Audio (Lateral) MOSFET's for Class AB - Overview, P-Spice URL's - Page 5 - 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 13th May 2012, 10:56 AM   #41
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Is it this ?
https://docs.google.com/open?id=0B83...VZpSUtxQ3pFWHM


I see , it doesn't always open
  Reply With Quote
Old 13th May 2012, 11:01 AM   #42
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Default Try this

Click the image to open in full size.

Taken from item No 34
  Reply With Quote
Old 13th May 2012, 11:57 AM   #43
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
That remote server pic (what's wrong with attachments?) only shows the follower output stage.
Where is the amplifier?
__________________
regards Andrew T.
  Reply With Quote
Old 13th May 2012, 12:13 PM   #44
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
That's the problem . I suspect the other part of the circuit shows some important detail . The other circuit I supplied seems similar . To be honest it seems overkill . I think the gentleman asking the question wants an answer without showing all of the circuit .

Last edited by nigel pearson; 13th May 2012 at 12:15 PM.
  Reply With Quote
Old 13th May 2012, 03:55 PM   #45
diyAudio Member
 
Join Date: Sep 2006
Quote:
Originally Posted by AndrewT View Post
Yes.
Almost every ClassAB push pull amplifier has a DC output offset adjustment.
Hi Andrew,

This is actually not quite true. Most solid state power amps do not have a DC offset adjustment. Typically, most have a capacitor (an electrolytic, unfortunately) in the shunt leg of the NFB network to reduce the closed loop gain to unity at DC, leaving only the input offset of the amplifier at the output. This is usually less than 10 mV in a well-designed amplifier. Better amplifiers use a DC servo for offset control, eliminating the need for the electrolytic. This will often get output offset below 5mV, depending on the input offset voltage of the op amp used in the servo.

However, in the current context of a no-feedback amplifier, you are correct. But if one is willing to allow for the "feedback" of a DC servo in a no-NFB amplifier, then a DC servo can be used here as well to eliminate the need for an offset adjustment.

Cheers,
Bob
  Reply With Quote
Old 13th May 2012, 07:52 PM   #46
diyAudio Member
 
Join Date: May 2008
Location: Vi
Perhaps my english is not enought but I don't understaind what is the problem. I don't whant to post the preamp section, It's not necessary. As I have say the final stage is drove by the cathode of half ecc83. The protection circuit protect by dc and short circuit. There is no dc correction, CIN1 and CIN2 prevent this possibility.

Rewind:
I found only a n-mos short. I can't found another ACD101NDD. I found a substitute, the question is: do I have to select 11 nmos and 11 pmos with the same caratteristic to obtain an accettable dc (near zero) at the output? Or the lateral mosfet haven't this problem?

This mosfet isn't cheap so I want to be quite sure that I don't spent money wastefully. Thaks.
  Reply With Quote
Old 13th May 2012, 10:50 PM   #47
diyAudio Member
 
Join Date: Mar 2007
Location: Oxfordshire
Click the image to open in full size.

Here is a small amplifier I was playing with . If wondering the VAS supply originally was to be higher ( +/- 25 V ) . Sounds better this way . I never finished this amp . It looks promising . It outperformed a boosted OPA 604 technically . Note it doesn't need an output cap .

Note how the FET's sit at very different voltages 1.471 and -1.962 form 0V reference . Although at 0.7 A and lower voltage the differences are typical . So exact matches are unlikely to be acheived . Exicon , BUZ and Hitachi devices are very similar .

Hopefully someone will make a recommendation to allow you a simple solution . A reliable reference voltage is required .

These are my notes . I never show them so only in a form I need .

I think someone will also say you need a high drive current for this . Being as optimistic as I can be 20 mA absolute minimum . 50 mA would be ideal .
  Reply With Quote
Old 24th June 2012, 01:38 AM   #48
vilfort is offline vilfort  United States
diyAudio Member
 
Join Date: Feb 2010
AndyVicus:

From what you are discussing it looks like you are building a MASSIVE source follower output stage to a tube driver? If this is correct, you do need a fair amount of current to drive the output stage with this many MOSFET pairs. Remember, they do have input capacitance. HAFLER and others used circa 10mA to drive 3 MOSFETs. You have 11. So shoot for 10mA X (11/3) = 40mA or so. You can get that easily from a EL34 or 2A3 or similar. Forget 6DJ8 or 6sn7 (unless you parallel 4 of them ).

