90+90 volt rails - 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 6th March 2009, 12:26 PM   #1
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
Default 90+90 volt rails

come across this schematic that looks a fairly simple and nice construction ....

the truth is that sudenlly i have the complete list of the original semiconductors available ( yeS !!!!) but what really troubles me is that from expirence it seems that rail voltage looks way higher than needed

also looking at this circuit notice that there is no VI limiters or any oher form of limiting and also heatsinks are notreally something huge ....

so my calculation say that this doesnt look safe ....

your opinion please ????
Attached Images
File Type: jpg armstrong amplifier.jpg (93.4 KB, 1112 views)
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 6th March 2009, 12:39 PM   #2
h_a is offline h_a  Europe
diyAudio Member
 
h_a's Avatar
 
Join Date: Sep 2006
Location: Graz, Austria
90 V rails with only 2 pairs of output transistors?

15 V rails for the frontend? Difference shamelessly burned with a resistor?

Does not charm me

Have fun, Hannes
  Reply With Quote
Old 6th March 2009, 02:36 PM   #3
wg_ski is offline wg_ski  United States
diyAudio Member
 
Join Date: Oct 2007
Just because whoever built the amp the last time used only two sets of output transistors doesn't mean you have to. Seems silly to have the VAS doubled up and skimp on outputs. I'd beef the drivers up to 15032/15033, but you could parallel the Jap types here, too.
  Reply With Quote
Old 6th March 2009, 02:40 PM   #4
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
Default yes.....

that is correct and thank you very much

but this is a factory made design called armstrong .... here is a link
http://www.audiomisc.co.uk/Armstrong/700/700page1.html
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 6th March 2009, 02:47 PM   #5
wg_ski is offline wg_ski  United States
diyAudio Member
 
Join Date: Oct 2007
Quote:
Originally posted by h_a
15 V rails for the frontend? Difference shamelessly burned with a resistor?
Let's see you find (affordable) JFETs that can handle the 90 volt rails. With two differential stages, you can get away with running the first one off lower voltage - its no different than an op-amp front end.


A word of caution - there isn't any frequency compensation in this amp schematic. It will need the usual collector-base caps on both sides of the VAS and because of the extra front end stage, a lead compensation cap as well. An experienced builder will know how to calculate this (or at least tune it in experimentally).
  Reply With Quote
Old 6th March 2009, 02:51 PM   #6
wg_ski is offline wg_ski  United States
diyAudio Member
 
Join Date: Oct 2007
Default Re: yes.....

Quote:
Originally posted by sakis
that is correct and thank you very much

but this is a factory made design called armstrong .... here is a link
http://www.audiomisc.co.uk/Armstrong/700/700page1.html
The schematic given may be incomplete (ie, no compensation values, no SOA limiters, etc). It also looks like 'consumer grade' electronics to me. Two output pairs will do 8 ohms just fine if that's all you ever drive. Sony receiver/amps can't handle anything but 8 ohm loads, either.
  Reply With Quote
Old 6th March 2009, 03:21 PM   #7
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
the Armstrong claims ONLY 200W for a BJT output stage from +-90Vdc.
The literature confirms 85Vpk output on music transients and also states that no current limiting nor protection is installed.

I suspect that a small transformer and low values of smoothing capacitance are being used to protect the output stage during abuse conditions.

Normally we'd expect 200W from +-60Vdc to +-65Vdc.
__________________
regards Andrew T.
  Reply With Quote
Old 6th March 2009, 04:25 PM   #8
wg_ski is offline wg_ski  United States
diyAudio Member
 
Join Date: Oct 2007
Quote:
Originally posted by AndrewT
the Armstrong claims ONLY 200W for a BJT output stage from +-90Vdc.

Gotta wonder if it will make point five past lightspeed (or the Kessel Run in sub-12 parsecs).
  Reply With Quote
Old 6th March 2009, 04:31 PM   #9
h_a is offline h_a  Europe
diyAudio Member
 
h_a's Avatar
 
Join Date: Sep 2006
Location: Graz, Austria
Quote:
Let's see you find (affordable) JFETs that can handle the 90 volt rails.
Naah!

Much more elegant possibilities available than to roast a resistor. Like use a cascode and employ a nice series regulator for the frontend. Or use the resistor at the very least as part of a CRC filter.

Not that it's strictly needed, but hey, using a power resistor feels just primitive IMHO. Does not speak in favour of the design.

Missing compensation does not either

If I have to rework that circuit before building it, I can build something entirely different instead as well

Have fun, Hannes
  Reply With Quote
Old 6th March 2009, 05:17 PM   #10
diyAudio Member
 
Michael Chua's Avatar
 
Join Date: Jul 2006
Location: Calais, ME
90V rails, 200W rating = Dynamic Headroom.

Would be wise to double the outputs.
__________________
AmpsLab.com
  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
Switching 230 Volt Transformer to 120 Volt OMNIFEX Parts 10 6th April 2008 04:34 PM
P3A on +/-12V rails 00940 Solid State 6 5th March 2008 12:44 PM
Rails voltages for A30 same Pass Labs 16 26th June 2007 07:14 PM
from +/-80v to +/-70v rails leander Solid State 14 13th September 2005 11:26 AM
Cap across rails? MikeW Pass Labs 12 24th August 2004 01:35 PM


New To Site? Need Help?

All times are GMT. The time now is 05:23 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