redresseur is the word for rectifier in french..
On the shielding issue, I had great success in magnetically induced hum reduction in my dht pre-amplifier by putting it inside a steel can. (Aluminum chassis) Mine was made by audio marginal in Quebec some years ago, but there are other sources now - take a look in the back of any recent audioexpress.
The steel can reduced hum at the output of the left channel of my pre-amp by more than 12dB. The output transformer was just a little too close to the power transformer..
You may also be able to find a steel can at one of your local hamfests..
On the shielding issue, I had great success in magnetically induced hum reduction in my dht pre-amplifier by putting it inside a steel can. (Aluminum chassis) Mine was made by audio marginal in Quebec some years ago, but there are other sources now - take a look in the back of any recent audioexpress.
The steel can reduced hum at the output of the left channel of my pre-amp by more than 12dB. The output transformer was just a little too close to the power transformer..
You may also be able to find a steel can at one of your local hamfests..
Thought I'd resurrect this thread, as I am in process of building a combination DAC/Raven preamp with power supply, all on same chassis.
Sides are made of teak wood, top plate is nickel plated steel.
I was considering the idea of shielding the DAC/signal portion of the wood chassis with either copper foil or nickel foil, both available from McMaster Carr for a somewhat reasonable price. I can get continuous lengths such that no soldering is needed (also avaliable in aluminum, brass, and stainless).
The way I see it, run a length of the foil around the circuitry under concern (cutting through the middle of the chassis), but don't close the loop, hopefully avoiding circulating currents. Bond the foil to chassis ground at one point.
Copper would give me good emi/rfi protection, as would the steel top plate. Just the bottom is exposed, which I suppose doesn't help the RF factor much. Every little bit helps, tho.
Would there be any advantage or disadvantage to using the nickel foil, with its magnetic shielding properties? I could easily shield the signal circuitry, but not easily shield the trannies. It seems to me this approach would confine spurious magnetic fields to the nickel foil, keeping it out of the sensitive innards. One bonding point avoids circulating currents. Eddy currents should be low due to physical distance from tranny to nickel foil.
Good idea, bad idea, or anal retentive?
Sides are made of teak wood, top plate is nickel plated steel.
I was considering the idea of shielding the DAC/signal portion of the wood chassis with either copper foil or nickel foil, both available from McMaster Carr for a somewhat reasonable price. I can get continuous lengths such that no soldering is needed (also avaliable in aluminum, brass, and stainless).
The way I see it, run a length of the foil around the circuitry under concern (cutting through the middle of the chassis), but don't close the loop, hopefully avoiding circulating currents. Bond the foil to chassis ground at one point.
Copper would give me good emi/rfi protection, as would the steel top plate. Just the bottom is exposed, which I suppose doesn't help the RF factor much. Every little bit helps, tho.
Would there be any advantage or disadvantage to using the nickel foil, with its magnetic shielding properties? I could easily shield the signal circuitry, but not easily shield the trannies. It seems to me this approach would confine spurious magnetic fields to the nickel foil, keeping it out of the sensitive innards. One bonding point avoids circulating currents. Eddy currents should be low due to physical distance from tranny to nickel foil.
Good idea, bad idea, or anal retentive?
Zigzagflux how much sheilding do you need ? I have some mu metal sheet a piece about 15"x 20" 1/16" thick.
Mu-metal is a alloy containing mostly nickel around 75% and the rest is iron. Copper, stainless steel, and aluminium will do nothing as far as sheilding magnetic flux period it won't work ,your thinking of a Fardays cage which stops emf.
Magnetic shielding materials need to conduct magnetic lines of force but preferably not become magnetized and mu metal doesn't.
Steel will work as Tubelab said, cold rolled work best because rolling it cold strains the crystalline structure stretching in only one direction. This forces the domains line up which can make it magnetized but this can be removed by heating it past 400 degrees Fahrenheit.
Hot rolled steel is rolled at a temp where the steel in a diffrent crystalline state. This structure changes as it cools and re-crystallizes which relieves some of the stress in the crystal lessening the magnetic properties.
