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Hydrogenaudio Forum => General Audio => Topic started by: extracampine on 2018-01-05 05:35:29

Title: Advice on transformer hum
Post by: extracampine on 2018-01-05 05:35:29
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.
Title: Re: Advice on transformer hum
Post by: silverprout on 2018-01-05 07:52:30
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.

We can’ t reconstruct an AC signal with passive components and every tentative of filtering is pointless if you don’t know what you are facing of.
You should try to fin a portable scope in order to analyse the AC signal.
Title: Re: Advice on transformer hum
Post by: Funkstar De Luxe on 2018-01-05 08:09:37
Sounds to me like the laminations in a transformer have deteriorated and it's allowing the plates to mechanically move. This produces a 50Hz/60Hz hum. It's a fairly common issue among older gear.

Unfortunately there no easy solution. If it has an external power supply you can replace that, however since you said that it "emanates from the components" I would say that they have internal power supplies.

What I do (because I found i quite distracting), is position my equipment far enough away that I can't hear it or put it in a case or a rack.

However, if anyone has a suggestion to resolve transformer hum, I'll be happy to hear it.
Title: Re: Advice on transformer hum
Post by: smok3 on 2018-01-05 11:13:22
I'd replace transformers, if you have some basic soldering skills the replacement on old stuff is fairly simple, since the stuff is big enough to be seen by naked eye.
Title: Re: Advice on transformer hum
Post by: Arnold B. Krueger on 2018-01-05 12:42:13
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.


An obvious solution is to replace all of the iron transformer power supplies in the acoustically humming components with switchmode power supplies.

They may still produce acoustic noise at the frequency of the current in their power transformers, but now that noise will be above 20 KHz.

Any fears you may have about doing this may be addressed by the fact that one of the quietest and lowest distortion amplifiers in the world (Benchmark AHB2) uses switchmode power supplies:

(http://1.bp.blogspot.com/-Z_qGRw9aoEI/VDU4ZLUa1pI/AAAAAAAADrM/JJBGiGOq4hU/s1600/AHB2_Top_Open.jpg)
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-05 13:43:42
Many thanks for these helpful replies.

silverprout: I don't have a scope, and I fear that this may be beyond my level of expertise; I have read that trying to analyse DC on an AC mains is quite tricky

Funkstar: I don't think that it is a problem with the transformer; it is relatively new, and I had recently returned the DAC to the manufacturer to check out, where they certified that it was completely silent with no hum. Putting the equipment further away is not an option for me in my room unfortunately; besides, I would rather tackle the source

smok3: see above - I don't think replacing the transformer is required

Arnold: switching the PSU is not something that I want to do since I paid £££s for the unit; if it does transpire to be a fault with the transformer assembly then I would ask for a replacement or refund; however as stated above, the unit was checked at the manufacturer recently where there were no issues with hum

Title: Re: Advice on transformer hum
Post by: Apesbrain on 2018-01-05 15:06:44
No joke: do you still hear the "hum" with everything unplugged from wall power?

If not, plug in each component independently until you find the culprit.  My experience with this issue is that you'll need to find a quieter brand/model.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-05 15:08:54
No joke: do you still hear the "hum" with everything unplugged from wall power?

If not, plug in each component sequentially until you find the culprit.  My experience with this issue is that you'll need to find a quieter brand/model.
When you say "everything", are you referring to my audio equipment, or everything in the house? If the former, then as stated above there is no hum when the unit is not powered on. If the latter, then no I have not tried this yet - would you recommend that I do so? And regarding your final sentence, as stated above, the brand/model is quiet as tested elsewhere - the hum seems to be at my property. I am going to try and plus it in elsewhere to to check.
Title: Re: Advice on transformer hum
Post by: DVDdoug on 2018-01-05 15:30:43
Quote
the unit was checked at the manufacturer recently where there were no issues with hum
They were probably checking for electrical/signal hum ("through the speakers").

