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Re: Advice on transformer hum

Reply #25 –
Arnold - thanks for the more technical explanation. Do you think that a DC blocker may help? Or any other remedy?

Rotareneg - I have tried pressing on the case. I have tried removing the case and pressing on the transformer or PCB. No changes.

Today I tripped all the switches on our consumer unit and left only the ring which contains the DAC open, switching off everything else on the ring to see if any other household appliance may be exacerbating it. No change unfortunately with the hum!

Re: Advice on transformer hum

Reply #26 –
Quote from: extracampine on
Arnold - thanks for the more technical explanation. Do you think that a DC blocker may help? Or any other remedy?

Rotareneg - I have tried pressing on the case. I have tried removing the case and pressing on the transformer or PCB. No changes.

Today I tripped all the switches on our consumer unit and left only the ring which contains the DAC open, switching off everything else on the ring to see if any other household appliance may be exacerbating it. No change unfortunately with the hum!

Given that the common power line frequencies are well down the slope of less audibility of lower frequencies, the ear is quite a bit more sensitive to the harmonics than the fundamentals by quite a bit. DC on a power line is usually due to some nonlinear element or load that adds even order distortion so the attachment applies. Ideally, the transformer would be so quiet that it wouldn't matter, but this isn't an ideal world. Another reason why I favor switchmode power supplies, even though they are sometimes the source of the harmonics.

Re: Advice on transformer hum

Reply #27 –
Quote from: extracampine on
Today I tripped all the switches on our consumer unit and left only the ring which contains the DAC open, switching off everything else on the ring to see if any other household appliance may be exacerbating it. No change unfortunately with the hum!
Very simple question: have you actually taken your devices to a friend's house some distance away to check whether the hum is still present? If it is, the devices are probably at fault. If it isn't, your mains supply is the source of the problem. Until you've established this one way or another, you can't begin to find a solution.

(I know you say that the manufacturer has tested and reported no hum, but you can't know for sure whether they were really checking for the same thing. No matter how carefully you word your description of a problem, people can misinterpret it. You need to personally check it out on another mains supply).

Re: Advice on transformer hum

Reply #28 –
Quote from: cliveb on
..................................................................................
Very simple question: have you actually taken your devices to a friend's house some distance away to check whether the hum is still present? If it is, the devices are probably at fault. If it isn't, your mains supply is the source of the problem. Until you've established this one way or another, you can't begin to find a solution.
................................................................
Yes, taking the units to a distant location should be one of the first tests for power line problems.
But while DC offset problems are mostly rather local, high line voltage (with respect to your unit's transformer design voltage) is becoming universal.  Last week our weather was very cold but our line voltage was 125V/125V. Now it's above freezing and the line voltage remains at 125V. 
Kevin Graf :: aka Speedskater

Re: Advice on transformer hum

Reply #29 –
This won't be much help, but I have a power amplifier that used to mechanically buzz when my TV was turned-on.  (It was plugged into a nearby outlet.)    I still have the amplifier (used for my subwoofers) but since I got a new TV it doesn't happen.

I always thought it was strange because it was a regular-old 60Hz linear transformer followed by a linear voltage regulator.   I don't own an oscilloscope (although I could have borrowed one from work) so I never "looked" at the power line to see what was happening.     But, it was a rather loud buzz and strong vibration that shouldn't  have been caused by some slight distortion or noise in the power line.   (And nothing else was affected, just that amplifier.)  

Re: Advice on transformer hum

Reply #30 –
Classe used very nice transformers that did not make noise. They used one of the same vendors we did and we've also had them in our shop for repair. The Lampizator is also not known for noise.

So I have a question: was there ever a time that these components did not exhibit the hum? IOW, did it recently show up or was it always there?

Re: Advice on transformer hum

Reply #31 –
IMO the quality is not involved here, even the highest quality transformers avaliable on earth will buzz with AC anomalies.

 

Re: Advice on transformer hum

Reply #32 –
Thanks for the ongoing insights here.

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 bit 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?



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.



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.

Atmasphere - that is a good question. I don't remember it being there initially though I may not have noticed it at that stage or maybe wasn't looking out for it. Once you've noticed it, you can hear it.

Thanks again for the help here.

Re: Advice on transformer hum

Reply #33 –
You are lucky that it was only a small shock. I worked with vacuum tubes long ago, and quickly learned to keep my fingers out of a device that was powered on.

Re: Advice on transformer hum

Reply #34 –
Quote from: extracampine on
Thanks for the ongoing insights here.

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 bit 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?



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.



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.

Atmasphere - that is a good question. I don't remember it being there initially though I may not have noticed it at that stage or maybe wasn't looking out for it. Once you've noticed it, you can hear it.

Thanks again for the help here.

The part labeled 'B' is an EI transformer. IIRC it is for housekeeping when power is off. At any rate, it might be possible to isometrically mount it. That way it would not transmit vibration to the cabinetry. BTW to damp the cabinetry is also possible, but I would do it with an extensional damping compound which is usually in sheets. You're not going to have much luck with a few rubber pads.

