Fully discrete, truly balanced CAST Class A preamplifier,

Since July 2019 the machine issued from July 2019 has been upgraded with a transformer for lower temperatures and long term power on.

Connect the CAST input of KRELL amplifier:

The HE-1 is compatible with the CAST input of KRELL amplifiers.

Only a pair of signal cables is needed to connect one end to Master 1 and the other end to the CAST input of the KRELL amplifier.

The output pins of Master 1 are defined as follows.

Pin 1, GND

Pin 2, Hot

Pin 3, Cold

Pin 4, GND

If the customer expects to connect the CAST input of the Krell amplifier, he can specify when placing the order, and we will increase the output signal to match the KRELL amplifier.

The updated design of HE-1.

Analog circuits are not upgraded as often as digital circuits. Especially for mature designs.

HE-1 has not changed its design since it was launched in mid-2015, not because we didn't want to but couldn't.

Until now, we introduced a new generation of design, mainly the input and output FET buffer stage, changed to lower distortion, better sound quality of the single-pole FET feedback-free buffer stage, using FET is now money may not be able to buy the new genuine Toshiba K170.

In addition to the power supply processing updates, with lower noise, darker music background.

Another update to the control circuit updates, and input short circuit function can be removed by the user without soldering.

HE-1 design and production overview.

Built-in regenerative power supply

True balanced all-transistor feedback-free CAST current transfer circuit.

The latest single-pole FET buffer design, a significant reduction in distortion and significant improvement in sound quality.

Use of three total power up to 260 W high-performance R cow and more than 100,000 UF of audio filter capacitors to ensure the purity of the power supply

Separate Class A power supply for regenerative power driver and audio signal amplifier respectively

True balanced all-transistor feedback-free CAST current transfer circuit

Four-channel 100-level digital control relay I/V conversion volume controller to avoid channel imbalance and sound quality degradation

Super exponential volume control feature, no matter what kind of amplifier is connected, the speaker can easily get the right volume

5 groups of inputs : XLR X2 / RCA X2 /CAST X1 (Even with RCA or unbalanced CAST input, HE-1 can still convert the signal to balanced CAST, XLR output.

3 groups of outputs : XLR / RCA / CAST (can output to three amplifiers simultaneously)

Detail of the Current Conveyor Technology :

What is regenerative power :

When music is life, power is water. Pure water creates wonderful life, and pure power reproduces the sound that pulls at the heartstrings.

Regenerative power supply is like having a private dedicated generator built into the machine.

It can filter out the interference on the power line to the maximum extent, providing super pure power supply to the audio amplifier, restoring the extremely low tainted and analog signal to the audio system and the user.

In the regenerative power supply design, 120V / 220V AC power is converted to DC power through the regenerative power input transformer, and then to the regenerative waveform generator and driver through a Class A shunt regulated power supply.

A balanced regenerative standard waveform generator generates an ultra-low distortion 50Hz waveform, which passes through a balanced gain amplifier and a powerful driver stage to drive the two regenerative power output transformers to output pure and stable voltage and frequency power, and then the left and right channels are independently powered by separate Class A parallel regulated power supplies.

The regenerative waveform generator and driver are powered by the Class A regulated power supply, so that their work is not affected by changes in the mains and interference.

Class A shunt regulator has a very high input impedance to block interference, to avoid interference through the utility power supply into the audio circuit to affect the sound quality, but also to avoid the left and right sound signal through the power supply to produce crosstalk to improve separation. The low output impedance has excellent linearity and speed, and is an excellent power supply voltage regulator circuit design.

Audio-gd in regenerative power supply design arguments.

1, By analyzing the internal design of the AP SYS-2722 and comparing it with actual tests, the distortion of a purely analog regenerative standard waveform generator is much lower than that of a digital synthesizer.

2, The digital driver stage can have higher power conversion efficiency, but the fully analog driver stage has more analog flavor.

3, 400Hz regenerative waveform frequency has higher power conversion efficiency, 50Hz regenerative waveform frequency is farther away from the human hearing sensitive area than 400Hz, and the sound quality is more mellow and natural.

CAST:

The HE-1 is a truly balanced design preamp that applies the latest CAST technology to advance the sound quality of the XLR input to be as good as CAST, with an all-transistor design that does not use OPA op amps in the audio circuitry (OPA op amps are DC servo circuits).

The HE-1 may look complex, but it is actually the simplest design in the world, with most of the components used for power processing. The simple and short signal processing channels result in a significant improvement in sound quality with minimal coloration.

