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Old 24th September 2011, 08:24 PM   #11
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Well if CMRR isn't important, it would be easier to just use single ended.

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Old 24th September 2011, 08:34 PM   #12
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CMRR is very important at millivolt levels.
At line level, CMRR is far less troublesome.
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Old 24th September 2011, 09:17 PM   #13
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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

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Old 25th September 2011, 12:42 AM   #14
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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.
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Old 25th September 2011, 05:34 PM   #15
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Quote:
Originally Posted by Michael Bean View Post
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:

Attachment 241560

Mike
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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Old 25th September 2011, 05:58 PM   #16
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OK, I see it now, I stand corrected.

Mike
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Old 30th September 2011, 03:44 PM   #17
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If you do decide to use an analog volume control, you could just use a Joshua Tree, which would have fewer tracking issues compared to a multi-gang pot.
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Old 1st October 2011, 05:30 PM   #18
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Brian; Space/ cost are deal breakers for JT. Have ordered Volumite and chip and we'll see what happens after build is complete. Will be looking for SPDIF module as soon as it comes available.
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