|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
|
|
Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
|
In Reply to: OT inside a feedback loop posted by Gingertube on April 4, 2007 at 20:50:28:
From the above, in a global feedback system, there are a couple of other "facts" that fall out.
In the forward path all other poles MUST be above the OT introduced pole by at least a factor of 3, preferably 5 to 10. MANY driver stages fall down at this point. The theory says that it doesn't matter where in the forward path the dominant pole is introduced and many an amp has been designed an built with "accidental" stability due to inadequate driver stage. Always check your amp open loop to find out where the most dominany pole is located and if required slug that stage harder whilst make sure ever other stage is significantly faster - if that turns out to be the driver stage, that is perfectly acceptable but do it by design rather than by accident.The feedback path MUST be faster than the forward path and here large values of feedback resistor interacting with Miller capacitance at tube grid can be a problem so most feedback is to a low impedance point - usually a cathode so that a low value of feedback resitor can be used and the capacitance at the feedback point will not cause a low pass filter at the frequencies of interest.
You can see why avoiding global feedback simplifies things enormously and reduces the possible number of problems.
Remember Kiss.
Simple circuits have simple problems
Simple problems have simple solutionsAs one of my software lecturers used to point out:
Its 3 times a difficult to debug your software as it is to write it.
If you are as clever as you possibly can be when you write it - when do you reckon you'll have it running by - answer NEVER.Cheers,
Ian
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- More rave - he must be bored - Gingertube 21:13:31 04/04/07 (1)
- On-yah, Ginge! (nt) - Allen Wright 01:20:11 04/05/07 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
