Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Why Do DACs Always Contain an Op-Amp?
Why Do DACs Always Contain an Op-Amp?
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 26th September 2018, 10:07 AM   #1
spaceman5 is offline spaceman5  Israel
diyAudio Member
 
Join Date: Nov 2016
Default Why Do DACs Always Contain an Op-Amp?

Hi


In the past 2 weeks I have purchased online several different DACs, to try them and see the difference in the sound they give.

One thing I noticed, is that their circuit is always composed of 3 main chips:
1) USB to I2S chip
2) DAC chip, which takes I2S and converts it to Analog
3) An Op-Amp


My question:
If the definition of a DAC is that it outputs Line Out, (which you should then connect to your amplifier)
then why is the Op-Amp needed?


Thank you

Last edited by spaceman5; 26th September 2018 at 10:11 AM.
  Reply With Quote
Old 26th September 2018, 10:15 AM   #2
JonSnell Electronic is online now JonSnell Electronic  United Kingdom
diyAudio Member
 
JonSnell Electronic's Avatar
 
Join Date: Dec 2012
Location: The Jurassic Coast, England. GB
Like a CD laser assembly, on most, the output must be converted from current, using an op amp, to voltage.
__________________
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
  Reply With Quote
Old 26th September 2018, 10:18 AM   #3
abraxalito is online now abraxalito  United Kingdom
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Send a message via Yahoo to abraxalito
Opamps are employed because that's a convenient way to perform a couple of functions at the output stage of a DAC chip - differential-SE conversion and filtering. Today's opamps have such good THD+N numbers that manufacturers' applications tend to use them exclusively so as not to compromise the attainable measurements from their chips.

There are of course other ways of implementing the diff-SE and filtering functions but none to my knowledge with THD+N numbers as low as those attainable from opamps.
__________________
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant - Alan Greenspan
  Reply With Quote
Old 26th September 2018, 10:18 AM   #4
picowallspeaker is offline picowallspeaker  Italy
diyAudio Member
 
picowallspeaker's Avatar
 
Join Date: Apr 2007
Anti-aliasing filter, which is a low pass filter.
__________________
Everything under and above heaven is in utter chaos
mare monstrum
  Reply With Quote
Old 26th September 2018, 10:26 AM   #5
billshurv is online now billshurv  United Kingdom
diyAudio Member
 
billshurv's Avatar
 
Join Date: Mar 2014
Why Do DACs Always Contain an Op-Amp?
The don't have to have an op-amp, they can have a discrete gain stage. Many DACs are current out, so you need an I/V stage, often implemented in an op-amp. Others have a voltage output, but you generally buffer that with a line driver of some sort.



There will be DACs for embedded applications that can drive line out directly
  Reply With Quote
Old 26th September 2018, 10:32 AM   #6
spaceman5 is offline spaceman5  Israel
diyAudio Member
 
Join Date: Nov 2016
Really interesting, thank you.

And notice how each one of you gave a different functionality that the op-amp performs..
(except JonSnell and billshurv, who discussed about the same thing)
  Reply With Quote
Old 26th September 2018, 10:41 AM   #7
wintermute is offline wintermute  Australia
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Why Do DACs Always Contain an Op-Amp?
They don't "always" contain opamps. My FetAudio FDA-1 DAC has a discrete transistor IV and no opamps

But as already mentioned opamps provide a low cost high performance option.

Tony.
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 26th September 2018, 10:56 AM   #8
spaceman5 is offline spaceman5  Israel
diyAudio Member
 
Join Date: Nov 2016
Quote:
Originally Posted by wintermute View Post
They don't "always" contain opamps. My FetAudio FDA-1 DAC has a discrete transistor IV and no opamps
Was the FDA-1 DAC created like that because it improves the sound over an Op-Amp?
  Reply With Quote
Old 26th September 2018, 01:10 PM   #9
Markw4 is offline Markw4  United States
diyAudio Member
 
Join Date: Jul 2016
Location: California
Quote:
Originally Posted by spaceman5 View Post
Was the FDA-1 DAC created like that because it improves the sound over an Op-Amp?
It is possible to make a $2,000, state of the art, highly regarded and Stereophile recommended dac, which is used by many audiophiles and audio professionals, based largely on a lot of opamps. To wit, Benchmark Media DAC-3. It uses LME49860 opamps.

There is no reason why a carefully designed dac can't sound great, world class in fact, using opamps.

However, the dacs you have been trying are all essentially junk, and junk for a lot of different reasons. Opamps-or-not should be the least of concerns.
  Reply With Quote
Old 26th September 2018, 01:23 PM   #10
spaceman5 is offline spaceman5  Israel
diyAudio Member
 
Join Date: Nov 2016
Quote:
Originally Posted by Markw4 View Post
However, the dacs you have been trying are all essentially junk, and junk for a lot of different reasons. Opamps-or-not should be the least of concerns.
I understand that you say this not because of the DAC chips (which some of them are ESS, Burr-Brown, and more),
but because of the implementation, as we spoke about.

They come as a ready made PCB (with soldered parts), but without an enclosure..
And as you could see, they were really cheap, around 15$ on average.

What in your opinion is a (starting) price for a DAC that is not junk?
(and would you narrow the chip also to 1-2 companies?)
  Reply With Quote

Reply


Why Do DACs Always Contain an Op-Amp?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
DACS vs Raspberry Dacs hifineo PC Based 22 9th May 2018 04:01 PM
Any 24 bit NOS DACs? labjr Digital Line Level 14 27th August 2011 11:23 AM
DACs Jerseydevildog Digital Source 1 25th November 2007 06:24 PM
USB DACs again Adam Reed Digital Source 5 5th February 2004 07:00 AM
Audio DACs, Instrumentation DACs. Brian Guralnick Digital Source 10 3rd November 2002 04:56 PM


New To Site? Need Help?

All times are GMT. The time now is 08:03 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki