Audio-GD Master 19 - Class A headphone amplifier
Audio-GD Master 19 - Class A headphone amplifier
Audio-GD Master 19 - Class A headphone amplifier

Audio-GD Master 19 - Class A headphone amplifier

CHF 1,049.00

Delivery time on request.
(All devices are handmade to customer order)


  • True symmetric ACSS design
  • Pure Class-A (9W @ 40 Ohm)
  • Preamp & Headphone Amplifier
  • 2 gain modes for high and low sensitivity


  • Fully balanced, pure Class A design with discrete analog stages without OPA or coupling caps in the signal channels.
  • Non-feedback analog ACSS output stage.
  • A total of 8 precisely matched 150W transistors (total 1200W) as output stages for realizing large class A output power.
  • Using two R-core transformers (100W total) as separate power supplies for the digital control components, right and left channels.
  • 4 groups of pure class A power supplies power the audio circuits.
  • More than 35,000uf audio grade NOVER capacitors are used to ensure ample and smooth power delivery.
  • Uses the highest quality components and precisely matched transistors, OCC wires.
  • Four-channel, 100-step relay-based digitally controlled volume control avoids channel imbalance and improves sound quality.
  • Supper exponential volume characteristic, easily adjust the volume with very high headphones/speakers without changing the gain mode.
  • 16.25DB in total 2 kinds of gain modes can drive the low sensitivity headphones very well.
  • 5 groups input: RCA X2, XLR X2, ACSS X1
  • Preamp output: XLR / RCA / ACSS
  • Headphone amplifier output: 4pins XLR X1 / 6.3MM X1

Technology Detail

Master 19 is a true balanced design utilizing the latest ACSS design that can improve the XLR connection to sound as good as the ACSS connection. They seem complex but in reality they are the simplest design the world has ever had, its a lot of components to process the power supply. The simplest and shortest signal path produces the most neutral and least colored sound.

The Master 19 uses a single-stage, ultra-low distortion ACSS amplifier soldered directly to the motherboard. It is a full Class A preamp/headphone amp and uses Class A power supplies.

ACSS is a non-feedback technology that uses discrete amplifiers. Most people know that the global feedback design performs better in test measurements, while the no-feedback design performs poorly in test measurements but offers better sound to human ears. Here there is a conflict between the classic circuits. However, the ACSS opens up a new field as it can offer a less colored, more neutral sound with very low distortion and high linearity. This allows it to maintain dynamics, detail and neutral tone without sounding bright or harsh.

All signal amplification is done by current, all transistors operate in pure Class A mode.

The output buffers of the Master 19 are equipped with 4 pairs of power transistors (150W / 15A) working in pure Class A mode, the output impedance is only 1 ohm and can drive most headphones and amplifiers.
At the master 19, all components of the four channels were precisely matched to each other before installation.

Strong Class A Output Stages

The Master 19 features 4 groups of diamond differential output stages as a balance drive stage, all parts have been pre-assembled precisely matched so that no human adjustment is required

The output stages had four pairs of 150W transistors, also working under pure class A condition, the balanced output mode had 4X times more power than the same condition single-ended mode.

The pure class A design had greater driving ability than the specifications, it drives the headphones no worse than a double performance class AB design, not to refer, the pure class A is the best sound design in value. The Balance Drive mode can kill the noise and distortion at the headphone end, much improve the sound stage, background and transparency, ect.

Power supply

Three special transformers power the audio and control circuitry separately.

The Master 19 uses 4 groups of pure Class A power supplies.
The Class A power supply connected in parallel has a very high input impedance to prevent pulses through the power supply from affecting the preamp, and a low one Very high speed and high linearity output impedance, so it is a very clean power supply.

The Master 19 uses separate linear power supplies for the display and control parts to avoid power line noise affecting the amplifier.


