How to cure power transformer buzz

kward

kward

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The last two Edcor power transformers I have purchased (two within the last 12 months) have buzzed pretty loudly after installed onto the chassis. I determined that the buzzing was not coming from loose end bells or less than tight mounting onto the chassis. Rather, it is coming from mechanical vibration of the wires on the high voltage winding. This last one rattled so loudly, even with no load connected, that it was just unacceptable. Mechanical hum coming from a transformer winding can be just as annoying as hum coming from the speakers.

So, in my attempt to address it, I first removed the power transformer from the chassis and powered it up with no load--still buzzed just as loudly. I then removed both end bells and powered it up again and it was quiet as a mouse.

So what's causing this hum only when the end bells are connected (I asked myself)? Some form of rigidity that is in place when the end bells are bolted down I thought. The entire transformer internals are wound on a plastic bobbin, then Mylar taped all around to hold all the wires in place. The wires themselves appear tightly wound.

I figured if I could anchor the bobbin to the iron core somehow that would not create weird magnetic hysteresis, this might reduce or eliminate the buzzing. Sure enough...taking several strips of cardboard folded back on itself and jamming those pieces into the area between the top of the bobbin and bottom of the iron core so that there was some damping of the rattling, seemed to cure it.

In my case the transformer was big enough where I needed to jam in cardboard pieces on both sides and on both ends of the bobbin.

Additionally, for just a bit more mechanical isolation, I got some rubber washers from the hardware store and placed those between the bottom of the end bell mounts and the top of the chassis where the transformer was mounted.

Doing both of those things has nearly completely cured the buzz. Transformer whispers along now with only a very slight buzz that is not discernible more than a foot or so away from the amp, even under full electrical load. So this is a "process" I am now going to apply for every Edcor power transformer I purchase.

Thought others might want to know about this little hack. Wood wedges might also work in place of cardboard--the kind you use to position a door frame in its mounting.
 
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Wedging the bobbin to the core sounds like a plan,,, I got lucky with chokes a couple of times by soaking the windings/core with varnish and letting it drip dry.... seemed to bond everything together... Rubber washers or grommets between the tx and chassis helps also... I have a phono preamp I built that needs to get this treatment!
 
I've used toroids in the past that buzz loudly between the hours of say 6 pm and 11 pm but are quiet at other times. Attributed that to a slight DC offset on the AC house wiring during those hours, maybe from a lot of the neighbors running their washing machines, vacuums, blenders, AC compressors, or maybe perhaps even the solar power inverters not up to snuff. (we have a lot of solar roof top systems in our area).
 
That's sad that Edcor don't bond the former/bobbin to the core :thumbsdown:

Premium end transformers have often used varnish dipping, or even vacuum impreg, and earlier method was to fully bathe the transformer in pitch within a box cover or bell-ends.

The 'wedge' technique sounds fine, especially if you can coat the material with some kind of glue or high-temp silicon rubber to restrain future movement, or any uneven pockets.
 
That's a good idea Tim. Next time I do this I will try wood wedges with silicon high temp glue slathered on them.
 
I just solved the high frequency buzz in my power transformer after years of experimentation. First I poured varnish on the PT while it was hot .of course I took off the thin plastic housing covers so the varnish would seep all over the laminations . My transformer stopped buzzing. I was very happy . But a year later the high tone buzz came back ,it was a pain . Obnoxiously loud. I tried gormets rubbers washers and tried all possible position s .

Today I flipped my PT and discovered the housing frame beneath which clips the PT tight was expanded from one of the sides . I put a good quality slim piece of hard teak wood only underneath that side and attached the screws through the PT legs and to the chassis. No gormets ,rubbers ,washers . I turned the screws just tight enough until the buzz went away . I dint make it too tight as the wood piece i used for stuffing wasn't very thin .

Here is a pic of the frame which clips the PT from down . You can see the frame has some how bent outwards over time (I don't know how ) so that was the reason my pt started buzzing . It's supposed to be clipped tight to the laminations touching it in parallel order .
2018-04-23_12.06.06.jpg
 
allanmatters said:
Here is a pic of the frame which clips the PT from down . You can see the frame has some how bent outwards over time (I don't know how ) so that was the reason my pt started buzzing . It's supposed to be clipped tight to the laminations touching it in parallel order .]
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Most of the smaller transformers are simply held together by a part of the frame clamping the laminations together. So, mounting the transformer securely is what is keeping its shape. I guess i have been fairly lucky in that issue of transformer vibrations has not been much of a problem. For my own builds i always try to get a potted trans.
 
primosounds said:
Most of the smaller transformers are simply held together by a part of the frame clamping the laminations together. So, mounting the transformer securely is what is keeping its shape. I guess i have been fairly lucky in that issue of transformer vibrations has not been much of a problem. For my own builds i always try to get a potted trans.
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I used to live in the gulf . I had shipped all my things back home in 2008 by ship. It took a month . My amplifier was in the cargo too . But god knows in what position the amplifier was placed by the people as it was clubbed with many other things

. Iam guessing it was probably placed in the wrong position like maybe tilted upwards from the front almost in a vertical position that is face up 90 degrees ,so due to the weight of the PT on a hanging side. it slowly shifted on one side causing the bend of the housing frame on the other side .

