Interesting site. Apparently they aren't concerned at all about RF Interference, as they offer no shielding what so ever. This is just a casual comment, after a casual browse of their site. Looks like lots of little antennas on the circuit boards.
I live very near a radio transmitter tower, so this is something I am concerned with a great deal.
I live very near a radio transmitter tower, so this is something I am concerned with a great deal.
kilowattski said:
Well, I've solved the issue about what to believe in such matters once and for all.
To me it's quite simple, we know that eddy currents is for real, and we know that RF noise is for real. I have failed to hear any influence on the music by eddy currents, but have frequently had RF niose problems due to cell phones,switch mode PSU's and motors.
Solution.....plenty of metal in the casing to keep the niose out.....and a lot of happy listening
Magura
anders.a said:
I personally couldn't care less about the magnetism of the heatsinks......if you take a look at the factors that we know influences the sound to an extent that we all can hear, the by far most important factor according to solid state devices and heatsinks is to make the best possible heat transfer from the device to the heatsink and to make the temperature steady and even for all the devices.
This is the reason I advocate sturdy heatsinks.
If you take a look at the average heatsink, the back-bone is too skimpy to actually utilize the heatsink. This is done in order to save material.
Like with engines "there is no replacement for displacement".
If you take a look at the heatsinks I use www.briangt.com/gallery/magura , you will see that they differ quite a bit from the heatsinks you see most people here use.
The heatsinks in the gallery are based on the same heatsinks as the ones I used for the AX-100 chassis "kits" I made for Steenoe and Seve.
They weigh in around 3kg. a piece
Magura
And I started playing with shielded wood for my cases. This is going to be the side wall of my stereo BrianGT 4780 chip amp. It's 6/4 walnut with a thin sheet of aluminum (flashing actually) laminated to it.
The steel box contains much of the EMI from the transformer, and the aluminum provides decent RFI from the outside world.
The steel box contains much of the EMI from the transformer, and the aluminum provides decent RFI from the outside world.
Attachments
This question is like the sex of the angels 
Aluminium is non magnetic if it’s pure! This is rare to find.... and very expensive!
In the market we find combinations of aluminium with and copper and others materials.
What I like in Al is the combination of low weight and thermal conductivity.
To isolate the transformer, caps and cables, I use a combination of kitchen aluminium sheets and plastic sheets.
You can find this in a Hypermarket.
This is how I do it:
-I cut 4 to 5 aluminium sheets
-Buy one box of 10 plastic A4 sheets
-Put the 4/5 aluminium sheets inside one plastic A4 sheet
-Use the cloth iron to glue it. ( use a towel between the iron and the plastic )
The plastic sheets that I am talking about are these ones:
(normally used in this kind of works)
Aluminium is non magnetic if it’s pure! This is rare to find.... and very expensive!
In the market we find combinations of aluminium with and copper and others materials.
What I like in Al is the combination of low weight and thermal conductivity.
To isolate the transformer, caps and cables, I use a combination of kitchen aluminium sheets and plastic sheets.
You can find this in a Hypermarket.
This is how I do it:
-I cut 4 to 5 aluminium sheets
-Buy one box of 10 plastic A4 sheets
-Put the 4/5 aluminium sheets inside one plastic A4 sheet
-Use the cloth iron to glue it. ( use a towel between the iron and the plastic )
The plastic sheets that I am talking about are these ones:
(normally used in this kind of works)
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Magnetism in aluminium - floating coils !!
I know that aluminium is not magnetic, as stated before in this thread, but isnt it inductive, i mean - if a magnetic field is imposed on an aluminium surface, it generates a opposite magnetic field. But it does not "remember" this magnetic field, ie it is only magnetic if influenced by a magnetic field ? Once we made an experiment with a large coil (severel kilos) that was placed on an aluminium plate (about 10 mm thick) and then connected it to a variac, and thus the large donut coil hovered about 1 cm above the aluiminium plate. Wouldnt the power field from a large toroid create the same effect, and thus induce some magnetism (and thereby voltage??) in a thick aluminium heat sink ??
Cheers !
Hans
I know that aluminium is not magnetic, as stated before in this thread, but isnt it inductive, i mean - if a magnetic field is imposed on an aluminium surface, it generates a opposite magnetic field. But it does not "remember" this magnetic field, ie it is only magnetic if influenced by a magnetic field ? Once we made an experiment with a large coil (severel kilos) that was placed on an aluminium plate (about 10 mm thick) and then connected it to a variac, and thus the large donut coil hovered about 1 cm above the aluiminium plate. Wouldnt the power field from a large toroid create the same effect, and thus induce some magnetism (and thereby voltage??) in a thick aluminium heat sink ??
Cheers !
Hans
You are perfectly right Hans, but the problem is that you have to choose between eddy currents and RF shielding. Eddy currents are usually not a problem if the grounding is made with a little common sense (star ground point). On the other hand shielding is a major issue, as noise is picked up from anything and everything if you have not done something to shield your amp. This is especially true for preamps, though I'd be hard pressed to explain why.
Magura
Magura
SMALl signals (low voltages) are more suseptable to RF interfereence, because with lower voltages, an RF induced voltage will be a larger percentage of the pverall signal.
For example, say you have a signal cable with a 2v p-p singnal and a speaker cable with 30v p-p signal exposed to the same RF interference. Let say the RF induced .01 V of noise. In the 2V singal, thats .5% of the overall signal, whereas in the speaker level signal, it's .03% (much less significant).
In addition, the low level signal is then going to be amplified, so that tiny RF induced signal is now quite large.
For example, say you have a signal cable with a 2v p-p singnal and a speaker cable with 30v p-p signal exposed to the same RF interference. Let say the RF induced .01 V of noise. In the 2V singal, thats .5% of the overall signal, whereas in the speaker level signal, it's .03% (much less significant).
In addition, the low level signal is then going to be amplified, so that tiny RF induced signal is now quite large.
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