Passive I/V Vref - 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 November 2005, 09:41 AM   #1
diyAudio Member
 
dsavitsk's Avatar
 
Join Date: Jan 2005
Location: Hartford
Default Passive I/V Vref

When using a passive I/V stage with a TDA1543 and the like there is a resistor from Iout to ground for each channel and a resistor from Vref to ground as well.

I am now trying to make a passive I/V stage for an AD1865N and I am not sure if there is an equivalent pin to Vref, or exactly how to go about this. Can anyone enlighten me on this?

Here's a link to the datasheet: http://rocky.digikey.com/WebLib/Anal...ata/AD1865.pdf

Thanks,

-d
  Reply With Quote
Old 21st November 2005, 01:03 PM   #2
diyAudio Member
 
Join Date: Nov 2004
Location: Kaunas,LT
As far as & know only TDA1543 hasn't diodes at the output.Other's dacs with current output voltage is limited.For passive i/u converter you can use resistor(about 20 ohm) or transformer and after output buffer with tube or opamp(with resistor you need analog filter). Good example is here http://www.geocities.com/yury_g/dac.htm.
  Reply With Quote
Old 21st November 2005, 04:50 PM   #3
bocka is offline bocka  Germany
diyAudio Member
 
Join Date: Jul 2003
Location: Hannover
Hi dariusku,

unfortunately the link doesn't work...

Quote:
For passive i/u converter you can use resistor(about 20 ohm) or transformer and after output buffer with tube
Although I don't like transformers in the audio path for a passive I/V stage it has its merits and transforms the voltage as well as the resistance to a (more reasonable) higher level. Instead of using an OP-Amp as buffer it's better to use a single emitter follower
  Reply With Quote
Old 21st November 2005, 08:23 PM   #4
diyAudio Member
 
dsavitsk's Avatar
 
Join Date: Jan 2005
Location: Hartford
The link works, you just have to remove the "." from the end of it (this is a bug in DIYAudio's software that puts it there.) The link, however, is to someone making a balanced DAC with 2 chips, so I am not sure if it is strictly applicable. Also, I am trying to avoid a transformer on the output. Perhaps I will try it for a later incarnation, but for now I am trying to keep things simple, small, and inexpensive as this is just a learning project.

The AD1865's datasheet does not say that there are protection diodes at the current output and they are not there in the block diagrams, though it also doesn't say they aren't there.

If I do just use a resistor, or perhaps use an opamp, then do I need a Zobel filter afterward?

Another thing that I am not at all clear about is the SJ (summing junction) pin. The above linked DAC ignores it. The datasheet example schematic that uses the Ioutput connects it to the Iout pin, and AudioNote's schematic connects it to ground. Any ideas?

Thanks,

-d
  Reply With Quote
Old 22nd November 2005, 03:07 PM   #5
diyAudio Member
 
Join Date: Nov 2004
Location: Kaunas,LT
& listen to balanced AD1865N-J dac with Lundahl transformer and AD797 buffer and it sounds very good.Transformer have several advantages:separate digital part from analogue,linear with small primary impedance,increase voltage so we need only one gain stage and no need additional filter.But output impedance is big so we need buffer(opamp,follower,tube).With tube output impedance is big too and better use transformer at the output(it increase quality and with opamp).Problem is get good transformer the best are NOS(UTC and others).AD1865 are very precisious so balanced connection is preferred(we get less noise because of no direct ground connection and twice bigger output current).But difference from single dac is small.
Some dacs don't like inductive impedance(like AD1862) but AD1865 works great with transformer.
With resistor we need several gain stage,analogue filter and results are worse.With relatively big resistance(100 ohm) sound is much worse because we get big voltage at the dac output and dac becomes non linear.
  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
SAA7323 Vref pin? jnewbold Digital Source 0 16th September 2008 03:35 AM
BG NX Hi-Q in super e-cap good enough for VD, VREF ? sceglar Digital Source 11 17th September 2005 09:23 AM
valve i/v with 2.7volt vref MarkHathaway Digital Source 14 10th July 2005 04:06 PM
Capcitor type for Vref fmak Digital Source 41 4th June 2004 11:03 AM
VREF as volume control Prune Digital Source 7 22nd April 2004 10:27 PM


New To Site? Need Help?

All times are GMT. The time now is 07:34 PM.


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