It took a month to reach by ship but then it was kept for another 6 months in storage in boxes unopened , so I am sure the position of the amp was not right for those 6 months . It was out of my control back then to even dream about it
 
allanmatters said:
I used to live in the gulf . I had shipped all my things back home in 2008 by ship. It took a month . My amplifier was in the cargo too . But god knows in what position the amplifier was placed by the people as it was clubbed with many other things

. Iam guessing it was probably placed in the wrong position like maybe tilted upwards from the front almost in a vertical position that is face up 90 degrees ,so due to the weight of the PT on a hanging side. it slowly shifted on one side causing the bend of the housing frame on the other side .

It took a month to reach by ship but then it was kept for another 6 months in storage in boxes unopened , so I am sure the position of the amp was not right for those 6 months . It was out of my control back then to even dream about it
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Moving is always a bitch. I hate moving.
 
Does anyone know what causes that sudden excitation or "vibration" when the end bells are brought close to the laminations? I tried the same process as the OP. First I took off the covers, almost dead silent. Then I brought them close while it was running and when I did, vibrations started up. Most of the sound seems to be coming from the covers, but maybe the core is starting to vibrate when they're brought close? Is there some sort of interaction with the covers, even though they're aluminum? The chassis is steel as well if that makes a difference. Although having just the covers off and the tranny sitting on some rubber washers on top of the chassis is very quiet.

Anyway, I tried jamming cardboard between the bobbin and laminations and that did help a bit. I also put strips of packing foam in the end bells as a test to see if that would help (I recall holding the covers with my hands and that seemed to dampen the sound, so I figured foam inside would too and it did a bit).

It's quieter now, but still the loudest in my fleet of tube amps. I'm just wondering if I also need to go back in and put rubber gasket material between the inside of the cover and the laminations to prevent any direct interaction there.

I also made little square pads of rubber gasket material for the tranny to sit on instead of directly contacting the chassis.

I tried with the tranny loaded and unloaded, same thing. I don't think it's faulty as there's been a couple other posts around the web about edcor power iron being noisy.

Any other thoughts would be appreciated!
 
Is the transformer itself making a mechanical buzz or is the buzz heard through the speakers? I’ve never had a situation where bringing the end bells in proximity to the transformer but not actually touching it caused a buzz either mechanical or amplified.

Steel chassis can sometimes be problematic since they conduct magnetic flux and can allow eddy currents to flow.
 
There's no buzz from the speakers, it's all mechanical. It also turns out, based on edcors website, that the bells are in fact steel. So between them, the steel chassis, and the iron core, maybe there's a loop happening? Basically hovering them over where they would otherwise be mounted about 1/4 inch away the vibration starts acting up. People mentioned the bells could be amplifying vibration, but there is no vibration if i just take off the bells and set the core up on some rubber washers and run the amp. Also, even now, with that packing foam inside and it up on that gasket material, there's less vibration with it all put back together. That being said, i can push on the bottom plate of the amp and can change the sound, so there might be some other reason vibration is getting in to the chassis. I want to say that one is caused by magnetic propagation as the transformer itself isn't really vibrating in and of itself. The only other thing I can think to do is pull it all back apart and do a better job wedging the space between the bobbin and laminations.
 
On my last build using an Edcor power transformer I potted it. That cured the vibration once and for all. I used thermally conductive epoxy that you normally use for setting ballast circuits in lighting arrays.

https://audiokarma.org/forums/index.php?threads/veruul-a-6av5-sweep-tube-amp.886571/#post-13151531

Only about 1 in 4 Edcor power transformers are quiet enough to use right out of the box in my experience. These days I just pot them all. It does add a little time and expense but well worth it in my opinion.
 
kward said:
...Additionally, for just a bit more mechanical isolation, I got some rubber washers from the hardware store and placed those between the bottom of the end bell mounts and the top of the chassis where the transformer was mounted...
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I used this same technique, with good results, to cure the mechanical buzz on the Edcor power transformer I used to replace the blown transformer in my Heathkit W-4. It is a shame that it seems Edcor has not addressed this transformer noise problem.
 
I have also had great luck dropping Edcor transformers in potting cans. Not because i heard a mechanical buzz, but because theres simply no easy way to mount these specific units.
This begs the question "why not send it back?" They market their products to amplifier builders. Hum is not a desireable characteristic of any amplifier, so you think they would try and make it right. Transformers arent exactly cutting edge technology and getting them to run quiet was something we had figured out nearly 100 years ago. Whats the issue all of a sudden guys?

Brings to mind a similar problem.
Mom bought a 2017 subaru, and it drank oil.
Come to find out the factory put out a service bulletin on the piston rings. They all fail and start to pump oil...
Piston rings have been settled science for 100 years. We know how to make good ones and we have it down to a science.

Wtf happened Subaru?
I put 400,000 miles on the 97 imprezza.

Someone cheaped out by saving a fraction of a cent per unit, got themselves a corner office and a beach house, and theyll never in their life have to change out a piston ring or a transformer which buzzes.

Its frustrating as hell.
 
To note, I've never ever had a Hammond power transformer that buzzed. I agree it's easily possible to build a quiet one. Also my builds may exacerbate the buzzing since I almost always use silicon rectification which switches off the current abruptly which may promote a little more buzz than when using a tube rectifier.

There was another thread a while back about buzzing Edcor power transformers (it was a sub theme within a larger thread) where the contributors were somewhat astonished that I had reported buzzing. Their reports were they (Edcor) never buzz. So go figure.

Personally I think Edcor's quality control drifts. I've seen wiring errors on their push pull output transformers as well. On the other hand, Edcor power transformers (other than the buzzing) are very well built, they are typically about 20% over rated so they run cooler, they are inexpensive, and they have a lot more choices available than Hammond.
 
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