dac I/V convertion with very low distortion - Page 11 - 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 10th August 2012, 04:34 PM   #101
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Looking again at post 99 the mirror around Q9, 10, 11, 12 is kind of redundant. The mirror that does the bal-unbal conversion is already a current source. Can be improved though.
Remove the base-collector short from Q17 and put in on Q23. Put in a helper transistor instead of short between base-collector of Q19, other side the same. That mirror has higher impedance and lower distortion.
  Reply With Quote
Old 10th August 2012, 04:35 PM   #102
Shinja is offline Shinja  Japan
diyAudio Member
 
Join Date: Jul 2008
Hi smms73
thank you for testing my propose.
it is disappointing the circuit have poor performance.
how is the post #99?

Quote:
Put in a helper transistor instead of short between base-collector of Q19,
does it mean to put emitter follower to supply base current of Q17 and Q23?

Last edited by Shinja; 10th August 2012 at 04:42 PM.
  Reply With Quote
Old 10th August 2012, 04:49 PM   #103
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by Joachim Gerhard View Post
Looking again at post 99 the mirror around Q9, 10, 11, 12 is kind of redundant. The mirror that does the bal-unbal conversion is already a current source. Can be improved though.
Remove the base-collector short from Q17 and put in on Q23. Put in a helper transistor instead of short between base-collector of Q19, other side the same. That mirror has higher impedance and lower distortion.
The ccs (q9,10,11,12) is necessary to feed the output. i have test all the possibilities you present, this is the best.
  Reply With Quote
Old 10th August 2012, 04:50 PM   #104
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Of cause then you have to raise the current in the right side of the input mirror to supply the output stage. This is interesting.
  Reply With Quote
Old 10th August 2012, 05:12 PM   #105
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
thanks for the explanation about noise. I was thinking that such a low difference in impedance were not so bad, anyway the circuit in post 99 is only a test circuit.

Unfortunately the current mirror degrades the distortion, this circuit has 0.0012% , its a great diference.
  Reply With Quote
Old 10th August 2012, 05:29 PM   #106
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Making of low distortion mirrors is possible.
Anyway, i am sure that you will find a satisfying solution.
  Reply With Quote
Old 10th August 2012, 07:57 PM   #107
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Circuit with bc327/337 , as predicted it's even better at low input impedances, and has only 0.00001% of distortion with a 1k source at 2ma, at 7.8ma and 10k input it has 0.000021%.
It should be also good for R/2R dac. I am very pleased with this results, and the final I/V converter will be very similar to this.
Thank you all for your support, and a special thanks for Joachim, for your help in dealing with the noise issue.
I will start a prototype to test this in real life.
Attached Images
File Type: jpg final_tt.jpg (304.4 KB, 372 views)
  Reply With Quote
Old 10th August 2012, 08:59 PM   #108
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
forgot to say that the input impedance is 2ohm can be further reduced with parallelling more bjt at the input or lowering the emitter resistances, but 2 ohm seems a low enough impedance for a current output dac.

The distortion is 0.000014% when simulated with the 6.2ma of offset at the input and 0.000017% (increase 2db in 2 harmonic ) without the offset so there is no problem in dealing with the offset of pcm1794, as i say before just increase 6.2ma in the upper current source, this results were simulated with 8ma/100k input.

Last edited by smms73; 10th August 2012 at 09:21 PM.
  Reply With Quote
Old 10th August 2012, 09:40 PM   #109
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by smms73 View Post
The distortion is 0.000014% when simulated with the 6.2ma of offset at the input and 0.000017% (increase 2db in 2 harmonic ) without the offset
sorry my mistake
The distortion is 0.000014% when simulated with the 6.2ma of offset at the input and 0.000008% (increase in 2 harmonic ) without the offset
  Reply With Quote
Old 10th August 2012, 10:09 PM   #110
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
This is a fantastic result. I am looking forward to your build.
  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 05:32 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