The HE-1 uses a single stage CAST amplifier circuit with extremely low distortion, whereas a typical OPA op amp uses a two-stage amplifier circuit inside. The device is mounted directly on the motherboard for better sound quality.

The CAST circuit is a transistor amplifier with no feedback at all. Many audiophiles know that a negative feedback design provides better test metrics, but a no-feedback design provides a better listening experience. This is a contradiction between traditional circuits. But the CAST circuit has opened up a new era by providing extremely low tone coloration, extremely neutral and natural sound with very low distortion and excellent linearity. So she can reproduce better dynamics and richer details without feeling rough and dry.

All signal gain stages operate in current transfer mode, all transistors operate in Class A status and use Class A power supplies.

The XLR and RCA output buffers use two parallel, unipolar, feedback-free Wolman FET buffers with an output impedance of only 10 ohms.

All components of the HE-1's balanced four channels are precisely matched for installation.

Volume Control Design:

The HE-1's volume control is different from other technologies. Traditional volume control is to place the volume control potentiometer at the input of the amplifier to attenuate the signal, low quality potentiometers cause loss of detail and channel imbalance, even with high quality potentiometers, the attenuation and re-amplification method will also cause loss of detail and degrade the signal-to-noise ratio.

But in HE-1, we use the I/V conversion type volume control method, the volume control is like a variable passive I/V converter installed into the output of the CAST amplifier, where the current signal works instead of the voltage signal (like the passive I/V converter output of the R-2R DAC chip), which can get a very straight frequency response and will not lose any detail. No detail is lost.

Consistency of volume control is the key to the performance and sound quality of a truly balanced amplifier. It must ensure precise control of the signals on all four channels. If the + and - signals of the balanced signal are not precisely controlled, the balanced output will produce severe distortion and make the sound quality and performance even worse than that of a normal unbalanced amplifier, wasting the design and high cost of a truly balanced amplifier.

The HE-1 uses a four-channel, digitally controlled relay-type volume control, which controls the volume by switching high-precision DALE resistors, eliminating channel unbalance and the inaccuracy of balanced signals + and -, and achieving the best sound quality and performance. Working in the field of current, there is no need to worry about the sound quality caused by the contacts of the relay.

HE-1 has 100 levels of ultra-exponential wide response volume control, with a variety of high and low sensitivity headphones or speakers are easy to adjust. When the user adjusts the volume, different relays switch the resistance, so the output may have a slight relay switching sound, once you stop adjusting the volume, the switching sound will disappear.

Corresponds to normal knob type volume range

Super exponential wide response volume control

Shielding:

HE-1 completely isolates the four parts of left and right amplifier, regenerative power driver and secondary power transformer, even the 120V/220V incoming line is separated by using thick aluminum plate.

HE-1 uses a heavy all-aluminum chassis to avoid eddy current conduction through the chassis to affect the sound quality.

Components:

The HE-1's balanced four-channel system is precisely matched with all components.

Since July 2019 the machines sent out from July 2019 have upgraded transformers with lower temperatures for long periods of time on.

Automatically turn off the display:

When the input channel is set to 5 and the volume is 0, turn the volume knob to the direction of off small, the second bit of the display shows "1", which means the display auto-off function is activated, the display will automatically go off after about 10 seconds without any operation, only a "- " indicates that the machine is on. If you want to cancel it, you can turn the volume knob to the direction of turn off when inputting channel 5 and volume 0, and then turn the second position to display "0".

Display function:

The first position is the input selection display.

The second digit is the Auto Off display.

The third and fourth digit is the volume display, the larger the value the louder the volume.

Shield the function of idle input.

This machine is designed with idle input short circuit shielding function in order to avoid interference between signal sources when connecting different sources.

This design is also used in many Hi End brand products.

Working principle:

If there is no idle input short-circuit function, suppose when input 4 and input 5 connected to two different external DACs, when the user selects either input 5 or input 4, the unselected input signal will be emitted across the line to mix into the selected signal, although this is very weak but will also lead to the sound quality This is very weak but can lead to deterioration of the sound quality.

When the idle input shorting function is available, when the user selects either input 5 or input 4, the unselected input will be shorted and no signal will be emitted across the line to interfere with the selected signal, so the sound quality will not be affected.

In the following cases, users need not shield the idle input function, you can open the machine, the corresponding channel short-circuit plug to dial out and need to dial out the two channels at the same time.

1, the same external signal source is not only connected to the analog input of the machine, but also connected to other amplifiers.

2, The same external signal source is connected to different inputs of the machine at the same time.