Wiring Balanced Volume Pots? - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, 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 18th February 2010, 10:48 PM   #1
diyAudio Member
Join Date: Feb 2010
Default Wiring Balanced Volume Pots?

hi folks,

I'm new to the forum, and hoping someone can help me out with a project. I'd like to wire up a passive stereo volume control with balanced line-level XLR or TRS 1/4" inputs and outputs.

I plan to use a dual-gang 10K Ohm log taper pot, but can't find any resources for wiring the balanced cable. How should I handle the second signal wire in the XLR connnector? I suppose I could connect it to ground, but that would negate the benefits of the balanced signal and add to the noise potential.

Any links to wiring diagrams or other help would be very much appreciated!
  Reply With Quote
Old 18th February 2010, 11:47 PM   #2
diyAudio Member
Join Date: Jun 2004
Location: Raleigh North Carolina
Check out figure 17 in this article: Chapter 4

I use "configuration B" as a passive volume control in my system when I need one and it works fine. I use 5K series resistors and a 10K pot.

You can ignore the surrounding circuitry for your application - just connect pin 2 (or tip) to one input phase and pin 3 (or ring) to other phase. Do not ground either phase. Same for the outputs which go to the grids in the figure.

  Reply With Quote
Old 19th February 2010, 12:27 AM   #3
diyAudio Member
Join Date: Feb 2010
-- Sorry if this is a repeat post. My first attempt didn't seem to work! --

Thanks for the reply, Dave! I have a few questions about the configuration you linked to, if you don't mind answering:

If I understand the schematic, and that may be a long shot, you're suggesting that both + and - signals from the XLR input connect to the pot via their respective series resistors, the + phase to the wiper and + output, the - phase to the pot's input lug(?) and - output. Input and output grounds connect via common ground (or simply to each other? perhaps via the pot housing?). The ground lug on the pot remains empty, yes? My guess here is that the audible signal is attenuated by adding more of the inverse phase signal via the pot?

Thanks for the help and the series resistor values, too!
  Reply With Quote
Old 19th February 2010, 06:36 PM   #4
Davey is offline Davey  United States
diyAudio Member
Join Date: Dec 2001
Location: Bremerton, WA.
The following stage will be a balanced (differential amplifier) so if you reduce the variable resistor value to zero ohms the two outputs would be at the same potential (no difference) and you'd have zero output.

The circuit Dave mentioned is fine. The only recommendation I would make is to tie the unused potentiometer lug to the wiper so if the pot develops noise or intermittent contact it wouldn't create an open circuit.

Since you have a log-taper pot it will work differently depending upon which "direction" you wire it in the circuit.

Hope that makes sense.


  Reply With Quote
Old 19th February 2010, 06:54 PM   #5
diyAudio Member
Join Date: Feb 2010
Hey Davey. Thanks for the clarification, and the tip for the open ground lug. I actually prototyped the circuit this morning with parts I had lying around, and it seems to work just fine! I've ordered some better-quality parts for the actual build, so I'm now waiting for the postman!

  Reply With Quote
Old 19th February 2010, 10:04 PM   #6
diyAudio Member
Join Date: Jun 2004
Location: Raleigh North Carolina
Hi Studiodog,

Yes, your supposition is correct as you have found by modeling it. Davey's point is well taken for the unused pin on the potentiometer.

One other thing - if the frame of the pot is metal, it should be grounded to the chassis. There may be a ground lug connected to the frame of the pot but this pin is not connected to the resistive element of the pot. The resistive element should not be connected to ground.

  Reply With Quote
Old 20th February 2010, 12:58 PM   #7
diyAudio Member
Join Date: Feb 2010
Cheers, gents!
  Reply With Quote
Old 21st April 2010, 02:31 PM   #8
diyAudio Member
Join Date: Sep 2009
Default El-cheapo solution for test running Aleph P ?

Hi all,

just stumbled over this thread looking for a quick & dirty volume control for test running an Aleph P.

Could I stay with the given values of stereo 10k log and 5K resistor in series each rail ?

Thanks in advance for your help!

  Reply With Quote
Old 26th April 2010, 01:15 PM   #9
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Fig17 confB will give an impedance balanced output.
ConfA will be virtually impossible to set to balanced output if the tracking of the pots varies even very slightly.

You could substitute a precision matched stepped attenuator, but that is either going to be very expensive or take you a very long time to match all the steps to <0.01%
regards Andrew T.
Sent from my desktop computer using a keyboard
  Reply With Quote
Old 6th May 2013, 04:44 AM   #10
diyAudio Member
hschaser's Avatar
Join Date: Aug 2012
Location: Singapore
Hi I am a newbie on DIY projects and am very interested to make a volume control for my balanced input amplifiers which have no attenuator. I have got myself a 5k stereo pot with 6 terminals. I had tried wiring the pin 2+ on 1 input and pin 3 on the other input. With no ground attached. There is no attenuation at all when I plug it into my system. Pls advise. Your help is most appreciated.
  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
Wiring a DPDT for direct in & 2-100k mono pots ..? JandG Tubes / Valves 2 5th December 2009 03:51 AM
volume pots for tube amp Miller-8 Parts 5 16th February 2007 04:29 PM
removed volume pots GainClone Digidoo Chip Amps 4 9th April 2006 08:42 PM
Volume pots: Why are low values better? Christer Parts 11 9th January 2006 10:41 PM
Best Volume Pots? A3rd.Zero Parts 18 2nd May 2004 04:00 PM

New To Site? Need Help?

All times are GMT. The time now is 08:26 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