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 27th January 2007, 11:44 AM   #1
roender is offline roender  Romania
diyAudio Member
 
roender's Avatar
 
Join Date: Sep 2006
Default Triple EF BJT power stage.

Hello all,

What do you think about this final EF stage?
What should I cut or keep? The main goal is stability, high input impedance and low distosion at 20Khz
Attached Images
File Type: jpg powerstage.jpg (55.3 KB, 680 views)
  Reply With Quote
Old 27th January 2007, 11:55 AM   #2
diyAudio Member
 
Join Date: Jul 2005
Location: Podkarpacie, Poland
What is R1 and R11. They will dissipate lot power. Isn't better to simply connect emiters by resistor, like in many others amp?
__________________
Wojtek
  Reply With Quote
Old 27th January 2007, 12:30 PM   #3
roender is offline roender  Romania
diyAudio Member
 
roender's Avatar
 
Join Date: Sep 2006
Quote:
Originally posted by wojtek5001
What is R1 and R11. They will dissipate lot power. Isn't better to simply connect emiters by resistor, like in many others amp?
It is a very simple way to discharge the base junction at HF and to prevent negative base impedance
  Reply With Quote
Old 27th January 2007, 01:29 PM   #4
diyAudio Member
 
Join Date: Jul 2005
Location: Podkarpacie, Poland
I think, that resistor between emiters Q1 and Q3 (optionaly pararell with cap) will do the same, like in Douglas Self amp. You should also insert some small resistors in series of output transistor bases (especialy when using cap mentioned in previous brackets )
__________________
Wojtek
  Reply With Quote
Old 27th January 2007, 01:33 PM   #5
roender is offline roender  Romania
diyAudio Member
 
roender's Avatar
 
Join Date: Sep 2006
The cap trick don't work at high freq. and base stopers increase phase shift
  Reply With Quote
Old 27th January 2007, 03:06 PM   #6
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
the Cordell thread seems to have confirmed that BJT output stages need about 15mV to 25mV across each of the emitter resistors to stay at or near optimum bias to help hide crossover distortion.

They also agree it is better to err on the high side rather than the low side (variations with junction/ambient temperatures) to stay above the 15mV lower limit for all operating conditions.

Your 100mA and 0r1 put you too far below the 15mV.

If you follow their advice then either bigger Re or some big sinks to dissipate more Iq.

Parallel pairs with low value Re will require more precise matching than with higher Re values.

I don't follow the diamond arrangemment of the emitter resistors on the drivers. I have to leave that to the experts.
__________________
regards Andrew T.
  Reply With Quote
Old 27th January 2007, 04:16 PM   #7
lineup is offline lineup  Sweden
diyAudio Member
 
lineup's Avatar
 
Join Date: Dec 2005
Location: the north
Quote:
Originally posted by wojtek5001
What is R1 and R11. They will dissipate lot power.
Isn't better to simply connect emiters by resistor, like in many others amp?

I have to agree.
So if this is good,
why don't you replace R5 with 2 resistors to supply lines?

Now, if it is good in place,
it is most probably good in the other place.
So:
Replace R1 / R11 with one resistor between emitters.
Just like R5.

The current variations caused by R1 and R11 which are loading the drivers
can NOT be good.
Imagine +/-20 Volt across those resistors ......

Besides, I think PSRR (supply rejection ratio) will be worse with those resistors.


Questions:
- What Supply voltage, you had in mind?
- What Output power you had in mind,
- And into What Load?



Regards
lineup
__________________
lineup
  Reply With Quote
Old 27th January 2007, 04:18 PM   #8
CBS240 is offline CBS240  United States
diyAudio Member
 
CBS240's Avatar
 
Join Date: Aug 2005
Location: K-town
Hi

What kind of front end is biasing this circuit?
It seems to me that R1 & R11 would cause Q1 & Q3 to conduct asymetrical current(referenced to audio voltage) and the input stage would have to correct for this extra error. If these resistors were replaced with CCS's, the impeadance above the CCS bias setpoint is very high and would reduce this extra error current load. I agree with wojtek5001 about the resistor/cap. Why wouldn't this work at higher frequencies? The point of this cap is to prevent cross-conduction at high frequencies by discharging the bases to turn them off. R5 could have a parralel cap as well. Base resistors will not cause as much phase shift as the extra darlington transistor will, as opposed to a two stage darlington. Maybe reduce the gain slightly but insure more equal current sharing. Vbe multiplier may be helpful in controling output bias setpoint.

Yes Lineup, PSRR would be worsened....



__________________
All the trouble I've ever been in started out as fun......
  Reply With Quote
Old 27th January 2007, 04:35 PM   #9
diyAudio Moderator Emeritus
 
lumanauw's Avatar
 
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
Hi, Roender,

R1 and R11 are interesting. Electrocompaniet 25WclassA also uses these resistors. In the later Electrocompaniet amp, R1 and R11 are replaced by CCS.

Quote:
It is a very simple way to discharge the base junction at HF and to prevent negative base impedance
How do you know it can prevent "negative base impedance"?
  Reply With Quote
Old 27th January 2007, 05:11 PM   #10
roender is offline roender  Romania
diyAudio Member
 
roender's Avatar
 
Join Date: Sep 2006
R1 and R11 is a well known practice in HF amplifiers, where is a must to use BE resistors.
CCS instead those resistors is a very good idea (will improve PSRR also).
The base current in predrivers is to small to replace r5 with cross resistors like in final stage.
The target power is 100w in 8ohm, power BJT's will be NJL0302/0281
  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
Triple emmiter follower bogdan_borko Solid State 48 24th February 2013 03:24 PM
Quad 303 triple cascade hahfran Solid State 33 4th October 2012 12:46 PM
Mastech Triple DC power supply rcchavez Power Supplies 0 11th July 2008 12:09 AM
Switches - Dual Triple Pole, Triple Throw jackinnj Swap Meet 0 27th January 2003 07:18 PM


New To Site? Need Help?

All times are GMT. The time now is 04:12 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