dac I/V convertion with very low distortion - Page 64 - 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, 08:58 AM   #631
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
The problem is not in that direction, the problem is the varying gain when we see different impedances in the equipment the DAC is attached to..there you may look into into something with a quite lowish impedance.

I know the current conveyor has no problem with a short, as the output is a current source.
  Reply With Quote
Old 14th November 2012, 09:32 AM   #632
Shinja is offline Shinja  Japan
diyAudio Member
 
Join Date: Jul 2008
smms,
I realized that we need to take care the input impedance next to your circuit.
e.g. SEPP JFET buffer or voltage follower with JFET opamp have high input "resistance" ,but large capacitance.
when the capacitance varies by input signal voltage, the actual IV impedance will vary and cause distortion.
  Reply With Quote
Old 14th November 2012, 09:58 AM   #633
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
PO6S-LOG 1,0K - Drehpoti. logarithmisch, 6mm, stereo 1,0 k-Ohm bei reichelt elektronik
This ones sound very good and they are cost effective. I think they are conductive plastic.
  Reply With Quote
Old 14th November 2012, 11:22 AM   #634
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Sorry MiiB, my mistake, I understand now.

Thanks Joachim, I will check that.

Shinja I think we can use a cascode that keep the source drain voltage constant, that will remedy the problem , for now I want to concentrate on the pcb, but please see if you can arrange some good buffer and post your ideas.
__________________
Sérgio Santos
  Reply With Quote
Old 14th November 2012, 11:42 AM   #635
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
This here could be a very good solution...for a complete circuit...Gain and offset set for the PCM1794

/M
Attached Images
File Type: jpg IV.JPG (115.1 KB, 310 views)
  Reply With Quote
Old 14th November 2012, 11:52 AM   #636
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
MiiB, good work with the buffers, thats the kind of thing i talk, in last post, i will check it better later. I think you have the polarity of the servo inverted, but i will check it later
__________________
Sérgio Santos

Last edited by smms73; 14th November 2012 at 11:58 AM.
  Reply With Quote
Old 14th November 2012, 11:57 AM   #637
MiiB is offline MiiB  Denmark
diyAudio Member
 
Join Date: May 2005
Location: Denmark
Polarity is correct.. It works and has nanovolt offset... the buffer in itself has -140dB distortion ans is not visible on the FFT. We have used this buffer in the Paradise, where we have seen it work very very good.. Its easy to implement and requires no selection.
  Reply With Quote
Old 14th November 2012, 12:55 PM   #638
Telstar is offline Telstar  Italy
diyAudio Member
 
Join Date: Dec 2007
Location: Italy
Quote:
Originally Posted by zenelectro View Post
It doesn't matter where you connect the servo, it is -always- in the audio
path. Over the years this discussion has come up repeatedly.

The servo has to adjust the -audio- OP DC level and do so by integrating
the audio itself. Every servo works this way, you can connect them wherever
you like but if they are to work, they are in the audio path.

As such they definitely are audible and can often sound worse than a good
coupling cap.
Therefore you also believe that the whole psu is in the audio path.
I don't have much experience on servos, but the switch that Segio is preparing will allow us to try with and without it.

Quote:
The optimum value of the LPF cap will probably be system / DAC dependent.
You might even get away without one, if the I-V is stable as such. The
1704 has low OOB noise.
WRT the 2k OP resistor, I would first try this I-V without an OP buffer.
It may well sound better 'in the raw' so to speak.
Absolutely. The analog lp filter has a very detrimental effect on sound, at least on 1704 and 1541 where I have always preferred the dac filterless. This is the beauty of multibit dacs- they don't *require* oob filtering.
Same thing for buffers- the b1 is NOT transparent. I'm still looking for one that truly is.

Another requirement of a good I/v is speed (phase linearity at hf), even some modern opamps fare well in this regard. I think that this circuit is very promising WRT.
__________________
"The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued." D. Masa, 1938
  Reply With Quote
Old 14th November 2012, 01:10 PM   #639
diyAudio Member
 
Join Date: Apr 2003
Location: Eastern Pennsylvania
Quote:
Originally Posted by MiiB View Post
Polarity is correct.. It works and has nanovolt offset... the buffer in itself has -140dB distortion ans is not visible on the FFT. We have used this buffer in the Paradise, where we have seen it work very very good.. Its easy to implement and requires no selection.
Are you absolutely certain the servo polarity is correct? It appears reversed to me as well.
__________________
Ken
  Reply With Quote
Old 14th November 2012, 01:32 PM   #640
diyAudio Member
 
zenelectro's Avatar
 
Join Date: Sep 2009
Quote:
Originally Posted by Telstar View Post
Therefore you also believe that the whole psu is in the audio path.
No. The PS rejection and servo are completely different issues.
You have to think about this a bit more - eventually you will see it.
Quote:
I don't have much experience on servos, but the switch that Segio is preparing will allow us to try with and without it.
Yes that will be a good exercise.
  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 05:28 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