zobel network / emitter resistors - 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 26th January 2004, 10:05 AM   #1
diyAudio Member
 
blu_line's Avatar
 
Join Date: Jan 2002
Location: The Netherlands
Default zobel network / emitter resistors

To zobel or not to zobel,that is the question !
Can any one give a reasonable explanation (or link to) why to zobel or not at the output of an Amp ?

Secondly,
In the emitters of the output stage there are low ohmic resistors (0.1 to 0.33 ohm).
Some say it s not necessary, others put them in !
What do you use ?
And i mean, how to get such low values (put some in parallel )
or ............... ?

grtz

Simon
  Reply With Quote
Old 26th January 2004, 10:27 AM   #2
DarkOne is offline DarkOne  Slovakia
diyAudio Member
 
DarkOne's Avatar
 
Join Date: Oct 2001
Location: Bratislava
You need to use emitter (source) resistors if you are paraelling output devices. No pair of transistors is super matched, you allways see some difference in Vbe (Vgs) and transconductance of transistors. Because of this you have to use emitter resistors to "symetrize" current flow trough devices.

Zobel network is used to eliminate parasitic hf noise inducted on cables.
  Reply With Quote
Old 26th January 2004, 10:27 AM   #3
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Default Commentable Thoughts

TO MY DEAR FRIEND BLU_LINE

SIR,
Zobel network enhances high- frequency Stability of amplifiers.
Zobel network prevents the amplifier from breaking up into high-frequency oscillations.
It acts as a shunt at the output of amplifier which inturns dampens the high impedance of very high frequency components[IF PRESENT] at output.

Secondly, The Emitter resistors,
Since the VBE characteristics of Transistors vary to some extent which hampers the equal current sharing between them when paralleling them .There fore to ensure proper current sharing one must implement emitter resistors and they also restrict the thermal runaway phenomena to some extent and thus contribute to stability and ensure stable biasing.

Therefore according to my opinion u must use Zobel network and must implement emitter resistors .

REGARDS
ampman
A friend in deed is afriend in need!
  Reply With Quote
Old 26th January 2004, 10:41 AM   #4
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
You still need emitter resistors even if you don't use parallel output devices. You need them to get some DC series current feedback to stabilise the Iq vs temp.


Jan Didden
  Reply With Quote
Old 26th January 2004, 10:42 AM   #5
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
If you have one pair of output devices you need emitter resistor to achieve temp stability and if you have more than one pair they will also create current sharing.

If you have mosfets you don't have to use these resistors if you have only one pair. In some cases you can also skip them if you more two pairs or more. This is valid for Hitachis lateral mosfets but for normal vertical ones I think source resistors are a must.

Zobel network, resistor + cap at the output is a frequency comensation for the output stage, even though it not seems so. If you don't have this res+cap the output stage will have a pole at a not so good freqeuncy, way too low (= oscillation).
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 26th January 2004, 10:44 AM   #6
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Default Re: zobel network / emitter resistors

Quote:
Originally posted by blu_line
And i mean, how to get such low values (put some in parallel )
or ............... ?
You only have to buy them. They are quite common, nothing unusual at all.
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 26th January 2004, 10:56 AM   #7
diyAudio Member
 
blu_line's Avatar
 
Join Date: Jan 2002
Location: The Netherlands
Quote:
You only have to buy them. They are quite common, nothing unusual at all.
Could you please name a manufacturer ?
Metal oxide /film or another ?

grtz

Simon
  Reply With Quote
Old 26th January 2004, 11:25 AM   #8
diyAudio Member
 
Audiofanatic's Avatar
 
Join Date: Oct 2002
Location: The Netherlands, Utrecht
Quote:
Originally posted by blu_line


Could you please name a manufacturer ?
Metal oxide /film or another ?

grtz

Simon

Hi Simon,

Have you ever heard of DALE/Vishay?
They are the best (for the money)
Peranders = right Caddock is better but realy expensive!

Best regards,


Audiofanatic
__________________
Be nice to animals.
  Reply With Quote
Old 26th January 2004, 11:28 AM   #9
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
You have also Caddock THE best(?) but they a bit expensive.

Vitrohm, danish, fair
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 26th January 2004, 11:36 AM   #10
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Carefull with the Caddocks, they use NiChr elements, low inductance, low noise, but very sensitive to overload. They can be easily destroyed by a few times rated current even on short peaks. It's in the data sheets, but I found out the hard way.

Jan Didden
  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
Zobel Network Corrections fotios Solid State 11 22nd February 2007 05:03 AM
zobel network and cat5 reddish75 Chip Amps 5 17th January 2007 09:31 PM
Zobel Network JiggaD369 Multi-Way 9 5th May 2005 12:27 AM
Zobel Network nuttinbutSQ Multi-Way 6 16th March 2004 08:19 AM


New To Site? Need Help?

All times are GMT. The time now is 06:22 AM.


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