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Neutralizing An Amplifier
Neutralizing An Amplifier
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Old 23rd November 2012, 01:11 PM   #21
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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This is the idea, it has been done several years in RF circuits, and rarely I saw it in audio circuits, but yesterday I made certain simulations in LTS, and is really better than I could imagine.

In my project, a 9.5 pF extends HL limit more than a decade.Note that no other value of component has been modified. In practice, it can easily implemented using 3-30pF, and adjusting them using 1KHz square wave, and watching the corners of the steeps.

But I didn't know if it affects sound.
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Old 23rd November 2012, 01:34 PM   #22
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Neutralizing An Amplifier
I forgot to mention that the Marantz 9 also used the cross-coupled cap trick. So this has a long and honorable history.
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Old 23rd November 2012, 01:39 PM   #23
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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10.04!
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Old 23rd November 2012, 01:48 PM   #24
DF96 is offline DF96  England
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The circuits are too small to see, but remember that this extra capacitance has to be driven by the anode current so be careful of slew-rate limiting.
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Old 23rd November 2012, 01:56 PM   #25
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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Quote:
Originally Posted by DF96 View Post
The circuits are too small to see, but remember that this extra capacitance has to be driven by the anode current so be careful of slew-rate limiting.
Thanks for the suggestion, but as I know this, you can see that I take the high voltage side from the WCF instead of directly from plate.

I don't know how to re-size the figures in this page, as I made it at full 1024*768 at my computer's screen.
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Old 23rd November 2012, 02:00 PM   #26
DF96 is offline DF96  England
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OK, a CF should help if quiescent current is high enough. One question: why not simply run with lower circuit impedances so the capacitance ceases to be a problem?
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Old 23rd November 2012, 02:06 PM   #27
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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My original idea was to made something similar to an operational amplifier of vacuum tubes. As you can see, there exist two inputs, an inverting and another NI, also at the outputs, having moderately high input impedance, gain and bandwidth, and relatively low output impedance, using only triodes, and single supply (in fact I have two, but none of them is negative). And finally, using as few capacitors in the signal path as possible.
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Old 23rd November 2012, 02:16 PM   #28
DF96 is offline DF96  England
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Interesting as an exercise in design, but why?
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Old 23rd November 2012, 02:34 PM   #29
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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For my audio project, link to the trafo thread:

Homebrew Toroidal Output Transformer

The idea is to apply certain amount of FB, mixed of positive current and negative voltage to obtain a near zero output impedances as is suggested in the NFB chapter of the Langford Smith book, and others I read. But for apply positive feedback, I believe that te amplifier must be stable before using it.
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Old 23rd November 2012, 04:04 PM   #30
DF96 is offline DF96  England
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Yes, the amplifier must be super stable before applying PFB.
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