Im trying to figure out a solution. I have an 15k/15k input transformer that is wound on a bobbin with nickel. Sounds amazing, but im getting buzz and hum. I have a cinemag input trafos, which are expensive, and I use it as my reference, and when connected to my amp, its super quiet. Having said that, Im trying to find a unique solution, but on the cheap. Im wondering if I coat the transformer with a heavy Shellac or other type of resin. Step 2, apply a 2-3 coats of this EMI Nickel Shield over the shellec coat. Then possibly put this input tranfos in a small plastic box, that is coated on the inside and outside. Giving this 3 barriers of EMI protection. Here is the Emi shield in a can
MG Chemicals 841 MGC-841 Super Shield Nickel Conductive Coating
Or is there a source for cheap MU Cans?
Mu Metal Shielding Cans | Magnetic Shields Limited
MG Chemicals 841 MGC-841 Super Shield Nickel Conductive Coating
Or is there a source for cheap MU Cans?
Mu Metal Shielding Cans | Magnetic Shields Limited
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Two quite different problems, two quite different solutions:
1. unwanted RF coming in or out: apply thin conductive layer (e.g. spray-on nickel)
2. unwanted low frequency magnetic fields coming in or out: place inside mu-metal shield
1. unwanted RF coming in or out: apply thin conductive layer (e.g. spray-on nickel)
2. unwanted low frequency magnetic fields coming in or out: place inside mu-metal shield
iron is cheaper - low carbon steel may be less effective than mu meta sheet but you can use thicker and most importantly more air spaced layers to redirect mag field
old style "tin can" may help, can bend up a box out of low carbon soft steel
it could be useful to reduce the interfering mag field at its source - twist power wires with their return path to reduce loop areas
"buzz and hum" suggest rectifier/cap line power xfmr currents are not being treated correctly, large loop areas from poor wiring/gnd choices and/or common path for the noisy rectifier/Cap current peaks and signal ground
hint - don't use the power xfmr CT as chassis/safety ground
I designed Scientific/Industrial instrumentation, including strain gage amps with Av up to 8000, transducers at the ends of 50' of cable and never used mu metal
old style "tin can" may help, can bend up a box out of low carbon soft steel
it could be useful to reduce the interfering mag field at its source - twist power wires with their return path to reduce loop areas
"buzz and hum" suggest rectifier/cap line power xfmr currents are not being treated correctly, large loop areas from poor wiring/gnd choices and/or common path for the noisy rectifier/Cap current peaks and signal ground
hint - don't use the power xfmr CT as chassis/safety ground
I designed Scientific/Industrial instrumentation, including strain gage amps with Av up to 8000, transducers at the ends of 50' of cable and never used mu metal
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It has the belly band as you can all see in the pic. But it doesn't seem to correct the problem.
How do I know if its: Unwanted RF coming in or out ?
Or
Unwanted low frequency magnetic fields coming in or out ?
Rayma was so thoughtful to send me a out a sheet of MU so I can bend up a box test. So this will be very helpful, Thanks Again Rayma!
Do I earth ground the MU box ?
Here is my cinemag. Its so quiet, its wonderful. But too expensive...
http://cinemag.biz/line_input/PDF/CMLI-15-15B.pdf
Notice the resistors in the primary and secondary. I wonder if I put some R's if that will help. However it would change the impedance.
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Experience? Actually, you can't tell for certain as RF can sometimes sound like buzz if it is modulated but buzz/hum are probably coming in as low frequency.erik777 said:
You are aware that mu metal always needs re-annealing after any metalworking?
Not necessary for magnetic shielding.
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