Moving the equipment elsewhere is not conclusive. The problem is you don't know what sort of AC problems are in the new location. If you try that again, try this: place one of those DC blockers in a junction box with some outlets on it (you can get the box and outlets at Menards) and put an power cord on it. This way you have a power cord that blocks DC. Bring that with you when you go to the new location. Please note- the DC blocker has to be installed correctly as does the power cord! If you mix the hot and cold side of the lines, bad things happen like deadly shocks. So if you don't know how to do that, have someone do it for you. The nice thing here is once this is done, the power extension can be handy.

Its a Bad Idea to poke around in power amps with the power on. You can damage expensive and now rare output transistors (in the case of Classe) and make the amp worthless!

Do you have a Digital VoltMeter (DVM)?  It might be a good idea to at least know what your line voltage is.

BTW- you had some DC Blockers- do you know how they were used?

Re: Advice on transformer hum

Reply #35 –
Thanks Atmasphere.

I will look into mounting that transformer. The problem is, it is currently bolted onto the base of the casing with 1 bolt being easily removable though with the other one being under the PCB. I will need to get some kind of telescopic wrench to reach in the and remove it I think. Will look into that today. Any suggestions on how to dampen/mount it?

You mention a DC blocker - I have tried this at home with no change to the hum. I can try the DC blocker elsewhere - though if this works elsewhere, what does it tell me about my problem? I had tried 2 different DC blockers at home - both connected directly to the DAC (mains--->DC blocker---->DAC) and to a power block feeding the DAC (mains--->DC blocker--->power block---DAC).

You mention that it is a bad idea to poke around in power amps - remember that this unit is a DAC. Though I imagine that the same principles apply!

I do have a multimeter, and will hopefully be able to test my mains voltage level later today.

Re: Advice on transformer hum

Reply #36 –
If the line voltage is excessive its not unusual for transformers to get noisy. The line should be no more than 125V for any reason- it can go higher for a second, that's all.

The other thing that can make power transformers become noisy is the 5th harmonic on the AC line. You need a power conditioner, a good one, to block that.

I would regard the use of a conditioner as a bit of a radical move (especially given the cost of a good one) so I would exhaust all the other solutions/possibilities first.

When you purchased the DC Blockers you have, was it because of the transformer hum?

Re: Advice on transformer hum

Reply #37 –
In my own, ill-informed opinion, you have some real problems here:

First: NO!, you should not be poking around in the DAC when it's powered on. I suspect we've all done it, but it is really dumb and dangerous.

Second: I would be concerned about getting that shock. If juice is running through bolts, that can't be good.

Third: Tube components have all kinds of inherent issues, transformers being one of the foremost.

Fourth: This is a tube design by someone who is considered by some to be a rank amateur. I enjoy his site, I have followed, lazily, his progress in the field, I appreciate reading him, I would never buy anything he makes.

Fifth: My very amateur, though not necessarily wrong, opinion is that you have passed the point where your problem is one that needs fixing to the point where you are wasting time and energy. Get a new DAC.

Sixth: There are many manufacturers who will sell you line conditioners, and almost all of them don't do shit. Frankly, you need an electrician. There are things that can be done, but they cost money and should be designed by people with the requisite skill and knowledge. Most power conditioners make attractive boat anchors, but little else.  

I have owned many, many, too many DACs. I have never had problems like what you are having, nor have I heard of anyone else having such problems. Solve your problem once and for all: buy a new DAC. Otherwise, you might rewire your whole home and still not fix it.

Re: Advice on transformer hum

Reply #38 –
Atmasphere - you mention 125V. Remember that I am in the UK! So voltage here is around 240V (with I believe limits of +10% and -6%). Regarding the power conditioner, I have an Audience aR4 currently. I found that this improved the sound in a relatively subtle way, though it does not affect the mechanical hum from the components. I did indeed purchase the DC blockers because of the transformer hum. I tried them and then returned them due to the lack of expected benefit.

jsrtheta - thanks for the further safety warning :) I will make sure the unit is off in future if sticking my fingers into it. Yes, I was unsure what to make of the shocks I received (it happened twice at the same point). I would have thought that if there is erroneous current running somewhere then there would be a functional issue with the unit (or worse) - though it works fine. Your thoughts regarding the company are noted. Whatever some people might think about the designer, the products themselves have accrued considerable acclaim from a variety of sources (i.e. not just those that are industry sponsored), and without any clear or consistent issues with hum (as far as I can tell from my reasonably extensive reading of websites and forums regarding the DACs).

You mention getting a new DAC - this remains an option, though I like the DAC and would rather fix the hum problem if possible. Remember that my other components are also affected by this hum (although to a somewhat lesser extent), and that the DAC did not hum at all on testing at the manufacturer. You mention "things that can be done" regarding the electricity supply - what did you have in mind?

