said:

Didn't matter whether the lamp was on or off, the hum was there as soon as the amp powered up.....but once that lamp was unplugged from the wall socket (and chucked in the dumpster!)  the hum disappeared permanently.  

 

Interesting! Did you try plugging the amp in somewhere else, other than at your house? I tried it at my work too and the hum remained the same - thus reducing the possibility of something like what you had experienced, I think. 

There are 2 types of people in this world - those who understand binary and those who don't.

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  • 2 weeks later...

Conducted a further experiment. I plugged the DAC in in a music shop some 35 minutes drive away to see if it would still hum whilst on a different part of the grid - and it did. So it would seem to be less likely that it is something else in my house, or the power supply to my house, which is causing the problem.

There are 2 types of people in this world - those who understand binary and those who don't.

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  • 1 month later...

A final update for anyone that is interested or experiencing a similar problem. I ended up returning the DAC to the manufacturer (Lampizator) a second time. This time they replaced the transformer with the one they are using in their newer DACs. I had thought that the noise was coming from the choke (what I had initially thought was a EI transformer), so was somewhat skeptical that replacing the toroidal transformer would make a difference. 

 

So on unpacking, inserting the tubes and making the various connections at the rear, with trepidation I pressed the power switch. And....BOOM the DAC blew up!! Just kidding...THERE WAS NO HUM!!! Hallelujah! Or, more accurately, there was a very low level of hum which is in keeping with the other audio components and not audible once a foot or two away from the DAC.

 

So after a (fairly) long road, this problem has been solved. Thanks to all for the advice given :) 

There are 2 types of people in this world - those who understand binary and those who don't.

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Yes, you really needed a fairly silent environment to pick up the hum (with no ambient noise in the background). I had worried about there being too much noise at the Lampizator testing lab and had mentioned this to them in my first email.

 

But that is how I (and likely others) like the listening room - silent! From some of the comments, I'm surprised that this isn't a more recognised issue. It's not that I have super-sensitive hearing or that my room is an anechoic chamber or anything! :D  

There are 2 types of people in this world - those who understand binary and those who don't.

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