Should a linear supply buzz or hum?

LordRadio · 12th January 2012

I'm not talking about the audio side, but the actual physical unit, if running under normal conditions - should it hum? I am assuming its the vibration coming from the transformer? It's mostly an annoyance in my dead silent control room but, yeah.

Any thoughts would be greatly appreciated!

tINY · 12th January 2012

That happens sometimes when the laminations aren't quite right on the xformer. Sometimes you can fix it by tightening screws or adding a clamp and rubber sheeting...

-tINY

LordRadio · 12th January 2012

Thanks Tiny!

._. · 13th January 2012

There are circuits you can build that eliminates toroid noises, I saw that on a diy site somewhere. But that noise only show up under certain circumstances apparently.

Maybe in some cases you can cast it in rubber/plastic?

Matt Syson · 13th January 2012

Hi
As Tiny said it is possible that a bit of careful tightening of screws may cure it.
Experiment by pressing on various parts using an insulated rod (pencil with rubber or similar)
to locate what is actually vibrating. It could be the laminations of a cheaply made transformer or even a piece of steel near the transformer that is responding to the magnetic field.
When you have found out you need a plan to stop it!
High temperature varnish on laminations, bits of rubber etc to stop metal vibrating.
Matt S

JohnRoberts · 13th January 2012

Yup, the force that causes the hum/buzz is a natural effect, different transformer construction is better or worse about silent running, and marginal sizing of the transformer iron for flux density can aggravate noise output. I have a cheap microwave that I can hear the even cheaper transformer complain at low line voltage.

I also encountered an obscure transformer noise from a trick dual voltage output DC-DC convertor. The design used a HF transformer and regulated the two outputs with the one transformer. It also buzzed at mains frequency like a buzz saw. I replaced the relatively expensive HF transformer with a simpler 1 voltage design, and used a linear regulator for the lower rail. A simple potted single inductor ran silently, as it should.

JR

sonick909 · 13th January 2012

I have 3 big Astron linear power supplies for my ham rigs and HF amp, and they all hum and run hot. Just the nature of the beast. If you get a buzz, then a screw or fastener etc. has worked it's way out due to the constant hum.

12th January 2012	#1
LordRadio Gear maniac Joined: Jan 2008 Posts: 231 Thread Starter	Should a linear supply buzz or hum? I'm not talking about the audio side, but the actual physical unit, if running under normal conditions - should it hum? I am assuming its the vibration coming from the transformer? It's mostly an annoyance in my dead silent control room but, yeah. Any thoughts would be greatly appreciated!

13th January 2012	#5
Matt Syson Lives for gear Joined: Sep 2004 Location: UK Posts: 4,822	Hi As Tiny said it is possible that a bit of careful tightening of screws may cure it. Experiment by pressing on various parts using an insulated rod (pencil with rubber or similar) to locate what is actually vibrating. It could be the laminations of a cheaply made transformer or even a piece of steel near the transformer that is responding to the magnetic field. When you have found out you need a plan to stop it! High temperature varnish on laminations, bits of rubber etc to stop metal vibrating. Matt S __________________ Matt S www.mseaudio.co.uk

13th January 2012	#6
JohnRoberts Lives for gear Joined: Nov 2006 Location: Hickory, MS Posts: 2,046	Yup, the force that causes the hum/buzz is a natural effect, different transformer construction is better or worse about silent running, and marginal sizing of the transformer iron for flux density can aggravate noise output. I have a cheap microwave that I can hear the even cheaper transformer complain at low line voltage. I also encountered an obscure transformer noise from a trick dual voltage output DC-DC convertor. The design used a HF transformer and regulated the two outputs with the one transformer. It also buzzed at mains frequency like a buzz saw. I replaced the relatively expensive HF transformer with a simpler 1 voltage design, and used a linear regulator for the lower rail. A simple potted single inductor ran silently, as it should. JR __________________ John Roberts www.CircularScience.com

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12th January 2012	#2
tINY Gear Guru Joined: Jul 2004 Location: Orygun Posts: 10,230	That happens sometimes when the laminations aren't quite right on the xformer. Sometimes you can fix it by tightening screws or adding a clamp and rubber sheeting... -tINY

13th January 2012	#7
sonick909 Gear Head Joined: Dec 2011 Posts: 68	I have 3 big Astron linear power supplies for my ham rigs and HF amp, and they all hum and run hot. Just the nature of the beast. If you get a buzz, then a screw or fastener etc. has worked it's way out due to the constant hum.