Shielding a Power Tranny

amisdad · 10th January 2006, 07:37 PM

I have built a 12AX7/EL84 SET, but need to eliminate some noise coming from the Power Tranny being too close to the output trannys. I had quite a bit of hum which was only noticable through headphones, but I moved the Output Trannys away which reduced the hum to a tollerable level though Headphones. I would like to eliminate it completely and I'm sure a proper shield would help even more. Is there a ready made, easilly available shield? What do you guys use? I could fabricate one, but what should I use?

anatech · 10th January 2006, 08:58 PM

Hi amisdad,
Try rotating the power transformer, or the output. Nail them down when you have the lowest level of hum.

-Chris

amisdad · 10th January 2006, 09:03 PM

Thanks for the reply. I have already found the positions with the least amount of hum which is very low. I'm sure if I had more room on my chassis, Id be able to get rid of it all, but I don't. So I'm thinking I need to make a shield. I've heard MU metal mentioned, but haven't found it yet. What exactly is it? Remember, I'm using this for headphones as well as Fostex/MLTL. The headphones are really sensitive and I want I silent noise floor.

anatech · 10th January 2006, 09:33 PM

Hi amisdad,
Try a steel shield first. I believe that copper sheet around the power transformer may help too, solder the ends and make it a close fit.

-Chris

Tony · 10th January 2006, 10:28 PM

this is it:

anatech · 10th January 2006, 10:41 PM

Okay, so remove it and have a listen (kidding!).

Do you have a piece of steel laying around to play with? Also, if you isolate the power transformer from the chassis, does the hum drop?

-Chris

tubelab.com · 11th January 2006, 01:15 AM

Several years ago I was working on a problem where the noise from the display (400Hz) was corrupting the VCO in a two way radio. Our mechanical engineering team had made some shields from several materials and I tested them all. The Mu-Metal shield worked the best, followed by cold rolled steel. I don't remember the details (20 years ago), but these two were the only materials that worked good enough. There were about 10 different ones including copper and aluminum.

Mu_Metal is a material designed for magnetic shielding. The metal case that a phono cartridge is made from is likely Mu-Metal.

beamnet · 11th January 2006, 08:09 AM

did they have a lead shield too?

lead whas the first thing thet came to mind for me..

Bas

EC8010 · 11th January 2006, 09:57 AM

Lead is for nuclear stuff - a very different kind of radiation...

beamnet · 11th January 2006, 10:12 AM

really?

so that means that i DO have to buy that nuclear fusion lifetime power supply on e-Bay!! Neat!!

So it works for subatomic particles....does that mean it is useless for magnetic shielding?

my experiments only covered earthed sheets of pertinax unetched pcb's

they did not make an audible difference. I gave up on magnetic shielding because someone said it was useless, but now i think of it, they shield speakers with steel too!

I WAS goint to add a steel shield between my trannies and the electronics, now my hopes are up for effectiveness!

Bas

10th January 2006, 07:37 PM	#1
amisdad diyAudio Member Join Date: Mar 2004 Location: Chicago	Shielding a Power Tranny I have built a 12AX7/EL84 SET, but need to eliminate some noise coming from the Power Tranny being too close to the output trannys. I had quite a bit of hum which was only noticable through headphones, but I moved the Output Trannys away which reduced the hum to a tollerable level though Headphones. I would like to eliminate it completely and I'm sure a proper shield would help even more. Is there a ready made, easilly available shield? What do you guys use? I could fabricate one, but what should I use?

10th January 2006, 10:28 PM	#5
Tony diyAudio Member Join Date: May 2003 Location: Palatiw, Pasig City	copper banding this is it: __________________ http://www.electronicslab.ph/forum/i...?topic=32688.0

11th January 2006, 01:15 AM	#7
tubelab.com diyAudio Member Join Date: Jul 2005 Location: South Florida	Several years ago I was working on a problem where the noise from the display (400Hz) was corrupting the VCO in a two way radio. Our mechanical engineering team had made some shields from several materials and I tested them all. The Mu-Metal shield worked the best, followed by cold rolled steel. I don't remember the details (20 years ago), but these two were the only materials that worked good enough. There were about 10 different ones including copper and aluminum. Mu_Metal is a material designed for magnetic shielding. The metal case that a phono cartridge is made from is likely Mu-Metal. __________________ Too much power is almost enough! Turn it up till it explodes - then back up just a little.

11th January 2006, 09:57 AM	#9
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	Lead is for nuclear stuff - a very different kind of radiation... __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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10th January 2006, 08:58 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi amisdad, Try rotating the power transformer, or the output. Nail them down when you have the lowest level of hum. -Chris

10th January 2006, 09:03 PM	#3
amisdad diyAudio Member Join Date: Mar 2004 Location: Chicago	Thanks for the reply. I have already found the positions with the least amount of hum which is very low. I'm sure if I had more room on my chassis, Id be able to get rid of it all, but I don't. So I'm thinking I need to make a shield. I've heard MU metal mentioned, but haven't found it yet. What exactly is it? Remember, I'm using this for headphones as well as Fostex/MLTL. The headphones are really sensitive and I want I silent noise floor.

10th January 2006, 09:33 PM	#4
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi amisdad, Try a steel shield first. I believe that copper sheet around the power transformer may help too, solder the ends and make it a close fit. -Chris

10th January 2006, 10:41 PM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Okay, so remove it and have a listen (kidding!). Do you have a piece of steel laying around to play with? Also, if you isolate the power transformer from the chassis, does the hum drop? -Chris

11th January 2006, 08:09 AM	#8
beamnet diyAudio Member Join Date: Jun 2004 Location: enschede	did they have a lead shield too? lead whas the first thing thet came to mind for me.. Bas

11th January 2006, 10:12 AM	#10
beamnet diyAudio Member Join Date: Jun 2004 Location: enschede	really? so that means that i DO have to buy that nuclear fusion lifetime power supply on e-Bay!! Neat!! So it works for subatomic particles....does that mean it is useless for magnetic shielding? my experiments only covered earthed sheets of pertinax unetched pcb's they did not make an audible difference. I gave up on magnetic shielding because someone said it was useless, but now i think of it, they shield speakers with steel too! I WAS goint to add a steel shield between my trannies and the electronics, now my hopes are up for effectiveness! Bas

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