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audio-gd DAC Head Amp Pre Amp Power Amp DIY Kits Cables



Real Balanced ACSS Preamp & Headphone amp

How to choice between Master-5 and Master-6?
The Master-5 and Master-6 had same PCB design. The Master-6 output stage without limit so can offer large output power.
If your headphones are not difficult to drive, the Master-5 is ok for the choice.
If you have some difficult drive headphones, choice the Master-6 can offer large output power.

Input:   XLR x2 / RCA x2 / ACSS x1  (Even with the single end ACSS or RCA input, Master-5 can conversion to XLR and balanced ACSS and RCA output from preamp , and conversion to balanced and single end headphone output.)
Preamp Output:   XLR x1 / RCA x1/ ACSS x1
Headphone amp output:    4pins XLR X1 /  3pins XLR X2 / Single end X1

Price: USD1450  (Excluding shipping cost)
Weight: Approximately 16kg
Dimension:  W430 X L430 X H93(MM)
Accessories: Power cable x1

                     Master-5 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-5 Preamp/HP button select between RCA / XLR of the preamp and headphone amp output, the ACSS signal output always available .
                     Master-5 is a class A amp, don't cover the vents please .

1, Master-5 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-5 on other gear, place a paper or other insulating material on top of other gear, because Master-5 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.

The reviews in headfi.



     Master-5 is a true balanced design applying the newest ACSS design which can improve the XLR connection to sound as good as the ACSS connection. They seem complex , but in fact they are the most simple design the world has ever had , their a lot components to process the power supply. The simplest and shortest signal journey brings out the most neutral and least colored sound.
             Master-5 applies ultra-low distortion single stage ACSS amplifier and soldered directly on the motherboard. It is a fully class A preamp / headphone amp and applies class A power supplies.

            The ACSS is a non-feedback technology made with discrete amplifiers. Most people know the global feedback design can offer better specs in test measurements, and non-feedback can't do well in test measurements but can offer better sound for the human's ears. Here is a conflict of the classic circuits. But the ACSS opens a new field, it can offer a least coloration sound which is more neutral with very low distortion and high linearity. So it can retain the dynamics, detail and neutral sound but not sound bright or harsh.
            All signal gain is in current, all transistors work in class A mode.
            The Master-5 output buffers are Non-feedback, for low impedance and ultra-low distortion , we applied two pare  MOSFET (K214/J77) and transistors (C5171/A1930)
connect with cascode  , the output impedance is only 1 ohms , it can drive most headphones and amps as well  .
            Master-5 has all components of four channels exactly matched before installation.

Power supply:    
Three special transformer are used to supply power separately for the audio and control circuit.
       Master-5 uses 8 groups of high-quality class A parallel connection PSU, four double-stages for dedicated DC supply.
            The class A parallel connection PSU has very high input impedance to avoid pulse through the PSU from affecting the preamp and low output impedance with very fast speed and high linear, so it is a very clean power supply.
            Master-5 applies two linear PSUs for the display and control parts, avoid the disturbances through power line from affecting the amplifier.

     Master-5 can input not only XLR balanced signal or RCA unbalanced signal, but also the top-grade ACSS current signal. It can also output RCA signal, balanced XRL signal, ACSS current signal to the power amplifier. Using RCA input, Master-5 can convert to balanced ACSS signal and output real balance signal from XLR and ACSS.
           Master-5 can output RCA, XLR and ACSS at the same time in preamp output model , in headphone amp model, Master-5 can output XLR ,single end for headphone, and ACSS for power amp at same time.
           The input channels of Master-5 adopt separated shielding method. When switching, the idle signal lines linked to the equipment and the ground wire are completely disconnected. The idle input ports of the equipment are shielded. In that case, the sound quality won't be affected even with more connected equipment.


