Noisy transformer

evanc · 17th December 2010, 08:20 PM

let me start by saying I am very new at this DIY audio stuff. Maybe this is something I should know, but I don't.

some time ago I built an aikido pre amp. I got the all in one board and parts from glassware audio. I used an Antek toroidal transformer 300 VA 230 volt. So far so good.

recently I finished a salas phono pre amp and shunt regulator. Still good. I noticed the phono pre got quieter when I put it's transformer in it's own box

The Aikido is fairly quiet, but not dead quiet, so I figure I should put it's transformer in it's own enclosure. I go ahead and find a steel box that just fits over the transformer and still fits in the preamps chassis. Great I think until I turn the thing on. The transformer buzzes and the center bolt gets hot?! I unplug it and check that I didn't short something out. I didn't. Take the box out It works fine put it in and it buzzes. Tell me why.....
Thanks, Evan

Bill_P · 17th December 2010, 08:26 PM

The chassis, box and bolt form a shorted turn. Insulate the bolt and try it again.

evanc · 17th December 2010, 08:34 PM

Bill, thanks for the time. You mean the box is acting like part of the transformer? I'm not sure I get it, but I will try isolating the bolt. I thought the box should be grounded to work as a better shield.
thanks again, Evan

Bill_P · 17th December 2010, 08:36 PM

You can keep the box grounded. Your present configuration has a continuous metal path through the center of the transformer and around the outside. This path needs to be broken somewhere and insulating the bolt from the box with a shoulder washer is probably easiest.

evanc · 17th December 2010, 08:37 PM

Easy enough...Thanks again

17th December 2010, 08:20 PM	#1
evanc diyAudio Member Join Date: Sep 2009 Location: New Jersey. About 1 hour from NYC and 1 min. from the beach	Noisy transformer let me start by saying I am very new at this DIY audio stuff. Maybe this is something I should know, but I don't. some time ago I built an aikido pre amp. I got the all in one board and parts from glassware audio. I used an Antek toroidal transformer 300 VA 230 volt. So far so good. recently I finished a salas phono pre amp and shunt regulator. Still good. I noticed the phono pre got quieter when I put it's transformer in it's own box The Aikido is fairly quiet, but not dead quiet, so I figure I should put it's transformer in it's own enclosure. I go ahead and find a steel box that just fits over the transformer and still fits in the preamps chassis. Great I think until I turn the thing on. The transformer buzzes and the center bolt gets hot?! I unplug it and check that I didn't short something out. I didn't. Take the box out It works fine put it in and it buzzes. Tell me why..... Thanks, Evan

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17th December 2010, 08:26 PM	#2
Bill_P diyAudio Member Join Date: Sep 2009 Location: New York, the vampire state	The chassis, box and bolt form a shorted turn. Insulate the bolt and try it again.

17th December 2010, 08:34 PM	#3
evanc diyAudio Member Join Date: Sep 2009 Location: New Jersey. About 1 hour from NYC and 1 min. from the beach	Bill, thanks for the time. You mean the box is acting like part of the transformer? I'm not sure I get it, but I will try isolating the bolt. I thought the box should be grounded to work as a better shield. thanks again, Evan

17th December 2010, 08:36 PM	#4
Bill_P diyAudio Member Join Date: Sep 2009 Location: New York, the vampire state	You can keep the box grounded. Your present configuration has a continuous metal path through the center of the transformer and around the outside. This path needs to be broken somewhere and insulating the bolt from the box with a shoulder washer is probably easiest.

17th December 2010, 08:37 PM	#5
evanc diyAudio Member Join Date: Sep 2009 Location: New Jersey. About 1 hour from NYC and 1 min. from the beach	Easy enough...Thanks again

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