The mechanical/acoustical hum might be normal for that unit because either they didn't notice it, or they don't consider it defective.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-05 15:48:24
They were probably checking for electrical/signal hum ("through the speakers").
The mechanical/acoustical hum might be normal for that unit because either they didn't notice it, or they don't consider it defective.
They were checking for mechanical hum, as the problem is a hum from the machine itself and not from the speakers. The hum is not considered normal, as the unit was completely silent in their tests (and appears to be for most other owners too).
Title: Re: Advice on transformer hum
Post by: Apesbrain on 2018-01-05 16:13:33
How is the HDPlex employed in your system?
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-05 16:15:55
The HDPLEX LPSU 100W is powered by mains AC, and supplies 3 rails of DC to the PC-based music player (to the USB card, SSD and mobo). The HDPLEX also emits a hum though last time I checked it was barely audible. I think that it had previously been more audible - hence I had moved it into a wooden unit in the listening room :)
Title: Re: Advice on transformer hum
Post by: Apesbrain on 2018-01-05 17:11:57
Is the problem there with the PC and power supply off and unplugged from the wall?  How about removed from the room?
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-05 19:07:50
The problem persists when I take the DAC upstairs and plug it into a power socket in the bedroom. As a test, I turned off the PC and LPSU and unplugged the LPSU - the hum remains.

One other thing maybe worth mentioning - when I first turn the DAC no, the hum is a lot louder for around 1 second before it reduces to the usual level. Don't know if this is of relevance.
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-05 19:38:05
The problem persists when I take the DAC upstairs and plug it into a power socket in the bedroom. As a test, I turned off the PC and LPSU and unplugged the LPSU - the hum remains.

One other thing maybe worth mentioning - when I first turn the DAC no, the hum is a lot louder for around 1 second before it reduces to the usual level. Don't know if this is of relevance.
That's normal but has a different cause- the core was magnetized from the last time it was on, and the core saturated until the AC degaussed it.

The DAC uses a toroid transformer. So does the Classe. Toroidal cores can easily saturate, and when they do, they become mechanically noisy.

The most common cause of continuous noise (both units are normally silent, so we can ignore 'cheap transformers' as a cause) is something called 'DC on the line' and is an asymmetry in the AC power waveform. Usually this is caused by a space heater or the like running on half power- and so is only drawing power on half of the AC power waveform. This does not have to be happening in your house- it might be the house across the street- any house that might be on the same line transformer that is on a telephone pole somewhere near you.

You certainly don't have to run switch mode power supplies!

There is a solution which is inexpensive. You use something called a 'DC blocker' and I have to say I'm surprised that no-one mentioned it earlier! A DC blocker is a rectifier pack whose individual rectifiers are bypassed by electrolytic caps. The caps conduct forward biased when the rectifiers are reverse biased (as they might be when DC is present); the caps are thus providing a bypass around the rectifiers.

Now Classe amps often have this circuit installed, but if the caps on it have failed then you have a problem. OTOH not all the models got this treatment, if you have an early Classe this might be the case.

The DC blocker need not be one for each component; you can have one run at the outlet and that should do the job. Here's an example where less caps are used but does the same thing:

http://www.diyaudio.com/forums/attachment.php?postid=16083&stamp=1012084233&s=

Here's a similar circuit. Scroll down to the 4th post:
http://www.audiocircle.com/index.php?topic=56754.0
Title: Re: Advice on transformer hum
Post by: Apesbrain on 2018-01-05 22:04:19
Take the DAC across town to a friend's house and see if it has the same problem there.
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-05 22:07:37
^^ no need- that is the problem.
Title: Re: Advice on transformer hum
Post by: silverprout on 2018-01-06 08:17:42
silverprout: I don't have a scope, and I fear that this may be beyond my level of expertise; I have read that trying to analyse DC on an AC mains is quite tricky

You need a scope and and some expertise in AC signal analysis.
Trying to solve a problem without seeing it will drive your mind into madness, you will experiment millions of theories and your problem will stay the same.

PS: Your toroidal transformer is a solid ferrite core with copper windings around it and theses kind of transformers are as impacted by magnetic flux anomalies as other types. Terefore they vibrate as well, all transfomers should be mechanically decoupled in order to avoid sad noises but commercial products are not... design flaw.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-06 19:38:12
There is a solution which is inexpensive. You use something called a 'DC blocker' and I have to say I'm surprised that no-one mentioned it earlier!

