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.

Onkyo Power Output Stage, capacitor between bases of EF pair?
Onkyo Power Output Stage, capacitor between bases of EF pair?
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 13th April 2007, 11:37 AM   #1
capslock is offline capslock  Europe
diyAudio Member
 
Join Date: Feb 2002
Location: Germany
Default Onkyo Power Output Stage, capacitor between bases of EF pair?

This is one of the seven power stages of a budget Onkyo AV receiver (TX-SR504E). Pretty conventional topology, nice choice of transistor and not too much open loop gain. I would probably use emitter degeneration on the input pair and either buffer or cascode the VAS, but that is a different story.

My question is about the output configuration. An undivided 82 R resistor is used between the emitters of the predrivers, which is nice, but it is paralleled by capacitor, which I think I have never seen before.

The purpose of the undivided resistor is to be able to be able to shift bias voltage from the non-active output base to the active base. If no cap is used, the total voltage between the bases of the output pair can also increase if the active transistor needs a high input current. With a capacitor in place, this is no longer possible. Why would one want to do this?
Attached Images
File Type: gif onkyo_power_stage.gif (17.6 KB, 271 views)
  Reply With Quote
Old 13th April 2007, 11:43 AM   #2
richie00boy is offline richie00boy  United Kingdom
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Onkyo Power Output Stage, capacitor between bases of EF pair?
Self explains it all. He calls it emitter follower type II.

The purpose of the shared resistor is to allow the base to be reversed biased for faster turn-off. The cap I don't quite recall it's purpose or if he recommended for or against it. I have a feeling he recommended for it.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
  Reply With Quote
Old 13th April 2007, 01:50 PM   #3
capslock is offline capslock  Europe
diyAudio Member
 
Join Date: Feb 2002
Location: Germany
Yes, I just reread that (it's been too many years). He does recommend a 1 F film capacitor to speed up the switch-off. Maybe this small value is a compromise that still gives the improvement at HF but also the benefit of higher drive voltage at low impedance loads at lower frequency.

I just did the bias calculations. The input pair has a current imbalance of 7 - 10%, depending on what you would want to assume for V_BE. Just changing R5114 to 932 R (910 + 22) would drop that into the 1% range!
  Reply With Quote
Old 13th April 2007, 01:58 PM   #4
Workhorse is offline Workhorse
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
That capacitor is used to speed upthe turnoff and helps in fast recovery during clipping, if you remove it, the amp would sound crackle when pushed to clipping...Try it!
  Reply With Quote
Old 13th April 2007, 02:27 PM   #5
mikeks is offline mikeks  United Kingdom
Account Disabled
 
Join Date: Jun 2004
Location: Animal farm
http://users.ece.gatech.edu/~mleach/lowtim/output.html
  Reply With Quote
Old 13th April 2007, 04:40 PM   #6
capslock is offline capslock  Europe
diyAudio Member
 
Join Date: Feb 2002
Location: Germany
Leach says the capacitor does no speeding up, but his argument is not quite clear to me. Assume the amp is being driven hard towards the positive side, so the upper driver draws more current than it would in idle. If there is a cap, it is going to clear out the lower output transistors base, too.
  Reply With Quote

Reply


Onkyo Power Output Stage, capacitor between bases of EF pair?Hide 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
Which high power CCS for output stage? andyjevans Tubes / Valves 25 4th May 2017 06:28 AM
Is the Toshiba 2SJ201/2SK1530 pair (Mosfet) suitable for output stage ? Johnix Solid State 23 4th August 2012 03:32 PM
Onkyo M 508 Capacitor goo jtee1340 Solid State 13 25th March 2005 01:54 PM
Output stage/preamp with gain: X-Bosoz with diff.-pair? Onvinyl Pass Labs 1 19th July 2004 09:29 AM
power output stage Jennice Pass Labs 22 19th June 2003 12:59 PM


New To Site? Need Help?

All times are GMT. The time now is 08:24 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.79%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki