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Volume control for balanced inputs

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Peter Menting

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Joined 2003
#1
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
 
#2
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.
 
#4
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
 
#8
This is the schematic for a balanced attenuator.
Input and output remain balanced.
 

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  • Balanced Attenuator.jpg
    Balanced Attenuator.jpg
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#13
Frank, thinking furter on the subject, using the schematic you posted would certainly compromize CMRR, which may not be important in a home where cables are likely to be rather limited in length, but more importantly, you would be compromizing the other advantage that balanced has over single ended, which is that signals are not ground referanced, so possibility for introducing ground loop issues is increased. (by the way, you left the ground connection out of the schematic). Another disadvantage in my opinion is it would require using two dual pots to control both channels. I think a better way would be to use something like this:

BALANCED ATTENUATOR.JPG

Mike
 
#14
Gentlemen; it would appear that this process involves a degree of uncertainty and I will experiment with both ideas. Initially however, I'll go with Volumite and judge whether or not to venture further. There is the possibility of single line level output pots from Ventus although that also has some drawbacks. Thank you for your input.
Brian look forward to getting the SPDIF module as it comes available.
Pete
 
#15
Michael Bean said:
Frank, thinking furter on the subject, using the schematic you posted would certainly compromize CMRR, which may not be important in a home where cables are likely to be rather limited in length, but more importantly, you would be compromizing the other advantage that balanced has over single ended, which is that signals are not ground referanced, so possibility for introducing ground loop issues is increased. (by the way, you left the ground connection out of the schematic). Another disadvantage in my opinion is it would require using two dual pots to control both channels. I think a better way would be to use something like this:

View attachment 241560

Mike
Click to expand...

A ground reference is not necessary on my circuit. When the pots are at maximum attenuation, the + and - (tip and ring) are connected together.
I've used your circuit and it works very well. The only problem is that the circuit provides signal attenuation ... even when the controls are at maximum resistance.
But you are correct. The circuit does compromise the CMRR. As you said, not a big problem with short cable runs. Not a big problem when using good quality shielded cables either.
 
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