Many thanks for the reply Atmasphere. But did you read my original post? I have already tried 2 different DC blockers (from MCRU and ATL Hifi), and neither worked. I suppose that perhaps the problem could still be DC, but I'm not sure. Any advice?
Title: Re: Advice on transformer hum
Post by: Funkstar De Luxe on 2018-01-06 20:42:56
We don’t read posts here. We just reply with verbose responses to inflate our egos.

If the sound is coming from the unit, and not through the audio path, it is the transformer inside. It’s not what you want to hear but that’s all there is.

Move it somewhere you can’t hear it or get your soldering skills up to scratch and replace it.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-06 21:14:29
Funkstar - I don't think that there is anything wrong with the transformer per se, as it was tested at the manufacturers and there was no hum there. It has been stated that DC offset tends to cause transformer hum so I would like to cure that to see if it is the culprit.
Title: Re: Advice on transformer hum
Post by: splice on 2018-01-07 01:31:35
Borrow or rent an isolation transformer, as used on construction sites etc. Try a shop that rents construction equipment (wheelbarrows, concrete mixers etc). They come in various sizes, 1 kW should be more than enough.
(No sense in renting one that's too big, you'll need to rent a wheelbarrow to carry it... :) )
Title: Re: Advice on transformer hum
Post by: silverprout on 2018-01-07 07:50:29
Borrow or rent an isolation transformer, as used on construction sites etc. Try a shop that rents construction equipment (wheelbarrows, concrete mixers etc). They come in various sizes, 1 kW should be more than enough.
(No sense in renting one that's too big, you'll need to rent a wheelbarrow to carry it... :) )

It apparentely seems to be an accurate blind shot, but if you need an isolation transformer you’d better go to your local shop and buy an APC Line-R 1200VA.
It cost around 70€ and there is a 1K isolation transformer inside.

Will it solve the problem ?
Title: Re: Advice on transformer hum
Post by: Arnold B. Krueger on 2018-01-07 11:47:57
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.

The hum in power transformers has three sources.

One source of transformer hum is ordinary magnetism or paramagnetism or ferromagnetism (different words for similar things related to atomic electron shell composition). Ferromagnetism is common in ferrous alloys, that is those that contain iron. Transformers are composed of laminated magnetic (iron-alloy or steel) cores for efficiency. The laminations magnetically attract each other when peak current is flowing through the transformer. They are only mechanically attached to each other when no current flows through them. Courtesy of the power line, the current through the transformer goes through peaks and zero twice per power line cycle at 50 or 60 Hz. The application and relaxation of magnetic attraction of the laminations, causing rattling by vibrating against each other is resisted by dipping the transformer into a polymer or varnish which hardens and glues the laminations together, hopefully.

Loose laminations can be caused by poor production techniques, poor materials, or wear and tear including heat. Note that tiny amounts of acoustic noise from this source are impossible to eliminate, they can only be reduced. For a graphic example of this, find a power substation where the transformers are large, accessible by the public and heavily loaded.

Another source is diamagnetism which is again caused by atomic electron shell composition, but is prevalent in non-magnetic metals such as aluminum and copper. Diamagnetic materials commonly repel  under the  same conditions that ferrous materials attract.

The third source of mechanical noise in transformers is called magnetostriction. It is a common property of magnetic materials to change size and shape in a varying magnetic field.

So, it may look like an inert lump, but a transformer is with power applied is actually very dynamic, with the iron core laminations, microscopically changing size, shape, and juxtapositioning, and the copper or aluminum windings reacting to the same varying magnetic field in opposite ways.

Totally silent transformers are therefore impossible, so this problem like so many problems in audio is just a matter of degree.

The obvious way to reduce the perceptibility of these problems is to raise the frequency of the power that is being handled by the transformer. Transformers that are solidly encapsulated in a block of polymer and/or sealed in a metal housing can help.

My comment about switchmode power supplies is actually not facetious at all.