Now for your DC offset problem: add a 100K trimpot in series with the 330K (R84) resistor after the zener on the negative rail. To give yourself a range, replace the 330K (R84) resistor with say 270K. Before turning the amp on set the 100K trimpot so that the 270K + pot = 330K. Turn on amp. Set BIAS. Allow to reach working temp. Now trim the 100K to 0mV between output and ground. In real life 5mV or so is acceptable.
  Reply With Quote
Old 24th June 2012, 10:50 AM   #49
diyAudio Member
 
tiefbassuebertr's Avatar
 
Join Date: Jul 2005
Location: D-55629 Schwarzerden
Quote:
Originally Posted by nigel pearson View Post
Click the image to open in full size.

Here is a small amplifier I was playing with . If wondering the VAS supply originally was to be higher ( +/- 25 V ) . Sounds better this way . I never finished this amp . It looks promising . It outperformed a boosted OPA 604 technically . Note it doesn't need an output cap .

Note how the FET's sit at very different voltages 1.471 and -1.962 form 0V reference . Although at 0.7 A and lower voltage the differences are typical . So exact matches are unlikely to be acheived . Exicon , BUZ and Hitachi devices are very similar .

Hopefully someone will make a recommendation to allow you a simple solution . A reliable reference voltage is required .

These are my notes . I never show them so only in a form I need .

I think someone will also say you need a high drive current for this . Being as optimistic as I can be 20 mA absolute minimum . 50 mA would be ideal .
This is one of the reasons, why I hate so called true complemetary output power stages. Vbe multiplier could be a simple solution. But this isn't also the royal way.

If you want to avoid such problems, go to my overview about output stages topologies without such push pull output stages:
Only N-Channel MOSFETs (NMOS); better Audio from non complements by Audio Power?
The mentioned topologies from the last post perhaps of interest for you.

Last edited by tiefbassuebertr; 24th June 2012 at 10:52 AM.
  Reply With Quote
Old 24th June 2012, 11:32 AM   #50
diyAudio Member
 
tiefbassuebertr's Avatar
 
Join Date: Jul 2005
Location: D-55629 Schwarzerden
Quote:
Originally Posted by Bob Cordell View Post
Hi Andrew,

This is actually not quite true. Most solid state power amps do not have a DC offset adjustment. Typically, most have a capacitor (an electrolytic, unfortunately) in the shunt leg of the NFB network to reduce the closed loop gain to unity at DC, leaving only the input offset of the amplifier at the output. This is usually less than 10 mV in a well-designed amplifier. Better amplifiers use a DC servo for offset control, eliminating the need for the electrolytic. This will often get output offset below 5mV, depending on the input offset voltage of the op amp used in the servo.
Cheers,
Bob
This I had observe in the same kind. My favorite solution isn't a DC offset servo; rather a MKP/MKS capacitor from 4,7uF until 47uF (for small sizes WIMA is a good solution) for electrolytic replace.
The high pass filter character is usefull in such cases, where is present a fat punchy and bloated bass transmission in the aera arround 40-80Hz.
After adjust the capacitance to the right value, the bass transmission is more clear and tight, particularly in cases, where a near-wall/near-corner loudspeaker installation has been realized.
If the high pass character of this capacitor is unwanted, there is the solution without the GND connection of the secundary windings. Instead this each power supply capacitor get in parallel a resistor (please note: the required voltage now must be the twice than before) and various modifications are to carry out at the input of LTP - I have posted the suited schematic anywhere here on diyaudio.

Regard this capacitor in the G-NFB network here on diyaudio there is a detailed discussion.
Who know the URL(s) ?

Last edited by tiefbassuebertr; 24th June 2012 at 11:39 AM.
  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
Spice models Exicon MOSFET's TS Solid State 4 12th February 2012 02:00 PM
Class AB, Class AB Non-Switching, Class AB Soft Non-Switching steph_tsf Solid State 4 15th March 2010 04:39 PM
Looking for lateral mosfet spice models ojg Solid State 3 16th November 2003 12:56 AM
JLH Class-A in a with MOSFET's tschrama Solid State 3 10th February 2002 04:23 PM


New To Site? Need Help?

All times are GMT. The time now is 04:23 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