Neutralizing An Amplifier - Page 3

Osvaldo de Banfield · 23rd November 2012, 01:11 PM

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.

SY · 23rd November 2012, 01:34 PM

I forgot to mention that the Marantz 9 also used the cross-coupled cap trick. So this has a long and honorable history.

Osvaldo de Banfield · 23rd November 2012, 01:39 PM

10.04!

DF96 · 23rd November 2012, 01:48 PM

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.

Osvaldo de Banfield · 23rd November 2012, 01:56 PM

Quote:

Originally Posted by DF96

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.

DF96 · 23rd November 2012, 02:00 PM

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?

Osvaldo de Banfield · 23rd November 2012, 02:06 PM

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.

DF96 · 23rd November 2012, 02:16 PM

Interesting as an exercise in design, but why?

Osvaldo de Banfield · 23rd November 2012, 02:34 PM

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.

DF96 · 23rd November 2012, 04:04 PM

Yes, the amplifier must be super stable before applying PFB.

23rd November 2012, 01:34 PM	#22
SY On Hiatus Join Date: Oct 2002 Location: Chicagoland	I forgot to mention that the Marantz 9 also used the cross-coupled cap trick. So this has a long and honorable history. __________________ "You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."

23rd November 2012, 01:39 PM	#23
Osvaldo de Banfield diyAudio Member Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina	10.04! __________________ Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001. Argentine Ham Radio LW1DSE since 1987.

23rd November 2012, 02:06 PM	#27
Osvaldo de Banfield diyAudio Member Join Date: Dec 2011 Location: Barrio Garay,Almirante Brown, Buenos Aires, Argentina	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. __________________ Osvaldo F. Zappacosta. Electronic Engineer UTN FRA from 2001. Argentine Ham Radio LW1DSE since 1987.

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23rd November 2012, 01:48 PM	#24
DF96 diyAudio Member Join Date: May 2007	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.

23rd November 2012, 02:00 PM	#26
DF96 diyAudio Member Join Date: May 2007	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?

23rd November 2012, 02:16 PM	#28
DF96 diyAudio Member Join Date: May 2007	Interesting as an exercise in design, but why?

23rd November 2012, 04:04 PM	#30
DF96 diyAudio Member Join Date: May 2007	Yes, the amplifier must be super stable before applying PFB.

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