Transistor case coupling?? - 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 7th September 2011, 09:33 AM   #1
diyAudio Member
 
Join Date: Jun 2009
Default Transistor case coupling??

Hi everyone, doing some repairs at the moment, and have came across something odd. On the amp pcb there are a few pairs of transistors, that have been placed face to face with the flat part of each case touching, and then held together with a piece of heatshrink.

I thought they may have been optical phototransistor couplings, but after looking at the schematics, they just appear to be standard transistors in darlington pair configurations. It even shows on the schematic what pairs are placed together, and in what configuration.

What is the reason for this? Is it for thermal reasons? Capacitive? Electromagnetic? All else I can think of is to prevent vibration relative to each to help reduce noise.

Any thoughts would be appreciated.
  Reply With Quote
Old 7th September 2011, 09:59 AM   #2
diyAudio Member
 
digits's Avatar
 
Join Date: Apr 2011
that's right, it is so the two transistors can thermaly track each other...
  Reply With Quote
Old 7th September 2011, 10:40 AM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
yes, this thermal coupling is commonly used in Long Tail Pair (LTP) and Current Mirror (CM) implementations. It massively reduces thermal drift of the output offset of a Power Amplifier.
__________________
regards Andrew T.
  Reply With Quote
Old 7th September 2011, 10:41 AM   #4
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
They will probably either be in a LTP (to maintain balance) or one will be part of a Vbe multiplier biassing the other. Keeping them at the same temperature means they track Vbe changes.
  Reply With Quote
Old 7th September 2011, 02:49 PM   #5
diyAudio Member
 
Join Date: Jun 2009
Makes sense! Thanks for your answers
  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
Polishing a case & what material is this case? 123audio Construction Tips 9 5th August 2011 01:16 AM
Can I build up these Darlington transistor if I use two BJT transistor ? gaborbela Parts 9 15th July 2010 06:30 PM
Class D Audio aluminum case or DIY amp case jtwrace Vendor's Bazaar 3 17th April 2010 02:51 PM
Can bias transistor mount on top(body) of output transistor?? Leolabs Solid State 23 16th February 2008 12:35 AM


New To Site? Need Help?

All times are GMT. The time now is 10:37 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