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Old 27th April 2013, 01:59 PM   #1
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Islander
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Question "Balanced" PGA2311?

Inspired by Bruno Putzeys "balanced volume controller", which is described in his article "The G Word" in the latest Linear Audio Vol. 5, I tried to make use of his explanations for a simple preamp with the ubiquitous PGA2311 instead of a potentiometer. I attached the schematic I've come up with until now, however there is a thing I'm not quite sure of: Is it even worth the effort? I'm using RCA connectors for the inputs and outputs, since I don't have any XLR equipment. Does my example here have any advantages over the "classic" ground plane or star ground attempts in this case? Does it make a difference at all? Or is it even worse?
Please tell me wether building this is promising or a waste of time...
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Old 27th April 2013, 02:10 PM   #2
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Hi Lasse,

Not sure from which angle you're coming. Bruno's very smart solution is for a balanced preamp where you want to control volume without very expensive pots. With his solution the only parameter to control the volume is the pot rotation of angle and, of course, that is inherently matched with a dual pot on a single spindel.
A PGA has an inherent matching of better than 0.5dB so the problem doesn't exist.
So if you want a single ended preamp and a PGA, the solutions to take from his article are those related to grounding, and you can read what his opinion is about planes and stars, the reasoning behind it and the solutions.

jan
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Old 27th April 2013, 02:18 PM   #3
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Hi Jan,

Quote:
Originally Posted by jan.didden View Post
So if you want a single ended preamp and a PGA, the solutions to take from his article are those related to grounding, and you can read what his opinion is about planes and stars, the reasoning behind it and the solutions.
I was treating the PGA like a simple pot in this case, since it has input, output and analog ground - three connections like a simple pot. This is not about the matching but the grounding. I was trying to make use of the figure 14 in the chapter "Let the Strong Help the Weak", and so I adapted his preamp circuit for this purpose. At least I thought I did...
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Old 27th April 2013, 02:26 PM   #4
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OK, I get you.

In following the article reasoning, you'd connect the ground references of the PGA to the ground references of the stage driving it, which is the right-hand side of the bottom 1k.

Then you need to check the Rout of the PGA and to make sure that both sides are impedance-balanced, maybe need to adjust one of the 22 ohms.

jan
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Last edited by jan.didden; 27th April 2013 at 02:28 PM.
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Old 27th April 2013, 02:52 PM   #5
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Thanks Jan, I'll give it a try.
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