HE-2 MK2

Quad split regenerative power supply powered mono power amplifier

30W pure Class A, 250W Class A (at 8 ohms per channel)

True balanced CAST negative feedback-free voltage gain stage design

Linear fax negative feedback-free output stage design

Uses 80 ON Semiconductor (formerly Motorola) output tubes

CAST and XLR balanced inputs

Built-in power supply soft-start circuit.

1 SET = 2pcs amplifiers + 2pcs regenerative power supplies

Difference with Master 2H:

We have tried using two Master 2Hs for Bi-Amp connection compared to one HE-2MK2 for regular connection and in our opinion one HE-2MK2 is superior in sound across the board.

About external power processors:

We do not recommend the use of an external active power processor, such as an external regenerative power supply, isolation transformer or power regulator.

Even in extreme cases of harsh power conditions, only a good quality passive power filter is required.

Overview:

Separate regenerative power supply (regenerative power supply for the gain board of the amplifier),

Fully negative feedback-free CAST circuit gain stage operating in pure Class A condition, with no OPA or coupling capacitors used in the signal path,

Completely feedback-free output stage with linear fax technology, avoiding switching distortion and providing excellent linearity, resulting in performance as good as a pure Class A amplifier without the high heat of a pure Class A amplifier

2 inputs: XLR / ACSS, even with XLR input, the signal is amplified by the CAST amplifier,

Uses 80 ON Semiconductor high power transistors. 30W pure Class A per channel, and 250W Class A (8 Ohms) output,

Six transformers with a total power of over 2000W and 260,000 UF filter capacitors for separate power supply to the left and right channels,

Eight pure Class A parallel regulated power supplies,

All high quality audio components are used, including DALE resistors, WIMA, custom NOVER (UK brand) capacitors and audio grade input and output sockets, gold plated RA power sockets,

All components of the four balanced channels are precisely matched for installation.

The following charts show the spectral range of various common instruments. The spectrum covers the range from 20Hz to 4KHz.

The different distortion levels must affect how the instrument sounds when played back. For example, if you play back a piano performance, and the distortion level in the different frequency bands varies greatly, the lower band may sound like a piano of brand A, the middle band like a piano of brand B, and the higher band like a piano of brand C.

The whole recording will sound like a mix of several different piano clips.

The graphs below show the distortion curves for this unit.

Noise + distortion at 8 ohms 10W output : approx. 0.03%

Noise + distortion at 8 ohms 50W output : approx. 0.04%

Noise + distortion at 8 ohms 100W output: approx. 0.05%

Fully analogue regenerative power technology:

The regenerative power supply is like having a private generator built into the machine.

It filters out the maximum amount of interference from the power lines and provides a super pure power supply to the audio amplifier, restoring a very low-dyed, analogue signal to the audio system and the user.

The regenerative power supply is designed so that 120V / 220V AC power is converted to DC power via a regenerative power input transformer, and then to a Class A parallel regulated power supply for the regenerative waveform generator and driver.

A balanced regenerative standard waveform generator generates an ultra-low distortion 50Hz waveform, which is balanced by a gain amplifier and a powerful driver stage to drive the three regenerative output transformers to produce a pure, stable voltage and frequency supply.

The regenerative waveform generators and drivers are powered by the Class A regulators so that their operation is not affected by changes in mains power or interference.

The Class A shunt regulator has a very high input impedance to prevent interference from entering the audio circuitry through the mains supply, and also to avoid crosstalk between the left and right sound signals through the supply to improve separation. The low output impedance provides excellent linearity and speed, making it an excellent power supply regulator design.

Audio-GD's arguments for regenerative power supply design:

1, The pure analogue regenerative standard waveform generator has much lower distortion than the digital synthesis generator, as demonstrated by internal design analysis and practical testing of the AP SYS-2722.

2, The digital driver stage can have a higher power conversion efficiency, but the fully analogue driver stage has more analogue flavour.

3, After long-term comparison and auditioning, the 400Hz regenerative waveform frequency has a higher power conversion efficiency, while the chosen 50Hz regenerative waveform frequency is further away from the human hearing sensitivity zone than 400Hz, resulting in a more mellow and natural sound quality.

Core:

The HE-2 MK2 is a truly balanced design post-amp that uses the latest CAST technology to advance the sound quality of the XLR input to be as good as CAST, with an all-transistor design (the OPA op-amp is a DC servo circuit).

The HE-2 MK2 may look complex, but it is in fact the simplest design in the world, with many of the components used for power processing. The HE-2 MK2 applies only a single "voltage" gain stage (operating in the CAST current transfer state is actually a current gain stage) to handle the gain of the signal (whereas an ordinary OPA op amp already contains two or three voltage gain stages). The simple and short signal processing channel results in a significant improvement in sound quality with minimal sound colouration.

