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Old 5th October 2009, 06:26 PM   #1
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Default Switch mode between Hawksford error correction and NFB by Unity Gain

Here an theoretical possible for select between two kinds for reduce of distortion. Anybody tested?
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Old 5th October 2009, 07:11 PM   #2
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Quote:
Originally Posted by tiefbassuebertr View Post
Here an theoretical possible for select between two kinds for reduce of distortion. Anybody tested?
Hi,

I've build some hawksford ec amps, but not tested this specific topology, and I have trouble understanding the Hawksford ec case. Can you post the schematic for 'Hawksford ec' like you did for 'nfb' please?

Edit: I now see, it's the upper case. Forget my post ....

jd
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Last edited by jan.didden; 5th October 2009 at 07:14 PM.
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Old 5th October 2009, 07:20 PM   #3
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I don't think that ec case works. Assume the opamp has gain A, the buffer is ideal and the load voltage is Vo. We see that the opamp Vout=Vo.
The inverting input is also Vo. The non-inverting input is also Vo. Vout opamp = A(-Vo+Vo)=Vo so Vo = 0. Independent of Vi.

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Old 5th October 2009, 07:31 PM   #4
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The OP-Amp must be a diamond transistor, not a normal type (see datasheet for AD844 e. g.)
http://www.analog.com/static/importe...eets/AD844.pdf
The buffer symbol in my simplefield schematics represented the internal buffer of the op amp so as an external power push pull buffer.
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Old 5th October 2009, 07:46 PM   #5
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Quote:
Originally Posted by tiefbassuebertr View Post
The OP-Amp must be a diamond transistor, not a normal type (see datasheet for AD844 e. g.)
http://www.analog.com/static/importe...eets/AD844.pdf
The buffer symbol in my simplefield schematics represented the internal buffer of the op amp so as an external power push pull buffer.
Ahh yes, I used that too. You must have read my article on the Hawksford ec amp in Elektor or AudioXpress...

So the opamp non-inverting input is a high-impedance voltage input, the inverting input is a low-impedance current input, and this current comes out of the opamp output in reverse polarity? Is that what you mean?

Yes that'll work.

jd
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Last edited by jan.didden; 5th October 2009 at 07:48 PM.
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