MOSFET amplifier - 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 3rd December 2006, 09:38 AM   #1
ash_dac is offline ash_dac  United Kingdom
diyAudio Member
 
Join Date: Jan 2005
Location: UK
Thumbs down MOSFET amplifier

Hi,

I found this amplifier design in a text book so I had a go at simulating it in LTSpice. In the original design the transitors were 2N929 and 2N657 but i've swapped these for BC547 for the simulation.


Click the image to open in full size.

Click the image to open in full size.


On the FFT analysis (not shown) there was a very large second harmonic (input stage used ?) .

Looks like a bit of a unstable design.

Has anyone ever built an amplifier like this ?
  Reply With Quote
Old 4th December 2006, 07:44 AM   #2
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Hi,

I think you should check your schematic: there seems to be a number of errors: i.e. coupling capacitors should be included in the gates of the power MOSFETs.
LV
  Reply With Quote
Old 4th December 2006, 12:17 PM   #3
ash_dac is offline ash_dac  United Kingdom
diyAudio Member
 
Join Date: Jan 2005
Location: UK
Quote:
Originally posted by Elvee
Hi,

I think you should check your schematic: there seems to be a number of errors: i.e. coupling capacitors should be included in the gates of the power MOSFETs.
LV
Sorry missed the coupling caps.
  Reply With Quote
Old 4th December 2006, 01:26 PM   #4
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Quote:
Originally posted by ash_dac


Sorry missed the coupling caps.
It isn't the only mistake: the arrangement of C3 and C4 makes no sense. To get meaningful comments (and simulation results), you need to check thoroughly the whole schematic.
LV
  Reply With Quote
Old 4th December 2006, 05:26 PM   #5
ash_dac is offline ash_dac  United Kingdom
diyAudio Member
 
Join Date: Jan 2005
Location: UK
Quote:
Originally posted by Elvee

It isn't the only mistake: the arrangement of C3 and C4 makes no sense. To get meaningful comments (and simulation results), you need to check thoroughly the whole schematic.
LV
Thanks for the pointer
  Reply With Quote
Old 4th December 2006, 06:09 PM   #6
ash_dac is offline ash_dac  United Kingdom
diyAudio Member
 
Join Date: Jan 2005
Location: UK
Click the image to open in full size.

Redrawn somewhat. C4 and C3 appear as on the page and may be a printing error.
  Reply With Quote
Old 5th December 2006, 08:55 AM   #7
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
There are lots of oddities: both FETs have the same average gate potential, the lower boostrap/feedback circuit seems completely awkward, etc.
In addition, even if the problems were to be fixed, it wouldn't be a very good circuit, with all the RC couplings, the need for a tightly regulated supply, the ground referenced to the negative rail, etc etc. It is a lousy text-book design and you' d better design something decent from scratch rather than lose time with such a lame duck.
LV
  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
Mosfet Amplifier Telnet100 Solid State 4 8th August 2012 09:53 PM
MOSFET/MOSFET amplifier jarek Pass Labs 21 22nd June 2004 05:04 PM
1kW MOSFET amplifier Kilowatt Solid State 207 28th March 2004 09:44 PM


New To Site? Need Help?

All times are GMT. The time now is 06:42 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