Testing Class B Output stage - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 26th January 2009, 08:24 PM   #1
Mark245 is offline Mark245  United States
diyAudio Member
Join Date: May 2006
Default Testing Class B Output stage


I have a question cencerning the testing of my class B output stage. I want to test this circuit on a breadboard and I want to know if it is ok to run this circuit with no heatsinks installed. I will be running the test with no load connected. I just want to make sure the voltage output is good. Is it ok to do this? I just want to test the circuit by itself before connecting it to the previous stages. It seems that it should be fine since there is no speaker connected that will draw a lot of current. I guess I should simulate this in spice as well.

Thanks in advance!

  Reply With Quote
Old 26th January 2009, 09:41 PM   #2
diyAudio Member
keantoken's Avatar
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
I would use heatsinks the first time, so that I could adjust the bias without worrying about blowing up my precious transistors and breadboard. O_O

It's probably best if you leave the heatsinks on. When you make a change to the circuit, you might have to change the bias again and if something's screwed up and there's no heatsink, BOOM.

So I would go through the trouble.

Might want to wait for a second opinion, more useful information could be on the way.

- keantoken
The Kmultiplier rail filter! -=- The Simple Kuartlotron Superbuffer!
Need something built, repaired or modded? PM me and ask what I can do!
  Reply With Quote
Old 26th January 2009, 09:50 PM   #3
diyAudio Member
Join Date: Aug 2004
Location: East coast of Jutland, Denmark
Hi Mark

If it is a real class B stage, then, in theory, you do not have any quiescent current, so it should be OK to test it without mounting the transistors on a heatsink.

If it is class AB (most is) you have a quiescent current of some value, and then it is depending of the supply voltage how much power there is dissipated in the transistors, and you have a great risk of smoking the transistors.
  Reply With Quote
Old 26th January 2009, 10:14 PM   #4
wg_ski is offline wg_ski  United States
diyAudio Member
Join Date: Oct 2007
Breadboards are a very good and reliable method for getting things to accidentally short or open. Push pull output stages of any kind don't like for that to happen. If you have to breadboard, use a lab power supply with a user-settable current limit.
  Reply With Quote
Old 26th January 2009, 10:58 PM   #5
Mark245 is offline Mark245  United States
diyAudio Member
Join Date: May 2006
Thanks everyone. Yes maybe I should use a lab power supply. I was thinking about using the unregulated raw dc power supply that I will use in the final version of this amplifier. However I have not installed the fuses yet.

Also, when I install the heatsinks, is it totally neccessary that I mount all the output transistors on the same heatsink? What about the bias transistor can I leave it off or should it be mounted too? I am trying to make this as easy as possible for a quick test but I don't want to risk blowing something up.

Thanks for all the replies so far!

  Reply With Quote
Old 26th January 2009, 11:47 PM   #6
diyAudio Member
Join Date: Nov 2005
Location: Southampton
To be safe, it is best to mount everything as you would in the actual amp. You don't need a big heatsink but I would recommend that you attach all of the output devices and very importantly the bias transistor to the same piece of metal.

Don't forget the lightbulb in series with the mains trick for when you first power it up.
  Reply With Quote
Old 27th January 2009, 12:27 AM   #7
diyAudio Member
nigelwright7557's Avatar
Join Date: Apr 2008
Location: Carlisle, England
I never connect the output transistors on first power up.
I run the output of the VAS back into the LTP for feedback.
At this point i would turn the bias volts down.

Only when I am convinced the driver is working fine do I consider connecting the output transistors.
Murton-Pike Systems PCBCAD51 pcb design software. http://www.murtonpikesystems.co.uk
  Reply With Quote
Old 27th January 2009, 10:23 AM   #8
diyAudio Member
east electronics's Avatar
Join Date: Jan 2006
Location: Athens GREECE

is something that exites me very very much ....can i get a schematic please ??????

thank you
  Reply With Quote


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
MOSFET or NPN for class A output stage AudioGeek Solid State 30 25th July 2008 07:34 PM
Aikido + class D in the output stage jmartins Tubes / Valves 2 6th June 2006 08:51 PM
CCS for PP Class A output stage? AudioGeek Tubes / Valves 5 24th January 2004 02:58 PM
Class A with AB Output-stage ManUtd Solid State 14 1st December 2003 05:49 PM
Class h or g output stage? Opie Solid State 1 24th October 2001 09:30 PM

New To Site? Need Help?

All times are GMT. The time now is 11:29 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2