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Old 23rd February 2013, 04:02 AM   #1
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Default My line buffer preamp

Hello

I've done, with Ltspice, a line buffer preamp with a gain of 1.4x , any opinions about it ?

Any improvements suggestions ?

I include the schematic and the asc file.

Thank

Bye

Gaetan
Attached Images
File Type: gif buffer-line-preamp.GIF (14.7 KB, 337 views)
Attached Files
File Type: asc line buffer preamp.asc (3.8 KB, 8 views)

Last edited by gaetan8888; 23rd February 2013 at 04:05 AM.
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Old 23rd February 2013, 04:07 AM   #2
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Looks a bit too much like an opamp Why not try single ended input?
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Old 23rd February 2013, 10:09 AM   #3
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Hello

Like that one ?

Bye

Gaetan
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File Type: gif Buffer line with_gains-pf5102--ver4.gif (14.0 KB, 290 views)
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Old 23rd February 2013, 10:17 AM   #4
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Yeah then instead of voltage feedback to the gate, how about current feedback to the source? Then a passive RF filter on the input, series L shunt C?
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Old 23rd February 2013, 10:29 AM   #5
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Hello

You mean moving it to between R10 and V3 ?

Thank

Bye

Gaetan
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Old 23rd February 2013, 10:34 AM   #6
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Between R10 and J3. J3's source.
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Old 23rd February 2013, 10:39 AM   #7
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Hello

I've just simulated the circuit with feedback between R10 and J3, the result are very bad.

Thank

Bye

Gaetan
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Old 23rd February 2013, 10:43 AM   #8
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It might be because of the 2nF (C4) capacitor - can't use a capacitor with CFB. Also the value of the feedback resistor probably needs reducing as its critical with CFB, unlike with VFB.
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Old 23rd February 2013, 10:49 AM   #9
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Hello

Your right, I've take out the capacitor and reduced the feedback resistor by half, but it may need more experiment since the thd is higher at -60db.

Thank

Bye

Gaetan
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Old 23rd February 2013, 10:58 AM   #10
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Hello

Here's the asc file of that last circuit with current feedback.

Thank

Bye

Gaaetan
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