Choosing op amps for Essence STX I/V stage - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, 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 24th July 2012, 10:16 AM   #1
diyAudio Member
 
Join Date: Jul 2012
Location: Hsinchu
Question Choosing op amps for Essence STX I/V stage

I recently bought a ASUS Essence STX, although it's far better than the integrated soundchip on my mainboard, I'm thinking about changing better op amps on the card.

The must-be-changed ones are those 2 JRCs in the I/V stage, it seems to be a lowcost solution, I can't even find the datasheet on the net.

I find some good op amps but choosing one from them seem to be a difficult trade-off on the electrical characteristics, the followings are what I found:

OPA627 (or similar ADA4627): Maybe the most well known audio op amp ever,
I found the PCM1704 from TI uses OPA627 in the I/V stage in the datasheet example diagram.


AD8620: Has similar characteristics from the OPA627/ADA4627, but has a little bit higher input bias current and a little bit lower dynamic performance.


AD827: A very fast op amp, originally designed for video purposes, but many people also use it in audio systems.
It really seems good for DAC output I/V conversion.PCM1794 datasheet says that
"Dynamic performance such as the gain bandwidth, settling time, and slew rate of the operational amplifier affects the audio dynamic performance of the I/V section."
But its noise is high in some extent for modern op amps, and it's bipolar-input,
I dont know why when it comes to DAC output buffer, some people will say that FET-input is better, could someone explain the reason?


LT1364: Similar to but faster than the AD827, and has the same questions.

LME49990/LME49720/AD797: These low noise and distortion series may be ideal for the preamp stage, many people also put them in the I/V stage and got satisfactory results.
But the dynamic performance is not so good as those ones above.
(I don't know how fast is really just enough for this kind of application.)

Or some people could recommend other good ones for me?

Last edited by delaluna; 27th November 2012 at 04:37 PM. Reason: Delete the questions of capacitive loads driving problem. (Explained by abraxalito at #10)
  Reply With Quote
Old 28th July 2012, 02:09 AM   #2
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Blog Entries: 101
Send a message via MSN to abraxalito Send a message via Yahoo to abraxalito Send a message via Skype™ to abraxalito
I have the Essence ST, same DAC circuitry as STX I believe. I changed to LM6172 and also reduced the size of the caps in the feedback loop. Much smaller caps work fine with LM6172 because of its phenomenal slew rate.

<edit> As for why people say FET input sounds better - its most probably about RF immunity of the LTP input. Best to do away with LTP all together in my view, the LM6172 has no LTP so FET vs bipolar becomes irrelevant.
__________________
No matter if we meanwhile surrender every value for which we stand, we must strive to cajole the majority into imagining itself on our side - Everett Dean Martin

Last edited by abraxalito; 28th July 2012 at 02:11 AM.
  Reply With Quote
Old 28th July 2012, 05:48 AM   #3
diyAudio Member
 
Join Date: Jul 2012
Location: Hsinchu
Quote:
Originally Posted by abraxalito View Post
I have the Essence ST, same DAC circuitry as STX I believe. I changed to LM6172 and also reduced the size of the caps in the feedback loop. Much smaller caps work fine with LM6172 because of its phenomenal slew rate.

<edit> As for why people say FET input sounds better - its most probably about RF immunity of the LTP input. Best to do away with LTP all together in my view, the LM6172 has no LTP so FET vs bipolar becomes irrelevant.
Well... Is it proper to reduce the capacitor value? Isn't that used to filter the high-frequency noise come out from the sigma-delta DAC?
  Reply With Quote
Old 28th July 2012, 05:20 PM   #4
diyAudio Member
 
Join Date: Jul 2012
Location: Hsinchu
There is an idea comes out from my brain: Transimpedence amplifiers do the job of "I/V conversion" so is it good to use those op amps with these kind of characteristic (such as low input resistance?)

Maybe the ADA4898 will work well?

High dynamic performance combined with low input resistance:
55V/s, 65MHz (-3dB freq.), Ri=5kΩ.

Has someone tried this?

