Pathos Amplifiers - 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 23rd January 2003, 01:41 PM   #1
diyAudio Member
 
Join Date: Jan 2002
Default Pathos Amplifiers

Having built some SE Class A amps... I am interested in the Pathos output stages....

Does anyone have a partial schematic or knows how it is wired?

Thanks!!!
  Reply With Quote
Old 23rd January 2003, 02:36 PM   #2
diyAudio Member
 
Join Date: Mar 2001
Location: USA
As I understand it, Pathos makes two types of output stages. For
class AB working, they use complementary MOSFETs in push-pull.
For single ended (or balanced SE) class A, they use their "INPOL"
circuit, described on their web site at www.pathosacoustics.com.

From descriptions I've read, I gather that INPOL is basically a
source follower loaded by a choke and coupled to the load by a
capacitor. The choke and cap together form an energy storage
system that supplies most of the dynamic output current, while
the source follower MOSFET controls the output voltage.

The key claim for this approach is that it allows the follower to
work under nearly constant-current conditions, so it can control
the output voltage with great accuracy.
  Reply With Quote
Old 23rd January 2003, 05:42 PM   #3
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
A follower loaded by a choke will see the full AC current
through the load. There is no mechanism in that arrangement
for constant current through the device.
  Reply With Quote
Old 23rd January 2003, 06:50 PM   #4
diyAudio Member
 
Join Date: Mar 2001
Location: High Point, NC
Wink Inpol this!

Kinda sorta what's goin' on
Attached Images
File Type: gif pathos.gif (7.8 KB, 5065 views)
  Reply With Quote
Old 23rd January 2003, 07:11 PM   #5
diyAudio Member
 
Join Date: Mar 2001
Location: USA
Quote:
Originally posted by Nelson Pass
A follower loaded by a choke will see the full AC current
through the load. There is no mechanism in that arrangement
for constant current through the device.
Then perhaps I have misconstrued the claims made on their web
site. Unfortunately I can't locate a copy of their patent, from which
one might better understand and assess these claims.

In any case, the schematic posted by scottnixon above seems to
agree with the basic description given by Pathos and others.
  Reply With Quote
Old 23rd January 2003, 07:22 PM   #6
diyAudio Member
 
Join Date: Jan 2002
Default modification....

Couldn't we choke load the 12AX7 cathode follower.... then use this to direct couple to the mosfets gates?

output operating current then dependent on the voltage drop across this choke.

Instead of a 12AX7... use a 6BX7 or something like that.

This would get rid of a coupling cap at least...

thoughts?
  Reply With Quote
Old 23rd January 2003, 10:42 PM   #7
diyAudio Member
 
Join Date: Mar 2001
Location: USA
Default I knew I wasn't making this up

Doing some more digging on this, I unearthed a review of the
Pathos Twin Towers amp by Dan Sweeny in Issue 116 (Feb '99)
of The Absolute Sound. In a sidebar on INPOL theory, he explains:

"Under no-signal conditions, the choke allows direct current to
flow unimpeded from the positive supply to ground [while] the
parallel capacitor ... provides additional energy storage while
equalizing the current draw for either half of the wave cycle, i.e.,
when the [output] MOSFET is sourcing or sinking current ...

"Impedances are set so that the total series impedance of the
capacitor plus the loudspeaker circuit is somewhat higher than
the impedance to ground; therefore current through the output
transistor never varies appreciably even though the internal
impedance of the MOSFET drops with increasing signal voltage."

In an effort to see if this could possibly be true, I quickly modeled
the INPOL output stage in Electronic Workbench. In this model at
least, the current through the MOSFET does vary by about 2:1 at
full output, just as it would with a constant current source load.
This appears to negate the claim of constant current operation.

This kind of choke loading does offer the benefit of cutting the
idle dissipation of the output stage in half when compared to a
CCS loading, as there is no need for a corresponding negative
power supply rail.
  Reply With Quote
Old 24th January 2003, 12:04 AM   #8
Pan is offline Pan  Sweden
diyAudio Member
 
Join Date: Sep 2002
Even though I donīt understand half of this circuit to me it looks like the caps are there for no reason.

Circlotrons choke amp has no cap at output and only a tiny amount of offset.

/Peter
  Reply With Quote
Old 24th January 2003, 04:55 PM   #9
The one and only
 
Nelson Pass's Avatar
 
Join Date: Mar 2001
"Impedances are set so that the total series impedance of the
capacitor plus the loudspeaker circuit is somewhat higher than
the impedance to ground; therefore current through the output
transistor never varies appreciably even though the internal
impedance of the MOSFET drops with increasing signal voltage."

That statement makes no sense to me at all, particularly
in reference to the Pathos schematic.
  Reply With Quote
Old 24th January 2003, 05:10 PM   #10
tvi is offline tvi  Australia
diyAudio Member
 
tvi's Avatar
 
Join Date: Apr 2001
Location: Moonee Ponds, Vic, Australia
The Closest Patent I have seen to the Inpol output stage
is US Pat 5498997 to Cristopher Schiebold, March, 12, 96

See pic

Regards James
Attached Images
File Type: gif schibold.gif (20.6 KB, 3995 views)
  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
Pathos Classic one priax Tubes / Valves 5 12th July 2013 02:32 PM
pro amplifiers vs. home audio amplifiers bonsai171 Solid State 26 25th February 2004 08:24 PM
5.1 amplifiers bryce Digital Source 0 13th February 2004 04:17 PM
Paradigm amplifiers? Anthem amplifiers? Corn-Picker Solid State 2 24th January 2004 03:10 AM
Many smaller amplifiers vs. bigger amplifiers. djdan Solid State 9 17th September 2002 04:40 PM


New To Site? Need Help?

All times are GMT. The time now is 02:55 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright Đ1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2