Can a buzzing transformer be fixed?

[guy48065]

Yesterday when browsing topics I saw a meme indicating that transformer hum causes the worst kind of stress headache. LOL
So I guess it's a common annoyance yet I didn't find any discussion of it when Searching for it.
I have this issue with the big amp that powers my subwoofers. With no signal my room is very quiet except for this transformer buzz. I have verified it truly is a mechanical buzz--not electrical hum coming out of the speakers.

Is there a fix for this problem or is it the end of the line for a vintage amp?

 

[somebodyelse]

It depends on the cause. Some related threads:
https://www.audiosciencereview.com/...-dc-blocker-to-help-stop-transformer-hum.948/
https://www.audiosciencereview.com/forum/index.php?threads/my-toroids-buzz.22587/post-750007
https://www.audiosciencereview.com/...hiit-vidar-amplifier-review.12633/post-375903

 

[Waxx]

Sometimes potting the transformer in resin can resolve this, but it has to be done right. The right material to do it is also not that common availeble, and often only in big quantities (so not so diy friendly).

 

[ZolaIII]

Douse it buzz without lo level inputs (RCA) plugged in?
If not switch the cable for a better and preferably shorter one and try to move is away from AC cable and sources as much as you can.

 

[Deleted member 48726]

Which amp is that? What kind of transformer does it have?

 

[guy48065]

Which amp is that? What kind of transformer does it have?

It's a Dynaco ST400. Ordinary square xfmr.
Photo from the web--I've never been inside it.

 

[SCR]

Partial disassemble and vacuum potting with epoxy would be a solution if the windings vibrate on the core.

Depending on the device you could also have the transformer rebuild or a new one
build in the same packaging size.
If the transformer is still fully functional a competent transformer engineer can measure the voltages and current in situ, and deduct the windings and wire diameter for the windings.

 

[Deleted member 48726]

It's a Dynaco ST400. Ordinary square xfmr.
Photo from the web--I've never been inside it.

Thank you.

It looks like there are screws in each corner of the trafo. I would try to tighten those. There are also some kind of screws fastening it to the chassis. Those might also be in need of tightening.

 

[Deleted member 48726]

Partial disassemble and vacuum potting with epoxy would be a solution if the windings vibrate on the core.

Depending on the device you could also have the transformer rebuild or a new one
build in the same packaging size.
If the transformer is still fully functional a competent transformer engineer can measure the voltages and current in situ, and deduct the windings and wire diameter for the windings.

Those solutions would work. But do not make a cost benefit analysis on this kind of work! Crazy overkill for an old amp..

 

[SCR]

I would never do BOM thinking on a vintage

 

[Deleted member 48726]

I would never do BOM thinking on a vintage

I can tell!

 

[JayGilb]

You might be able to add some rubber grommets into the transformer/chassis mounting holes and see if that helps.
It's easy to dive into a rabbit hole trying different solutions without a satisfactory result.

 

[guy48065]

Not a problem when you enjoy the tinkering.

 

[Cbdb2]

Have you checked for DC on the incoming AC?

 

[guy48065]

Have you checked for DC on the incoming AC?

I've read that's an intermittent problem, and mostly noticed on toroids.
Mine is humming full time, and has for years.

I opened it up today. Lamination screws are tight, mounting screws are, too. Now I'm screwed.

 

[Deleted member 48726]

I've read that's an intermittent problem, and mostly noticed on toroids.
Mine is humming full time, and has for years.

I opened it up today. Lamination screws are tight, mounting screws are, too. Now I'm screwed.

Try to loosen it and mount it on little washers between it and the chassis.

 

[ChaZam]

Try to loosen it and mount it on little washers between it and the chassis.

I did this on an old step tranny I had and it worked like a charm.

 

[DanielT]

You might be able to add some rubber grommets into the transformer/chassis mounting holes and see if that helps.
It's easy to dive into a rabbit hole trying different solutions without a satisfactory result.

I made sure all the screws were really tight at the transformer and between the trafo and the chassis BUTt before that I cut out a rubber sheet and placed it between the transformer and the chassis of my vintage amp Luxor 7082A. It worked! I hardly hear the mechanical vibrations from the transformer now. Then I have to lean into the amp, almost put my ear to it, to hear that hum. So that fix worked for me anyway.

I am attaching blurry pictures that show a bit of how I did it.

 

[popej]

Buzzing can be due to transformer core saturation. This can happen because of too high input voltage, lower frequency or DC offset. If that is the case, you can try to lower supply voltage. Most electronics should work ok, only your amp will deliver less power.

I had the same problem with Paradigm subwoofer. My guess was that they have designed transformer for 60Hz, but my network is 50Hz. I have build a simple autotransformer to reduce voltage. I have bought standard transformer 230V:12V with power comparable to subwoofer supply, wired it as autotransformer an put it in a box with power cord and power socket. Then I have connected power supply through this box and no buzzing since then.

 

[Deleted member 48726]

Buzzing can be due to transformer core saturation. This can happen because of too high input voltage, lower frequency or DC offset. If that is the case, you can try to lower supply voltage. Most electronics should work ok, only your amp will deliver less power.

I had the same problem with Paradigm subwoofer. My guess was that they have designed transformer for 60Hz, but my network is 50Hz. I have build a simple autotransformer to reduce voltage. I have bought standard transformer 230V:12V with power comparable to subwoofer supply, wired it as autotransformer an put it in a box with power cord and power socket. Then I have connected power supply through this box and no buzzing since then.

That's actually something that can be an issue as well with vintage gear. Transformers designed with 220 VAC in mind and now we (at my place at least) get over 240 VAC