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-   -   Volume control for balanced inputs (http://www.diyaudio.com/forums/twisted-pear/197180-volume-control-balanced-inputs.html)

Peter Menting 23rd September 2011 09:38 PM

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

Frank Berry 23rd September 2011 09:57 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 02:24 PM

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

Peter Menting 24th September 2011 06:10 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 06:41 PM

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

Michael Bean 24th September 2011 07:17 PM

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

Mike

Frank Berry 24th September 2011 07:24 PM

Quote:

Originally Posted by Michael Bean (Post 2722638)
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 08:26 PM

1 Attachment(s)
This is the schematic for a balanced attenuator.
Input and output remain balanced.

Michael Bean 24th September 2011 09:05 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 09:12 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.


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