Last edited by delaluna; 28th July 2012 at 05:26 PM.
  Reply With Quote
Old 28th July 2012, 09:52 PM   #5
diyAudio Member
 
Join Date: Jun 2004
Location: Connecticut
ADA4898 is a good choice but if you don't have a fast oscilloscope you will not be able to verify stability with these fast op-amps. I'd rather listen to a stable JRC or NE5532 than something more exotic but oscillating.
  Reply With Quote
Old 29th July 2012, 07:46 AM   #6
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Quote:
Originally Posted by chris719 View Post
ADA4898 is a good choice but if you don't have a fast oscilloscope you will not be able to verify stability with these fast op-amps. I'd rather listen to a stable JRC or NE5532 than something more exotic but oscillating.
Very sound advice there from Chris.

Swapping Op-Amps... you have checked to see it's stable haven't you ?

The OPA2134 gives very good results in many applications and is pretty docile in use.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 29th July 2012, 09:56 AM   #7
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Blog Entries: 101
Send a message via MSN to abraxalito Send a message via Yahoo to abraxalito Send a message via Skype™ to abraxalito
Quote:
Originally Posted by delaluna View Post
Well... Is it proper to reduce the capacitor value?
If its proper to seek for better sound, then yes.

Quote:
Isn't that used to filter the high-frequency noise come out from the sigma-delta DAC?
Its possible to add more stages to the downstream filter if you're worried about the HF noise. In my way of thinking its mainly there to ensure the opamp doesn't go into slew limiting (highly nonlinear).
__________________
No matter if we meanwhile surrender every value for which we stand, we must strive to cajole the majority into imagining itself on our side - Everett Dean Martin
  Reply With Quote
Old 29th July 2012, 11:08 AM   #8
diyAudio Member
 
Join Date: Jan 2010
It's been a while now since I had my Essence STX (experiment with external power & clock / cap upgrade went wrong and busted my unit), but the best ever opamp swap that I made was to change the opamps in the buffer stage to LME49710HA (metal can version).

You'll need an adapter; LME49710HA is a single opamp, you'll need two to replace the one in the buffer position. The ones I used were from Brown Dog : Single-to-dual Op-AMP Adapter - DIP version (p/n 021001). You'll need to shoehorn the legs of the metal can into the appropriate pins.

If it sounds like a bit of effort, it is kind of. But I think you'll find that it's well worth it.

From what I recall, there's quite an extensive thread on upgrades / tweaks to the Essence STX over at head-fi. That's where I got the metal can idea.
  Reply With Quote
Old 29th July 2012, 11:17 AM   #9
diyAudio Member
 
Join Date: Jul 2012
Location: Hsinchu
Yeah, the stability of op amps when they driving capacitive loads is always a crucial problem, especially for audio DAC I/V stage because it's followed by a filter stage. And that's why I think OPA627 or ADA4627 is not proper for this position, AD8620 can be more stable, AD827 can be very very stable, and the others... should be tested instrumentally.

Maybe put a capacitor in the feedback loop can suppress but not to eliminate this kind of problem.
  Reply With Quote
Old 29th July 2012, 01:08 PM   #10
diyAudio Member
 
abraxalito's Avatar
 
Join Date: Sep 2007
Location: Hangzhou - Marco Polo's 'most beautiful city'. 700yrs is a long time though...
Blog Entries: 101
Send a message via MSN to abraxalito Send a message via Yahoo to abraxalito Send a message via Skype™ to abraxalito
Driving an RC filter - where the R is into the high hundreds of ohms - does not constitute a capacitive load. That's because capacitors only cause stability issues by introducing phase shift at higher frequencies - with the series R the phase shift doesn't appear at the opamp output but on the C.
__________________
No matter if we meanwhile surrender every value for which we stand, we must strive to cajole the majority into imagining itself on our side - Everett Dean Martin
  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
Asus Essence STX Extension Oustide The Case? Drweird PC Based 42 6th March 2012 05:55 PM
New Asus Xonar Essence STX Drivers Brian Kingsbury PC Based 6 9th March 2011 09:52 AM
I2s from asus essence stx? bambadoo Digital Line Level 1 19th February 2011 01:05 AM
Issues Of Asus Xonar Essence Stx fotios Digital Line Level 0 12th May 2009 09:42 PM
Asus Xonar Essence STX analog input? fotios Digital Line Level 1 25th April 2009 10:55 PM


New To Site? Need Help?

All times are GMT. The time now is 05:50 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