dac I/V convertion with very low distortion - Page 28 - 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 21st August 2012, 12:00 AM   #271
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
I think smms73 realy ment to use the output of the LME49600 as input then ground the input ( there is a 200 Ohm resistor in series ), use a floating supply and couple out the signal like in the SEN, CAN with electrolytics and ballast resistors. It COULD work, The internals of the LME49600 are scary similar to smms73s input stage but "the other way around", so smms73 input stage is in fact an "inverted diamond buffer". If that works or not i can not tell but i have some BUF634 that are very similar and i could simply build it and test it. Just for fun.
  Reply With Quote
Old 21st August 2012, 02:08 AM   #272
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
I meant to say OPA1641 in post #270.
But as Joachim said, any unity gain follower will work (better or worse).
Just like the JFETs in SEN or CEN.

Cuurent consumption of the OPA1641 is very low at 1.8mA.
The batteries will last forever ...........




Patrick
__________________
xen-audio.com

Last edited by EUVL; 21st August 2012 at 02:14 AM.
  Reply With Quote
Old 21st August 2012, 02:30 AM   #273
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
The OPA1641 is certainly one of the best sounding Opamps at the moment.
  Reply With Quote
Old 21st August 2012, 08:15 AM   #274
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by EUVL View Post

Cuurent consumption of the OPA1641 is very low at 1.8mA.
The batteries will last forever ...........
Ok. let's think for a while...

The dac output 7.8ma pp but the quiescent current of the opa1641 is only 1.8ma.
This will make the output transistores of the op amp work in class B.
Thats the reason i say to use a buffer or a discrete op amp with a greater quiescent current.
But as the dac has a -6.2ma offset current, maybe the opa1641 will be in class A.

one way or another you will have a close feedback loop, so maybe is better to use a classical i/v (no need for battery) .

But this start to be a joke of Shinja, then why not build it just for fun
  Reply With Quote
Old 21st August 2012, 08:48 AM   #275
smms73 is offline smms73  Portugal
diyAudio Member
 
smms73's Avatar
 
Join Date: Jul 2005
Location: Lisboa, Portugal
Quote:
Originally Posted by MiiB View Post
I really hope this leads somewhere...I have a concept that i would like to post, but it does not have the really strong point of the circuits here ....the elegant handling of the base currents... but it's more a final servo-ed circuit that could be PCB'ed built and work.
Please do post your circuit.
I´m sorry the evolution is a bit slow, but things are moving.

Sadly, i have discover that the relative high Cob of the bc227/327 increases instability,
especially in the output transistors. So, for now i will be using 2n3904/3906 for testing porposes, and wen i have a working prototype i will try with others transistors.

If someone knows of a transistor with low base spreading resistence and low Cob please inform.
One good quad transistor seems to be the that300 made by thats corporation ( Rbb of 25 ohm and 3pf cob),
  Reply With Quote
Old 21st August 2012, 08:59 AM   #276
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
The internals of the LME49600 are scary similar to smms73s input stage but "the other way around", so smms73 input stage is in fact an "inverted diamond buffer".
Yes Joachim its a diamond buffer, the circuit can achieve very low distortion, because don´t have voltage variations, in that way we get rid of distortion cause by Cob variations and BJT Zout, and of course the base currents.
This circuit just work as a all. If you want the low distortion that this is capable you have to use it like that.
  Reply With Quote
Old 21st August 2012, 01:09 PM   #277
diyAudio Member
 
dirkwright's Avatar
 
Join Date: May 2011
Location: Virginia
Did someone call for a bigger hammer?

When you have no loop feedback and want to work in Class A, you have to juice it up a lot! Heatsinks on the first BD139/140 pair are required!

With 1.41 Vrms output, THD is 0.00038%. S/N is 130dB.
Attached Images
File Type: jpg BD139 IV converter.JPG (58.9 KB, 347 views)
  Reply With Quote
Old 21st August 2012, 01:44 PM   #278
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
> The dac output 7.8ma pp but the quiescent current of the opa1641 is only 1.8ma.

If you use PCM1704, then Iout is 1.2mA, and I am still in Class A with the OPA1641.

For a DAC with 8mA Iout, you can use 5x OPA1641 in parallel, the brutal way.

> But as the dac has a -6.2ma offset current, maybe the opa1641 will be in class A.

That will solve it, using the offset current to bias the OPA.

> one way or another you will have a close feedback loop, so maybe is better to use a classical i/v (no need for battery).

Or use a passive IV (someone suggested 0.8R at the other thread) and amplify the signal 100x ??


Patrick
__________________
xen-audio.com
  Reply With Quote
Old 21st August 2012, 11:38 PM   #279
Shinja is offline Shinja  Japan
diyAudio Member
 
Join Date: Jul 2008
Quote:
If someone knows of a transistor with low base spreading resistence and low Cob please inform.
2sa1015/2sc1815 is 30Ω/50Ω of rbb and 4pF/2pF of Cob.
these transistors are very popular in japan, for general purpose .

2sa970/2sc2240 are much low noise ,so it must be smaller rbb, but no informations on the datasheet.

other japanese small signal, through hole transistors for low noise purpose (such as MC head amp) are all gone.
the rests will be discontinued soon.(above listed too)
they are already NRND status.
  Reply With Quote
Old 21st August 2012, 11:43 PM   #280
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
2SA970, 2SC2240 have aprox. the same Rbbe´then 2SA1015, 2SC1815.
2SA1015, 2SC1815 have lower Cob then BC327,337 but lower early voltage.
I would say they are pari. I use them quite often.
  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 11:29 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