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Old 3rd May 2014, 02:19 PM   #1
tigox is offline tigox  Portugal
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Question Differential preamplifier

So, in my years studying amplifiers and preamplifier (still learning :P) I've only seen single ended preamplifiers if you might believe it; but lately I've dived a little bit into class d amplifiers, and i'm beginning to notice that many class d amplifiers if not all, have differential inputs, how do i build a filtered preamplifier for these differential inputs? :/
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Old 3rd May 2014, 02:44 PM   #2
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It is only the front end that is balanced, after the first op amp the signal is then unbalanced. +ve signal goes to +ve input and -ve signal to inverting input. The reason for balanced signal leads is to help with noise pickup with leads.
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Old 3rd May 2014, 03:51 PM   #3
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Originally Posted by JonSnell Electronic View Post
It is only the front end that is balanced, after the first op amp the signal is then unbalanced. +ve signal goes to +ve input and -ve signal to inverting input. The reason for balanced signal leads is to help with noise pickup with leads.
What do you mean by only the front end might i ask?

Oh, so these balanced inputs serve to eliminate noise from ground currents?
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Old 4th May 2014, 05:42 AM   #4
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Its not essential to have differential output to feed a differential input. Balanced ins do work OK when fed unbalanced outs. Yes having a balanced input can help rejection noise currents in grounds, unbalanced ins are particularly susceptible to that.
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Old 5th May 2014, 12:10 PM   #5
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Originally Posted by abraxalito View Post
Its not essential to have differential output to feed a differential input. Balanced ins do work OK when fed unbalanced outs. Yes having a balanced input can help rejection noise currents in grounds, unbalanced ins are particularly susceptible to that.
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Old 6th May 2014, 11:17 AM   #6
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Have you read Jensen's app note 003?

http://www.jensen-transformers.com/an/an003.pdf

section2.4 shows a cheap mod to allow every unbalanced Source to properly drive a balanced input and get the full benefit of the interference rejection of a balanced impedance connection.

If you are really interested in balanced connections then read the whole site:
http://www.jensen-transformers.com/apps_wp.html

and read all the balanced papers/articles of D.Self, Rane, Cordell, ESP, Pass
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Old 6th May 2014, 05:18 PM   #7
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Take a look at the OPA1632 datasheet -- all you need to know.
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Old 6th May 2014, 05:34 PM   #8
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Originally Posted by jackinnj View Post
Take a look at the OPA1632 datasheet -- all you need to know.
uhh.. i may be naive but i can't seem to find it :/
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Old 6th May 2014, 05:48 PM   #9
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http://www.ti.com/lit/ds/symlink/opa1632.pdf
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