Tube DIY Asylum

RE: ??

50.4.127.98

PakProtector

In Reply to: RE: ?? posted by Ralph on January 10, 2025 at 09:10:17

You said to 'linearize' the FB with a resistive network. Not needing to quote you( I think ). Resistors, being linear are not going to make any non-linear input, linear.

Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

Follow Ups:

Now I'm sure you misinterpreted my comment. - Ralph 09:59:19 01/13/25 (2)
The context lost was the bit about how the feedback has to be mixed with the incoming audio. To do that it must be inverted with respect to the feedback signal that is used when feedback is applied to the cathode.

In a PP amp this is fairly easy since there are usually coupling caps involved with driving the grids of the output stage. They can be set up to drive the other power tube, thus inverting the output. Or the plate connections of the power transformer can be reversed.
- RE: Now I'm sure you misinterpreted my comment. - PakProtector 08:50:13 01/15/25 (1)
  Well...yes. Seemed you were going for something other than basic NFB application when you wrote of mixing NFB in a more linear way:
  
  So it would seem that what you want to do is mix the audio and the feedback in a more linear way.
  
  and then using resistors to accomplish this:
  
  That can be done by using a series resistance with the incoming audio signal and use a simple divider network to mix the feedback with it, before it enters the tube.
  
  Thanks for clarifying anyway... :)
  
  Douglas
  
  Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
  - The best way to understand this is how opamps do it. - Ralph 09:05:13 01/15/25 (0)
    Well...yes. Seemed you were going for something other than basic NFB application when you wrote of mixing NFB in a more linear way:
    
    I'm looking for the same loop gain and the same damping the feedback loop might have if applied to the cathode. The difference is because the grid has so much higher impedance the feedback values have to change to accommodate that.
    
    Opamps use this exact technique to do their feedback. This does mean you need an inverting input. If the feedback is applied to the cathode the amp circuit is usually non-inverting. So some sort of accommodation needs to be made to allow the input to be inverting.

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