Hum from a toroidal transformer

[JSmith]

Easiest option? Return the product and get/swap for a model with the SMPS (linked earlier);

... which doesn't even use a SMPS1200A400. 1500 in the model number may indicate peak power of 1500W (not finding any specific specs).


JSmith

 

[pjug]

This is a point that's been made repeatedly, and it very well might be the case. But in my experience a toroidal does not hum unless there's DC in the AC line. It's absolutely the case that a better-made toroidal might not hum when hooked up to a dirty AC supply while a poorly made one might. But it's also the case that all toroidals are more susceptible to DC-based saturation humming than laminated-sheet EI transformers are.

I'm sure there must be toroidals out there that are so poorly made that they will mechanically hum even with a super-clean AC source. But that hasn't been my experience. In my experience some of them hum based on local conditions, and all of them that hum are helped significantly by a DC blocker. YMMV of course, but if someone is happy with their amp otherwise and they're sure the hum is mechanical (rather than coming through the speakers), and they've tried turning off flourescent lights and old fridges and moving the amp's AC cord to a different circuit and so on, and it still hums, then a DC blocker is the logical next step.

I can't say I have enough experience to say how rare it is but I have a toroid that hums (in NAD C370). Nothing can stop it. A friend has the same. I even cut the wrapping on mine and potted it under pressure, in addition to the usual messing with clamping and orientation. Tried it other places. Currently it hums away at another house where another toroid Class AB is silent. You just can't do anything if you have a transformer like this.

I wouldn't want to argue with you about it except I think it is important for the OP to know a DC blocker is worth trying but it might not solve the problem and he shouldn't keep pulling his hair out thinking the transformer is not the problem if turns out it really is the problem.

 

[tmtomh]

By following the steps you outlined, you've effectively ruled out DC as an issue, rather than confirming its presence on the AC mains.

No, because the DC is not necessarily coming from something inside one’s own home.

 

[Old_School_Brad]

No, because the DC is not necessarily coming from something inside one’s own home.

Let's see..

• Grid regulations limit DC injection to a maximum of 0.5%.
• Even as little as a few hundred millivolts of DC can cause a toroidal transformer to hum.

Since 0.5% of 120V AC is 600mV DC, it’s possible for the grid to stay within legal limits while still causing issues.

I'd say only after verifying that the amplifier is functioning properly and that no internal faults are causing the issue should you consider a DC blocker. Using one might mask a deeper problem rather than truly fixing it.

 

[Geert]

No, because the DC is not necessarily coming from something inside one’s own home.

Grid regulations limit DC injection to a maximum of 0.5%

I never had a hum problem in my home until I bought an Atoll amp. Hum audible at the listening position ... My Hifi system has a dedicated mains supply so switched off everything else in the fuse box, amplifier kept on humming ... Installed a DC blocker, problem gone (https://audiosciencereview.com/foru...-to-help-stop-transformer-hum.948/post-874360). Replaced the Atoll with a Cambridge Audio amp (again with a lineair power supply) a year later, no hum problem without DC blocker (unless you put your ear against the speaker).

 

[Speedskater]

Audio Engineering Society paper:

MEASURING ACOUSTIC NOISE EMITTED BY POWER TRANSFORMERS
Menno van der Veen (Plitron Transformers)

One moment, please...

 

[mhardy6647]

I mean... power supplies with good ol' E-I core power transformers are still an option.
R-core, if you feel the former is (so to speak) antediluvian.
EDIT: to reiterate what's been said, delicately, in numerous posts throughout this thread; mechanical hum of toroids is a thing. More of a thing than mechanical hum for other PT topologies (which can and does occur, but empirically seems to be far less common as an issue than for toroids).

Or -- yeah -- presumably an SMPS would solve the problem, too.

PS Based on everything that's been reported so far, DC on the mains still looms large as an option! It is not difficult to test for, although, of course, having some understanding of the hazards is prudent.
Has the OP checked for a loose bolt and/or inadequate (or perhaps nonexistent) mechanical isolation of the toroid, yet? Certainly these are the easiest things to do (other than direct assessment of the DC offset on the mains, which I understand is scary to some people*).

_____________
* Heck, even I would be extra-wary if our power "at the wall outlets" were 240 VAC and not 120 V.

 

[Old_School_Brad]

I never had a hum problem in my home until I bought an Atoll amp. Hum audible at the listening position ... My Hifi system has a dedicated mains supply so switched off everything else in the fuse box, amplifier kept on humming ... Installed a DC blocker, problem gone (https://audiosciencereview.com/foru...-to-help-stop-transformer-hum.948/post-874360). Replaced the Atoll with a Cambridge Audio amp (again with a lineair power supply) a year later, no hum problem without DC blocker (unless you put your ear against the speaker).

There’s more than one way to approach the problem -both minds and transformers vary in their sensitivity and temper.

