variable resistor - 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 13th May 2010, 07:02 PM   #1
akis is offline akis  United Kingdom
diyAudio Member
 
Join Date: Jul 2008
Default variable resistor

I want to examine the possibility of creating a variable resistor to retain the parameters of a normal, good quality fixed value resistor. The main quality is little or no change with temperature, current, voltage and frequency.

A potentiometer, I found, is too noisy and unstable, does not like DC through it and so on.

A simple transistor can act as a variable resistor between collector and emitter, unfortunately I do not know how to control it so its "resistance" stays the same regardless of Vce and Ic.

Any ideas? I skipped-read the thread about the LED controlled resistor thingy, and maybe this is a solution?
  Reply With Quote
Old 13th May 2010, 07:25 PM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Check out stepped attenuators.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 13th May 2010, 07:56 PM   #3
akis is offline akis  United Kingdom
diyAudio Member
 
Join Date: Jul 2008
Ah I see, a huge switch with dozens of resistors. Just like what I have on my ageing bench power supply.
  Reply With Quote
Old 13th May 2010, 08:11 PM   #4
akis is offline akis  United Kingdom
diyAudio Member
 
Join Date: Jul 2008
Forgot to say that is certainly a possibility and in that case I'd use just 4 settings, I would not need more. A rotary switch with 4 positions, and 4 resistors. Maybe 6 positions and 6 resistors.

But if I wanted something that will do the job on the PCB, not at the front panel so the signal does not have to travel over extra wires.
  Reply With Quote
Old 13th May 2010, 08:59 PM   #5
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Digital pot chip then.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 14th May 2010, 02:11 AM   #6
diyAudio Member
 
sumaudioguy's Avatar
 
Join Date: Jan 2010
Location: Midwest U.S.A.
I think the potentiometer problems you experience are from cheap pots. Try a wire wound in the 500 ohm size.

Like this except PCB? 43C1500 Honeywell Potentiometers

or this? Digi-Key - SP140-1.0K-ND (Manufacturer - 140-0-0-102)
__________________
What the other guy said----Standing on the shoulders of giants.
New avatar- no more little array
  Reply With Quote
Old 14th May 2010, 10:47 AM   #7
akis is offline akis  United Kingdom
diyAudio Member
 
Join Date: Jul 2008
These pots are very expensive, I can buy two Eminence Stonehenge 12" speakers for that price, and the speakers are the most crucial and expensive part.

My solution will be to use 4 or 6 resistors, placed very close to the transistor (1/4 "), so that the voltage across them stays close to the transistor. There will be 4 or 6 short leads/tracks to a rotary switch (1.5" track + 2-3" leads), and those will be connected to earth. The whole switch will be earthed. Hopefully this will limit noise and distortion.
  Reply With Quote
Old 14th May 2010, 11:15 AM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
the 12 position rotary switch is quite cheap.
It can be bought in 4 versions:
12w 1p
6w 2p
4w 3p
3w 4p
__________________
regards Andrew T.
  Reply With Quote
Old 14th May 2010, 11:28 AM   #9
akis is offline akis  United Kingdom
diyAudio Member
 
Join Date: Jul 2008
Yes I will use a rotary switch, I already have a bunch in my toolbox. The comment about "pots are very expensive" refered to the previous post and some very very expensive wire-wound pots
  Reply With Quote
Old 14th May 2010, 12:20 PM   #10
diyAudio Member
 
Join Date: Mar 2007
Location: Canandaigua, NY USA
What are you trying to do? Is this something that will be adjusted often like a volume control, or an internal function like bias that's just adjusted every now and then?

CH
__________________
I may be barking up the wrong tree, but at least I'm barking!
  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
Volume control : - pot' or pot' variable feedback resistor (gain) ? ash_dac Solid State 5 1st August 2006 05:07 AM
How do you make an audio potentiometer into a variable resistor? Darren Nemeth Parts 1 10th February 2005 07:15 AM
screen-plate resistor and grid leak resistor metebalci Tubes / Valves 4 26th February 2004 03:18 AM
Using a variable resistor in the feedback loop. darren01 Chip Amps 9 30th December 2003 10:05 AM
Potentiometer VS variable resistor for level adjusting Bricolo Everything Else 5 1st March 2003 01:31 AM


New To Site? Need Help?

All times are GMT. The time now is 11:56 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