Application : Generally the IC op-amp application is designed for industrial usage. When the IC op-amp is used for audio, the performance is less than satisfactory. This discrete op-amp uses accurate matching of components and audiophile grade resistors, combined with dedicated audio design circuitry which gives a smooth and natural output sound. This discrete op-amp can be used to replace existing op-amp in amplifier or CD/DAC as an upgrade.

Quality assurance: Every OPA is thoroughly tested twice on professional equipments , Our priority is Quality first, followed by Efficiency.

OPA – Earth : Audio-GD’s generation discrete op-amp has been sold throughout the world by other marketing means. This discrete op-amp utilizes integrated cascode circuit with the schematic based on single channel circuit which is an improvement based on new improved parameters and technology. The sound characteristics is neutral and natural. THD Less than 0.0005%(1KHz), Operating voltage：±9 TO ±25V，Open loop gain：35DB，Operating current： Approx. 28MA（Single OPA），Approx. 56MA（Dual OPA）. Products have been upgraded to Cap Model, using EVOX MMK capacitors.

Audio-GD were the first to make and sell HDAM (OPA): They were the first to make and sell OPA-EARTH or sometimes called " HDAM " in China and overseas market .

OPA - Moon : This discrete op-amp uses dual differential gain stage and single ended output stage circuit design , we try and audition for a long period of time . The OPA-Moon sound characteristics is a bit of tube-like (vacuum valve) , soft and slightly thick, and full of emotions . THD Less than 0.0008%(1KHz), Operating voltage ：±9 TO ±25V，Open loop gain：33DB，Operating current：Approx. 28MA（Single OPA），Approx. 58MA（Dual OPA) Products have been upgraded to Cap Model, using EVOX MMK capacitors.

OPA-SUN (Version 2) : This discrete op-amp uses full balanced circuit design which is widely appreciated by our Hong Kong and American followers among our other products. THD Less than 0.0003%(1KHz), Operating voltage ：±12 TO ±20V，Open loop gain：36DB，Operating current：Approx. 25MA（Single OPA），Approx. 50MA（Dual OPA）.(Products have been upgraded to Cap Model, use EVOX MMK capacitors. )

What's new of SUN (Version 2) : Audio-GD  started selling the new version from 15th September , 2008.  Taking into consideration customer feedbacks and suggestions, they adjusted the circuits and parts , improved upon the earlier version and came up with OPA-SUN (Version 2),  OPA-SUN (Version 2) does not sound as bright as  the original SUN,  but  it maintains the energy, huge dynamics and good impulse response (fast).

The discrete op-amp not only can replace typical single or double output op-amp, but it also has a separate earth(ground) wire which can be connected to the earth of the player. Even if the earth wire is not connected or used, the output sound will have slight difference. The user can choose to decide on their own configuration, but we recommend connecting the earth wire to ground.  Please do not connect OPAs earth wire to AC power socket ground.