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tadgesualdo

Op amp theory Q's

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Hi TG,
The OPA2134 is an excellent audio opamp but isn't much better than a TL072.
Its power bandwidth is 230kHz, not 8MHz. The power bandwidth of a TL072 is 100kHz.
An opamp's output is slew-rate-limited above its max power bandwidth but still has gain up to its gain-bandwidth-product (GBP), which for the OPA2134 is 8MHz to 10MHz. The GBP of a TL072 is 3MHz. At the GBP the internal gain of an opamp is unity.

Like all normally compensated opamps that work at a gain of unity without oscillating, its internal frequency response is reduced above only 10Hz.
It has a fantastic gain of 2 million below 10Hz but at 1kHz its gain is only (!) 10,000. Therefore with negative feedback its distortion emerges from its noise above 1kHz.

The distortion of all opamps increases with a higher output level, with a higher amount of closed-loop gain and with a higher amount of loading.

Look at what this expert has to say:
http://www.dself.dsl.pipex.com/ampins/ampins.htm
I have Ante's book but haven't opened it yet.
I frequent DIYaudio.com but some audiophiles there don't know what they are talking about, describing audio like it is visual. Most don't know the difference between a resistor and a capacitor. 

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I found one thanks, I have been reading, this is what I needed, but to be quite honest you do need a little bit of background to grasp all of it.  It would be nice to for things to be written in a bit more common language, I miss some of the detail stuff.

TG :)

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Hi all,

Ok I have another question regarding op amp theory.  What is the best way to make a op amp buffer?  Most times you see two 10K resistors for this with a non-inverting input, but would not just a short between the output and the negative input work the same?  What is the difference?

Now with inverting inputs this seems to get more complex, because doesn't the input inpedance of the opamp have an effect on the feedback circuit, and needs to be taken into account?

Thanks,
TG :)

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