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Real Balanced ACSS Pure Class A Preamp

Price: USD1180  (Exclude shipping cost)
Please send your address, name  to
audio-gd@vip.163.com get the quote.



The unit include below remote
Summarize Use Manual Specs Shipping Cost

Audio-gd products had design and test based on the AP SYS-2722 (The top-drawer professional equipment in world)

Connect with KRELL amplifiers:

          Master 1 is compatible with KRELL amplifiers CAST inputs.

          A cable can be made with one side connecting to Master 1 ACSS outputs, other side to a  KRELL amplifier CAST inputs.

         The ACSS output pins:
         Pin 1, GND
         Pin 2, Hot
         Pin 3, Cold
         Pin 4, GND

         KRELL amplifiers have lower gain versus audio-gd Master series amplifiers when using the CAST connection, so customers can custom order the Master 1 to have higher ACSS output gain if expecting to connect to KRELL amplifiers.

What's new in the Master 1 2017 version:

         The analog circuits design is slower develop compare to the digital design. Especial the excellent design.

         Master 1 released since 2012, we have not change its design , we always like to upgrade the design but we can't .

        Now we are release the new version, the most improve is applied the single polarity FET buffer stages in input and output, which is had a bit lower distortion and improve on the sound quality.
        The Single polarity FET stages are the non feedback design and applied the Toshiba K170 , which is even had money but can not buy from market nowdays.

        The others improve on power supplies for less noise and darker black back stage.

        The control parts let  users can disable the input short by themselves without soldering work.

Master 1 summarize :

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) with separate power supplies for the digital components and right and left channels.

More than 45,000uf audio grade NOVER capacitors are used to ensure ample and smooth power delivery.

A total of 8 groups of high-quality class A parallel PSU's, four double-stages for dedicated DC supply.
To achieve a high S/N, the control circuit is powered with separate regulators.

Uses high 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

Memorizes all settings and resumes the last settings when powered on.




             Master-1 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-1 applies ultra-low distortion single stage ACSS amplifier and soldered directly on the motherboard. It is a fully class A preamp 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 XLR /RCA output buffers are Non-feedback, for low impedance, we applied a two-stage parallel connection, the output impedance is only 10 ohms.

             Master-1 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-1 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-1 applies two linear PSUs for the display and control parts, avoid the disturbances through power line from affecting the amplifier.


            Master-1 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-1 can convert to balanced ACSS signal and output real balance signal from XLR and ACSS.

            Master-1 can output RCA, XLR and ACSS at the same time.

            The input channels of Master-1 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-1 , 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  dual FET  non-feedback buffer output stages offer the very low output impedance  .

            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-1 is applied a four channels digital control relays based volume control. .Master-1 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-1 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 .
While change the volume, the different relays break or close, it may had slightly switch sound on output and disappear while stop change the volume.


           Master-1 has complete separation of left, right amplifier channels, power supply, and transformer.

           Master-1 uses heavyweight all-aluminum alloy chassis to prevent the eddy current of transformers from interfering on circuit board. 


           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-1 all parts of four channels had exact match before install.


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