I had a Yamaha P2700 with a large EI transformer that wouldn't stop humming, no matter what I tried. I suspected the windings had loosened.
Every other humming transformer in amplifiers I’ve dealt with was resolved by either placing small insulation pads in the right spots or tightening the EI core's threaded rods.
I guess that means I live in an area with very little DC contamination.

 

[Old_School_Brad]

____________
* Heck, even I would be extra-wary if our power "at the wall outlets" were 240 VAC and not 120 V.

Both have the potential to be lethal and should be treated with equally (high) caution.

If I take a leak near a high-voltage livestock fence, I’m not sure how much voltage it has, but I always make sure to keep a safe distance no matter what.

 

[mhardy6647]

Both have the potential to be lethal and should be treated with equally (high) caution.

If I take a leak near a high-voltage livestock fence, I’m not sure how much voltage it has, but I always make sure to keep a safe distance no matter what.

Well, there is that, and I do concur. I would think that most folks at a site like this know how to deal with such things, though. Nothing to be afraid of -- indeed, fear is the most dangerous response to such situations (perhaps even worse than overconfidence). Healthy respect and understanding are key.

Yeah, we have electric fences on our vegetable gardens in season to dissuade the woodland creatures. Because the gardens are small and the "energizers" are fairly large, contacting the fence when it is pulsing and when one is grounded will indeed get one's attention. DT.

PS I hate getting shocked by AC. That deep buzzing sensation is very unpleasant...

 

[ErVikingo]

tighten the Trafo (mechanically) and add a HumDinger. I have 2 of them on my system filtering just in case.

 

[tmtomh]

Let's see..

• Grid regulations limit DC injection to a maximum of 0.5%.
• Even as little as a few hundred millivolts of DC can cause a toroidal transformer to hum.

Since 0.5% of 120V AC is 600mV DC, it’s possible for the grid to stay within legal limits while still causing issues.

I'd say only after verifying that the amplifier is functioning properly and that no internal faults are causing the issue should you consider a DC blocker. Using one might mask a deeper problem rather than truly fixing it.

Let's review:

I recommended a DC blocker if eliminating potential DC sources in one's own home did not fix the problem.

You responded: "By following the steps you outlined, you've effectively ruled out DC as an issue, rather than confirming its presence on the AC mains."

I responded by noting that no, this is not necessarily true, because sources of DC don't only come from within one's own home.

And you then responded, "it’s possible for the grid to stay within legal limits while still causing issues."

That is precisely my point: DC can absolutely be present in the AC supply at levels that can cause issues, especially with toroidals as they are more susceptible to those issues than EI's are. It would be nice if you'd acknowledge that you're actually agreeing with what I said rather than proving it wrong, although I won't get my hopes up given our past exchanges here.

My understanding is also that in dense environments with multiple homes connected to the same transformer, a neighbor's devices can cause voltage drops, added noise, and other issues in one's own home AC supply - though I freely admit that while I have read that these effects can include DC injection, I am not certain if that is the case.

In any event, if a toroidal is particularly susceptible to DC-induced hum, we can speculate as to whether it's poorly made, or it's well-made but the AC supply has a good amount of DC in it, or perhaps the toroidal's build quality is mediocre and the AC is a bit dirty with DC. The average home user will have no way of making those distinctions, particularly since the standard for "good" vs "bad" toroidal core construction employed in this thread so far is quite fuzzy.

And speaking of fuzzy, if you could specifically list some common, testable faults that would result in mechanical toroidal hum in an otherwise normally functioning amplifier, and which would not be simply "bad quality toroidal," that would be helpful.

 

[tmtomh]

I never had a hum problem in my home until I bought an Atoll amp. Hum audible at the listening position ... My Hifi system has a dedicated mains supply so switched off everything else in the fuse box, amplifier kept on humming ... Installed a DC blocker, problem gone (https://audiosciencereview.com/foru...-to-help-stop-transformer-hum.948/post-874360). Replaced the Atoll with a Cambridge Audio amp (again with a lineair power supply) a year later, no hum problem without DC blocker (unless you put your ear against the speaker).

I've had similar experiences - and just in case my prior comments have not been clear on this point: of course not all toroidals hum. Many don't hum at all no matter what you plug them into.

Further, if folks want to take the view that any toroidal that hums when plugged into AC is by definition substandard in its build quality, they can take that position. And in that case the proper course of action is to get rid of the component in question. To each their own.

But my view is that that some toroidals hum and some don't, and I do not have a basis to conclude that this variability maps reliably or inevitably onto a binary condition of good vs bad transformer build quality. And I don't think anyone else has a solid evidentiary basis to conclude that either. All toroidals are more susceptible to DC induced hum, and so to me the fact that some of them do end up humming in some situations is not by itself an indicator of a fault or a build quality problem.

 

[Old_School_Brad]

Let's review:

I recommended a DC blocker if eliminating potential DC sources in one's own home did not fix the problem.

