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Old 19th August 2013, 06:34 AM   #421
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thanks locky !
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Old 6th November 2013, 06:46 PM   #422
Sk8Ter is offline Sk8Ter  United States
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Default Thinking of purchasing one of these

guys I have never used a curve tracer but am a quick study! I have BP ouputs i want to match and some smaller driver and signal transistors....this should do the job...

the question is did anyone adapt to measure/match op amps? this would be very helpful for what i need to do..


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Lawrence
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Old 6th November 2013, 07:42 PM   #423
1audio is offline 1audio  United States
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What are you trying to match on opamps? While there are curve tracer methods for opamps you can do the same with a few simple test fixtures. A lot depends on what you want to know and what data sheet factor you want to check. Many datasheets, especially older ones include test circuits and that's a good starting point. You would need a good dual adjustable bench supply, a suitable signal source and whatever is appropriate for measuring the target parameter, a meter, oscilloscope or possibly distortion analyzer.
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Old 6th November 2013, 07:51 PM   #424
Sk8Ter is offline Sk8Ter  United States
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Hello Thanks for your reply...I am mainly looking for gain matching and linearity matching...and or any inconsistency between them


Lawrence
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Old 6th November 2013, 08:44 PM   #425
1audio is offline 1audio  United States
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Probably the easiest and best would be the method on page 7 of this app note: http://www.ti.com/lit/ds/symlink/opa2604.pdf . What it does is reduce the available gain to drive the feedback network so the intrinsic distortion is reduced less by the feedback.

There are variations in the datasheets for other low distortion opamps. The distortion measured is directly proportional to the linearity.

Usually this turns out to be useful only for finding defective parts. Good IC's are really uniform making the whole effort tedious and somewhat pointless.
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Old 6th November 2013, 09:22 PM   #426
Sk8Ter is offline Sk8Ter  United States
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Default Thanks

Hi Thanks but I was hoping that i could use the curve tracer to test a bunch of these opamps...

to be honest I do not trust opamps and want to match gain and linearity/distortion....please remember this is for an audio device 2channel etc..



Lawrence
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Old 6th November 2013, 09:37 PM   #427
rsavas is offline rsavas  Canada
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Lawrence,

You set the gain of a opamp by determining the feedback ratio. Accuracy is a function of the resistor ratio accuracy Usually you use 1% R's for this. For very precise ckts you use even higher precision R's, but they are not generally needed for audio work because 1% gain accuracy is more than enough for most audio ckts.

BTW, what do you not trust?
Quote:
to be honest I do not trust opamps
Gain set by you R selection.
Linearity/distortion. You do not trust what TI specifies, good luck proving them wrong. I do not think that you can afford the equipment necessary to make a claim like that.

Rick
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Old 6th November 2013, 10:16 PM   #428
Sk8Ter is offline Sk8Ter  United States
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Default yes sir

Yes personally dont care to prove anything to anyone its for my own enjoyment Thanks anyways


Lawrence
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Old 6th November 2013, 10:21 PM   #429
1audio is offline 1audio  United States
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Its true that if you need either really precise gain (.0001% or better) or very large gain more that 120 dB the open loop gain will be an issue. It terms of nonlinearity the opamps of a given type will be very similar. These are usually controlled by passive R's and C's on the chip.

The manufacturing process is designed and optimized to yield really consistent parts. Most IC processes are more controlled than discrete parts. Any significant variations would make a part with 1 billion transistors impossible to make and Intel makes lots of them.
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Old 6th November 2013, 10:38 PM   #430
Sk8Ter is offline Sk8Ter  United States
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yes Sir you defiantly know much more then I... but I shure would like to make shure what i am installing is a good match and working properly

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Lawrence
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