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

Solid State Talk all about solid state amplification.

16W Class A - inspired by JLH
16W Class A - inspired by JLH
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 12th November 2018, 04:19 PM   #91
Mark Johnson is offline Mark Johnson  United States
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
16W Class A - inspired by JLH
Quote:
Originally Posted by john_ellis View Post
The correct equation for the feedback ratio is, of course,
F=Rg/(Rg+1/(1/Zcf+1/Rf))
where Zcf is the impedance of the feedback capacitor, Rf the feedback resistor and Rg the "grounding" resistor.
(This is a complex number expression, just in case someone does not realise).
This starts to become important at very low frequencies. The simplifying assumption (Cf=Infinity) rather than (Cf=1000 microfarads), introduces a magnitude error of 0.1 dB at 1.5 Hertz. And the error gets larger and larger, as the frequency falls farther and farther below 1.5 Hz.

The simplifying assumption also introduces a phase error. Calculating phase using the simplifying assumption introduces an error of 8 degrees at 1.5 Hz, and the error is 1 degree at 13 Hz.
  Reply With Quote
Old 12th November 2018, 04:35 PM   #92
john_ellis is offline john_ellis  United Kingdom
diyAudio Member
 
Join Date: Sep 2006
Indeed. The equation dealt with not the LF time constant but the HF. This was to explain the apparent 10MHz unity loop gain frequency.
The full expression including the LF time constant is
F=(Rg+Zcg)/(Rg+Zcg+1/(1/Zcf+1/Rf))

where Zcg is the impedance of the decoupling capacitor (1mF) in series with Rg.
There will indeed be phase errors at LF as with nearly all feedback networks using this approach, but errors of 0.1dB/1 degree well below audio band is probably not too relevant.

Last edited by john_ellis; 12th November 2018 at 04:47 PM.
  Reply With Quote
Old 15th November 2018, 03:54 AM   #93
mjona is offline mjona  New Zealand
diyAudio Member
 
Join Date: Jul 2007
Location: Upper Hutt
Quote:
Originally Posted by PRR View Post
Not in the least. JLH would not approve.

mjona said "any". I happened to have the PL400 plan handy. mjona is correct: here it is "required" for current-sharing.
In fact JLH designed a quasi-complementary amplifier for Hi-Fi News and illustrated this in two books he wrote. These style of amplifiers are not picture perfect but they work.

This style of output stage might have been used in the present design. I see this approach as hard to ignore but it has been overlooked.
  Reply With Quote
Old 16th November 2018, 04:33 PM   #94
john_ellis is offline john_ellis  United Kingdom
diyAudio Member
 
Join Date: Sep 2006
Project update ...
I have started to populate a prototype PCB based on Prasi's layout. There is a slight problem I didn't spot earlier (one reason to check the PCB before signing off). Will need to obtain some parts I don't have "in stock" so should be ready to test in about a week.

Last edited by john_ellis; 16th November 2018 at 04:38 PM.
  Reply With Quote

Reply


16W Class A - inspired by JLHHide 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
Inspired by FW M2 AUTOFORMER Circlomanen Pass Labs 19 4th October 2016 01:11 PM
Class D amp inspired by YES Jamh Class D 2 9th January 2016 10:54 PM
Inspired by? Hylle AKSA 7 22nd March 2012 07:01 AM
(Inspired by Ron) ibR 108 horn Leonidas Full Range 30 13th December 2010 09:27 AM
Building an B-15-inspired amp DolganoFF Tubes / Valves 10 5th November 2010 09:47 PM


New To Site? Need Help?

All times are GMT. The time now is 03:42 PM.


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