Furthermore, the ineffectiveness of human hearing at ultrasonic or even high sonic frequencies (e.g. noisy 15,575 kHz transformers and deflection yokes in NTSC TVs) can be observed from the fact that these and switchmode power supplies, potentially generating tons of acoustic noise at high sonic and ultrasonic frequencies, are generally well-tolerated by humans.

Title: Re: Advice on transformer hum
Post by: Rotareneg on 2018-01-07 17:12:15
Considering that DAC uses tubes for some reason, powering it with a switch mode power supply might be considered heresy by those who feel having vacuum tubes in a DAC is a good idea in the first place.

Besides direct sound radiation from a vibrating transformer or other inductor, there might also be some mechanical resonance going on where the case and/or circuit board is vibrating in response to a transformer. You might try pressing on the case in different spots (including the bottom) when it's on to see if it has any effect.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-07 17:48:44
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!
Title: Re: Advice on transformer hum
Post by: Arnold B. Krueger on 2018-01-08 14:06:55
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.
Title: Re: Advice on transformer hum
Post by: cliveb on 2018-01-08 14:15:44
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).
Title: Re: Advice on transformer hum
Post by: Speedskater on 2018-01-08 20:22:16
..................................................................................
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. 
Title: Re: Advice on transformer hum
Post by: DVDdoug on 2018-01-08 20:58:33
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.)  
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-09 00:00:53
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?
Title: Re: Advice on transformer hum
Post by: silverprout on 2018-01-09 06:13:43
IMO the quality is not involved here, even the highest quality transformers avaliable on earth will buzz with AC anomalies.

Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-09 14:01:40
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?

(http://i65.tinypic.com/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.

(http://i64.tinypic.com/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.

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.
Title: Re: Advice on transformer hum
Post by: pdq on 2018-01-09 14:15:37
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.
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-09 23:52:01
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?

(http://i65.tinypic.com/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.

(http://i64.tinypic.com/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.

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?
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-10 10:33:05
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.
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-10 19:24:20
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?
Title: Re: Advice on transformer hum
Post by: jsrtheta on 2018-01-11 02:32:21
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.

Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-11 14:56:43
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?

Title: Re: Advice on transformer hum
Post by: Arnold B. Krueger on 2018-01-11 17:47:53
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. :-(. 
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-11 19:53:29
@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.
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-11 20:56:57
@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.
Title: Re: Advice on transformer hum
Post by: Hubert Watson on 2018-01-12 19:57:49
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.
Title: Re: Advice on transformer hum
Post by: jsrtheta on 2018-01-12 20:24:29
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.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-12 21:18:04
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...
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-12 22:24:51
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?
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-13 09:54:13
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.
Title: Re: Advice on transformer hum
Post by: Arnold B. Krueger on 2018-01-13 13:34:22
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.


Title: Re: Advice on transformer hum
Post by: saratoga on 2018-01-13 22:53:41
Return the amp and ask for a replacement or refund.
Title: Re: Advice on transformer hum
Post by: JabbaThePrawn on 2018-01-14 14:42:22
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.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-15 10:46:51
Think we might be getting a bit sidetracked. The problem is with a DAC, not an amp. I do indeed have a Classe amp, which does emit some mechanical hum, though that is not a particular problem as it is quiet enough to be inaudible from the listening spot. The DAC hum however is audible and I am still trying to fix this issue.

Further to some of the posts above - I tested the voltage at my house yesterday - and the multimeter was reading 245 and 246V. So I would have thought that the voltage level is OK at least?
Title: Re: Advice on transformer hum
Post by: Hubert Watson on 2018-01-15 18:02:31
I know this a DAC hum thread, but in regard to the mechanical amplifier hum, what model of Classé amp do you own?
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-15 20:22:26
Think we might be getting a bit sidetracked. The problem is with a DAC, not an amp. I do indeed have a Classe amp, which does emit some mechanical hum, though that is not a particular problem as it is quiet enough to be inaudible from the listening spot. The DAC hum however is audible and I am still trying to fix this issue.

Further to some of the posts above - I tested the voltage at my house yesterday - and the multimeter was reading 245 and 246V. So I would have thought that the voltage level is OK at least?

