Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Miller capacitance in feedback amplifiers
Miller capacitance in feedback amplifiers
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th July 2018, 03:15 AM   #1
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Default Miller capacitance in feedback amplifiers

The issue I am concerned about is the load capacitance seen by a MM phono cartridge driving a two stage feedback amplifier. In the case of a single stage with no FB Miller is pretty straightforward being proportional to the gain of the stage. If we add a second stage and bring FB from the second plate to the first stage cathode does the cartridge still see the same capacitance (approx. Cgp*A) or is it modified by the FB?
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.
  Reply With Quote
Old 16th July 2018, 04:43 AM   #2
MarcelvdG is offline MarcelvdG  Netherlands
diyAudio Member
 
Join Date: Mar 2003
Location: Haarlem, the Netherlands
It is reduced by the feedback. (That also means that the + 1 term you neglected becomes a larger part of the total capacitance.)

Just look at the ratio of the AC voltage needed to drive the output stage and the input voltage of the first stage and add 1. Then multiply Cgp by that number. If the closed-loop gain drops with frequency, it could be that you mainly get a resistive effect rather than a capacitive effect:
  Reply With Quote
Old 16th July 2018, 08:21 AM   #3
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Many feedback amplifiers have an inductive input and output impedance, over some frequency range, due to the loop gain dropping with frequency.
  Reply With Quote
Old 16th July 2018, 06:36 PM   #4
mashaffer is offline mashaffer  United States
diyAudio Member
 
Join Date: Jun 2004
Location: Indiana
Thanks. That makes sense.
__________________
The only reason I drive the 91 Colony Park is that I can't afford a 65. Me old school? Couldn't be.
  Reply With Quote

Reply


Miller capacitance in feedback amplifiersHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Control Grid Feedback (as opposed to Cathode FB) and Miller Capacitance ballpencil Tubes / Valves 10 18th November 2015 12:07 AM
'Local Feedback and Nonlinearity of Multistage Feedback Amplifiers' mikeks Solid State 62 20th July 2005 08:03 AM
Miller feedback cap value? cunningham Solid State 7 2nd August 2004 12:11 AM


New To Site? Need Help?

All times are GMT. The time now is 07:05 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki