Help needed with Mosfet power amp - 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 16th October 2012, 07:56 AM   #1
Niquel is offline Niquel  Spain
diyAudio Member
 
Join Date: Feb 2012
Default Help needed with Mosfet power amp

Hi there,
I am newbie with mosfet and I am trying to understand a power amp schematic with these Hitachi complementary transistors. I would appreciate if someone could tell me what's the purpose in using bjts from source to gate in the schematic below and how is this topology called (if there is any) to search more information and study it with more detail.
Thanks in advance.
Attached Images
File Type: png MOSFET PAMP.png (123.6 KB, 95 views)
  Reply With Quote
Old 16th October 2012, 08:11 AM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
The bjts are used for current limiting (protection). Looking at one side, when the voltage across R13 reaches sufficient to turn on TR4, then TR4 begins to "short" the drive to the FET and provides limiting. R11 and R12 make a divider. When the voltage on the base of TR4 reaches 0.7 volts the limiting begins.

The amp is a standard configuration. DC coupled with a LTP (long tailed pair) input stage and source follower outputs. The voltage gain of the circuit is R8 divided by R6. C3 ensures the gain rolls off at low frequencies and is unity (1) at DC.

C3 and C1 could usefully be made a little larger.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 16th October 2012, 08:31 AM   #3
diyAudio Member
 
Zero Cool's Avatar
 
Join Date: Sep 2004
Location: MN
that looks like a Tube works guitar amp! and as such C3 and C1 are probably purposely small!
__________________
It's not about what you can BUY...It's about what you can BUILD!
  Reply With Quote
Old 16th October 2012, 09:26 AM   #4
Niquel is offline Niquel  Spain
diyAudio Member
 
Join Date: Feb 2012
Mooly, thank you for your feedback, really helpful.
Zero Cool, It is the Marsh...5213 (mosfet twin reverb 100 W), why you say purposely small?.

Thanks once more
  Reply With Quote
Old 16th October 2012, 12:48 PM   #5
diyAudio Member
 
Zero Cool's Avatar
 
Join Date: Sep 2004
Location: MN
you may want to limit the low frequencies of a guitar amp vs say a bass amp or home audio amp where you want the full extension.

Low "E" on a guitar is 82hz so limiting the lows down around 30-40hz would clean up the low end a bit and most guitar speakers don't have a lot of excursion capability so limiting the amp down around 30-40hz would help protect the speakers against mechanical damage!
__________________
It's not about what you can BUY...It's about what you can BUILD!
  Reply With Quote
Old 16th October 2012, 03:10 PM   #6
Niquel is offline Niquel  Spain
diyAudio Member
 
Join Date: Feb 2012
Thank you Zero, very didactic.
Cheers!
  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 Power AMP monkey29 Chipamp 1 1st September 2010 07:33 AM
Small Power D class MOSFET Amplifier Needed!! Kazus Class D 8 12th March 2009 03:58 PM
Wanted: H&H MosFet V800 Power Amp SkipperSims Parts 4 8th November 2008 01:40 PM
MOSFET power amp help pollypocket Solid State 19 7th December 2006 07:01 PM
450W@8 Ohms Mosfet amp schematics needed ZuMbAiU Solid State 31 18th January 2006 11:47 PM


New To Site? Need Help?

All times are GMT. The time now is 10:45 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