The problem with using steel is if it becomes magnetized it can effect chokes or other inductors if there field lines are parallel to each other.
Zigzagflux pm me with how much you need and I will give it to you all I ask is you pay the shipping.
Nick
Mu-metal is a alloy containing mostly nickel around 75% and the rest is iron. Copper, stainless steel, and aluminium will do nothing as far as sheilding magnetic flux period it won't work ,your thinking of a Fardays cage which stops emf.
Magnetic shielding materials need to conduct magnetic lines of force but preferably not become magnetized and mu metal doesn't.
Steel will work as Tubelab said, cold rolled work best because rolling it cold strains the crystalline structure stretching in only one direction. This forces the domains line up which can make it magnetized but this can be removed by heating it past 400 degrees Fahrenheit.
Hot rolled steel is rolled at a temp where the steel in a diffrent crystalline state. This structure changes as it cools and re-crystallizes which relieves some of the stress in the crystal lessening the magnetic properties.
The problem with using steel is if it becomes magnetized it can effect chokes or other inductors if there field lines are parallel to each other.
Zigzagflux pm me with how much you need and I will give it to you all I ask is you pay the shipping.
Nick
jnb said:
Exactly. I'm doing the same. Originally was going to use copper foil, but the discovery of nickel made me think about the magnetic issues. As long as I'm splitting the chassis, why not surround the whole audio section, for optimal shielding?
nhuwar said:
Yes, which is why I re-thought the copper path, and am considering nickel. Appreciate the offer Nick; if I am going to take this approach, I may take you up on it. A small fee is no problem to me. The only benefit to buying from McMaster is that I can get a continuous strip. I will need at least 4"x40", I think
I guess I still want to conclude the procedures. Now that I think about the nickel foil, it somewhat makes sense for there to be a complete magnetic path, whereas before I considered NOT closing the loop. To close or not to close, that is the question. I lean towards closing.
Try these guys:
http://www.lessemf.com/mag-shld.html
They seem to have about a million different shielding materials, including mu-metal. My understanding is that mu-metal is very difficult to work; whenever you cut or bend it, it's permeability drops quite a bit.
Aloha,
Poinz
http://www.lessemf.com/mag-shld.html
They seem to have about a million different shielding materials, including mu-metal. My understanding is that mu-metal is very difficult to work; whenever you cut or bend it, it's permeability drops quite a bit.
Aloha,
Poinz
I was offering because I have about 150 pounds of the stuff in various shapes and sizes. As for the drop in permeability I'm not sure I will have to look up data on it but that can be reversed by heating above it re-crystallization temp it after you form it which I don't know right now but I can look it up at work tomorrow.
In case you where wondering how I know all these stuff I have been a metalugical technician for 10 years so I know a little bit about metal.
I just looked at mcmaster 20 bucks a foot for a 4 mil thick piece by 4 inch's thats pricey but it's adhesive back which is very very nice so I guess I would pay for the convenience.
But just6 in case the offer still stand.
Nick
In case you where wondering how I know all these stuff I have been a metalugical technician for 10 years so I know a little bit about metal.
I just looked at mcmaster 20 bucks a foot for a 4 mil thick piece by 4 inch's thats pricey but it's adhesive back which is very very nice so I guess I would pay for the convenience.
But just6 in case the offer still stand.
Nick
Yah, that's what I understood; that it's a heat treat/annealing issue.
So, post back; how hot you got to get it, and (being ferrous), how slow you got to cool it down? A lot of these high alloys are air hardening, so you got to actively slow the cooling process, or they'll harden.
And, how much does the permeability actually drop, I wonder. Down like iron? A few percent? It's easy to blow effects like this out of proportion.
A Hui Hou,
Poinz
So, post back; how hot you got to get it, and (being ferrous), how slow you got to cool it down? A lot of these high alloys are air hardening, so you got to actively slow the cooling process, or they'll harden.
And, how much does the permeability actually drop, I wonder. Down like iron? A few percent? It's easy to blow effects like this out of proportion.
A Hui Hou,
Poinz
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