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Old 27th June 2003, 01:23 AM   #1
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Default Why not "instrumentation amplifiers"

ok, I was reading one of the ADI ap-notes on instrumentation amplifiers, I realize that they aren't any good as integrators and differentiators, are somewhat expensive -- but why aren't people using them as gain blocks in audio applications? Is it just the expense, is it the necessity of nulling offset, <em> dit a mois pour
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Old 27th June 2003, 04:38 AM   #2
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Default Maybe you don't use them.......

I know people who do.....especially for balanced inputs.

Jocko
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Old 27th June 2003, 06:02 AM   #3
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... because most people don't listen
to instrumental music ? .......



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Old 27th June 2003, 06:26 AM   #4
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Lots of people DO use them. I have a phono stage design which uses BB INA103's in the front end.

They can be quite good, amazingly good, but as you stated, they aren't as universal as an op-amp.


Sheldon
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Old 27th June 2003, 06:42 AM   #5
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Default Re: Why not &quot;instrumentation amplifiers&quot;

Quote:
Originally posted by jackinnj
ok, I was reading one of the ADI ap-notes on instrumentation amplifiers, I realize that they aren't any good as integrators and differentiators, are somewhat expensive -- but why aren't people using them as gain blocks in audio applications? Is it just the expense, is it the necessity of nulling offset, &lt;em&gt; dit a mois pour

...see:

http://www.jensen-transformers.com/an/ingenaes.pdf
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Old 27th June 2003, 06:59 AM   #6
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[QUOTE]Originally posted by stokessd
[B]Lots of people DO use them. I have a phono stage design which uses BB INA103's in the front end.

-----------------------------------------------
I have one of these in a Carver Active/Passive Preamp. The balanced output is passive; the single ended has gain and contains the IN103. In comparison with the passive mode, the single ended mode doen't sound very good at all - you wouldn't use it unless you MUST.
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Old 28th June 2003, 08:07 AM   #7
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Default they work...

yes,I built the design found in 'audio amateur' 6/95 ; 'An instrumentation preamp' and over the yrs. substituted various op-amps for the originally speced tl-072's. I am quite impressed with this simple design and still use it today-
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Old 28th June 2003, 09:10 AM   #8
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Default Re: they work...

Quote:
Originally posted by vince8
yes,I built the design found in 'audio amateur' 6/95 ; 'An instrumentation preamp' and over the yrs. substituted various op-amps for the originally speced tl-072's. I am quite impressed with this simple design and still use it today-

Do you have the schematic...can you post it?
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Old 28th June 2003, 01:07 PM   #9
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Default Re: they work...

Quote:
Originally posted by vince8
yes,I built the design found in 'audio amateur' 6/95 ; 'An instrumentation preamp' and over the yrs. substituted various op-amps for the originally speced tl-072's. I am quite impressed with this simple design and still use it today-
Are you sure the design wasn't in 2/95 "An Instrumentation Preamp" ?

While there are now better power supply designs, the author did add a soft start feature which prevented turn-on thump, and a soft-finish feature which powered off the preamp first, then the power supply. The pre-amp used multiple TL-072's in an "instrumentation" configuration, but not an off-the-shelf instrumentation operational amplifier.

I have some ADI and TI (Burr-Brown) Instrumentation ampls to play with. I guess the thing to do is compare to the TL-072's.

Jack
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Old 28th June 2003, 01:27 PM   #10
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Here's a link to the Analog Devices article on Instrumentation Amplifiers: http://www.analog.com/UploadedFiles/...06604AN244.pdf
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File Type: gif isntrumentation.gif (6.5 KB, 335 views)
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