How to choose the output models in Master-8 : 
                     Master-8 have a switch on rear can select between high power model and low power model base on different headphones request . ( Before select , Must power off and waiting least 10 seconds ) , both models are working on without "switch distortion" Class A state.
                     Master-8 have a switch on rear can select the gain boost on XLR and RCA input model for some low output level source can cooperate with Master-8 perform high power output. ( Before select please lower the volume at first )

High and low power output model select by users
Fully balanced class A design built by discrete analog stages without any OPA and couple caps in the signal channels.
Non- feedback ACSS analog output stage .
Uses three R-core transformers (135W total) separate power supplys for the digital part , right channel and left channel.
More than 50,000uf audio grade NOVER capacitors are used to ensure ample and smooth power feed.
A total of 8 groups of high-quality class A parallel connection PSU, four double-stages for dedicated DC supply. To achieve high S/N, the control circuit is powered with separate regulator.
Uses most Hi-end grade parts and exact match transistors.
Four-channel 99 steps digitally controlled relay-based volume control to avoid channel imbalance and improve sound quality.
5 Channel 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 it could resume the last settings when power 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 select between RCA / XLR of the preamp and headphone amp output, the ACSS signal output always available .
                     Master-8 is a class A amp, don't cover the vents please .
                     Master-8 have 3 feet under bottom side for the best balance state , if customers want 4 feet , please ask the custom order .
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 on top of each other, if necessary to stack Master-8 on other gear, place a paper or other insulating material on top of other gear, because Master-8 has conductive aluminium feet.
                     3, Attention must be given to matching suitable power cable and signal cable.

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.)