Its a bit on the high side but nominal.

If we don't have to worry about the Classe, what happens if you apply pressure to the top cover of the DAC?
If that shuts it up, then mechanical vibration through the chassis is the issue, and damping the cover could really help. But as I mentioned earlier, some rubber pads aren't going to sort it out.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-16 16:47:44
Atmasphere - I do indeed believe that mechanical vibration through the chassis is at least part of the issue.

However, pressing on the  top of the DAC (avoiding the tubes or at least the tube holes if the tubes are removed) does not seem to alter the hum at all. What does appear to alter the hum somewhat is removing the chassis altogether (i.e. leaving only the base and the front plate). When this is done, the hum is less and possibly below the threshold of being a problem. If the casing were then to dampen this sound further it would likely be OK. The problem is, the casing appears to worsen the hum.

Whilst I remain keen to address the root cause of the problem, if there is anything that can be done casing-wise then of course I would be keen to try it! As mentioned earlier, I tried putting a rubber washer in-between the 2 screws that fasten the chassis to the front panel, though this did not alter it. I considered putting washers in-between all the smaller screws that hold the casing to the base panel, though this would be extremely fiddly to do.

Hubert - the amp is a Classe-CAP2100 (2x100W stereo amp).
Title: Re: Advice on transformer hum
Post by: cliveb on 2018-01-16 18:16:11
However, pressing on the  top of the DAC (avoiding the tubes or at least the tube holes if the tubes are removed) does not seem to alter the hum at all. What does appear to alter the hum somewhat is removing the chassis altogether (i.e. leaving only the base and the front plate). When this is done, the hum is less and possibly below the threshold of being a problem. If the casing were then to dampen this sound further it would likely be OK. The problem is, the casing appears to worsen the hum.
There are two ways that the casing might accentuate the hum:

1. The case has a mechanical resonant frequency that coincides with the vibration in the transformer and is therefore excited by it. Pressing down on the case would alter its resonant frequency so that it is no longer excited. Since doing so does not reduce the hum, this is probably not the mechanism in play.

2. The other mechanism is that the case is acting as a resonator for the noise inside - like the body of a violin or acoustic guitar. Pressing down on the case won't affect this very much, since it's more to do with the shape and volume of the interior space. Given what you have reported, this seems the more likely explanation for what's going on.
Title: Re: Advice on transformer hum
Post by: DVDdoug on 2018-01-16 23:21:05
extracampine,

If the hum is really annoying to you, I suggest you cut your losses and buy something less exotic.    You bought something exotic and you got exotic problems.   :(  

Seriously...  vacuum tubes have been obsolete since the 1960s (although guitar players still like tube distortion).    It's super-silly to put tubes in a DAC.   There are DAC chips that don't need any additional active electronics in the signal path, although you might want an op-amp buffer on the output.

I don't have a separate DAC but I've got a $20 USB soundcard and a $300 AVR and there are no "sound quality" issues.   I've got a couple computers with no sound quality problems but they do have audible fans and that might annoy you as much as the hum .
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-16 23:58:51

However, pressing on the  top of the DAC (avoiding the tubes or at least the tube holes if the tubes are removed) does not seem to alter the hum at all. What does appear to alter the hum somewhat is removing the chassis altogether (i.e. leaving only the base and the front plate). When this is done, the hum is less and possibly below the threshold of being a problem. If the casing were then to dampen this sound further it would likely be OK. The problem is, the casing appears to worsen the hum.

Whilst I remain keen to address the root cause of the problem, if there is anything that can be done casing-wise then of course I would be keen to try it! As mentioned earlier, I tried putting a rubber washer in-between the 2 screws that fasten the chassis to the front panel, though this did not alter it. I considered putting washers in-between all the smaller screws that hold the casing to the base panel, though this would be extremely fiddly to do.


OK- if you are alright working with the unit while the case is off, if it were me I would be using a plastic straw and probably also a light metal rod, each pressed against the power transformers in the unit, with the other end at my ear. IOW, using them as a stethoscope to see which transformer is making the noise.

