Noisy transformer

[muuki]

Hi everyone

I recently bought a second-hand amplifier . Everything works fine, but the transformer makes a noise that's audible even from my sitting place. I got a DC blockers, which has reduced the noise, but it's still there. Is this an issue? Will it get worse?

Thanks in advance!

 

[DVDdoug]

Is this an issue?

Only to the extent that it bothers you.

Will it get worse?

Nobody can answer that!

If it's coming from inside the transformer there's probably nothing you can do. But if the transformer is causing something else to vibrate you can try tightening the screws (if it's mounted with screws) or maybe you can make a modification with rubber gromets or something like that...

 

[EERecordist]

I would highly doubt the DC blocker and would return it if you can.

Is this a tube power amp transformer? If there is mechanical vibration, you should be able to feel 50-60Hz vibration with your fingers. As others suggest, you might be able to create a soft mount. McIntosh the high end tube amp maker pots theirs in tar inside a metal can.

If it is electrical hum, very likely in an older amp or preamp, a tech can replace the electrolytic capacitors in the power supply and all the power supply bypass capacitors. It is time consuming because someone has to look up all the values and order replacements which fit the original part form factor.

 

[egellings]

Hi everyone

I recently bought a second-hand amplifier . Everything works fine, but the transformer makes a noise that's audible even from my sitting place. I got a DC blockers, which has reduced the noise, but it's still there. Is this an issue? Will it get worse?

Thanks in advance!

If it's an E-I laminated core transformer, it likely has 4 bolts holding the stack and end covers together. Maybe you could try tightening those a bit. If you remove the end covers and look at the bobbin (usually square or rectangular in cross section) the transformer is wound upon you may see a wedge piece stuck between the winding and the core, used to jam the center laminations together. Check that the wedge is tight, and if not find a way to tighten it a bit, either by replacing it with a larger one, or maybe just jamming it in a bit more. Of course if the transformer is a small high frequency switch mode type emitting a high frequency squeal, then I don't know how you'd remedy that outside of removing it and potting it and then reinstalling it. The power transformers on my home-brewed tube amps don't buzz, because apparently, they don't get high on electricity.

 

[Speedskater]

In the past, I have replaced the transformer bolts (and nuts & larger washers) with stainless steel ones.
Stainless steel bolts are stronger and can be tighten more.

 

[Count Arthur]

Stainless steel bolts are stronger and can be tighten more.

That's not actually correct. Bolts come in various grades with different properties and if you look at yield and tensile strength, stainless Grade A2 and A4 bolts are quite low. The only benefit of stainless bolts, is that they are stainless.

Grades of Bolts - Bolt Grade Marking Chart | AFT Fasteners

AFT Technical Resources. A chart to identify bolt grades using bolt grade markings; also provides a strength chart for common grade bolts.

www.aftfasteners.com

Regardless, you don't need to tighten a bolt with 200 N-m of torque for a transformer, so pretty much any grade will be fine.

 

[kyuu]

That's not actually correct. Bolts come in various grades with different properties and if you look at yield and tensile strength, stainless Grade A2 and A4 bolts are quite low. The only benefit of stainless bolts, is that they are stainless.

It depends. High-carbon steel is definitely stronger than stainless in most respects. However, stainless can be stronger than low-carbon steels. Also, it's generally more ductile than either, so it can deform more without breaking.

But of course you're right, you shouldn't be needing to torque anything in your electronics to the level where you need to worry about the strength of the bolt. Unless maybe it was made with pig iron.

 

[Speedskater]

I think that the original bolts were brass. Not magnetic steel.
But then was more than 30 years ago.

 

[muuki]

Hi

Thanks everyone for your input and explanations.

I’m trying to negotiate with the seller (I got it from a HiFi shop) to have it fixed, but he insists that it’s normal and happens with big transformers 200w to 8 ohms. The amp is from 2011-12.

I asked him to check the bolts to see if the problem can be solved. It’s still on guarantee.

 

[Zek]

he insists that it’s normal and happens with big transformers 200w to 8 ohms

If it's a 200W transformer, then it's not a big transformer and it's not normal to hear that hum.
If the amplifier has an output power of 200W at 8 ohms, then you need a much bigger transformer.
What amplifier is in question?

 

[HaveMeterWillTravel]

I think that the original bolts were brass. Not magnetic steel.
But then was more than 30 years ago.

Depending on the construction, non-magnetic may have some benefit. So low magnetic stainless steel may be better.
But any steel would be significantly 'stronger' than brass in any event.

Hi

Thanks everyone for your input and explanations.

I’m trying to negotiate with the seller (I got it from a HiFi shop) to have it fixed, but he insists that it’s normal and happens with big transformers 200w to 8 ohms. The amp is from 2011-12.

I asked him to check the bolts to see if the problem can be solved. It’s still on guarantee.

What amp make/model is this? Is this the main power transformer or an output transformer? (such as most tube or McIntosh amps)

In either case 200W into 8Ω is not a particular large nor uncommon amplifier. I have kilowatt class amps whose transformers make no noise.
*IF* an otherwise properly working power transformer is making audible noise, it often is due to an appreciable DC on the power.
If it were that and assuming the DC blocker was decent, it should have eliminated it.

Do you have access to a Volt/DMM to measure the DC across line and neutral?

 

[pjug]

Normal is probably not the right word but it is common enough. If it is loud enough to bother you I would not keep the amp since you are unlikely to do much about it. I have an old amp with a transformer that hums and I tried everything I could think of, even potting the thing under pressure. It still hums.

 

[muuki]

I forgot to post the outcome, the DC blocker completely eliminated the hum issue.