Electronics Overview

Operational Amplifiers (Opamps)

LM4562NA

This opamp may well be the best known audio opamp among PC audio enthusiasts. Since first released, the chip made its way from the benches of the DIY'ers and enthusiasts to the soundcards companies.  This chip has been seen on many modern audio designs from many companies and for good reason.

As you can see by the above THD Vs frequency graph the LM4562NA keeps excellent THD ratings across the audible range. Depending on the design and circuit load the LM4562 can produce THD ratings as low as 0.00003%.  This chip is also very quick with a slew rate of +/- 20V/µs (typ) and a GBP of 55Mhz.  These opamps are used as buffers on both ST and H6 cards for the line outputs.

LM4562NA specification sheet

JRC2114D

These opamps are used for the differential Current to Voltage (I/V) conversion section on both the Essence ST and the H6 card.  Although in these circuits they produce some excellent results, from a design standpoint they are still considered generic opamps.

The reference circuit for the DAC's used on these cards call for the NE5532 but the designers at ASUS opted for the NJM2114D and while it is still a generic opamp it has more audio muscle then the NE5532 they could have used.  The 2114D is a bit slower than the LM4562NA with a slew rate of 15V/µS (typ) and offers an THD % rating of 0.0005.

NJM2114 Specification Sheet

Headphone Amplifier TPA6120A2

The headphone output on the ST is an amplified output for compatibility with many different grades of headphones.  The cards drivers allow setting different output gain ranges for whatever headphone you have.

Head amp specification sheet

Capacitors

The Essence ST uses some very high grade audio capacitors usually not seen on PC soundcards.  The units the designers opted for are the Nichon "fine Gold" audio grade capacitors.