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-   -   Feedback with a choke ? (http://www.diyaudio.com/forums/tubes-valves/179331-feedback-choke.html)

el156 17th December 2010 06:16 PM

Feedback with a choke ?
 
Hi
Does someone knows what happens if we use a choke instead of the normal resistor to the feedback loop? It would be afecting more the bass then the middle/hi freq i think ,i would like to make a test but i dont have a suitable choke to the job. Is it a nice test to do , or i should be gardening instead of messing around with tubes or maybe choose another hobby?:D

DF96 17th December 2010 07:02 PM

If you mean a choke in series (with a resistor to ground) then the result will be gain rising with frequency. The opposite of a capacitor.

To a first approximation, the closed-loop gain pattern is the opposite of the feedback network response. So flat feedback gives flat gain. High-pass feedback (e.g. a capacitor) gives low pass gain. Low pass feedback (your choke idea) gives high pass gain.

Do some reading on negative feedback - almost any electronics textbook will cover it.

el156 17th December 2010 07:16 PM

Quote:

Originally Posted by DF96 (Post 2402076)
If you mean a choke in series (with a resistor to ground) then the result will be gain rising with frequency. The opposite of a capacitor.

To a first approximation, the closed-loop gain pattern is the opposite of the feedback network response. So flat feedback gives flat gain. High-pass feedback (e.g. a capacitor) gives low pass gain. Low pass feedback (your choke idea) gives high pass gain.

Do some reading on negative feedback - almost any electronics textbook will cover it.

What i was thinking is that we need feedback to lower the output impedance and distortion for the bass,without afecting the mid and hi frequency,because i prefer the mid and hi without feedback....well maybe was only a crazy idea...

DF96 17th December 2010 07:36 PM

Unfortunately you can't easily separate the various different effects of feedback, except by having different amplification channels for different frequency ranges. Feedback to reduce bass output impedance also reduces bass gain, so you get a high-pass filter. You can balance off frequency effects in the forward (open-loop gain) against frequency effects in the feedback, but then it gets complicated.


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