Trimming ganged potentiometers with... trimpots? - 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 17th February 2005, 02:18 PM   #1
RHosch is offline RHosch  United States
diyAudio Member
Join Date: Sep 2003
Location: SouthEast
Default Trimming ganged potentiometers with... trimpots?

(Since the original posting of this thread in the Solid State forum had no replies after a couple of days, I thought I'd ask here and see if there was any more interest.)

It seems the most common usage of ganged potentiometers is for multichannel volume control, in which case you want a 0db attenuation option. However, suppose you want to control a variable resistance value in several channels at once, say for a filter applied to multiple channels, and the resistance range is >>0 to <infinity.

To bring for example a 0-50k pot into the correct range might require a 50k series resistor with each pot in the gang. Ganged pots are notoriously bad for matching between channels, but with 50k series resistance for each pot would it not make sense to use a PCB mount trimpot in series as well to obtain better matching? Such as a 40k fixed resistor and 10k trimpot? Or perhaps leaving the fixed resistor out completely? If there was concern about the coarseness of adjustment I suppose multiturn pots wouldn't break the bank.

I'd rather not get into "sound of different pots" discussions for now, and focus instead on practical problems. I can see two different methods for calibrating each channel; (1) measure the end resistance and trim so that all channels are matched, or (2) turn the ganged pot to a "median" or "most common" position (i.e., if the pot dial goes from 1-10, do the matching at 5), which should be a known value, and trim all channels to match that known value for that position. What pros/cons do you see for those two methods?

I'm not sure about the type of mismatching most common in pots. One would be a variation in end resistance with matched beginning resistances. i.e., three pots might read 0-50, 0-48, and 0-55. In that case each degree of turn would produce a different resistance change in each pot, and the trimming method above would simply shift the errors from one end to the other (or center the error, which in itself might be a good thing). The other would be shift in beginning resistance with good tracking between pots. i.e., three pots might read 2-50, 0-48, and 7-55. I somehow doubt things are that pretty.

Which error is most common? If it is the first, is the accumulation of error over the wiper range pretty linear, or is most of the variance in for example the first 10 degrees of wiper rotation?

Comments are most welcomed.
  Reply With Quote
Old 18th February 2005, 10:46 PM   #2
RHosch is offline RHosch  United States
diyAudio Member
Join Date: Sep 2003
Location: SouthEast
Well, with well over 100 combined views and no replies, I guess I'll just have to let you guys know the results after I've assembled a 10-gang pot and tried this technique to improve matching.
  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
Advice on trimpots. Colescuttle Parts 6 29th March 2009 04:37 PM
Trimming ganged potentiometers with... trimpots? RHosch Solid State 1 16th February 2005 08:05 PM
6-Ganged Potentiometers? EchoWars Parts 36 24th August 2003 09:51 PM

New To Site? Need Help?

All times are GMT. The time now is 08:21 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