F5 type amp but with higher power - diyAudio
Go Back   Home > Forums > Amplifiers > Pass Labs

Pass Labs This forum is dedicated to Pass Labs discussion.

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 28th December 2009, 04:44 AM   #1
fab is offline fab  Canada
diyAudio Member
 
fab's Avatar
 
Join Date: Mar 2004
Location: Canada
Default F5 type amp but with higher power

Hi,

I have already built the F5 as per original schematics. I like the sweet sound of the amp for moderate listening levels but I would like to get more power and more voltage gain while keeping it simple (like the F5).

I saw some posts on making the F5 balanced X amp but it is not my goal.

This is the schematics I came up with to get about 80-90W rms (8 ohms).
The heatsink size would allow about 10Wrms (8 ohms) class A and the rest of power in class AB.

It has a cascode input to handle higher voltage rails.
It has a mosfet driver stage to increase the drive current (35ma) for the 4 pairs of mosfet outputs. This vertical mosfet driver also allows to get more gain from input stage (higher drain resistance) at the same time because of the high threshold voltage compared to lateral mosfet or BJT...

To keep enough feedback factor while increasing the voltage gain to about 26db, the open loop gain is increased by paralleling output mosfet and modifying the input stage bias (3 ma).

Can you comment if this design has some potential...

Thanks

Fab
Attached Images
File Type: png Fab-HPF5_amp.PNG (29.7 KB, 606 views)
  Reply With Quote
Old 28th December 2009, 02:29 PM   #2
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
seems like a possible way to go.

I'd not want to use any bipolar transistors myself...

Of course it is no longer an F5 at this point.

Where are you picking up the extra gain... maybe you can post the gains per stage (OL)? Is it all in the cascode?

_-_-bear
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 28th December 2009, 10:43 PM   #3
fab is offline fab  Canada
diyAudio Member
 
fab's Avatar
 
Join Date: Mar 2004
Location: Canada
Default Open loop gain

Quote:
Originally Posted by bear View Post
seems like a possible way to go.

I'd not want to use any bipolar transistors myself...

Of course it is no longer an F5 at this point.

Where are you picking up the extra gain... maybe you can post the gains per stage (OL)? Is it all in the cascode?

_-_-bear
Hi Bear,

Most of the extra gain comes from the added parallel mosfets where the mosfet in common source configuration has a gain of about RL * gm where RL = 8 and gm = [5 -7] for IRFP240/9240. Thus each added pair adds about 5 of gain or so. Thus if 3 pairs gives about 15 of gain than it corresponds to the loss of feedback factor due to the closed loop gain increase from original F5 design...

The cascode should not add much gain but the Rload of the jfet input is increased by reducing the Id and having the VGSoff the IRF610(9610) requiring more voltage drop across Rload.

Yes it is no longer an F5 but can it provide good sound (at higher audio level)even if different?

I wonder if only 3 pairs with higher bias would provide better sound than with 4 pairs...

Also, regarding the cascode with bipolar, is my "floating" reference a good idea?

Thanks

Fab

Last edited by fab; 28th December 2009 at 10:54 PM. Reason: explanation on added gain
  Reply With Quote
Old 28th December 2009, 10:53 PM   #4
fab is offline fab  Canada
diyAudio Member
 
fab's Avatar
 
Join Date: Mar 2004
Location: Canada
Default Remove bipolar...

Quote:
Originally Posted by bear View Post
seems like a possible way to go.

I'd not want to use any bipolar transistors myself...
....
_-_-bear
Like this cascode:
Attached Images
File Type: png Fab-HPF5_amp_jfet-cascode.PNG (28.7 KB, 494 views)
  Reply With Quote
Old 28th December 2009, 10:58 PM   #5
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
The placement of the limiters will probably blow out the
drivers. Probably better to just take the limiters out.

  Reply With Quote
Old 29th December 2009, 01:04 AM   #6
fab is offline fab  Canada
diyAudio Member
 
fab's Avatar
 
Join Date: Mar 2004
Location: Canada
Default Limiters

Quote:
Originally Posted by Nelson Pass View Post
The placement of the limiters will probably blow out the
drivers. Probably better to just take the limiters out.

I do not understand why. It takes quite a large amount of load current to activate them. My simulator does not show clipping until less than 1 ohm load. Unless you mean that I should limit more the current...

thanks

Fab
  Reply With Quote
Old 29th December 2009, 02:17 AM   #7
a.wayne is offline a.wayne  United States
Sin Bin
 
Join Date: May 2008
Location: Front Row Center
1 ohm Hmmmmm .... i can test for you .....
  Reply With Quote
Old 29th December 2009, 02:40 AM   #8
fab is offline fab  Canada
diyAudio Member
 
fab's Avatar
 
Join Date: Mar 2004
Location: Canada
Quote:
Originally Posted by a.wayne View Post
1 ohm Hmmmmm .... i can test for you .....
Of course, this is a simulator...
  Reply With Quote
Old 29th December 2009, 04:50 AM   #9
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
Quote:
Originally Posted by fab View Post
I do not understand why. It takes quite a large amount of load current to activate them. My simulator does not show clipping until less than 1 ohm load. Unless you mean that I should limit more the current...
M9 and M10 are Mosfet followers. They can deliver a lot
of current, and you are more or less shorting their Sources
to the rails.

Current will flow, sparks will fly.

  Reply With Quote
Old 29th December 2009, 07:09 AM   #10
fab is offline fab  Canada
diyAudio Member
 
fab's Avatar
 
Join Date: Mar 2004
Location: Canada
Default Limiters...

Quote:
Originally Posted by Nelson Pass View Post
M9 and M10 are Mosfet followers. They can deliver a lot
of current, and you are more or less shorting their Sources
to the rails.

Current will flow, sparks will fly.

I think I understand now...
Do you mean that if the current limiters are activated one day than I could blow off the M9 and M10

Thanks

Fab
  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
What's the Idle Current of the F5 Power Amp NV&H Pass Labs 56 3rd February 2010 11:56 AM
What type of Relay for a power amp? Electro-mechanical? Brit01 Solid State 8 11th August 2008 03:46 PM
if I have an amp with less 15W of power, what type of speaker would you recommend? jarthel Multi-Way 17 6th July 2007 10:21 AM
Higher power amp PCBs for pro audio? massappeal129 Solid State 2 10th February 2003 01:24 PM
Super-power amps - higher current better than higher voltage Circlotron Solid State 34 28th June 2002 05:01 AM


New To Site? Need Help?

All times are GMT. The time now is 06:45 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