Another quasi-complementary design - Page 3 - 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 12th March 2005, 02:59 AM   #21
quasi is offline quasi  Australia
diyAudio Member
 
quasi's Avatar
 
Join Date: Sep 2004
Location: Adelaide, Australia

One more thing R21, R23 & R25 are on the wrong side of the FET. With the resistors on the source the current sharing works better because as current increase through one FET the voltage drop across the source resistor increases. This means that the gate to source voltage is reduced and the FET backs off.

This is a common mistake with quasi-complimentary amps and this part of the topology is often confused with NPN/PNP output stages.

Cheers
  Reply With Quote
Old 12th March 2005, 06:03 AM   #22
quasi is offline quasi  Australia
diyAudio Member
 
quasi's Avatar
 
Join Date: Sep 2004
Location: Adelaide, Australia
Default High Power Version;

This is the same amp modified to handle much higher rails.

By using the seperate 100v feed on the positive side of the input and driver stage the amp can swing the output closer to the positive rail and provide more power.

The main difference is the addition of a cascode arrangement in the driver stage using P channel FETs.

With the right power supply this amp should be able to deliver around 350 watts into 8 ohms and around 650 into 4 ohms.

This design is intended as a PA amplifier driving big speakers.

Cheers
Attached Files
File Type: pdf artck nmos1v2hp.pdf (52.1 KB, 1984 views)
  Reply With Quote
Old 12th March 2005, 05:13 PM   #23
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Quote:
Originally posted by quasi
One more thing R21, R23 & R25 are on the wrong side of the FET. With the resistors on the source the current sharing works better because as current increase through one FET the voltage drop across the source resistor increases. This means that the gate to source voltage is reduced and the FET backs off.

This is a common mistake with quasi-complimentary amps and this part of the topology is often confused with NPN/PNP output stages.

Cheers
This is not strictly true, either way can work. The reason that it works if you use what appears to be drain resistor is because of the local feedback wrapped around the output device. Peter Baxandall wrote a letter in Wireless World in September 1969 describing the operation.

However, I believe that in case of the schematic posted you are correct as the local feedback does not take place in the same way and thus the resistors should be in the sources.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 12th March 2005, 07:40 PM   #24
diyAudio Member
 
traderbam's Avatar
 
Join Date: Jan 2002
Location: Earth
Hi Quasi,
Interesting design. I understand you haven't built it yet. Have you simulated it?
My question is about the stability of the feedback loop...have you estimated/simulated the phase margin?
BAM
  Reply With Quote
Old 17th March 2005, 06:49 PM   #25
edl is offline edl  Hungary
diyAudio Member
 
edl's Avatar
 
Join Date: Oct 2004
http://www.audiofanatic.it/Schemi/Ti..._MOS_BUZ23.jpg
  Reply With Quote
Old 17th March 2005, 10:42 PM   #26
quasi is offline quasi  Australia
diyAudio Member
 
quasi's Avatar
 
Join Date: Sep 2004
Location: Adelaide, Australia
Default Interesting

I wonder why they use such a complicated thermal compensation circuit. Well I better build my version then and find out.

I still think that the negative rail output FETs are on the wrong side i.e. they should be on the source. It does make the short cct protection slightly easier to configure though.

Looks like they are only running around 4 mA of driver current per leg.


Cheers
  Reply With Quote
Old 18th March 2005, 10:55 AM   #27
quasi is offline quasi  Australia
diyAudio Member
 
quasi's Avatar
 
Join Date: Sep 2004
Location: Adelaide, Australia
Quote:
Originally posted by traderbam
Hi Quasi,
Interesting design. I understand you haven't built it yet. Have you simulated it?
My question is about the stability of the feedback loop...have you estimated/simulated the phase margin?
BAM
No I haven't built it yet or simulated it (I don't have sim software). I'll build one over the next week or so. I'll probably just build one to test it and then use it as a sub-amp or something...hmm.

The feedback loop is one I have always used (and almost everyone else too). I see no reason for it not to be stable.

Anyway I'll update in a week or so.

Cheers
  Reply With Quote
Old 25th March 2005, 01:46 PM   #28
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Smile Re: Re: confusion

Quote:
Originally posted by richie00boy
quasi,

Thanks for the compliment You do not need to include a normal diode in the lower zener diode because there is absolutely no risk of current reaching up through it.



Hi Kanwar,

No, you must include the diode. As you say the voltage will be clamped at 12V, but surely it's far better to stop the spurious transients even being a problem. They will cause distortion.
Hi buddy,
The voltage will be clamped with respect to VGS in positive direction and the diode in series only exhibits forward drop.
I see no reason for its place.
In negative direction[without the diode]the voltage will be clamped to forward drop of zener itself.
kindly correct me if am wrong,

regards,
kanwar
  Reply With Quote
Old 25th March 2005, 06:21 PM   #29
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
You are right. I'm just saying that the diode prevents even having to even clamp any voltage in the negative direction. If any voltage gets up to the gate it will cause distortion. The gate will not be destroyed without the diode, I'm just recommending it to obtain minimum distortion.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 27th March 2005, 02:05 PM   #30
diyAudio Member
 
Workhorse's Avatar
 
Join Date: Dec 2004
Smile Hi buddy

Thanks for your suggestionable comment.

Thanks again!
regards,
kanwar
  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
quasi-complementary output Vlad Pass Labs 4 13th April 2010 12:07 PM
quasi complementary old school design rtill Solid State 3 11th August 2009 03:29 PM
Quasi or full complementary. pro Solid State 7 14th September 2004 09:26 PM


New To Site? Need Help?

All times are GMT. The time now is 08:58 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