Emitter resistor at output stage transistor. - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 19th March 2012, 12:28 PM   #11
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
Many NAD amplifier lacked emitter resistors, they did, however, have problems with the drivers running away and blowing up.

If you choose not to use emitter resistors on the outputs, I suggest using base resistors on the outputs to avoid the drivers blowing up.

Some Carver amplifiers used emitter resistors as low as 0R05 (50 mill-ohms) !!!
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 19th March 2012, 09:47 PM   #12
65 DegN is offline 65 DegN  United States
diyAudio Member
 
Join Date: Mar 2012
Back in the 1970's I modified a Dynaco ST120 by supplying more available current from the power supply(s), doubling the number of output transistors, using a wakefield water cooled heatsink, removed the 5.1 V zener, and removed the emmitter resisters as I speculated that these would have a compression effect on signal.
The amp put out 120 watts per channel @ 4 ohms (vs ~40 watts stock) @ < 0.1% THD 20 ~ 20 Khz.
I don't recall how this affected crossover distortion.
  Reply With Quote
Old 20th March 2012, 07:34 AM   #13
diyAudio Member
 
Join Date: Aug 2011
My 12 year old designed amp was also no ballast resistor, it was still stable working fine nowadays.
I was currently designing/testing my new amplifier, below is my prototype one which also no ballast resistors.
Click the image to open in full size.

Dual darington power transistors are used for compensation circuit.
The THD measured by PC oscilloscope is 0.05% @17Vrms 1khz no load.
Circuit topology is about current feedback(feedback only from VAS) then no feedback in current buffer and output stage.

Click the image to open in full size.

Unfortunately I have no more accurate analyzer to compare the result between have or no of this resistor.

I still believe that no resister should better in the real world, but I still seen the most hiend amplifier still have this resistors.

Need more opinion from you..
__________________
My DIY audio site.

Last edited by smithomo; 20th March 2012 at 07:38 AM.
  Reply With Quote
Old 20th March 2012, 08:00 AM   #14
diyAudio Member
 
bobodioulasso's Avatar
 
Join Date: May 2008
The art of point to point wiring!
  Reply With Quote
Old 20th March 2012, 08:57 AM   #15
diyAudio Member
 
astankov's Avatar
 
Join Date: Dec 2009
Location: Pernik
Quote:
Originally Posted by bobodioulasso View Post
The art of point to point wiring!
Or the possibility to blow the whole thing up with just one wrong touch
  Reply With Quote
Old 20th March 2012, 09:00 AM   #16
CBS240 is offline CBS240  United States
diyAudio Member
 
CBS240's Avatar
 
Join Date: Aug 2005
Location: K-town
Quote:
Originally Posted by DF96 View Post
A BJT, unless it has internal ballast resistors, will have an effective emitter resistance which varies with current. There may be some limit caused by device bulk resistance but this is likely to vary between samples and it will be small. To a first approximation you have to provide the same resistance at quiescent current. The lower the emitter resistor, the higher the quiescent current. You could end up in Class A, where an external resistor is really there for overload protection only.
I agree. One way to look at it is the emitter resistor reduces the % difference of the variance in Gm as the output stage conducts large and small currents. On the flip side, it also reduces current gain by providing some negative feedback in the form of emitter degeneration. Trading current gain magnitude for more linear gain, reducing the % difference of variance in Gm....they are related. You trade low output Z for more linear transconductance. Now if you wanted to lower output Z there are other ways such as HEC but that topic has been thoroughly discussed. As the signal passes through crossover, the slope of the distortion components created by the varying output Z in this region is very steep indicating high order frequencies and may be out of range for the global fb loop to compensate for. Besides, who wants to pass all that HF distortion crap through every stage of their amp? Best to comprimise. DF96 posted earlier a way to figure the best comprimise emitter resistor values. Or you can go crazy with local loops and such, complicating things.
__________________
All the trouble I've ever been in started out as fun......

Last edited by CBS240; 20th March 2012 at 09:13 AM.
  Reply With Quote
Old 20th March 2012, 02:38 PM   #17
diyAudio Member
 
Join Date: Sep 2004
Location: New Zealand
Hi smithomo
Thats nice work and if it works it works, but Bob Pease (dec) I think has more wires, which just indicates such connection method to trial a circuit is quite valid.

Cheers / chris
Attached Images
File Type: jpg bob.jpg (14.8 KB, 328 views)
  Reply With Quote
Old 20th March 2012, 05:11 PM   #18
65 DegN is offline 65 DegN  United States
diyAudio Member
 
Join Date: Mar 2012
Quote:
Originally Posted by bobodioulasso View Post
The art of point to point wiring!
I particularly like the TO220 wired directly to and bolted to the TO3.
  Reply With Quote
Old 21st March 2012, 06:57 AM   #19
diyAudio Member
 
Join Date: Aug 2011
Quote:
Originally Posted by Chris Daly View Post
Hi smithomo
Thats nice work and if it works it works, but Bob Pease (dec) I think has more wires, which just indicates such connection method to trial a circuit is quite valid.

Cheers / chris
Hi Chris Daly,
It is for trial as you said, I just to know how it work in practical. Currently it is not a fully load testing, my test power supply is not enough powerful.

What I may do next is to design the pcb with have blank space for Re then let see how it sounding to my ear.

However some more thing have to do as trial as well such regulation power supply for VAS.
__________________
My DIY audio site.
  Reply With Quote
Old 27th March 2012, 12:14 PM   #20
diyAudio Member
 
Join Date: Aug 2011
Can anyone advise me what kind of resistor do this best?
- Carbon film
- Metal film?
- WW?
__________________
My DIY audio site.
  Reply With Quote

Reply


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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
four transistor emitter follower (diamond buffer) as power output stage? capslock Solid State 113 12th August 2013 07:16 PM
Output Power PP AB Stage - Value of Emitter Resistor for thermal Bias Stability tiefbassuebertr Solid State 1 30th November 2010 03:40 PM
Diodes from colector to emitter in power output transistor destroyer X Solid State 28 26th February 2010 03:04 PM
AVR7000, emitter resistor value, increase number output devices? DiMenSioN Solid State 4 22nd August 2008 07:57 PM
Class (A)B output stage: why 2 emitter resistors, why not 1? deleveld Solid State 23 13th December 2006 07:10 PM


New To Site? Need Help?

All times are GMT. The time now is 07:00 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2