I've tried both the AnTec AS-4218 and AS-3218 which have a "static shield between primary and secondary coils to improve the isolation and noise interference. And they also have the magnetic shield around the outside to reduce the magnetic leakage." I'm assuming the magnetic shield AnTec uses may be Mu Metal, but not sure.
Still some hum that can be detected within 2 feet of the speakers (88 dB efficiency) but not at the listening position. Trying to figure out the next steps in quieting the hum.
Still some hum that can be detected within 2 feet of the speakers (88 dB efficiency) but not at the listening position. Trying to figure out the next steps in quieting the hum.
The ones I've seen (Amveco, I think) had what appeared to be a steel strip around the circumference, overlapped and tack welded. I say some sort of steel (?) as it was magnetic, slightly springy, and rusting. The outer steel strips were NOT grounded, unlike the interwinding electrostatic shield- in my case.
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.
The AnTeks are similar but the metal strip around the circumference of the toroid is under the plastic insulation wrap. Not sure if its grounded nor the type of material used (steel, Mu-Metal or ?).
It's a GOSS band (Grain Oriented Silicon Steel), magnetic sheilding; I've seen similar used on speaker magnets.
A picture for those who haven't seen one.
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I would be very interested to hear about your results with the mu metal in place. I'm using an Antek AS-4218 and also have a slight hum. Doesn't interfere with listening, but I know its there.
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. When I disconnect the source, the noise drops to 100uVrms (as measured with Fluke 101). Running unshielded Antek 400VA 18V trafo at front of 4U DIYA store 300mm deep Dissipante case with Edcors near the rear. Using Mark Johnson capacitance multiplier for the PSU (with 2 x 10,000uF caps ea).
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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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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/sol...sy-capacitance-multiplier-58.html#post5572538
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/sol...sy-capacitance-multiplier-58.html#post5572538
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.
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...
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.