Once you've done that, report back with any findings.

Have you contacted the manufacturer regarding this issue?
Title: Re: Advice on transformer hum
Post by: Chibisteven on 2018-01-17 01:11:06
My advice is to get rid of that DAC, it's poorly made garbage.  It seems to be far more trouble than it's worth.  I can understand if it was antique or a collectable that is worth something then it maybe worth fixing but this doesn't appear to be the case here.  DACs are a dime a dozen and shouldn't be causing this much grief.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-17 11:17:27
OK- if you are alright working with the unit while the case is off, if it were me I would be using a plastic straw and probably also a light metal rod, each pressed against the power transformers in the unit, with the other end at my ear. IOW, using them as a stethoscope to see which transformer is making the noise.

I think that it is the smaller transformer which I had identified above that is making the noise. I tried prodding it with a rod and also unscrewing it altogether and placing a bit of rubber underneath it though that didn't really seem to help.

Have you contacted the manufacturer regarding this issue?

Yes, I actually sent the unit back to the manufacturer for testing, and there was no hum evident there. I am going to take the DAC to a music shop or 2 this coming weekend to see if it hums there.

My advice is to get rid of that DAC, it's poorly made garbage.  It seems to be far more trouble than it's worth.  I can understand if it was antique or a collectable that is worth something then it maybe worth fixing but this doesn't appear to be the case here.

Well, as mentioned above this is a very highly regarded DAC and I do like the way it sounds - hence my efforts to address this problem rather than simply swap the DAC. But you are right, changing it for another DAC is always an option.

Title: Re: Advice on transformer hum
Post by: pdq on 2018-01-17 13:24:58
That you "like the way it sounds" is very suspicious. A DAC should not "sound" like anything. It should be simply the equivalent of a straight wire, and if you are attributing anything more to it then you are deluding yourself.

Please accept the advice that you have been given and replace this troublesome device with one that works just as well but does not cause the problems.
Title: Re: Advice on transformer hum
Post by: Arnold B. Krueger on 2018-01-17 14:05:28
Well, as mentioned above this is a very highly regarded DAC and I do like the way it sounds - hence my efforts to address this problem rather than simply swap the DAC. But you are right, changing it for another DAC is always an option.

The statement that the "Limpizator" DACs are "...highly regarded..."  is strictly a matter of a tiny noisy pocket of personal opinon, and requires considerable Cherry Picking to arrive at.

From a technical standpoint, it is a DAC that is intentionally mis-designed and from the pictures, mis-constructed.  It is a blatant example of anti-technology, anti-craftsmanship and anti-engineering.

The most obvious example of mis-design is the the reliance on throwback anti-engineering, one major aspect  of which is the use of an obsolete DAC chip with far less than SOTA performance and elimination of the digital filter and aperture correction that was origionally part of its design. This issue is so strong that it leads to easily measurable frequency response errors that might even be audible.

I could point out that the DAC has tubes, that may look great to some but add expense, complexity, reduce reliability, and possibly hinder sonic accuracy. But this is a level of rationality that I expect to get no traction at all with rabid subjectivists. :-)

Another mis-design element is the avoidance of modern technology for building audio gear that is inherently free of hums and buzzes due to the power line.

The most obvious example of mis-construction is the choice of an inappropriate but inexpensive style of the power transformer, and its location.

If I were to be such a Luddite that any of this weirdness appealed to me, I'd obtain an inexpensive solid state DAC and an equalizer for a fraction of the trouble, size, energy consumption and expense, that had vastly greater flexibility, and the ready ability to remove the equalizer or at least zero out its controls should a burst of sanity ever enter my brain. :-)



Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-17 19:59:50


I think that it is the smaller transformer which I had identified above that is making the noise. I tried prodding it with a rod and also unscrewing it altogether and placing a bit of rubber underneath it though that didn't really seem to help.

Have you contacted the manufacturer regarding this issue?

Yes, I actually sent the unit back to the manufacturer for testing, and there was no hum evident there. I am going to take the DAC to a music shop or 2 this coming weekend to see if it hums there.


It does sound like the problem is line related.

