Resistor Noises: How to reduce them - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 1st August 2005, 04:46 AM   #1
diyAudio Member
 
Join Date: Jan 2004
Location: Bangkok, Thailand
Default 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 2-ohm resistors and get the noise
power half of what we'd get had we used a 1 ohm resistor.
(Assuming 1-ohm and 2-ohm 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
  Reply With Quote
Old 1st August 2005, 07:25 AM   #2
bocka is offline bocka  Germany
diyAudio Member
 
Join Date: Jul 2003
Location: Hannover
Quote:
For example, we we want 1 ohm resistance, we can parallel 2 pieces of the 2-ohm resistors and get the noise power half of what we'd get had we used a 1 ohm resistor.
Paralleling two ideal 2 ohm resistors gives exactly the same noise figure as one 1 ohm resistor.
  Reply With Quote
Old 1st August 2005, 11:02 AM   #3
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
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.
  Reply With Quote
Old 1st August 2005, 11:41 AM   #4
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
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
  Reply With Quote
Old 1st August 2005, 01:37 PM   #5
diyAudio Member
 
Circlotron's Avatar
 
Join Date: Jun 2002
Location: Melbourne, Australia
Default Re: Resistor Noises: How to reduce them

Quote:
Originally posted by SeanPool
(Assuming 1-ohm and 2-ohm resistors generate equal noise
power)

Quote:
Originally posted by ilimzn
Resistor voltage noise En=2*SQRT(k * T * B * R)
R = resistance in ohms
High value resistors are noisier than low value ones, so what is gained by summing/cancellation of non-correlated noise from the paralleled resistors is is lost by having to use larger (noisier) resistors to begin with.

Blasted numbers!
__________________
Best-ever T/S parameter spreadsheet.
http://www.diyaudio.com/forums/multi...tml#post353269
  Reply With Quote
Old 1st August 2005, 02:03 PM   #6
diyAudio Member
 
Join Date: Jan 2003
Location: Hyderabad, India
Send a message via Yahoo to johnthetweeker
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.
__________________
John (not the baptist)
  Reply With Quote
Old 1st August 2005, 06:32 PM   #7
diyAudio Member
 
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:
Resistor voltage noise En=2*SQRT(k * T * B * R),
Yes, the "average" noise power generated by paralleling n resistors will be the same (not larger, not smaller) as using only one resister. (The average noise power is found using the autocorrelation of the voltage across the resistor, assuming the voltages across the resistors are uncorrelated and have zero mean).

-Sean
  Reply With Quote
Old 1st August 2005, 06:40 PM   #8
diyAudio Member
 
Join Date: Jan 2004
Location: Bangkok, Thailand
Thanks John.. The web is very informative.


-Sean
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Clicking noises... audio-kraut Digital Source 2 23rd December 2006 04:06 PM
How to calc Resistor Values to reduce Voltage? riotubes Parts 6 31st October 2006 01:58 AM
HK 730 making noises... RockysDad Solid State 2 24th December 2005 01:45 AM
QUAD ESL 63 noises tabaregg Planars & Exotics 2 15th December 2004 11:28 PM
Rod Elliot P3A amp noises tktran Solid State 2 18th March 2003 08:04 PM


New To Site? Need Help?

All times are GMT. The time now is 04:12 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2