Shipped since July 2019, the unit has upgraded the transformers , can power on long term.

Different to 2015 Edition:
         The 2019 Edition upgraded and has two different volume control characters, can perform high and low gain modes without change the amp's parameter so without effect on sound quality. And addition a super gain control.
         The L gain mode has 16DB gain, for drive the headphones which have over 100DB sensitivity or work as preamp.
         The H gain mode has 25DB gain, for drive the headphones which have 80-100DB sensitivity.
         The S gain mode has 31DB gain, for drive the headphones which have 80-100DB sensitivity but with the low output level sources (Available on RCA/ XLR inputs ). 

Connect with KRELL amplifiers:
          HE 9 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 HE 9 to have higher ACSS output gain if expecting to connect to KRELL amplifiers.

Audio-gd regenerative power supply history
        The HE series products had the longest term of design and test  in audio-gd history .  Even though audio-gd had release the regenerative power supply products since 2006, and Mr. Kingwa had publish the article in the <Radio & TV> magazine explain the technology detail .
        The HE series products had finished the design in the New Year of 2014 , we were plan to release them in the date of audio-gd 10  anniversary , but for got the best sound quality and performance, we have even 3 times change the full design for made the compare, and compare different power frequency and voltage, create the longest design term record.
       The HE series products have better detail and dynamic reproduce ,blacker backstage ,better focus and larger sound stage , but the sound is better analog .
       The right saddle must is set on the right horse ,if you had not enough good system units, and had not enough cable match experiences, don't waste the money on HE series products.
      Please note the HE series products are upgrade from Master series, even though the price had a big rate increased but the sound quality had not same rate improved.

The different between HE-1 and HE-9:
       The HE-1 is a decent preamp , HE-9 is a preamp with headphone amp, their sound quality is close, if customers want the headphone output, choice the HE-9 is proper.

Summarize
Built in regenerative power supply
Uses three R-core transformers (In total 260W ) and more than 100,000uf audio grade NOVER capacitors are used to ensure ample and smooth power delivery.
Separate class A PSUs power supply for regenerative drivers ,Left and Right channel audio signal amps .
Total applied 8 pcs exact matching 150W transistors ( In total 1200W )  as the output stages  for implement large class A output power .
Uses most Hi-end grade parts and exactly matched transistors, OCC wires.
Four-channel 100 steps digitally controlled relay-based volume control avoids channel imbalance and improves sound quality .
Supper Exponential Volume Characteristic,  easy match the volume with very high headphone / speaker without change the gain mode.
16,25,31DB in total 3 type gain modes can drive the low sensitivity headphone very well.
5 groups input:  RCA X2, XLR X2, ACSS X1
Preamp output :   XLR / RCA / ACSS
Headphone amp output:    4pins XLR X1 /  3pins XLR X2 / 6.3MM X1

Click to read the ACSS technology :
Detail of the Current Conveyor Technology

What's the regenerative power supply :

             While audio is life , the Power supply is water , Pure water create the wonderful life ,clean power supply reproduce the beautiful sound .
             The regenerative power supply like a proprietary electric generator built in the unit.
             It can block most disturb from the power line , supply the ultra clean power supply for the audio amps , reproduce the most neutral and analog sound like audio signal for the system and the users.
             In the regenerative power supply design, the AC power through the regenerative input transformer , conversion to DC power ,through the class A PSUs power supply for the regenerative wave generator and driver stages .
             A balance regenerative regular wave generator produce the ultra low distortion 50Hz wave ,through the balance  gain amps and the strong  output stages , drive the regenerative transformers produce the clean and steady AC power supply feed to the separate class A PSUs power supply for the L and R channel preamps .
            The class A parallel connection PSU has very high input impedance to avoid disturb through the PSU from affecting the signal parts and low output impedance with very fast speed and high linear,  it is a very clean power supply.
             Audio-gd on the regenerative power supply design points  :
                    1, Through analyzed the AP SYS-2722 ,do a lot practises ,test and listen  , full analog design of the  regular wave generator have much lower distortion than the digital generator.
                    2, Digital drive stages  have higher efficiency , but full analog drive stages  have much better analog sound like .
                    3, 400Hz regenerative wave have higher efficiency , 50Hz regenerative wave had much far away the human ears sensitivity area than the 400Hz, boost the sound have much better analog sound like.

            

ACSS:
             HE-9 is a true balanced design applying the newest ACSS design which can improve the XLR connection to sound as good as the ACSS connection. The HE-9 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.
            HE-9 applies ultra-low distortion single stage ACSS amplifier , an OPA already had built in two stages amplifier. they are soldered directly on the motherboard.

            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 area, all transistors work in class A mode and applies class A power supplies.
             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.
             HE-9 has all components of four channels exactly matched before installation.

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 ,in the attenuation then gain the signal mode ,still cause the detail lose and cause the S/N worst .
           In the HE-9 , 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  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 HE-9 is applied a four channels digital control relays based volume control, through changing the DALE resistors to control the volume for avoid channels imbalanced ,achieve the best performance and sound quality of the gear.
            HE-9 have 100 steps volume control, applied Supper Exponential Volume Characteristic, easy match the volume with different power amp and speaker .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.
              Supper Exponential volume characteristic                   The Volume steps comparison to normal volume knob       
                                                                                         
Shield: 
         HE-9 has complete separation of left, right amplifier channels, regenerative drivers and transformer, even the 230V / 120V power input lines had shield in the two thick aluminum boards .
         HE-9 uses heavyweight all-aluminum  chassis to prevent the eddy current of transformers from interfering on circuit board. 

Components:
         Uses all audiophile grade components, including DALE resistors, WIMA caps, custom order NOVER (UK brand) caps, all audiophile grade input & output sockets (Neutrik ) and gold IEC socket.  HE-9 all parts of four channels had exact match before install.