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positive feedback musings...

5/19/2000 4:21 PM
ken gilbert	positive feedback musings... ok. i'm starting to pursue doing more with less. part of that could be accomplished by the judicious use of positive feedback, to increase gain and distortion. assume, for the text of these proposals, that adequate DC blocking caps are employed wherever necessary. most people, when wrapping NFB about a single stage, will take a simple resistor and place it from plate to grid. the grid is akin to the inverting input of an opamp, since it's out of phase with the output, and some level of NFB results. how about if we instead use the other input to the stage, the NON-INVERTING input... this is the cathode. of course, it's of a lower impedance, and in this scenario must not be completely bypassed for obvious reasons. but by injecting a sample of the plate's signal to the cathode we can effectively INCREASE the dynamic signal Vgk, thereby increasing the gain of the stage. this is closely akin to the common practice of coupling two consecutive cascaded stage's cathodes, except it can be accomplished around a single stage. i'd try it out now but i'm at the damned day job; the workbench is out of reach. any thoughts? kg

5/19/2000 4:21 PM

ken gilbert

positive feedback musings...

ok. i'm starting to pursue doing more with less. part of that could be accomplished by the judicious use of positive feedback, to increase gain and distortion.

assume, for the text of these proposals, that adequate DC blocking caps are employed wherever necessary.

most people, when wrapping NFB about a single stage, will take a simple resistor and place it from plate to grid. the grid is akin to the inverting input of an opamp, since it's out of phase with the output, and some level of NFB results.

how about if we instead use the other input to the stage, the NON-INVERTING input... this is the cathode. of course, it's of a lower impedance, and in this scenario must not be completely bypassed for obvious reasons. but by injecting a sample of the plate's signal to the cathode we can effectively INCREASE the dynamic signal Vgk, thereby increasing the gain of the stage.

this is closely akin to the common practice of coupling two consecutive cascaded stage's cathodes, except it can be accomplished around a single stage.

i'd try it out now but i'm at the damned day job; the workbench is out of reach.

any thoughts?

kg

Replies:

Gil Ayan q{how about if we instead use the o... -- 5/19/2000 4:37 PM
GFR You'll need another stage for buffe... -- 5/19/2000 7:10 PM
ChrisM I don't think this is going to achi... -- 5/19/2000 8:53 PM
MBSetzer Well Ken, thought I would add my 2c... -- 5/19/2000 9:04 PM
Peter S I remember reading in guitar player... -- 5/19/2000 10:58 PM
andyfuchs Dynaco's Pas-3 phono preamp used a ... -- 5/20/2000 4:02 PM
Ken Gilbert thanks for all the thoughtful repli... -- 5/20/2000 4:07 PM
Chris Barrow As far as I can tell, all of the Me... -- 5/21/2000 6:23 PM