Volume control:
  The volume control is also different from conventional technology. Conventional volume control technology is the volume control implement in the analog amp input stage through a volume pot to reduce the signal  . The volume pots quality effect the sound quality direct , the low quality volume pot cause lost the detail and channels imbalance cause the soundstage distortion  . Even the high performance volume pot still cause the detail lose. Whatever quality volume pots, must cause the S/N worst .
But in the Master-5 , we applied the I/V conversion volume control , the volume control just  a variable passive I/V conversion place at the ACSS amp output , where the output is the current signal, not the voltage signal. The volume control is I/V conversion, and the volume depends on the current (I) conversion to the voltage (V). (Like R-2R D/A chips output passive I/V conversion)  It can keep the signal frequency band flat and not lost any detail. It can't degrade on sound quality in every volume level . After the volume , there are four groups  diamond non-feedback buffer output stages offer the very low output impedance  .
            Mark Levinson also knows that current volume control has great benefits, so in their Top End preamp NO.32 volume control, they use many components to change the signal to current signal (I), then implement the volume control , and then change back to voltage signal (V) again. But Master-5 is simply a more complete work in terms of the current signal, and technically, it is superior to conventional technology. The less conversion bring much neutral sound .
            The volume control quality is much important in the real balance gear . It must guarantee the four channels signal control exact to achieve the performance of the real balance gear .  If the cool and hot of the balance signal can't guarantee exact, the balance output will has large distortion cause the sound quality and performance even much worst than a single end gear waste the  balance gear  design and the cost.
            In Master-5 is applied a four channels digital control relays based volume control. .Master-5 has total four channels through changing the DALE resistors to control the volume for avoid channels imbalanced ,achieve the best performance and sound quality of the gear.
           Master-5 allow users select between 99 steps exponential characteristic volume control and 70 steps linear characteristic volume control, whatever volume control allow users smooth to control the volume level .

Master-5 has complete separation of left, right amplifier channels, power supply, and transformer.
         Master-5 uses heavyweight all-aluminum alloy chassis to prevent the eddy current of transformers from interfering on circuit board. 
    Master-5 applies optical couple isolation for the MCU and the control implementations to prevent the MCU affecting the audio parts.

 Uses all audiophile grade components, including DALE resistors, WIMA & SOLEN caps, custom order NOVER (UK brand) caps, all audiophile grade input & output sockets (Neutrik ) and gold IEC socket.  Master-5 all parts of four channels had exact match before install.

 How to choose the settings in Master-5 :
   With the Master-5, the user has a choice of 70 steps ( Linear characteristic ) and 99 steps ( Exponent characteristic) of volume control, and you can also choose whether to have volume memory.
1. Choose 70/99 steps volume control:
Step A: Push out the "Debug" switch.
Step B: The display shows as pictures below.
Step C: Push the volume button, choose between 70 or 99 on right.
Step D: Push in the "Debug" switch.

                                             70 step volume control                                         99 step volume control

2. Choose volume memory:
Step A: Push out the "Debug" switch.
Step B: Push the selector button; the display shows as pictures below.
Step C: Push the volume button, choose display "ON" or "OF" on left.
Step D: Push in the "Debug" switch.
                                               Volume memory active.                                        Volume memory off.


Improvement may result in changes in specifications and
design without notice.




S/N Ratio


+7 DB (70 steps volume control) (XLR)
+13DB (99 steps volume control) (XLR)

+13 DB (70 steps volume control) (XLR)

+19DB (99 steps volume control) (XLR)

Volume characteristic

Linear @ 70 steps
Exponent @ 99 steps

Headphone amp Output Power

50 ohm:   1700MW
100 ohm: 2400MW
300 ohm: 1200MW
600 ohm:   600MW
(Balanced , Class A)
40 ohm:   9000MW
50 ohm:   7000MW
100 ohm: 3500MW
300 ohm: 1200MW
600 ohm:   600MW
(Balanced , For >20 ohm headphones)

 Preamp Output Level (Max, RMS)

9.5V @ RCA
 19V @ XLR
4.8MA @ ACSS

Output impedance

1 ohm @ XLR
>10M ohm @ ACSS

Input impedance

90K ohm @ XLR
<10 ohm @ ACSS

Frequency Breadth

20Hz - 20KHz ( <0.15DB )

Channels cross
> 130DB

Channels imbalance
< 0.05DB

Power Requirement

1 Version  100-120V  AC 50/60 Hz
2 Version  220-240V  AC 50/60 Hz

Power Consumption

45W class A @240V or 120V

45W idle @240V or 120V

Transformer Power

135W (3 transformers)

Package Weight

Approximately 16KG


Power cord  X1

Operating Temperatures

+5 XC to +40 XC

Operating Humidity

5 % to 90 % (without dew)



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