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Old 2nd November 2003, 09:33 PM   #1
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Default Discussions on Balenced Amplifers

ok, this is a subject which i think is pretty interesting. i must say that there is an interest on this forum about balenced inputs and outputs.

now so far the best gainclone only balenced implementaion was just 2 amplifers giving a differential in - differential out.

the only single gainclone implementation i've seen was a AC-coupled difference amplifer. the problem is that this circut isn't balenced unless there is no signal or noise. otherwise the noise rejection will depend upon the voltage to the noninverting terminal, so more noise = less rejection of noise!

i made a simple volume control that is balenced, but it is obviously conditionally balenced -- it works on the principle that the source and destination is balenced.

now i was looking over the specs of the lm4780, mind you not the choice of many, but still the CMRR of the chip falls severly, so any noise rejection will be limited more to lower frequencies. fine this works for hum if hum is the problem.

so i wanted to start a hopefully meaningful discussion on how best to implement a balenced input amplifer
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Old 3rd November 2003, 07:17 PM   #2
GregGC is offline GregGC  Canada
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What do you say about that?
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Old 3rd November 2003, 08:01 PM   #3
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Default Re: Discussions on Balenced Amplifers

Quote:
Originally posted by theChris
so i wanted to start a hopefully meaningful discussion on how best to implement a balenced input amplifer
Here's my two cents worth.

se
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Old 3rd November 2003, 10:49 PM   #4
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Quote:
Originally posted by GregGC
What do you say about that?

the input impedce for input 1 is dependent on the input voltage for input 2, thus the circut isn't really balenced, just a difference amplifer.

as for the transformer, well, no arguments there
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Old 12th November 2003, 08:21 AM   #5
mskeete is offline mskeete  United Kingdom
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do a search on the google for superbal
you can find an example circuit here
http://www.dself.dsl.pipex.com/ampin...d/balanced.htm
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Old 12th November 2003, 06:12 PM   #6
agent.5 is offline agent.5  United States
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How about a tube balanced to unbalanced converter, as the buffer of an IGC?

http://www.tubecad.com/june99/page12.html
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Old 12th November 2003, 06:43 PM   #7
Mad_K is offline Mad_K  Norway
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Quote:
Originally posted by mskeete
do a search on the google for superbal
you can find an example circuit here
http://www.dself.dsl.pipex.com/ampin...d/balanced.htm

This is one of the pages I read when making my bal. gainclone

I can't understand what all the fuzz is about. min. 45dB CMRR, and 0,00078dB signal imbalance (10 ohm SE output Z from source). Who needs higher performance than this for audio?
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Old 12th November 2003, 07:58 PM   #8
GregGC is offline GregGC  Canada
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Mad_K,

I guess the fuzz is that +in has 110k impedance to GND and -in 9.1k impedance to gnd in your case.
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Old 13th November 2003, 04:58 AM   #9
Mad_K is offline Mad_K  Norway
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my XBZLS couldn't care less
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Old 13th November 2003, 05:10 AM   #10
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Default Re: Re: Discussions on Balenced Amplifers

Quote:
Originally posted by Steve Eddy


Here's my two cents worth.

se
A much better idea than most of the others presented.
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