dac I/V convertion with very low distortion - Page 65 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

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 14th November 2012, 01:36 PM   #641
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
The servo is connected to the negative input of the Fet opamp...In LT spice it nulls the offset...
  Reply With Quote
Old 14th November 2012, 01:40 PM   #642
diyAudio Member
 
zenelectro's Avatar
 
Join Date: Sep 2009
Quote:
Originally Posted by MiiB View Post
The servo is connected to the negative input of the Fet opamp...In LT spice it nulls the offset...
Miib, the servo you have shown is wrong polarity - needs inverting. This is for sure.
  Reply With Quote
Old 14th November 2012, 02:04 PM   #643
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
somethings funny...or a little weird... regardless of the connection the modeled servo nulls the offset. If I remove it the offset is 60 mV... hmm
  Reply With Quote
Old 14th November 2012, 03:09 PM   #644
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
In the design of that buffer have you guys think about adding a battery to the gate of the upper jfet, with less than 1nA of leakage current a litio battery will last forever. And the voltage of source to drain of the lower jfet will be higher .

I like the BF862
Attached Images
File Type: png jfet_cascode.png (8.4 KB, 304 views)
__________________
Sérgio Santos
  Reply With Quote
Old 15th November 2012, 06:51 AM   #645
diyAudio Member
 
Join Date: Jan 2011
Location: Germany
I agree that the voltage is too low across drain source. What I do instead, but that takes a few more components, is to use a Zener diode with LP filter, and then a transistor. You can then set VDS to what you prefer.


/S

Quote:
Originally Posted by smms73 View Post
In the design of that buffer have you guys think about adding a battery to the gate of the upper jfet, with less than 1nA of leakage current a litio battery will last forever. And the voltage of source to drain of the lower jfet will be higher .

I like the BF862
  Reply With Quote
Old 15th November 2012, 07:32 AM   #646
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
What is the benefit of a higher VDS..?? and Why would you want to create a fixed Cascode..?? then the voltage swing would still have to throw charge so the capacitance comes into play.

Last edited by MiiB; 15th November 2012 at 07:34 AM.
  Reply With Quote
Old 15th November 2012, 07:46 AM   #647
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
In praxis our buffer works very well although the output transistor has only Vgs of the cascode transistor from drain to source.
  Reply With Quote
Old 15th November 2012, 09:13 AM   #648
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
I Agree.. this is the most transparent buffer I have ever tried...just an impedance converter, to me as transparent as a piece of wire.
  Reply With Quote
Old 15th November 2012, 01:21 PM   #649
diyAudio Member
 
Join Date: Jan 2011
Location: Germany
Well, to have a fixed VDS is the point

Reasons for higher VDS than VDS = Vp:
1) I can have a VDS that makes the semiconductor sounds best
2) Use a VDS where the JFET is most linear
3) Higher VDS means lower capacitances

Attached are two different ways to cascode for higher than VDS = Vp.



Quote:
Originally Posted by MiiB View Post
What is the benefit of a higher VDS..?? and Why would you want to create a fixed Cascode..?? then the voltage swing would still have to throw charge so the capacitance comes into play.
Attached Images
File Type: gif Cascode JFET Buffer-1.gif (9.9 KB, 249 views)
File Type: gif Cascode JFET Buffer-2.gif (10.7 KB, 247 views)
  Reply With Quote
Old 15th November 2012, 01:38 PM   #650
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Our design is a driven, floating cascode, your design is a fixed cascode, parallel symmetric.
  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
ultra low noise low distortion preamplifier needed neazoi Solid State 13 11th October 2011 01:03 PM
IRF610 I/V convertion from Pass Labs D1 dac - single ended schiller Digital Line Level 5 15th October 2009 04:33 PM
Distortion+low volume.. GeirW Tubes / Valves 5 25th November 2004 12:04 PM
Best low-noise low-distortion buffer? borges Solid State 7 9th December 2003 12:40 PM


New To Site? Need Help?

All times are GMT. The time now is 02:51 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