Volume control for balanced inputs - diyAudio
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Old 23rd September 2011, 08:38 PM   #1
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Default 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
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Old 23rd September 2011, 08:57 PM   #2
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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.
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Old 24th September 2011, 01:24 PM   #3
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I would use a Volumite for the Opus. Cheaper, easier and better.
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Old 24th September 2011, 05:10 PM   #4
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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
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Old 24th September 2011, 05:41 PM   #5
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Spdif modules will be available in a couple weeks (waiting on a batch of boards)
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Old 24th September 2011, 06:17 PM   #6
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Using a dual pot on balanced input will totally destroy common mode rejection ratio.

Mike
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Old 24th September 2011, 06:24 PM   #7
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Quote:
Originally Posted by Michael Bean View Post
Using a dual pot on balanced input will totally destroy common mode rejection ratio.

Mike
No it will not.
The circuit remains balanced.
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Old 24th September 2011, 07:26 PM   #8
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This is the schematic for a balanced attenuator.
Input and output remain balanced.
Attached Images
File Type: jpg Balanced Attenuator.jpg (14.8 KB, 515 views)
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Old 24th September 2011, 08:05 PM   #9
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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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Old 24th September 2011, 08:12 PM   #10
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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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