The HE-2 MK2 uses a single stage CAST amplifier circuit with extremely low distortion and is mounted directly on the motherboard for better sound quality, and uses a Class A power supply.

The CAST circuit is a transistorised amplifier with no feedback at all. Many audiophiles know that a negative feedback design provides better test metrics, but a feedback-free design provides better listening. This is a contradiction between traditional circuits. But the CAST circuit breaks new ground by offering extremely low tone coloration, a very neutral and natural sound with very low distortion and excellent linearity. As a result, it reproduces dynamics and detail without sounding rough and dry.

The gain of the signal operates in current mode, using a unique set of open-loop current mirrors for extremely low distortion amplification. All devices in the signal section operate in Class A.

The CAST section is powered by four high-performance all-transistor Class A shunt regulated power supplies.

The Class A parallel regulated power supplies have very high input impedance and very low output impedance, effectively isolating the audio circuitry from the power supply to avoid power supply interference entering the audio circuitry and providing a clean and fast power supply to the circuitry.

All components of the HE-2 MK2's balanced four channels are precisely paired and mounted.

Drive:

Powerful high power components and power reserves ensure that the output can drive most loudspeakers. The four channel feedback-free diamond output stage uses 80 ON Semiconductor high power transistors. The filtering capacity is up to 260,000 UF and the six transformers have a total power of over 2000 W.

Inputs:

The HE-2 MK2 accepts XLR signals as well as CAST current transfer inputs. Either way, the HE-2 MK2 is gain amplified in CAST mode.

Isolation:

The HE-2 MK2 uses a heavy, all aluminium chassis to avoid transformer eddy currents being transmitted through the chassis to the circuit board. The signal gain board, output board and transformer are completely isolated by a thick aluminium plate.

Components:

All high grade audio components are used, including DALE resistors, WIMA and SOLEN capacitors, custom NOVER (UK brand) capacitors as per our requirements and audio stage input and output sockets, gold plated RA power sockets. The output stage uses 80 ON Semiconductor high power transistors. all components of the HE-2 MK2's balanced four channels are precisely paired and mounted.

First time connection of the HE-2 MK2：

When connecting the HE-2 MK2 for the first time, please first connect the DC power cable from the power processor to the power amplifier (the power cable is an accessory that comes with the machine; the DC power cable casing is threaded, so screw the casing tightly after connecting. When removing the power cable, be sure to unscrew the housing until it is fully unscrewed and unplug the DC power cable by holding the plug housing in your hand, do not remove the cable itself).

Then make sure that the power switches of all four units are switched off and connect the four 220V power cables. Connect the signal cables from the preamp to the power amplifier and make sure that the signal selector switch on the back of the amplifier is in the correct position.

HE-2 MK2 Switching Notes:

This unit is a 4-part design containing two regenerative power processors and two power amplifiers. Always switch on and off as follows.

Switching on:

Turn on the power to the signal source, preamp etc., then turn on the two regenerative power processors (the smaller two), after about 10 seconds you will hear a loud "pop" inside the machine, then turn on the two power amplifiers (the larger two).

Switching off:

Power off the two power amplifiers (the larger two) first, then you can power off the two regenerative power processors (the smaller two) and the preamp sources etc. in turn.

Please note that:

1,We do not recommend replacing the DC power cable as incorrectly connecting the DC power cable may result in damage to the regenerative power processor and the power amplifier.

If you must replace the DC power cable, the DC power cable plug is marked with the numbers 1 to 4. The same cable must be connected to the same numbered pins on both plugs when making the connection. Please note that damage caused by this is not covered by the warranty and will have to be repaired at your own expense.

PIN1 : Positive power

PIN2 : GND

PIN3 : GND

PIN4 : Negative power

If using a high quality audio signal cable as a DC power cable, make sure that the diameter of the copper core of the cable is large enough and that the cable length is as short as possible. For a two core, one shield signal cable, connect PIN1 to the red signal cable, PIN2 and PIN3 to the shield and PIN4 to the white signal cable on both plugs.

2, HE-2MK2 with the power cable is not able to play the sound quality of the machine, but only to provide users with a connection to test whether the machine can work properly. We recommend that users purchase a better quality power cable to connect to the unit, while power amplifiers require a good quality, sturdy power cable.

How to connect a preamp with RCA outputs.

An unbalanced preamp will not perform natively and it is not recommended to connect a preamp with RCA outputs for use.