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1st August 2005, 03:46 AM  #1 
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Join Date: Jan 2004
Location: Bangkok, Thailand

Resistor Noises: How to reduce them
I just figured if we parallel n exact same resistors together,
we will get 1/n times the noise power of each resistor. For example, we we want 1 ohm resistance, we can parallel 2 pieces of the 2ohm resistors and get the noise power half of what we'd get had we used a 1 ohm resistor. (Assuming 1ohm and 2ohm resistors generate equal noise power). Is this already well known besides the fact that n parallel resistors would reduce the tolerance error by n times? Any opinions? Sean 
1st August 2005, 06:25 AM  #2  
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Quote:


1st August 2005, 10:02 AM  #3 
diyAudio Member

when designing regulators balance the amount of current drawn in the error sense circuit with the theoretical noise  i.e. if you have enough current to spare, 1 milliamp drawn by the divider will be less noisy than 100 microvolts  seems simple enough.

1st August 2005, 10:41 AM  #4 
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Join Date: Feb 2005
Location: Zagreb

Resistor voltage noise En=2*SQRT(k * T * B * R),
k = Bolzman constant T = temperature B = bandwidth of interest R = resistance in ohms Depending on material you also have other noise sources, usually proportional to current. Paralleling n resistors does not reduce noise or tolerance by a factor of n, but by a factor of SQRT(n) because the noise in n resistors is not correlated. If you use that fact and include it in the equation above, you will see that n parallel resistors of X ohms generate exactly the same noise voltage as a resistor of X/n ohms. I would say you have assumed a bit too much about your facts 
1st August 2005, 12:37 PM  #5  
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Re: Resistor Noises: How to reduce them
Quote:
Quote:
Blasted numbers!
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1st August 2005, 01:03 PM  #6 
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Yes, lower resistence means lower noise, whether you use a single resistor or paralleled bunch. But there is some dependency on the type of resistor you use. Wirewound resistors are quieter than the other types.
Take a look here: http://www.aikenamps.com/ResistorNoise.htm To reduce thermal noise, you could try cooling down the circuit with a peltier block or something. But practically, you may have to cool down to liquid nitrogen temperatures to get significant reduction in noise. John.
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1st August 2005, 05:32 PM  #7  
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Join Date: Jan 2004
Location: Bangkok, Thailand

Your opinions are much appreciated. I was wrong I see now that my assumption that the noise power was independent of the resistance is way too much. I agree with ilimzn:
Quote:
Sean 

1st August 2005, 05:40 PM  #8 
diyAudio Member
Join Date: Jan 2004
Location: Bangkok, Thailand

Thanks John.. The web is very informative.
Sean 
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