Volume control for balanced inputs

Peter Menting · 23rd September 2011, 08:38 PM

Have a Ventus that currently uses single ended input with an individual volume control for each channel. (Old ears need more adjustments!) Am switching to Opus to drive it and am uncertain as to how to wire pots when using balanced input. Any help for the newby/old guy?
Pete

Frank Berry · 23rd September 2011, 08:57 PM

If you are feeding a balanced output into a balanced input, you can build a volume control using a dual (stereo) pot for each channel.
It's wired just like any other level control pot. The + preamp output goes through one section and the - preamp output goes through the other section.
Do the same for the other channel.
There are other methods if you can afford to lose some audio level between your preamp and your power amp.

BrianDonegan · 24th September 2011, 01:24 PM

I would use a Volumite for the Opus. Cheaper, easier and better.

Peter Menting · 24th September 2011, 05:10 PM

Frank; Thanks for the info--I wondered if the dual pot was necessary---also have some concern over the tracking error between pot halves and what effect it might have.
Brian; I will start out with Volumite and see what my "earspeakers" tell me. By the way, any idea when the SPDIF module will come available again? It and volumite are the last links in the chain for my headamp.

Pete

BrianDonegan · 24th September 2011, 05:41 PM

Spdif modules will be available in a couple weeks (waiting on a batch of boards)

Michael Bean · 24th September 2011, 06:17 PM

Using a dual pot on balanced input will totally destroy common mode rejection ratio.

Mike

Frank Berry · 24th September 2011, 06:24 PM

Quote:

Originally Posted by Michael Bean

Using a dual pot on balanced input will totally destroy common mode rejection ratio.

Mike

No it will not.
The circuit remains balanced.

Frank Berry · 24th September 2011, 07:26 PM

This is the schematic for a balanced attenuator.
Input and output remain balanced.

Michael Bean · 24th September 2011, 08:05 PM

To retain high common mode rejection ratio the resistances must be matched to high precision, that's not going to happen with pots in there.

Frank Berry · 24th September 2011, 08:12 PM

It's line level.
In the real world, the slight difference in resistance between the + and - legs of the attenuator will not be a problem.

23rd September 2011, 08:38 PM	#1
Peter Menting diyAudio Member Join Date: Jul 2003 Location: Blackstone VA	Volume control for balanced inputs Have a Ventus that currently uses single ended input with an individual volume control for each channel. (Old ears need more adjustments!) Am switching to Opus to drive it and am uncertain as to how to wire pots when using balanced input. Any help for the newby/old guy? Pete

23rd September 2011, 08:57 PM	#2
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	If you are feeding a balanced output into a balanced input, you can build a volume control using a dual (stereo) pot for each channel. It's wired just like any other level control pot. The + preamp output goes through one section and the - preamp output goes through the other section. Do the same for the other channel. There are other methods if you can afford to lose some audio level between your preamp and your power amp. __________________ Frank

24th September 2011, 01:24 PM	#3
BrianDonegan diyAudio Member Join Date: Dec 2004 Location: Rock Ridge	I would use a Volumite for the Opus. Cheaper, easier and better. __________________ Twisted Pear Audio

24th September 2011, 05:41 PM	#5
BrianDonegan diyAudio Member Join Date: Dec 2004 Location: Rock Ridge	Spdif modules will be available in a couple weeks (waiting on a batch of boards) __________________ Twisted Pear Audio

24th September 2011, 08:12 PM	#10
Frank Berry diyAudio Member Join Date: Sep 2003 Location: Midland, Michigan	It's line level. In the real world, the slight difference in resistance between the + and - legs of the attenuator will not be a problem. __________________ Frank

24th September 2011, 05:10 PM	#4
Peter Menting diyAudio Member Join Date: Jul 2003 Location: Blackstone VA	Frank; Thanks for the info--I wondered if the dual pot was necessary---also have some concern over the tracking error between pot halves and what effect it might have. Brian; I will start out with Volumite and see what my "earspeakers" tell me. By the way, any idea when the SPDIF module will come available again? It and volumite are the last links in the chain for my headamp. Pete

24th September 2011, 06:17 PM	#6
Michael Bean diyAudio Member Join Date: Sep 2004 Location: Minneapolis, Minnesota, USA	Using a dual pot on balanced input will totally destroy common mode rejection ratio. Mike

24th September 2011, 08:05 PM	#9
Michael Bean diyAudio Member Join Date: Sep 2004 Location: Minneapolis, Minnesota, USA	To retain high common mode rejection ratio the resistances must be matched to high precision, that's not going to happen with pots in there.

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