Audio GD Master 9P MK2 - Dual Mono Headphone Amplifier

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

2 variants

Master 9PS MK2 ("Smooth")
8 Toshiba 15A /150W output transistors for a warm and smooth sound

Master 9PN MK2 ("Neutral")
8 ON Semiconductor 15A /230W output transistors for a neutral and transparent sound

Highlights

• True balanced dual integrated mono power amp
• Dual mono headphone amplifier, true balanced, class A
• 70W+70W @ 8 ohms ,14W+14W @ 40 ohms
• Headphone output options with neutral and simulated vacuum sound for customer selection on front panel
• ACSS amplifier without negative feedback
• 5 group inputs
• "Linear Fidelity" technology
• Soft Start Power Design

Are 70W+70W enough?

The Master 9P MK2 is 70W+70W into 8 ohms, even at 60W output the THD+N is still low at 0.055% at 1KHz and 0.004% at 20KHz, much lower than some 60W output amps, but the Specify 150W maximum power.

Normally with transistor power amplifiers it is recommended that the actual output power is about 1/5 to 1/3 of the maximum output power to keep the distortion as low as possible, so the Master 9P MK2 does the same can work well like some 200W power amplifiers.

For the home audio system, if the speaker with less than 86DB sensitivity, the listening room is generally around 20 square meters, if the listening room is larger, the speaker has generally higher than 88DB sensitivity, for these situations, 1W/each channel average power can already boost the speaker for normal listening, even with the really loud listening, 5W/each channel average power can already boost n ahe 100DB on the 88DB sensitivity speakers. In that case, the Master 9P MK2 still has 14 times the reserve power. Of course there is no doubt for driving a headphone.

True dual mono construction

Fully symmetrical design, the amplification stages and pre-stages work in class A, built with discrete analog stages without OPA or coupling caps in the signal channels.

The output transistor stages are very linear, they sound like a pure Class A design, but without the high heat generation of the pure Class A design.
Uses 8 pieces ON Semiconductor transistors, each piece has a power of 15A/230W (Master 9P MK2N). Supports 70W X2 (8 ohms) output, 14W X2 (40 ohms).
The capacitance of the whole machine reaches as high as 100,000uF, with two circuit cores in a total of 600W power, which is larger than some 200W power amplifiers.

A total of 4 groups of high-quality Class A parallel circuits supply the amplification stages.

• Two gain modes with 100 levels exponent character volume control, high gain has 34DB, low gain has 20DB, no problem drive any high or low sensitivity headphones and speakers.
• 5 groups input: RCA X2, XLR X2, ACSS X1
• Speaker output *1 pair
• Headphone amp output: 3pins XLR X2 / 4pins XLR X1 /6.3MM X1
• Headphone output options with neutral and simulated vacuum sound for customer selectable on front panel

The non-negative feedback output stages were equipped with the "Linear Fidelity" technology:

With the Master 9P MK2, the "Linear Fidelity" technology was applied to the output stages . The power amps have no negative feedback but are able to keep distortion low and smooth and have excellent linear performance.
In some power amp designs, distortion is very different at different power levels Even at a single power level, distortion is very different across the frequency band, especially at the low and high frequencies.

The blue line of the graph below shows the distortion as a function of frequency at 8 ohms and 20W output power of a well-known power amplifier worth approx. USD10k.

Current Conveyor Technology

Core

The Master-9P is a true balanced design utilizing the latest ACSS design that can enhance the XLR connection to be just as good sounds like the ACSS connection. It seems complex but in reality they are the simplest design the world has ever had, it's a lot of components to handle the power supply.

The Master 9P power stage has only a single "voltage gain stage" for signal processing, but works in ACSS mode, so it is actually a current gain stage instead of a voltage gain stage, while normal OPA chips already contain two or three voltage gain stages . The simplest and shortest signal path produces the most neutral and least colored sound.

The Master-9P uses an ultra-low-distortion single-stage ACSS amplifier soldered directly to the motherboard. The amplification stages and pre-stages work in class A.

The output transistor stages work with a high quiescent current. The diamond cross output stage design can avoid "switch distortion" as well as the class A amplifier.

ACSS is a non-feedback technology with fully discrete amplifiers. Most people know that the global feedback design can perform better in test measurements, while the no-feedback design does not perform well 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. So it can keep the dynamics, detail and neutral sound but not sound bright or harsh.

All signal amplification is in the form of current, which is achieved by the unique excellent open-loop multi-output mirror. The result is incomparably precise and extremely low distortion of the amplification signal. The entire signal path is balanced and all transistors operate in Class A mode.

The ACSS devices use 4 groups of high-quality Class A parallel switching power supplies for the dedicated DC power supply. The class A parallel switching power supply has a very high input impedance to prevent pulses from the power supply from affecting the gain stages and a low output impedance with very high speed and high linearity, making it a very clean power supply.
Drives

The massive use of high-performance parts and the robust power supply guarantee a powerful current output that will drive most existing loudspeakers.
The Master-9P uses four channels with non-feedback output stages, consisting of 8 ON Semiconductor transistors. Each piece has an output of 15A/230W. The capacitance of the whole machine reaches up to 100,000uF. Two transformers with a total power of 600 W are used.

Impedance matching

There are many different DACs in the world that have different design and output impedance.

In order to avoid the effects of the different output impedances of the DACs on the sound quality, in the Master 9 4 groups of expensive single-polarity class A FET cascode buffers were built into the input. All input signals passing through these FET buffers have a very low output impedance, even if the source has high or low output impedance.

The FET buffers operate in pure Class A condition and have such short signal paths that they can keep the sound quality without discoloration, dry and harsh.

Volume control

The volume control is also different from traditional 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 power 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 9P MK2 we have the I / V conversion volume control, the volume control only has a variable passive I / V conversion place at 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 cannot degrade the sound quality at any volume. According to the volume, there are four groups diamond non-feedback buffer output stages, provide the 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.

Specifications

S/N Ratio	>110DB (Full scale)
Gain	34 DB (high gain) 20DB (low gain)
Output (Speaker)	70W*2 @ 8ohm 100W*2 @ 4ohm
Output (Headphone)	35W*2 @ 15 ohm 20W*2 @ 25 ohm 14W *2 @ 40 ohm 6W*2 @ 100 ohm 2W*2 @ 300 ohm 1W *2 @ 600 ohm
Input sensitivety	0.55V RMS @ XLR 2mA RMS @ ACSS
Input impedance	47K ohms @ RCA 94K ohms @ XLR <10 ohms @ ACSS
THD+Noise	THD+N at 8 ohms 20W (<0.055% at 1K, <0.002% at 20KHz, 2VRms XLR input) THD+N at 8 ohm 60W (<0055% at 1K, <0.005% at 20KHz, 2VRms XLR input )
Frequency Breadth (ACSS input)	<2.5DB at 200KHz (8 ohm 1W output, 2VRms XLR input)
Channels cross 𩇕	>-120DB
Channels imbalance 𩇕	< 0.05DB
Power Requirement	1 version 100-120V AC 50/60 Hz 2 version 220-240V AC 50/60 Hz
Power Consumption	50W static @240V or 120V
Transformer Power	600W (2 transformers)
Package Weight	Approximately 21KG
Product Weight	Approximately 18KG
Dimensions 𩇕	W430 X L485 X H123 (MM, Fully aluminum )
Accessories	Power cord X1

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