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Old 9th October 2008, 05:01 PM   #1
CJ900RR is offline CJ900RR  Sweden
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Question LME49810 fully balanced?

I've been lurking on a design for the LME49810 for a while now and then I started thinking, is it possible to make the design fully balanced, and maybe even the LM38** to?

I don't know so much about this but I was thinking something like the attached image. Is this doable and would I benefit from it? Have anyone here been doing a fully balanced design with a chipamp successfully?
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File Type: jpg balanced.jpg (54.9 KB, 639 views)
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Old 9th October 2008, 09:04 PM   #2
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Yes, our moderator, BWRX, has several different balanced chipamp designs.

But, it seems that balanced is the most standard way to design an amplifier regardless if input is three conductors or only two.

Opinion:
Our unbalanced amplifiers are really (in my opinion) supposed to be just like balanced amplifiers that "just happen" to have an RCA jack input.

Example, whatever you do to the "- input" is also supposed to be done to the "+input" else there's distortion. Thus, they're all supposed to be balanced or "reasonably" balanced. Funny way to look at it, isn't it?
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Old 10th October 2008, 06:09 PM   #3
AndrewT is online now AndrewT  Scotland
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Hi,
how do you control the gain?
What does that do to the impedance of the -ve input?
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Old 10th October 2008, 11:06 PM   #4
CJ900RR is offline CJ900RR  Sweden
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Quote:
Originally posted by danielwritesbac
Yes, our moderator, BWRX, has several different balanced chipamp designs.

But, it seems that balanced is the most standard way to design an amplifier regardless if input is three conductors or only two.
Hello Daniel!

Thanks for that, but I have all ready searched the forum and read about BWRX's adventures with the instrumental gainclone I have scattered a lot of info there but I still had to ask.


Quote:
Originally posted by AndrewT
Hi,
how do you control the gain?
What does that do to the impedance of the -ve input?
Hi Andrew. Sorry for that. It was meant to be a simplified image but I did it wrong as you have pointed out. Please see new image, still simplified though...
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File Type: jpg balanced.jpg (63.2 KB, 502 views)
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Old 11th October 2008, 08:26 AM   #5
AndrewT is online now AndrewT  Scotland
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pin 5 is a virtual earth.
Check the impedance on the -ve input.
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Old 11th October 2008, 08:24 PM   #6
BWRX is offline BWRX  United States
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Default Re: LME49810 fully balanced?

Quote:
Originally posted by CJ900RR
Is this doable and would I benefit from it?
It is doable and you would benefit from it if you used it with a balanced source. If you've already read through the LM3875 instrumentation thread then you know I chose to add the differential buffer because it will give you a high impedance input for both + and - inputs, allowing you to use both balanced and unbalanced sources.
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Old 11th October 2008, 10:56 PM   #7
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Default Re: Re: LME49810 fully balanced?

Quote:
Originally posted by BWRX
. . . add the differential buffer because it will give you a high impedance input for both + and - inputs, allowing you to use both balanced and unbalanced sources.
"Anvil-size" clue dropped.
Love those!
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