Modifying Emitter Follower type I - 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 May 2013, 10:55 AM   #1
Skorpio is offline Skorpio  Denmark
diyAudio Member
 
Join Date: Mar 2004
Location: Denmark
Default Modifying Emitter Follower type I

Hi,

A am currently modifying an old amp and the driver/output is a type I emitterfollower. As type II has better performance, I want to upgrade.

The two driver resistors are 220R. I want to lift them from output and connect them in series (440R total). Will this affect stability or other things?

I see also that there are different views on decoupling the resistor:

D. Self:
5.3.3 Switchoff distortion. (Distortion 3c)
The EF Type II configuration in Fig 13b is at first sight merely a pointless variation on Type I, but its valuable property is that the shared driver emitter-resistor Rd, with no output-rail connection, allows the drivers to reverse-bias the base-emitter junction of the output device being turned off..
Speed-up capacitor Cs improves this action, preventing the charge-suckout rate being limited by the resistance of Rd. A 1 uF speed-up capacitor can half the THD at 40kHz, implying cleaner switchoff.

The second influence on turnoff is the value of the driver emitter or collector resistors; the lower they are the faster the stored charge can be removed. Applying these two criteria can reduce HF distortion markedly, but of equal importance is that it minimises overlap of output conduction at HF, which if unchecked gives an inefficient and potentially destructive increase in supply current.
Distortion In Power Amplifiers

Leach:
Fig. 8(b) shows a simplified diagram of the amplifier output stage (the driver transistors are omitted) with a capacitor shown in parallel with R36. Because the VBE multiplier holds the voltage across R36 constant, the addition of the capacitor has no effect on the voltages at the bases of Q18 and Q19. If speedup caps are necessary, they should be added in parallel with R41 and R42. However, these 10 ohm resistors are too small for the speedup caps to have any effect
The Leach Amp - Output Stage

What would You recommend?

  Reply With Quote
Old 8th May 2013, 04:46 PM   #2
orbanp is offline orbanp  Canada
diyAudio Member
 
Join Date: Jul 2007
You did not mention what power is your amplifier. Upgrade the final configuration, though most probably you will not notice much difference.
If anything changes, it could be high frequency parasitic oscillations at switchover, at least that I found when I simulated various output configurations. The speed up capacitor helps quenching the oscillations.
The other change might be different final bias. When bringing up your new circuit, start from zero final bias current and increase it to the desired value. Previous setting might be too high!
Probably best advice is to plug your modified circuit into the Spice simulator and see what effect the various values would have!
The Leach amp circuit is different, it uses a CFP configuration (Sziklay pair), that stage itself could be oscillating. The resistors series to the base of the final transistors are to prevent this.
The leach amp is also generally higher power than Self's blameless amp.

Good luck, Peter
  Reply With Quote
Old 10th May 2013, 06:33 AM   #3
Skorpio is offline Skorpio  Denmark
diyAudio Member
 
Join Date: Mar 2004
Location: Denmark
Thanks for replying!

I changed the circuit some days ago, and no changes in bias or oscillations were present. It seems to have a small sonically20638616rovement, but not sure here at this stage...


Regarding Leach, look at figure 8.b and compare with Self
  Reply With Quote
Old 10th May 2013, 12:57 PM   #4
orbanp is offline orbanp  Canada
diyAudio Member
 
Join Date: Jul 2007
You are correct, the Leach amp does not use CFP output stage.
Not sure what I was thinking...
(one should not believe everything one is reading on the internet ;-)

Last edited by orbanp; 10th May 2013 at 12:59 PM.
  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
Emitter follower related question IG81 Solid State 16 16th November 2009 12:51 PM
Offset Compensated Emitter-follower... mikeks Solid State 24 5th June 2006 08:10 PM
Complex Emitter follower Banfi T. Solid State 104 1st April 2003 10:05 PM
Help a nOOb out with an emitter-follower... EchoWars Solid State 8 8th January 2003 09:40 PM


New To Site? Need Help?

All times are GMT. The time now is 08:27 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