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Official M2 schematic
Official M2 schematic
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Old 10th October 2018, 07:21 AM   #3111
qwertyl is offline qwertyl  United Kingdom
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Originally Posted by xrk971 View Post
Nitto No. 597B Mu-Metal (Ultraperm 80) sheeting formed into a 44mm L x 35mm W x 16mm deep rectangular cover (self stick adhesive on one side makes construction easy) placed over Edcor brings 500uV rms noise at output down to 300uV.
Have you just glued the box onto Edcor? Is it grounded?
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Old 10th October 2018, 10:39 AM   #3112
xrk971 is online now xrk971  United States
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Glued on using self stick adhesive in inside. Not grounded.
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Old 10th October 2018, 11:30 AM   #3113
qwertyl is offline qwertyl  United Kingdom
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Glued on using self stick adhesive in inside. Not grounded.
Thanks. Will try to do the same.
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Old 13th October 2018, 11:07 PM   #3114
WKCox is offline WKCox  United States
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I have a 2' x 4" x 0.01" piece of Mu-Metal foil coming from McMaster Carr to experiment with shielding. Kind of an expensive experiment at $122 for this small piece.
Two U-shaped pieces of foil, rotated 90 degrees from each other, that clip on the Edcor. Reduces hum by slightly greater than 50%. Can now hear hum only within 1 foot from the woofer in a very quite room.
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Old 14th October 2018, 04:26 AM   #3115
xrk971 is online now xrk971  United States
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Using the self adhesive corner tabs for a tight seal with mumetal foil, I got 80% reduction.

I finally solved my ground loop hum problem with single power trafo and two cap Mx with one pair of bridges cs two pairs. Bridges power pair of cap Mx in parallel. Noise of now 100uV rms on one channel and 300uV rms on the other.

https://www.diyaudio.com/forums/soli...ml#post5572538
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Old 14th October 2018, 02:02 PM   #3116
qwertyl is offline qwertyl  United Kingdom
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Mu-metal boxes on Edcors and steel tubes around power toroids - noise almost completely gone
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Old 14th October 2018, 02:26 PM   #3117
xrk971 is online now xrk971  United States
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Originally Posted by qwertyl View Post
Mu-metal boxes on Edcors and steel tubes around power toroids - noise almost completely gone
Nice work - glad the my metal shield worked for you too.

Great idea to use use black iron plumbing trimmings for trafo shield. Will have to see if there are any scraps from my local hardware store.
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Old 14th October 2018, 02:50 PM   #3118
qwertyl is offline qwertyl  United Kingdom
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Nice work - glad the my metal shield worked for you too.

Great idea to use use black iron plumbing trimmings for trafo shield. Will have to see if there are any scraps from my local hardware store.
Thanks. To be honest the steel shielding for power toroids didn't make much difference in my case, most noise reduction thanks to mu-metal boxes...
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Old 15th October 2018, 06:23 PM   #3119
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Originally Posted by WKCox View Post
Two U-shaped pieces of foil, rotated 90 degrees from each other, that clip on the Edcor. Reduces hum by slightly greater than 50%. Can now hear hum only within 1 foot from the woofer in a very quite room.
Thanks for sharing this info! Have you experimented with raising the transformer above the mounting plate? In my case, I found that raising the toroid approx. 1" on a block of wood reduced the hum significantly. It had a far greater effect than rotating the transformer, or even mounting it vertically. Just a thought..
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Old 16th October 2018, 12:34 AM   #3120
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Thanks for sharing this info! Have you experimented with raising the transformer above the mounting plate? In my case, I found that raising the toroid approx. 1" on a block of wood reduced the hum significantly. It had a far greater effect than rotating the transformer, or even mounting it vertically. Just a thought..
Very interesting! No, I have since mounted the transformer vertically, using an L-bracket which helped reduce, but not eliminate the noise. I have not tried raising the transformer. Sounds like something I will try. Thanks for the tip.
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