Zen -> Cen -> Sen, evolution of a minimalistic IV Converter - Page 12 - 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 9th September 2011, 10:19 AM   #111
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Piersma, i would call that a compound input stage. I have played around with the principle.
I like the adjustable input offset. Of cause your stage needs a floating supply plus a conventional supply. My idea with the output buffer has the same unconvenience.
What are the 10nF caps for or do i read it wrong ? I would use a high value electrolytic
in that place to lower noise by 3dB.
Here is a paper that describes the compound input stage :
http://www.linearaudio.nl/Miscellane...20aes%20pp.PDF
  Reply With Quote
Old 9th September 2011, 10:20 AM   #112
diyAudio Member
 
Joachim Gerhard's Avatar
 
Join Date: Mar 2009
Post 109, d..... that is really quiet.
  Reply With Quote
Old 9th September 2011, 10:28 AM   #113
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
The BJT models are just those from manufacturer.

The JFET models are based on those in the forum, but with the Vth adjusted to match Idss.
If you already have a basic model, you can compare the constants to those in post#104 & 109.
The text is clearly visible.

I don't have the asc files with me. Otherwise no problem to post them.


Patrick
  Reply With Quote
Old 9th September 2011, 05:03 PM   #114
Piersma is offline Piersma  Netherlands
diyAudio Member
 
Piersma's Avatar
 
Join Date: Jan 2003
Location: Netherlands
Default Caps

hi Joachim,

The capacitors (i.e. 100nF) are there only in a real life implementation to keep the basis of the BJT's firmly connected to (HF) ground.
(suppressing superious signals)

To maintain a low noise configuration a bigger cap is needed, say 47uF.
  Reply With Quote
Old 10th September 2011, 09:33 AM   #115
Alexium is offline Alexium  Ukraine
diyAudio Member
 
Join Date: May 2010
Guys, how do I calculate R and C values for a given DAC chip? I'm interested in trying out Sen.
  Reply With Quote
Old 10th September 2011, 11:29 AM   #116
diyAudio Member
 
tiefbassuebertr's Avatar
 
Join Date: Jul 2005
Location: D-55629 Schwarzerden
Quote:
Originally Posted by Alexium View Post
Guys, how do I calculate R and C values for a given DAC chip? I'm interested in trying out Sen.
perhaps this help:
Digi Scoop 1
  Reply With Quote
Old 10th September 2011, 05:31 PM   #117
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
> how do I calculate R and C values for a given DAC chip?

What do you intend to use ?


Patrick
  Reply With Quote
Old 10th September 2011, 06:54 PM   #118
Alexium is offline Alexium  Ukraine
diyAudio Member
 
Join Date: May 2010
Quote:
Originally Posted by EUVL View Post
What do you intend to use ?
You mean which DAC? PCM1794A (7.8 mA p-p) and PCM1798 (4 mA p-p). I'd like to know how to tune Sen parameters for these DACs.
  Reply With Quote
Old 10th September 2011, 08:15 PM   #119
EUVL is offline EUVL  Europe
diyAudio Member
 
Join Date: Oct 2003
Firstly, a declaration of interest.
I published these articles and make these evaluation kits available to encourage you to understand circuits, apart from building them.
"You" meaning the DIY forum in general and not a particular person specifically.

So if you were looking for a simple answer to enable you to go and build without understanding, you might well be disappointed with my answers.
So be warned.

But take PCM1798 as an example.

They have not published any internal circuits, which makes life somewhat difficult.
But table 3, fig. 24 & 29 gives you sufficient information to make an educated guess.
I don't have these parts; I have not measured them. So don't take my answers as definitive.
I am just illustrating how to do it, rather than giving you a definitive solution.

Table 3 says at no signal, there is a negative current of -3.5mA.
That means that the sum of Idss of the upper FETs has to be larger than that of the lower FETS, in order to supply this 3.5mA.
In the SEN circuit, you might need to add a source resistor to the lower FETs and trim that for zero DC out.

It also says that Vout of U2 in Fig.24 is -2.87V with no signal and Riv=820R.
That implies the output voltage of the DAC is at 0V.
(Vout - 3.5mA x 820R = -2.87V, hence Vout = 0V)
So the gates of the JFETs are still to be connected to Gnd.

To work out R_iv.
Assume you would like 2Vrms per phase, as most standard CD players.
2Vrms is approx. 5.6 p-p. The output current is 4mA p-p.
So R_iv = 5.6 / 4 = 1.4k.

As I said in the article, the JFET bias should be at least 2x the p-p output current amplitude.
So 8mA total Idss is minimum.

Hope the explanation is clear enough that you can work out for yourself for PCM1794.


Patrick
  Reply With Quote
Old 10th September 2011, 09:26 PM   #120
Alexium is offline Alexium  Ukraine
diyAudio Member
 
Join Date: May 2010
Thank your for detailed explanation, Patrick. The algorithm is perfectly clear, I sure can recalculate for 1794. Still don't understand how the circuit works, though, but that's my personal problem.
Is my understanding correct that I should use unipolar 18V voltage source and not a bipolar +/- 18?
I also wonder what's the point of doubling JFETs in Sen vs Cen. Scrolled through the thread but didn't see an explanation. Could you explain in few words?

Last edited by Alexium; 10th September 2011 at 09:31 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
FOR REGA Turntable>>> The heavy weight + Vta adjuster+ceramic ball prooptiki Swap Meet 1 22nd May 2010 05:57 PM
Multi-DAC: Lynx AES16 -> DIR9001/SRC4392 (-> SRC4192) -> PCM1794A novec Digital Line Level 11 11th May 2010 11:57 AM
> Audio <> music <> quick <> synergy <> angst>? rick57 Everything Else 0 4th May 2007 04:03 PM
&gt;&gt;&gt; cheap 50,000uF 60V capacitors here &gt;&gt;&gt; Lubomir Swap Meet 0 1st February 2007 03:36 PM


New To Site? Need Help?

All times are GMT. The time now is 10:55 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