Re: Advice on transformer hum

Reply #39 –
Quote from: extracampine on
You mention getting a new DAC - this remains an option, though I like the DAC and would rather fix the hum problem if possible. Remember that my other components are also affected by this hum (although to a somewhat lesser extent), and that the DAC did not hum at all on testing at the manufacturer. You mention "things that can be done" regarding the electricity supply - what did you have in mind?

Based on your pictures, your DAC uses one of the cheapest, most primitive and most potentially troublesome kind of transformers, especially from the standpoint of generating acoustic noise. 

Aside of the problem of being based on an audible operational frequency, it is of the I-E format, as opposed to the possibly preferred toroid alternative, and additionally is not in a shielded box or fully encapsulated in what is called a "Potting compound".

You got what you paid for no matter what price it cost you. :-(. 

Re: Advice on transformer hum

Reply #40 –
@jsrtheta +1

@extrcampine OK- so what is your line voltage? If over 245 it could be contributing to the problem.

If you take the equipment elsewhere, bring the DVM with you to see what the line voltage is.

The Lampizator DACs I've seen use both toroid and EI core transformers. Any chance you can get the cover off the DAC and start it up? I've used a plastic straw and also an insulated screwdriver to suss out mechanical noises by using them as a stethoscope; if you can sort out which transformer noisy that might help.

Re: Advice on transformer hum

Reply #41 –
Quote from: Atmasphere on
@jsrtheta +1

@extrcampine OK- so what is your line voltage? If over 245 it could be contributing to the problem.

If you take the equipment elsewhere, bring the DVM with you to see what the line voltage is.

The Lampizator DACs I've seen use both toroid and EI core transformers. Any chance you can get the cover off the DAC and start it up? I've used a plastic straw and also an insulated screwdriver to suss out mechanical noises by using them as a stethoscope; if you can sort out which transformer is noisy that might help.

Re: Advice on transformer hum

Reply #42 –
Arnold B. Krueger,

With all due respect, that Benchmark AHB2 amp is a beautiful amp, but when they say:

"THE QUIETEST, CLEANEST AUDIO AMPLIFIER ON THE PLANET"  and it sells for $2995.00

Isn't that a little too "audiophile"?

A Crown XLS DriveCore 2 Series amp is a lot cheaper.

Re: Advice on transformer hum

Reply #43 –
I was not looking to troll you over Lampizator (and no, you didn't accuse me of that). And I've never owned one of his DACs. But I would listen to Arnie's comments, and add that this may be a situation where the design and implementation are at fault and, more importantly, where this problem is a merely a harbinger of other problems to come. When Arnie talks transformers, I would listen.

Re: Advice on transformer hum

Reply #44 –
I certainly am listening. The fact remains however that my Classe amp also hums (though to a lesser extent); and also that the DAC did not hum on testing at the manufacturer. This makes me wonder if there is something with my power supply...

Re: Advice on transformer hum

Reply #45 –
How loud is the hum? Can you hear it from your listening chair?

FWIW its unusual for this sort of thing to represent a reliability problem.

When did you first notice the hum?

Re: Advice on transformer hum

Reply #46 –
The hum is loud enough to hear from the listening chair in a silent room. The chair is about 3 to 4 metres away.

Hard to say how loud it is otherwise. Definitely abnormal I would have thought. I recorded it with my phone; listen to the WAV file below. The last 4-5 seconds of the sample are when I turn my phone round the right way, and when you can hear the hum better.

https://www.sendspace.com/file/ey7erf

Not exactly sure when I first noticed it. It may have been present since when I got the DAC a number of months ago.

Re: Advice on transformer hum

Reply #47 –
Quote from: Hubert Watson on
Arnold B. Krueger,

With all due respect, that Benchmark AHB2 amp is a beautiful amp, but when they say:

"THE QUIETEST, CLEANEST AUDIO AMPLIFIER ON THE PLANET"  and it sells for $2995.00

Isn't that a little too "audiophile"?

A Crown XLS DriveCore 2 Series amp is a lot cheaper.

Note that by avoiding making claims about that amp sounding like anything in particular, I avoided problems with just about everybody that mattered.  :-) Of course, the thing is a price/performance disaster if audible sound quality matters the most to you.

I'm sure that I could stump the stars with an ABX of it versus a 200 wpc switchmode module from one of eBay's pacific rim sources.


Re: Advice on transformer hum

Reply #48 –
Return the amp and ask for a replacement or refund.

Re: Advice on transformer hum

Reply #49 –
Well, the good news for the original poster is that Classé Audio appears to be back in business, as part of the Sound United (Denon, Marantz, Polk Audio, Definitive Technology, etc.) group. This was announced just a few days ago and reported here, amongst other sites: https://www.stereophile.com/content/classé-audio-revived Yes, I know Stereophile isn't exactly popular on here, but it's the first report I found on Google.

I don't know what commitment the revived brand has toward upkeep/repair of older models, but it won't kill you to ask. However, one comment on the linked article does mention that their product support for Boston Acoustics isn't the greatest.
 
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