ASUS Xonar Essence STX soundcard review

Soundcards and Speakers 106 Page 8 of 18 Published by

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Electronics Overview

Opamps (operational amplifier)

There has been much discussion around the audio forums about opamps lately, what they are, what they do and how do you change them.  This card actually has three stereo opamps for the stereo output. 

This design is a bit unique on a consumer level soundcard and the design is seen more on discrete DAC modules and headphone amplifier units.  The first two opamps are the JRC 2114Ds these opamps units are used as a differential input Current to Voltage section (I/V).  These opamps take the output from the DAC chip and convert it for use by the final buffer opamp (LM4562NA).

ASUS Xonar Essence STX ReviewNJM2114D

The NJM2114D could be considered a generic unit by some but has found its way into many audio designs in the consumer electronics market and Pro-audio market also.  This opamps is a drop in replacement for the NJM5532 which has become a staple in many audio designers tool kits.  The 2114 is superior to the 5532 in many ways and will give superior performance when used in place of, with a slew Rate of 15V/µS and a Gain bandwidth of 15Mhz (typ).  ASUS could have used the 5532 here but opted for the NJM2114D for the better specifications.

ASUS Xonar Essence STX ReviewLM4562NA

The famous LM4562, this opamp has gained quite a following, first adopted and used by the DIY crowd for replacing lesser opamps and upgrading their soundcards, DACs and other audio devices.  The device gained attention from soundcard houses and can now be found on productions soundcards from various manufacturers.  This opamp won awards for National Semi and is a great opamp when comparing price to performance.  Bragging 0.00003% (typ) for THD+n and a quick slew rate of 20V/µ and a bandwidth of 55mhz.  This was actually a great choice for the final buffer stage.

DAC+Opamps

Now lets try and put the puzzle pieces together and illustrate how the Essence STXs opamps are used with its DAC.

ASUS Xonar Essence STX Review

This is a block diagram of the DAC with the opamps at the left hand side offering the I/V section and filter/buffer section.  In layman terms; at the left hand of the diagram each small rectangle represents 1 NJM2114D chip and 1 half of the LM4562 chip.

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