dac I/V convertion with very low distortion - Page 81 - 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 3rd February 2013, 05:24 AM   #801
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
You just invented the series capaciantance bridge.
  Reply With Quote
Old 3rd February 2013, 05:34 AM   #802
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by smms73 View Post
Is simpler to improve the input stage to make it immune to voltage variation in the rail , is better to leave the ccs cascoded by the output stage. Believe-me .
Or... not believe . in simulation it seems there is nothing to gain in cascoded the ccs with the output stage, but with measurements in the prototype it was better, i have to take a better look.
__________________
Sérgio Santos
  Reply With Quote
Old 3rd February 2013, 09:35 AM   #803
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
The CCS can also be bettered by inserting a Jfet CCS instead of the two 10 K.ohm resistors, then you take the influence from Rail variations out.

I like the scaling by inserting more current-summing legs, as apposed to unbalancing the mirror.

Casodede mirrors are more than 10 fold higher in impedance and with the beta helper you can get really High.
  Reply With Quote
Old 3rd February 2013, 01:46 PM   #804
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by keantoken View Post
Also, your cross-connected Baxandall type VAS is good but I compared it to the traditional complimentary Common-base Baxandall VAS and it has inferior PSRR. Have you tried Edmond's arrangement in figure 5 here?
I have now simulate the two circuits. And i also get just a little beter PSRR with the baxandall pair but its a minor difference, and i have better distortion figures with my type of connection also a minor diference. Both get good behavior with a square wave input.

I do not care to much about PSRR because the power supply that i use have already very low noise, it is similar to your The K Multiplier

In the begining i use only capacitance multiplier, with very low noise also but using a cfp gives a lower output impedance, there is very low A.C. current in the power supply rails, so the output impedance of the power supply is not that important.

The first picture are the output noise of a 7815 regulator , second the noise at the output of the cfp capacitance multiplier.
The third picture is the measurement of distortion of the real circuit with a input impedance of 3k 8ma p-p and 2v rms out (is the same as the sound card i use) .
Attached Images
File Type: png 7815.PNG (57.6 KB, 341 views)
File Type: png psuply_out.PNG (55.8 KB, 334 views)
File Type: png imagem.PNG (50.2 KB, 328 views)
__________________
Sérgio Santos

Last edited by smms73; 3rd February 2013 at 01:51 PM.
  Reply With Quote
Old 3rd February 2013, 02:09 PM   #805
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by MiiB View Post
The CCS can also be bettered by inserting a Jfet CCS instead of the two 10 K.ohm resistors, then you take the influence from Rail variations out.
Yes using a jfet ccs will be better, the resistors were used for the dc servo . The variations in Vce of the ccs transistor will make variations in the base current , so for take the influence from Rail variations out, you have to insure that the Vce from this transistor is stable, one way is cascode it with a fet or mosfet.
__________________
Sérgio Santos
  Reply With Quote
Old 3rd February 2013, 02:23 PM   #806
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
This is a preamplifier with the same principles that we are talking here, it has a gain of 16x with 250 ohms in R2 if you want lower gain you have to increase this resistor 500 ohms for a gain of 8x and 1k for a gain of 4x. the maximum voltage out is 16 volts p-p.

I have post it here with other 2 for my one and there are also some circuits design by Dado and keantoken, I recomend that you take a look.

Current conveyor as a voltage amplifier


The distortion is 0.000069% at 4 V p-p with a gain of 16x

This is a basic circuit and can be improve further , It also needs a output buffer to lower the impedance , but that is another story.
Attached Images
File Type: png ccs_gain.png (66.8 KB, 329 views)
__________________
Sérgio Santos

Last edited by smms73; 3rd February 2013 at 02:30 PM.
  Reply With Quote
Old 3rd February 2013, 03:02 PM   #807
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by keantoken View Post

As I understand you referenced the drivers to the rail to effectively cascode the CCS. However this leaves the input stage open to rail variations. If you decouple R15 with a lytic and delete R10/R24 decoupling, and then improve the CCS, you will lave less overall Iq modulation which I think will result in more PSRR.
You are right Kean , is better to have the voltage reference to ground, Thanks very much for the tip .
Joachim have already advice for that matter some time ago. And at that time i did not see it . I will make that change.
__________________
Sérgio Santos
  Reply With Quote
Old 3rd February 2013, 06:05 PM   #808
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
If you use a cascoded JFet current source It's possible to inject the servo-current between the two JFets, the you get both high impedance and Servo adjustment.

Line stage looks really good, open-loop and with the possibility of an truly non degrading volume-control...
  Reply With Quote
Old 3rd February 2013, 10:45 PM   #809
diyAudio Member
 
keantoken's Avatar
 
Join Date: Aug 2006
Location: Texas
Blog Entries: 2
To lower output impedance could you rework the input to accept feedback? After all there is a lot of spare gain if you remove R2. Perhaps you could do a compromise and have say 100R output impedance.
  Reply With Quote
Old 5th February 2013, 09:43 PM   #810
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
kean using a global feedback loop is a possibility , but I will not go that way , at least not now.

Instead i present a simple buffer that uses a complementar feedback pair , I know much of people in this forum don´t like cfp , but i found it very interesting .
I think that much of the bad reputation that cfp has, is because people do not use a mean to prevent oscilations that can occur in some situations.
In a not so long time ago i expriment a I/V converter with a differential cfp pair and when i was measure distortion , some times a little oscillation of high frequency occurred, but as all of the circuits that i had seen with cfp do not has any mean of oscillation prevention, i did not use any also , inserting a capacitor C1 like in this pictures is very effective in stabilize the cfp loop, that sollution work very well .
Attached Images
File Type: png cfp.png (9.0 KB, 240 views)
__________________
Sérgio Santos

Last edited by smms73; 5th February 2013 at 09:52 PM.
  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 04:34 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