Please help me understand this feedback

martyh · 13th November 2011, 09:35 PM

I’m not sure I am thinking about this the right way and any help you can offer is appreciated.

For the purposes of finding the feedback voltage applied to the grid of the second stage do I need to consider the output Z of the previous stage to be in parallel with RG? Also, what about the input z of the second stage in this drawing? Is that also in parallel with RG? I am thinking yes for both but... I don’t know.

Thanks,
Marty

hemgjord · 13th November 2011, 09:49 PM

Yes on both.

/Olof

martyh · 13th November 2011, 11:20 PM

Ahhh… thank you, thank you
If I finally have my mind around this..RFB above the parallel impedances forms a frequency dependent voltage divider for the feedback AC. Assuming negative feedback… Vout from the stage on the left should equal the grid swing required for the stage on the right + the applied feedback voltage if the output voltage on the tube on the right is to have Vout closed loop = Vout open loop. Am I on the right track?

13th November 2011, 09:49 PM	#2
hemgjord diyAudio Member Join Date: Apr 2007	Yes on both. /Olof __________________ I'm not allowed to do magic, union rules...

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13th November 2011, 11:20 PM	#3
martyh diyAudio Member Join Date: Feb 2004 Location: Wisconsin	Ahhh… thank you, thank you If I finally have my mind around this..RFB above the parallel impedances forms a frequency dependent voltage divider for the feedback AC. Assuming negative feedback… Vout from the stage on the left should equal the grid swing required for the stage on the right + the applied feedback voltage if the output voltage on the tube on the right is to have Vout closed loop = Vout open loop. Am I on the right track?

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