Log or Lin? - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 22nd February 2008, 09:58 PM   #1
diyAudio Member
 
Aidan135711's Avatar
 
Join Date: Feb 2008
Default Log or Lin?

Finally got my LM4766T amp going.Now I need a pot.
Ready made stepped attenuators are too expensive and I can't seem to find enough info on how to build my own so I choose to use some sort of high accuracy stereo pot.
Do I use a 100k log or 100k lin pot for input?
Or can someone show me the way to some stepped att. diagrams?
  Reply With Quote
Old 22nd February 2008, 10:12 PM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
It depends on the input impedance of the chip amp. If you want to use a 100k pot which is quite high impedance, I would try a linear pot.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 22nd February 2008, 10:21 PM   #3
diyAudio Member
 
Aidan135711's Avatar
 
Join Date: Feb 2008
I just checked the datasheet and it shows 10k pot on input.My mistake.
So,if I use 10k pot ,should it be log or lin?
  Reply With Quote
Old 22nd February 2008, 11:09 PM   #4
diyAudio Member
 
Join Date: Oct 2004
Use a log.
  Reply With Quote
Old 22nd February 2008, 11:17 PM   #5
diyAudio Member
 
Join Date: May 2006
Just found this on another post, enjoy!

http://www.penguinlovers.net/audio/Attenuator.html


Cheers
Sparks
  Reply With Quote
Old 23rd February 2008, 08:55 AM   #6
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Yes if 10k use logarithmic.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 23rd February 2008, 11:00 AM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
you can use a lin with log faking resistor added.

The slight advantage of the lin track is better matching of resistance. This can affect balance between channels and becomes a bigger problem at high attenuation rates.

When mimicing a log pot with a lin pot+faking resistor it is usual to select a lin~=10times log value and then add a wiper to signal ground resistor ~10%to 15% of lin pot value.
eg 10klog or 100klin+12k resistor.
__________________
regards Andrew T.
  Reply With Quote
Old 23rd February 2008, 05:53 PM   #8
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Hi guys!

I've noticed that some sources, usually (not always) headphone sources, may have a cap at the output that causes the bass to vanish if a 10k pot is used.

Unless tried, you wouldn't believe that Alpha's A20K ($1) plus ordinary 24 gauge solid conductor copper, could be a viable solution.

Whether that's true or not, it can give you a baseline from which to evaluate other options.
  Reply With Quote
Old 23rd February 2008, 06:44 PM   #9
diyAudio Member
 
Aidan135711's Avatar
 
Join Date: Feb 2008
I just read profsparks link about building a ladder stepped att.
I might have a go at making one of those,however in his resistor calculator table,should position 1 read -80db not -8db,or am I mis-understanding something?

http://www.penguinlovers.net/audio/Attenuator.html
  Reply With Quote
Old 24th February 2008, 09:49 AM   #10
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
-80db or -infinitydb are the choices. The 8 is an attempt to write the symbol for infinity which is similar to an 8 on it's side with the right hand end open.
If Rg=0 then attenuation is theoretically infinity.
If Rg = 1r0 then attenuation is -80db.
__________________
regards Andrew T.
  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



New To Site? Need Help?

All times are GMT. The time now is 03:59 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