You responded: "By following the steps you outlined, you've effectively ruled out DC as an issue, rather than confirming its presence on the AC mains."

I responded by noting that no, this is not necessarily true, because sources of DC don't only come from within one's own home.

And you then responded, "it’s possible for the grid to stay within legal limits while still causing issues."

That is precisely my point: DC can absolutely be present in the AC supply at levels that can cause issues, especially with toroidals as they are more susceptible to those issues than EI's are. It would be nice if you'd acknowledge that you're actually agreeing with what I said rather than proving it wrong, although I won't get my hopes up given our past exchanges here.

That's pretty much what I said in the comment you quoted, while still pointing out, in my opinion, that jumping straight to a DC blocker before checking for loose parts or missing insulation in the amplifier seems a bit off. I’m not sure why your responses seem so heated -this is just about transformers, let's keep it light.

And speaking of fuzzy, if you could specifically list some common, testable faults that would result in mechanical toroidal hum in an otherwise normally functioning amplifier, and which would not be simply "bad quality toroidal," that would be helpful.

Loose center bolt, loose top shim, resonating top-covers, loose shielding, etc.
I've also had good results placing small insulation pads in places under the transformer, putting a bit of pressure to it at the right spot.
Whether people think this is due to a "bad transformer" or not, I’m not really concerned. If I can get it to run quietly, that's good enough for me.

 

[Old_School_Brad]

Well, there is that, and I do concur. I would think that most folks at a site like this know how to deal with such things, though. Nothing to be afraid of -- indeed, fear is the most dangerous response to such situations (perhaps even worse than overconfidence). Healthy respect and understanding are key.

Yeah, we have electric fences on our vegetable gardens in season to dissuade the woodland creatures. Because the gardens are small and the "energizers" are fairly large, contacting the fence when it is pulsing and when one is grounded will indeed get one's attention. DT.

PS I hate getting shocked by AC. That deep buzzing sensation is very unpleasant...

As a child, I’ve had hundreds of jolts from fences -those two-wire ones. To get in and out of the fields, we’d bend down and step in between. The really bad times were when we got shocked by the bottom wire, and our body would jump up into the top one just in time to get another one.

However, 230 VAC is much scarier. That tingling sensation can linger for a long time afterward. I’ve never had a cross-body shock, though -only across the same hand or between fingers. Usually with my head buried in an electrical cabinet -makes me appreciate and remember the helmet at all times..

 

[Geert]

But my view is that that some toroidals hum and some don't, and I do not have a basis to conclude that this variability maps reliably or inevitably onto a binary condition of good vs bad transformer build quality. And I don't think anyone else has a solid evidentiary basis to conclude that either.

In my experience it can be a quality or design problem. For example a transformer that does not fully comply with EU power standards and is designed or built for a voltage that's a bit lower (very common in lot's of countries) can hum when connected to 240V because it will be running closer to (or in) saturation. And then there's also the quality and size of the core.

 

[ErVikingo]

That's pretty much what I said in the comment you quoted, while still pointing out, in my opinion, that jumping straight to a DC blocker before checking for loose parts or missing insulation in the amplifier seems a bit off. I’m not sure why your responses seem so heated -this is just about transformers, let's keep it light.


Loose center bolt, loose top shim, resonating top-covers, loose shielding, etc.
I've also had good results placing small insulation pads in places under the transformer, putting a bit of pressure to it at the right spot.
Whether people think this is due to a "bad transformer" or not, I’m not really concerned. If I can get it to run quietly, that's good enough for me.

I grew up in an island on the Caribbean; as a matter of practice, my father would open up amps and other components before plugging them in to check for stuff that was either lose or out of place (handling or deficient assembly). In my case, before I recommissioned my large Thresholds and my Decware conditioner, I checked if the trafos were reasonably tight.

When i had vibration, I checked all again, call the oem and called the power company. Power company came and replaced the transformer feeding mine and my neighbor's homes and the noise went away. I had purchased a couple of AVA HumDingers and decided to keep them in the loop (already paid for!)

 

[Steven Holt]

Guys, is it possible that this unit is not grounded properly? Because that's the first thing I would check.

 

[Maciekw]

Thank you very much for all your comments.
Today the DC blocker from IFI has arrived. I immediately connected it to the amplifier and received two messages.
The first is bad. Despite using the DC blocker, the transformer is still as loud.
The second is good. The cause of the noise is not my power grid. At least in terms of the DC component.
By the way, I measured the mains voltage at the socket. It is about 220÷225V in the socket at my place. Thus, the cause of the noise is not too high voltage.
I had the electrical system inspected a year ago, that's how I know it's not a grounding problem either.

 

[tmtomh]

Whether people think this is due to a "bad transformer" or not, I’m not really concerned. If I can get it to run quietly, that's good enough for me.

We definitely agree on that!