Resistor distortion - diyAudio
Go Back   Home > Forums > Design & Build > Parts
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

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
Thread Tools Search this Thread
Old 11th December 2010, 08:13 PM   #1
Art M is offline Art M  United States
diyAudio Member
Join Date: Oct 2010
Location: SF Bay Area
Default Resistor distortion

How do I go about selecting resistors that exhibit a low Voltage Coefficient of resistance when presented with the large voltage swings present in a power amplifier ? It appears that the distortion problem was discussed about at:

Slones 11.4 'Blameless'

I have not been able to find any further information with references to specific part classes.

This note talks about the problem:
  Reply With Quote
Old 11th December 2010, 08:58 PM   #2
jcx is offline jcx  United States
diyAudio Member
Join Date: Feb 2003
Location: ..
Default Vishay, Caddock, Alpha...

"Bulk metal resistors have almost unmeasurable voltage

or make all of your feedback dividers out of equal valued, identical type reisistors - they will each have the same power and temp rise - to the degree their individual thermal environments match - then the division ratio is independent of temp, V coefficients

Last edited by jcx; 11th December 2010 at 09:00 PM.
  Reply With Quote
Old 11th December 2010, 09:58 PM   #3
diyAudio Member
Join Date: Mar 2001
Location: Auburn, WA (somewhere between Seattle and Tacoma)
Blog Entries: 1
Send a message via ICQ to Damon Hill
Resistive voltage coefficient, unlike temperature coefficient (and noise), is a little-recognized source of non-linearity; perhaps a very minor contributor overall but worth minimizing since distortion in audio design is otherwise being driven down to very tiny levels. I think it's possible to classify by basic resistor material types, and then by specific manufacturers and products.

Carbon resistors (composition or film) have the worst voltage coefficient, then metal oxide and cermet; metal film, and wirewound and bulk metal foil have the least. Metal film resistors with the lowest Tc often claim a lower voltage coefficient, such as Vishay-Dale's PTF series.

Thus you'd be looking for a Tc of 100 ppm, preferably 25 ppm or better; Vishay's Z-foil resistors are below 1 ppm and probably the most stable resistor made. Unfortunately, they are very expensive and nearly unavailable in resistance above about 250 Kohms. I use the older bulk foil types because they're more commonly available and a bit less expensive. Caddock is a highly regarded manufacturer of high voltage and high resistance parts.

Also, derate resistors by using a higher wattage part where space permits; many film resistors are rated for less than a quarter watt and may be otherwise perfectly suitable for a given application, but a physically larger part with say a half-watt rating will be less stressed by heat and voltage.

Traditionally, many tube afflictionados prefer the "warm" sound of composition resistors and dislike the "sterile" neutral sound of the better quality film and bulk metal types. Vishay's bulk metal foil resistors can be thought of as miniaturized wirewound
with a non-inductive construction. I'm not sure whether inductance really matters in most audio resistor applications; overall quality of construction and perhaps in end cap construction are cited as potential sources of non-linearity, too.
  Reply With Quote
Old 13th December 2010, 08:00 AM   #4
diyAudio Member
Join Date: Dec 2005
Location: Kuala Lumpur
Voltage coefficient gets worse at higher values, so putting a few cheap metal oxide resistors in series wins twice - lower values and less voltage on each part
  Reply With Quote
Old 13th December 2010, 01:11 PM   #5
expert in tautology
diyAudio Member
bear's Avatar
Join Date: Apr 2002
Location: New York State USA
There is/was a discussion of this in the John Curl Blowtorch Pt II thread...

_-_-bear -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
  Reply With Quote
Old 13th December 2010, 01:30 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Default SMD resistor distortion

was it 5th element that reported a massive drop in measured (not simulated) distortion when he changed an SMD resistor for another with higher voltage rating?
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote


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
Which resistor type for emitter resistor? sajti Parts 25 8th April 2009 06:12 AM
K50 lm1875 feedback resistor distortion waz664 Chip Amps 7 3rd October 2007 07:21 AM
Non Linear Distortion testing - Harmonic Distortion JMB Multi-Way 0 20th July 2004 02:54 PM
screen-plate resistor and grid leak resistor metebalci Tubes / Valves 4 26th February 2004 03:18 AM
What is the best resistor? CryingDragon Solid State 8 9th October 2002 02:38 AM

New To Site? Need Help?

All times are GMT. The time now is 11:41 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2