How to choose the output modes in Master-8: 
                     Master-8 has a rear switch which selects between high and low power mode based on different headphone requirements. (Before selecting, unit must power off for at least 10 seconds) , both modes work without "switch distortion" in Class A state.
                     Master-8 has a rear switch which selects gain boost for XLR and RCA inputs allowing for low output level sources to perform at high power output. (Before selecting high output mode, lower source volume as a precaution)

High and low power output mode selected by user
Fully balanced class A design built by discrete analog stages without any OPA or coupling caps in the signal channels.
Non- feedback ACSS analog output stage.
Uses three R-core transformers (135W total) separate power supplies for the digital components, right and left channels.
More than 50,000uf audio grade NOVER capacitors are used to ensure ample and smooth power delivery.
A total of 8 groups of high-quality class A parallel connection PSU's, four double-stages for dedicated DC supply. To achieve a high S/N ratio, the control circuit is powered with separate regulators.
Uses most Hi-end grade parts and exactly matched transistors.
Four-channel 99 steps digitally controlled relay-based volume control avoids channel imbalance and improves sound quality.
5 analog inputs:  RCA X2, XLR X2, ACSS X1
Preamp output :   XLR / RCA / ACSS
Headphone amp output:    4pins XLR X1 /  3pins XLR X2 / Single-ended X1
Memorizes all settings and resumes the last settings when powered on.

Note:
                     Master-8 can work with all sources and power amps in the world, but its ACSS output can only work with audio-gd Master series power amps.
                     Master-8 Preamp/HP button selects between RCA / XLR of the preamp and headphone amp output, the ACSS signal output is always active.
                     Master-8 is a class A amp, covering the vents is not advised.
                     Master-8 has 3 feet for best balance and minimal interference, 4 feet are available upon request when ordering.
Advice:    1, Master-8 has extremely high fidelity; its SQ is neutral. It can show how good or how bad a recording or source is.
                     2, It is better not to stack gear, if it's necessary to stack the Master-8 on top of other gear, place a peice of paper or other insulating material on top of the other gear, as the Master-8 has conductive aluminium feet.
                     3, Attention must be given to matching suitable power and signal cables.

A review of our preamp and power amp from John Darko.
http://www.digitalaudioreview.net/2011/09/audio-gd-c39-mk3-pre-and-c10-se-power-acss/

The reviews in headfi.
http://www.head-fi.org/t/570722/audio-gd-Master-5-balanced-head-amp-preamp-is-released

　

Modification guide on headphone jack for 4-pin balanced headphone output.
   Click here to read:   modification guide
Parts for the modification is USD30. (Includes one female 4-pin plug and one male 4-pin plug, some tapes and some WBT tin solder.)