If you reinstalled the mounting screws, they would have transmitted the vibration past the rubber pad.

My suggestion would be to isometrically mount the noisy transformer. If it employs mounting screws, obtain some rubber grommets from the hardware store. Grommets have 4 dimensions- the inner diameter that accepts the mounting screw, the overall outer diameter, the hole size in which it fits, and the material thickness that it can accommodate.

You will need some longer mounting screws as well as 2 washers for each screw and a self locking nut for each screw.

Select a grommet, you don't need a big one, maybe the outside diameter might be 1.5cm. Measure the hole size it needs and select a drill that is the same diameter. You will use this drill to drill out the mounting holes in the chassis for the transformer (assuming there is room; the examples that I have seen do have room). Having done that, install the grommets. Install a washer on a screw, feed the screw through the grommet from below, install the second washer on top, so it is between the grommet and transformer resting on top, then install the self locking nut to hold the transformer in place. You don't want it particularly tight, but it should be snug. Do this for the other mounting screw as well.

If this is done right, the transformer will be mechanically isolated from it mounting and thus unable to transmit vibration to the chassis.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-19 22:49:18
Thanks for the further replies.

I understand that there are many differences of opinion regarding DACs (and indeed other components, leaving alone cables), and tempting as it is to behave otherwise, my intention here was not to get drawn into a debate on the relative merits of the various implementations. I would rather stay on track with the issue of the hum/buzz if possible - though thanks for the food for thought.

Atmasphere - thanks for the interesting thoughts. I have no experience of isometrically mounting anything. What you describe sounds like it may be worth a try, though it also sounds like a reasonable amount of work. I had already removed the transformer mounting screws and placed the transformer on top of a relatively thin bit of rubber - which made little difference once the case was back on. Is the technique which you described likely to yield substantial improvements over this?

I was planning to take the DAC to an audio store for further investigation tomorrow, though a snowfall has meant that sledging with the kids may take priority and this will have to wait until next week :)
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-01-19 23:45:17
Atmasphere - thanks for the interesting thoughts. I have no experience of isometrically mounting anything. What you describe sounds like it may be worth a try, though it also sounds like a reasonable amount of work. I had already removed the transformer mounting screws and placed the transformer on top of a relatively thin bit of rubber - which made little difference once the case was back on. Is the technique which you described likely to yield substantial improvements over this?


No. That suggests that the toroid is making the vibration, not the smaller EI core.

Stay warm!
Title: Re: Advice on transformer hum
Post by: pelmazo on 2018-01-20 13:04:19
The EI core may actually be a choke. There are connections on the PCB which are labelled CHOKE.

Lampizator may have constructed a choke-filtered power supply. Chokes are designed to tolerate DC, but they may hum, too, particularly when they saturate.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-20 14:53:10
Interesting further thoughts. It does indeed have a choke power supply. But it seems that the hum is coming from that area rather than the larger round toroidal transformer. Alternatively, I suppose that it could be coming from something under the PCB (which is mounted upside-down), but then I would have to remove this also which might be difficult. If you hear hooves think horses, and so I had assumed that it was the EI transformer that was the culprit.
Title: Re: Advice on transformer hum
Post by: pelmazo on 2018-01-20 15:07:23
People often use separate heater transformers, so that they can switch on tube heating before they energize the rest of the circuitry. In the old days, when the rectifiers were also tubes, that happened automatically, because the rectifier tubes had to heat up before they passed current. But these days there will be silicon rectifiers, which need no heating to pass current.

So maybe there's another transformer hidden somewhere, for the tube filaments.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-01-21 12:36:13
Perhaps there is. The DAC does have a tube rectifier as you mention.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-02-01 13:10:35
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.
Title: Re: Advice on transformer hum
Post by: Atmasphere on 2018-02-01 22:50:37
If that's the case, I'd send it back to Lampizator with instruction to fix it this time.
Title: Re: Advice on transformer hum
Post by: extracampine on 2018-02-06 22:49:34
OK, I had it checked by a local electrical engineer - he seemed to think that the level of transformer hum was within manufacturers tolerances.
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