John Curl's Blowtorch preamplifier part II - Page 160 - diyAudio
Go Back   Home > Forums > Member Areas > The Lounge

The Lounge A place to talk about almost anything but politics and religion.

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 26th September 2009, 03:15 PM   #1591
Netlist is offline Netlist  Belgium
diyAudio Moderator Emeritus
 
Netlist's Avatar
 
Join Date: Jan 2003
OT stuff split to here: Split from Blowtorch thread
  Reply With Quote
Old 26th September 2009, 04:22 PM   #1592
PMA is offline PMA  Europe
Design engineer, consultant
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
synO8, the BT input stage is a V/I converter, not a voltage amplifying stage. Though voltage noise is not any superb, it is about 7nV/rtHz. Better than many opamps.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html

Last edited by PMA; 26th September 2009 at 04:25 PM.
  Reply With Quote
Old 26th September 2009, 04:33 PM   #1593
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally Posted by PMA View Post
synO8, the BT input stage is a V/I converter, not a voltage amplifying stage. Though voltage noise is not any superb, it is about 7nV/rtHz. Better than many opamps.
What is the purpose of using low noise JFETs in the input stage. Any N/P channel JFET devices, matched at the same level, will do exactly the same. Not to mention you could raise the supply voltage to, say, +/-24V. Here goes the myth of BT being impossible to reproduce, due to lack of Toshiba devices.

Set aside 7nV/rthz is almost one order of magnitude of what a low noise opamp can do today.
  Reply With Quote
Old 26th September 2009, 04:39 PM   #1594
PMA is offline PMA  Europe
Design engineer, consultant
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
The supply voltage is +/-30V, IMO.
Regarding JFETs, these low Vp devices have higher transconductance than the high Vp parts, and low noise. Operated at high Id, they have very good linearity (interesting that EB operates them too low).
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 26th September 2009, 04:40 PM   #1595
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Syno8, please tell me which input devices that you would chose for the comp diff input stage for line amp operation?
We have used Toshiba devices, because they became the world standard, years ago, and there are not many good substitutes.
Now please, without just empty criticism, give us some part numbers that you would prefer that offer similar performance, without significant compromise.
  Reply With Quote
Old 26th September 2009, 04:47 PM   #1596
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally Posted by PMA View Post
The supply voltage is +/-30V, IMO.
Regarding JFETs, these low Vp devices have higher transconductance that the high Vp parts, and low noise. Operated at high Id, they have very good linearity (interesting that EB operates them too low).
It is impossible to have a coherent discussion.

I have just mentioned that the input stage has the gain < 1 and hence doesn't have the slightest positive impact in the overall gain and noise. The JFET transconductance doesn't really matter, it does not appear in the first order approximation of the overall gain.

You feed 2SK389/2SJ109 at +/- 30V and you'll maybe see what's going to happen. 2SJ109 has Vgdmax = 30V and that includes the voltage swing.
  Reply With Quote
Old 26th September 2009, 04:51 PM   #1597
PMA is offline PMA  Europe
Design engineer, consultant
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
syn08, the JFETs sit at 15V defined by MOSFETs (half supply voltage). Try to look at the circuit. I have analyzed it in deep, you only criticize. Or you only do not understand discrete electronic circuits.
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html

Last edited by PMA; 26th September 2009 at 04:58 PM.
  Reply With Quote
Old 26th September 2009, 04:56 PM   #1598
PMA is offline PMA  Europe
Design engineer, consultant
diyAudio Member
 
PMA's Avatar
 
Join Date: Apr 2002
Location: Prague
voltages
Attached Images
File Type: png for_syn08.PNG (24.4 KB, 305 views)
__________________
Pavel Macura
http://web.telecom.cz/macura/audiopage.html
  Reply With Quote
Old 26th September 2009, 05:06 PM   #1599
diyAudio Member
 
john curl's Avatar
 
Join Date: Jul 2003
Location: berkeley ca
Thanks PMA, it would seem that Syn08 has not really looked carefully at the circuit. Of course, I never run the actual devices at their max rating, too much potential for leakage, even with 1K drive impedance or so. Wavebourn did run devices close to the max rating, at least in worst case, but he was using a 1G input resistance or about 1 million times higher resistance that we would be with the the Blowtorch input stage. Where was Syn08 then, when he could have criticized something that really could go 'off the rails'?
  Reply With Quote
Old 26th September 2009, 05:07 PM   #1600
syn08 is offline syn08  Canada
Account disabled at member's request
 
Join Date: Aug 2005
Location: Toronto
Quote:
Originally Posted by PMA View Post
voltages
Great, now apply input signal and swing the output towards the rails.
  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



New To Site? Need Help?

All times are GMT. The time now is 04:12 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