The Master 19 can not only feed in balanced XLR signals or unbalanced RCA signals, but also the first-class ACSS power signal. It can also output RCA signals, balanced XRL signals and ACSS power signals to the power amplifier. Using RCA input, the master can convert 19 to balanced ACSS signal and output true balanced signal from XLR and ACSS.

The ACSS input/output can be compatible with KRELL CAST products and SATRI technology gears. The XLR/RCA connector is compatible with all audio devices in the world.

Master 19 can output RCA, XLR and ACSS simultaneously in preamp output model, in headphone amp model, Master 19 can output XLR, single-ended for headphones.

The input channels of the Master 19 have separate shielding. When switched, the idle signal lines connected to the device and the ground wire are completely disconnected. The free input connections of the device are shielded. In this case, the sound quality will not be affected even if multiple devices are connected.

Volume control

The volume control also differs from conventional technology. Conventional volume control technology is to implement volume control in the analog amplifier input stage through a volume control to reduce the signal.

The quality of the volume control directly affects the sound quality. With low quality volume control, details are lost, and imbalance of channels leads to distortion of the soundstage. Even the high output volume controls still cause the detail to be lost. Regardless of the quality of the volume control, the S/N must be the worst.

But in the Master 19 we have the I / V conversion volume control, the volume control only has a variable passive I / V conversion place the ACSS amplifier output, where the output is the current signal, not the voltage signal. The volume control is an I/V conversion, and the volume depends on the conversion of current (I) to voltage (V).(Like R-2R D/A chips that output passive I/V conversion) It can keep the signal frequency band flat and doesn't lose details It can't degrade the sound quality at any volume. According to the volume, there are four groups of diamond non-feedback buffer output stages, which provide very low output impedance.

The quality of the volume control is very important in the real balance gear. It must guarantee the four channels signal control accurate to achieve the performance of the real balance gear. If the cool and hot of the balance signal can not guarantee accurate, the balance output has large distortion will cause the sound quality and performance even worse than a single end gear wasting the balance gear design and cost.
A four-channel digital volume control with relays is used in the Master 19. Master 19 has a total of four channels by changing the DALE resistors to avoid the volume control for the channels unbalanced, achieve the best performance and sound quality of the device.

Master 19 has 100 steps of volume control, achieving control range 90DB (usually the steps volume ports, potentiometer volume port, relay base volume control all have around 70DB range), very smooth control range on the first 50 steps, along with 20DB high gain, so can very easily adjust the volume for both high/low Sensitivity headphones and speakers. While changing the volume, the various relays break or close, it can easily change sound on the output and disappear while stop changing the volume had.


Uses only audiophile grade components including Toshiba transistors, WIMA caps, custom order NOVER (UK brand) caps, all audiophile grade input and output jacks. Master 19 all parts of four channels had exact match before installation.


S/N Ratio




THD + N <0.005%


Low Gain : +16DB (XLR)
High Gain : +25DB (XLR)

Volume characteristic

100 steps Supper Exponential Volume Characteristic

Headphone amp Output Power
(Balanced , Pure Class A )

40ohm: 9000mw
100ohm: 3800mw
300ohm: 1250mw
600ohm: 630mw

Headphone amp Output Power
(Single-ended , Pure Class A )

40ohm: 2500mw
100ohm: 1050mw
300ohm: 350mw
600ohm: 175mw

Preamp Output Level (Max)

10V @ RCA
20V @ XLR
2.4+2.4MA @ ACSS

Output impedance

1 ohm

Input impedance

90K ohms @ XLR
<10 ohms @ ACSS

Frequency Breadth (XLR input)

20Hz - 20KHz ( +/- 0DB )
1Hz - 220K (+0DB, -3DB)

Channels cross

> 130DB

Channels imbalance

< 005DB

Power Requirement

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

Power Consumption

45W @240V or 120V

Transformer Power

100W (2 transformers)

Package Weight

Approximately 7KG


W360 X L360 X H85(MM, Fully aluminum )


Power cord X1